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  • 1.
    Akram, Shazad
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Alam, Farhan Muhammad
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Sidén, Johan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Capacitive and optical sensing for automatic detection and characterization of cleaning sponges in fiber optic microduct installations2019Inngår i: Proceedings - 2019 8th International Workshop on Advances in Sensors and Interfaces, IWASI 2019, IEEE, 2019, s. 274-278, artikkel-id 8791315Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Optical fiber duct installation requires blowing of cleaning sponges for dirt and moisture removal before blowing the fiber cables. The traditional method requires one operator that blows the sponge and one operator in the receiving end that manually evaluate the sponges until a dry sponge is received. The proposed system eliminates the need of a second operator by introducing a solution for automatic sponge detection and characterization of moisture in sponges at the receiving end. An optical sensor is used for detection and a capacitive sensor is developed to measure the sponge's wetness. Sensor data is automatically transmitted back to the operator at the feeding end via a mobile phone. The system is characterized to work with sponges ranging from saturated with wetness to what is deemed as dry. 

  • 2.
    Akram, Shazad
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Sidén, Johan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    LTspice electro-thermal model of joule heating in high density polyethylene optical fiber microducts2019Inngår i: Electronics (Switzerland), ISSN 2079-9292, Vol. 8, nr 12, artikkel-id 1453Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    At present, optical fiber microducts are joined together by mechanical type joints. Mechanical joints are bulky, require more space in multiple duct installations, and have poor water sealing capability. Optical fiber microducts are made of high-density polyethylene which is considered best for welding by remelting. Mechanical joints can be replaced with welded joints if the outer surface layer of the optical fiber microduct is remelted within one second and without thermal damage to the inner surface of the optical fiber duct. To fulfill these requirements, an electro-thermal model of Joule heat generation using a copper coil and heat propagation inside different layers of optical fiber microducts was developed and validated. The electro-thermal model is based on electro-thermal analogy that uses the electrical equivalent to thermal parameters. Depending upon the geometric shape and material properties of the high-density polyethylene, low-density polyethylene, and copper coil, the thermal resistance and thermal capacitance values were calculated and connected to the Cauer RC-ladder configuration. The power input to Joule heating coil and thermal convection resistance to surrounding air were also calculated and modelled. The calculated thermal model was then simulated in LTspice, and real measurements with 50 µm K-type thermocouples were conducted to check the validity of the model. Due to the non-linear transient thermal behavior of polyethylene and variations in the convection resistance values, the calculated thermal model was then optimized for best curve fitting. Optimizations were conducted for convection resistance and the power input model only. The calculated thermal parameters of the polyethylene layers were kept intact to preserve the thermal model to physical structure relationship. Simulation of the optimized electro-thermal model and actual measurements showed to be in good agreement. 

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  • 3.
    Alishah, Rasoul Shalchi
    et al.
    Univ Tabriz, Tabriz, Iran.
    Hasani, Mir Yahya
    Islamic Azad Univ Tabriz, Tabriz, Iran.
    Hosseini, Seyed Hossein
    Univ Tabriz, Tabriz, Iran.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Babalou, Milad
    Univ Tabriz, Tabriz, Iran.
    Analysis and Design of a New Extendable Sepic Converter with High Voltage Gain and Reduced Components for Photovoltaic Applications2019Inngår i: 2019 10th International Power Electronics, Drive Systems and Technologies Conference (PEDSTC), IEEE, 2019, s. 492-497, artikkel-id 8697249Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a high step-up DC-DC converter which is appropriate for Photovoltaic systems. This topology has been combined from an extended switched-capacitor and a common SEPIC converter. Low components and high-voltage-gain are the main benefits of the introduced topology. Low rate current ripple, easy control and continuous input current are other advantages of the presented structure. Integrating the switched-capacitor with the SEPIC converter leads to increase the output voltage with variable conversion ratio which can be used for a wide range of loads. The switched-capacitor converter provides a constant dc output voltage while the SEPIC converter extracts maximum power of PV panels because it operates under control of duty cycle. Continuous input current is highly suitable for PV applications. The operating principles and steady-state analysis of the suggested topology are discussed in detail. In order to assess the effectiveness of the presented topology, it has been simulated on PSCAD/EMTDC software.

    Fulltekst (pdf)
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  • 4.
    Ambatipudi, Radhika
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Kotte, Hari Babu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Comparison of Two Layered and Three Layered Coreless Printed Circuit Board Step-Down Power Transformers2011Inngår i: 2011 INTERNATIONAL CONFERENCE ON INSTRUMENTATION, MEASUREMENT, CIRCUITS AND SYSTEMS (ICIMCS 2011), VOL 2: FUTURE COMMUNICATION AND NETWORKING, Shenzhen: IEEE conference proceedings, 2011, s. 59-62Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper the comparative results of two layered and three layered coreless Printed Circuit Board (PCB) step down 2:1 power transformers operating in MHz frequency were addressed. The  two different step down transformers approximately having same self inductances, one in two layer and the other in three layer were designed and evaluated for the given power transfer application. The performance characteristics of these transformers under similar conditions were measured and the comparative parameters of these transformers in terms of their resistances, self, leakage, mutual inductances, and coupling coefficient are analyzed. For the given output power, the measured energy efficiency of the three layered transformer is improved by 3% and the area is reduced by 32% compared to two layered transformer. The efficiency of the three layered transformer is 94.5% approximately for an output power level of 25W at an operating frequency of 2.5MHz

  • 5.
    Ambatipudi, Radhika
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Kotte, Hari Babu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Coreless Printed Circuit Board (PCB) StepdownTransformers for DC-DC ConverterApplications2010Inngår i: PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY, ISSUE 70, OCTOBER 2010, ISSN:1307-6892, France: World Academy of Science Engineering and Technology , 2010, s. 380-389Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, multilayered coreless printed circuit board (PCB) step-down power transformers for DC-DC converter applications have been designed, manufactured and evaluated. A set of two different circular spiral step-down transformers were fabricated in the four layered PCB. These transformers have been modelled with the assistance of high frequency equivalent circuit and characterized with both sinusoidal and square wave excitation. This paper provides the comparative results of these two different transformers in te rms of their resistances, self, leakage, mutual inductances, coupling coefficient and also their energy efficiencies. The operating regions for optimal performance of these transformers for power transfer applications are determined. These transformers were tested for the output power levels of about 30 Watts within the input voltage range of 12-50 Vrms. The energy efficiency for these step down transformers is observed to be in the range of 90%-97% in MHz frequency region.

  • 6.
    Ambatipudi, Radhika
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Kotte, Hari Babu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Effect of Air Gap on the Performance of Hybrid Planar Power Transformer in High Frequency (MHz) Switch Mode Power Supplies (SMPS)2012Inngår i: Proceedings of INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A half bridge transformer with novel winding strategy was designed and tested up to the output power level of 50W with a maximum energy efficiency of 98% in 1-6 MHz frequency region. In this paper, the effect of air gap on the performance of the designed transformer for high frequency (MHz) Switch Mode Power Supplies (SMPS) was studied and analyzed. The air gap of the transformer was varied from 0 – 2mm and the effect on self, leakage, mutual inductances, coupling coefficient and power transfer capability was recorded in 1 - 6MHz. The parameters of the transformer with different air gaps were extracted using network analyzer. The transformer was excited with sinusoidal voltages using power amplifier and the performance characteristics such as input impedance, power transfer capability and hence the energy efficiency was measured. At a particular operating frequency of 3MHz, the maximum power transferred for the given excitation voltage with 0mm air gap was found to be 22W whereas it is only 8W with the 2mm air gap . The measured energy efficiency of the transformer at 3MHz with 0mm and 2mm air gap was found to be 93% and 79% respectively. With this study, for the given power transfer application, at a particular high frequency operation of converter, an optimum air gap without sacrificing the energy efficiency and core saturation was proposed

  • 7.
    Ambatipudi, Radhika
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Kotte, Hari Babu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Effect of Dielectric Material on the Performance of Planar Power Transformers in MHz Frequency Region2012Inngår i: Proceedings of INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, the effect of two different dielectric materials in planar printed circuit board (PCB) transformers applicable for power transfer applications in MHz frequency region is discussed. The 2-D model of the planar transformer was developed and the effect of the dielectric material on the magnetic field and the current distribution in the transformer was analyzed. Based on the FEA analysis, the power transformers of two different dielectric materials were designed, manufactured and characterized by using ‘S’ parameters obtained from network analyzer in order to determine the performance of dielectrics at high frequencies. The electrical parameters such as inductances, capacitances and resistances of the transformers were obtained and the changes in these parameters with the variation of the dielectric material were analyzed in the MHz frequency. This paper discusses the effect of dielectric material on the magnetic field distribution and the current density which results in the variation of the coupling coefficient and the eddy current losses of the transformer. By changing the dielectric material from a traditional FR-4 to a Rogers, the coupling coefficient was improved by a maximum of 5% and the copper losses of transformer were also decreased in the MHz frequency region. The power gain/energy efficiency obtained from the network analyzer with a resonant capacitor is verified with those obtained using a power amplifier and the simulations. An overall energy efficiency improvement of about 2-5% was achieved with a Rogers’s material in MHz frequency region compared to traditional FR-4 laminate.

     

  • 8.
    Ambatipudi, Radhika
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Kotte, Hari Babu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    High Performance Planar Power Transformer with High Power Density in MHz Frequency Region for Next Generation Switch Mode Power Supplies2013Inngår i: 2013 Twenty-Eighth Annual IEEE Applied Power Electronics Conference And Exposition (APEC 2013), IEEE conference proceedings, 2013, s. 2139-2143Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The authors report the utilization of the core based transformer for power transfer applications with high power density and high energy efficiency in the MHz frequency region. A custom made POT core center tapped transformer of 4:1:1 turn’s ratio using novel winding strategy with the core diameter of 16mm is designed and evaluated. The designed transformer has been characterized using sinusoidal excitation for a given output power in the frequency range of 1 – 10MHz and determined the operating frequency region of the transformer. The power tests of the transformer has been carried out up to the power level of 62W at an operating frequency of 6.78MHz with a peak energy efficiency of 98.5% resulting in the record power density of ~1100W/in3. The designed transformer has been characterized using class E isolated DC-DC converter topology at an output power of approximately 18W. The simulated energy efficiency of the converter is 88.5% under the full load condition. This work provides the significant step for the development of next generation high power density isolated converters (both AC/DC and DC/DC) in MHz frequency region

  • 9.
    Ambatipudi, Radhika
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Kotte, Hari Babu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Radiated Emissions of Multilayered Coreless Printed Circuit Board Step-Down Power Transformers in Switch Mode Power Supplies2011Inngår i: 8th International Conference on Power Electronics - ECCE Asia: "Green World with Power Electronics", ICPE 2011-ECCE Asia 2011, IEEE conference proceedings, 2011, s. 960-965Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper addressesradiatedEMI issues in Coreless PCB step-down transformers used for power transfer applications. In case of SMPS circuits, since the waveforms are not sinusoidal in nature, most of theradiatedemissionsare not only from fundamental frequency component but also from harmonic contents. According to antenna theory,radiatedEMI for three different power transformers of different radii were estimated for fundamental frequency of 2MHz to 300MHz. The computations were made for both sinusoidal and square wave excitations and at a load power of 20W. The calculatedradiatedpower obtained for simulated waveforms and for practical measured current waveforms are in good agreement with each other up to certain bandwidth. These computational results confirm thatradiatedpower can be reduced in three layered 2:1 transformer compared to two layered 2:1 transformer. Also theradiatedemissionsare negligible in case of sinusoidal excitations compared to square wave excitations. © 2011 IEEE.

  • 10.
    Andersson, Henrik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Processing and Characterization of a MOS Type Tetra Lateral Position Sensitive Detector with Indium Tin Oxide Gate Contact2008Inngår i: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 8, nr 9-10, s. 1704-1709Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A 2-D tetra lateral position sensitive detector (PSD) based on the metal-oxide-semiconductor (MOS) principle has been manufactured and characterized. The active area of the device is 5 nun x 5 mm and the intention is to use the central 4 nun x 4 nun for low nonlinearity measurements. The gate contact is made of indium tin oxide (ITO) that is a degenerate electrically conducting semiconductor, which, in addition, is also transparent in the visible part of the spectrum. The use of a MOS structure results in a processing with no necessity to use implantation or diffusion in order to make the resistive p-layer as in a conventional p-n junction lateral effect PSD. Position measurements show good linearity in the middle 4 nun x 4 mm area. Within the middle 2.1 mm x 2.1 mm, the nonlinearity is within 1.7% of the active area with a position detection error of maximum 60 mu m. Measured MOS IV characteristics are compared to a level 3 spice model fit and show good agreement. The threshold voltage is determined to be -0.03 V. Responsivity measurements show a high sensitivity in the visible spectral region.

  • 11.
    Bakar, Muhammad Abu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Alam, Farhan Muhammad
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    A phase shifted full bridge converter with novel control over the leakage inductance2016Inngår i: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE), Institute of Electrical and Electronics Engineers (IEEE), 2016, artikkel-id 7695545Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The electronics industry is progressing towards the high density board solutions due to the requirement of compact and intelligent electronic systems. In order to meet the industry demands, the power system is required to be of high power density. This article proposes one of the solution to improve the power density for the medium power applications. In phase shifted full bridge converter, the intrinsic leakage inductance of the main transformer is not high enough to obtain the zero voltage switching of the power switches for the entire operating conditions. An additional shim inductor is usually connected in series with the primary winding of the main transformer to increase the collective leakage inductance. This additional shim inductor degrades the power density of the converter. This paper proposes a method to embed and control the resonance inductance inside the main transformer. In addition to the increased inter-winding spacing, this paper proposes a practical approach to integrate the ferrite rods inside the main transformer for further increase in the leakage inductance. A power transformer is constructed and investigated by using the modelled equations to estimate the leakage inductance. A prototype phase shifted full bridge converter is also developed to investigate the performance of the proposed transformer. The converter is designed for the switching frequency of 400kHz, and tested up to 600watts output power at the input voltage of 200Vdc. The performance of the proposed converter is also compared with the converter of using an external inductor. The investigations show that, in addition to the improved power density, the converter with the proposed transformer is more efficient than the converter with the traditional transformer.

  • 12.
    Bakar, Muhammad Abu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Alam, Farhan Muhammad
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Dual-mode stable performance phase shifted full bridge converter for wide input applicationsInngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Artikkel i tidsskrift (Fagfellevurdert)
  • 13.
    Bakar, Muhammad Abu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Alam, Farhan Muhammad
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Modeling and Characterization of Series Connected Hybrid Transformers for Low-Profile Power Converters2020Inngår i: IEEE Access, E-ISSN 2169-3536, Vol. 8, s. 53293-53306Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Compact and low profile power converters are the main business of today's power industry. A significant volume of a power converter is occupied by the power transformer. This article proposes a unique solution that would make the power converters low profile. Instead of designing a power converter by using a single bulky transformer, the solution proposed is to split the main bulky transformer into a number of low profile transformers. This not only reduces the total weight and volume of the converter but also the total transformer losses. The use of more than one transformer in series reduces the applied voltage on the transformers, which minimizes the required turns ratio and decreases the stress on the secondary rectifiers and filter elements. Moreover, the decrease in the applied voltage reduces the proportional loss per transformer and makes it possible to design a hybrid transformer by combining Litz wire and traces of a printed circuit board. The reduced copper loss and lower heat dissipation per transformer simplify thermal management. An analytical comparison is made between the utilization of a single transformer or a number of transformers. The procedure of splitting a volume of a single transformer into a number of small transformers has been comprehensively discussed. The idea is investigated both experimentally and in computer simulation for an example application of a phase shifted full bridge dc-dc converter. The converter is characterized up to a load power of 2.2 kW at Vin = 400 Vdc and Vout = 48 Vdc. To make the approach more practical, the transformers are modeled using the traditional analytical method. The design of the example application using the split transformer approach reduces the total transformer weight by 45%, compared to the traditional approachwith a single transformer. The converter also shows good performance with a maximum efficiency of 96%.

    Fulltekst (pdf)
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  • 14.
    Bakar, Muhammad Abu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Alam, Farhan Muhammad
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Das, Moumita
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Barg, Sobhi
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Reconfigurable three state dc-dc power converter for the wide output range applications2019Inngår i: IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society, Lisbon: IEEE, 2019, s. 4911-4916Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Improving the dc voltage gain of power converters has been the primary focus of the current and past research in the area of power electronics. This work presents another solution to widen the range of the output voltage. It proposes three reconfigurable steps for the output voltage. The range of theoutput voltage varies up to four times the base level. These configurations together vary the output voltage from 15 to 96 volts. A soft switched dc-dc power converter is built with the traditional topology of phase shifted full bridge converter along with improved characteristics. For better management of thetransformer loss, a configuration of four transformers has been employed. The proportional gate drive approach is implemented to obtain four similar isolated blocks of the output voltage. This makes it possible to either configure these blocks all in series,parallel or in series/ parallel combination of two. The concept is verified in a low-profile prototype. The hardware is characterized up to the load power of 1kW for the input voltage of 400Vdc. The converter reports better efficiency over the complete range of output voltage.

    Fulltekst (pdf)
    fulltext
  • 15.
    Bakar, Muhammad Abu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Alam, Farhan Muhammad
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Shalchi Alishah, Rasoul
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Characterization of phase shifted full bridge converter along with GaN devices and series-connected hybrid transformers for medium power applications2020Inngår i: / [ed] IEEE, 2020Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Compact power converters are the major concern of today’s power industry. This article proposes GaN devices based isolated dc-dc phase shifted full bridge converter along with the configuration of four series-connected hybrid transformers. The series connection of transformers reduces the applied volt-second on each transformer which reduces the proportional losses and simplify thermal management. This configuration also reduces the required turn’s ratio as well as bringing down the stress on the secondary devices and filters. The converter is characterized in a compact prototype up to the load power of 2.2 kW for Vout=48 Vdc at Vin=400 Vdc. The converter reports satisfactory performance with a maximum efficiency of 96%.

  • 16.
    Bakar, Muhammad Abu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    A Modified Higher Operational Duty Phase Shifted Full Bridge Converter for Reduced Circulation Current2020Inngår i: IEEE Open Journal of the Industrial Electronics Society, ISSN 2644-1284Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Besides many advantages, the reduction in the operational duty of traditional phase shifted full converter limits its scope in applications where a wide range of input voltage is the main requirement. Operation with low duty cycle extends freewheeling interval, which results in degraded performance such as more circulation current, increased conduction loss in power devices, narrow range of zero voltage switching and increased EMI. To overcome these drawbacks, this work suggests a modified phase shifted full bridge converter that keeps the operational duty of the converter high for a wide range of input voltage. This cuts the freewheeling interval and improves performance. The proposed converter consists of four low profile transformers having reconfigurable interconnection structure. There are two distinct reconfigurable modes, a low gain mode and a high gain mode, which can be adopted in accordance with the variation in line voltage. The proposed work is validated in LTspice simulation and hardware characterization for a wide range of input voltage 100-400Vdc/12Vout and up to the load power of 1.2kW.

    Fulltekst (pdf)
    fulltext
  • 17.
    Bakar, Muhammad Abu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    An improved modelling and construction of power transformer for controlled leakage inductance2016Inngår i: Environment and Electrical Engineering (EEEIC), 2016 IEEE 16th International Conference on, IEEE, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work, a transformer with increased leakage inductance for the soft switched power applications is presented as a practical solution by constructing a transformer with good control over the leakage inductance. An analytical reluctance based model is presented, which accurately predicts the leakage inductance. With the presented approach, a transformer is designed with a leakage inductance varying between 3-7μH. Increasing the efficiency and improving the power density has been the main focus of power electronics researchers in the recent years. In this regards, transformers with increased leakage inductance are becoming more popular in order to accomplish different soft switching concepts and for improving the power density.

  • 18.
    Bakar, Muhammad Abu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Ambatipudi, Radhika
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    High frequency (MHz) soft switched flyback dc-dc converter using GaN switches and six-layered PCB transformer2016Inngår i: IET Conference Publications, UK: Institution of Engineering and Technology, 2016, Vol. 2016, s. 1-6, artikkel-id CP684Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The increased switching losses with increasing switching frequency are the biggest concerns in designing high power density converters. This paper presents the investigation of an energy efficient DC-DC flyback converter in combination with six layered printed circuit board transformer. The recorded efficiency of the low profile transformer for the frequency range of 1-5MHz is 98% at power density of 770W/in3. The proposed converter is characterized for frequencies up to 4MHz by using possible soft switching techniques such as Boundary Mode and Quasi Resonant Mode. The emerging Gallium Nitride (GaN FET) devices are used as power switch. The control is incorporated with Digital Signal Processor (dsPIC) for both the Boundary and Quasi Resonant Modes of operations. The proposed flyback DC-DC converter is tested on a prototype Printed Circuit Board (PCB). The performance of the proposed converter is investigated for the telecom input voltage range of 36-72Vdc. The maximum obtained energy efficiency of the converter is about 94%. According to the authors' knowledge, this is the maximum efficiency ever achieved in flyback converters switching in MHz frequency range. The results are very encouraging for the development of high frequency, high power density and low cost isolated power converters.

  • 19.
    Bakar, Muhammad Abu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Haller, Stefan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Contribution of Leakage Flux to the total Losses in Transformers with Magnetic Shunt2020Inngår i: International journal of electronics (Print), ISSN 0020-7217, E-ISSN 1362-3060Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To execute soft switching methods in resonant power converters, transformers with larger leakage inductance are getting more attention. Many papers have constructed various concepts in this regard. However, a discussion about, how the transformer efficiency is affected is lacking in the literature. This paper analyses the effects of the increased leakage inductance on the performance of the transformer. A transformer for increased leakage inductance is modelled and constructed to investigate the losses. The model discusses the effects of increased leakage inductance either by increasing the inter-winding spacing or by integrating the magnetic shunt within the transformer. The investigations show that increasing the leakage inductance by inserting a magnetic shunt can have severe degrading effects on the performance of the transformer, if not designed adequately. Additional losses are also calculated and the effects are verified by the experiments.

  • 20.
    Barg, Sobhi
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Alam, Farhan Muhammad
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Modeling of the Geometry Effect on the Core Loss and Verification with a Measurement Technique Based on the Seebeck Effect and FEA2019Inngår i: IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society / [ed] IEEE, IEEE, 2019, s. 1832-1837Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, the effect of the core geometry of non-toroidal magnetic cores on the magnetic loss is investigated. A frequency dependent core material-geometry loss factor is developed. This factor is function of the change in the non-toroidal core section and the Steinmetz parameter “β”. In addition, the temperature effect is included in the developed loss model for wide range of frequency and magnetic flux density. The model is applied for ER core and 3C92 ferrite material. The core loss measurements are performed using a Peltier cell. The principle of operation of the Peltier cell is based on the Seebeck effect, which convert the heat flow due to the temperature difference into electric power.  The calibration of the Peltier cell is validated with a resistive load and a relative error lower than 1% is achieved. The accuracy of the developed model is assessed with FEA and the experimental results. A maximum error of 10% is registered of the developed core loss model.

    Fulltekst (pdf)
    fulltext
  • 21.
    Barg, Sobhi
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Multi‑objective Pareto and GAs nonlinear optimization approach for fyback transformer2019Inngår i: Electrical engineering (Berlin. Print), ISSN 0948-7921, E-ISSN 1432-0487, Vol. 101, nr 3, s. 995-1006Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Design and optimization of high-frequency inductive components is a complex task because of the huge number of variables to manipulate, the strong interdependence and the interaction between variables, the nonlinear variation of some design variables as well as the problem nonlinearity. This paper proposes a multi-objective design methodology of a 200-W flyback transformer in continuous conduction mode using genetic algorithms and Pareto optimality concept. The objective is to minimize loss, volume and cost of the transformer. Design variables such as the duty cycle, the winding configuration and the core shape, which have great effects on the former objectives but were neglected in previous works, are considered in this paper. The optimization is performed in discrete research space at different switching frequencies. In total, 24 magnetic materials, 6 core shapes and 2 winding configurations are considered in the database. Accurate volume and cost models are also developed to deal with the optimization in the discrete research space. The bi-objective (loss–volume) and tri-objective (loss–volume–cost) optimization results are presented, and the variations of the design variables are analyzed for the case of 60 kHz. An example of a design (30 kHz) is experimentally verified. The registered efficiency is 88% at full load.

    Fulltekst (pdf)
    fulltext
  • 22.
    Bertilson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Hjelm, Mats
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Petersson, Sture
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Monte Carlo Simulation of 4H and 6H-SiC short channel MOSFETs2001Inngår i: High Temperature Electronics Network. HITEN ; 4 (Oslo) : 2001.06.05-08: Proceedings of the International Conference on High Temperature Electronics : held in Oslo, Norway, 5th - 8th June 2001, Oxford: Oxford Applied Technology Ltd, , 2001, s. 199-Konferansepaper (Fagfellevurdert)
  • 23.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nästa generations kompakta spänningsomvandlare2012Inngår i: Thule, Kungl. Skytteanska Samfundets Årsbok 2012, ISSN 0280-8692, Vol. 1, nr 1, s. 153-157Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 24.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Simulation and Optimization of SiC Field Effect Transistors2004Doktoravhandling, monografi (Annet vitenskapelig)
  • 25.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Transformer2010Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    A printed circuit board transformer comprises at least one primary winding and one secondary winding, each in the form of at least one layer of turns inside or at the surface of a printed circuit board. The transformer is designed for a step-up/down-operation. Each of the two layers (10, 11) has an elongated winding element (12, 13, 13′) substantially following an elongated winding element of the other layer while being in an overlapping relationship therewith as seen perpendicularly to said printed circuit board over substantially the entire extension of said winding elements. A second (11) of the layers belonging to the secondary winding has a fewer number of turns than the first (10) of said layers belonging to said primary winding.

  • 26.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Dubaric, Ervin
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Hjelm, Mats
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Petersson, Sture
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC2001Inngår i: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 10, nr 3-7, s. 1283-1286Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The 4H-SiC static induction transistor (SIT) is a very competitive device for high frequency and high power applications (3-6 GHz range). The large breakdown voltage and the high thermal conductivity of 4H-SiC allow transistors with extremely high current density at high voltages. The SIT transistor shows better output power capabilities but the unity current-gain frequency is lower compared to a MESFET device. In this work we show, using a very accurate numerical model, that a compromise between the features given by the SIT structure and the ordinary MESFET structure can be obtained using the vertical MESFET structure. The device dimension has been selected very aggressively to demonstrate the performance of an optimized technology. We also present results from drift-diffusion simulations of devices, using transport parameters obtained from the Monte Carlo simulation. The simulations indicate that 2H-SiC is superior to both 4H and 6H-SiC for vertical devices. For lateral devices, 2H-SiC is slightly faster compared to an identical 4H-SiC device

  • 27.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Dubaric, Ervin
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Petersson, Sture
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Simulation of a low atmospheric-noise modified four-quadrant position sensitive detector2001Inngår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 466, nr 1, s. 183-187Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A modified four-quadrant position sensitive detector (PSD) is developed. This structure is less sensitive to atmospheric turbulence that is a major drawback with the traditional four-quadrant detector. The inter-electrode resistance is as high as for the four-quadrant detector, which is an advantage compared to the lateral effect PSD. The linearity for the modified four-quadrant detector is good in the whole active range of sensing. The structures are limited to small sensing areas with well focused beams and are suitable for use in detectors up to 1 mm in size.

  • 28.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Harris, C
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Calculation of lattice heating in SiC RF power devices2004Inngår i: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 48, nr 12, s. 1721-1725Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Silicon carbide MESFET devices are suitable for high-speed and high-power applications. In this paper we are studying thermal effects in 4H-SiC RF power devices. The simulations are based on a combination of 2D device simulations for the electrical transport, and 3D thermal simulations for the lattice heating. We show that the method gives good accuracy, efficiency, flexibility and capacity dealing with tasks, where a 2D coupled electrical-thermal simulation is not sufficient. We also present an improvement of Roschke and Schwierz mobility model, based on Monte Carlo simulations for the temperature dependencies of the mobility parameters beta and v(sat).

  • 29.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Harris, C.I.
    Comparison of bipolar and unipolar SiC switching devices for very high power applications2007Inngår i: Silicon Carbide and Related Materials 2006, Trans Tech Publications Inc., 2007, Vol. 556-557, s. 975-978Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Both unipolar and injection SiC devices can be used for high voltage switching applications; it is not determined, however, for which applications one approach is preferred over the other. In this paper, simulation studies are used to compare the suitability of unipolar devices, in this case a JFET (Junction Field Effect Transistor) against an equivalent FCD (Field Controlled Diode) configuration up to very high voltages. The calculations are performed in a finite element approach, with commercial drift-diffusion software. Numerous drift layers have been simulated in a Monte-Carlo approach to ensure that the optimal design of the drift layers for different breakdown is used. In a static case, purely conductive losses in the drift layer in both unipolar and injection configuration are compared. Additionally the total losses are studied and compared in switched applications for different switching frequencies and current levels.

  • 30.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Optimization of 2H, 4H and 6H-SiC high-speed vertical MESFETs2002Inngår i: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 11, nr 3-6, s. 1254-1257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Silicon carbide vertical MESFET devices are well suited for high speed and high power electronic devices. In this work we have optimized the geometry of vertical MESFETs for microwave applications, using iterative two-dimensional simulations. Relevant parasitics are included in the simulations to investigate the performance of realistic devices. The state of the art device has f(T)=7 GHz and we show that vertical MESFETs fabricated with traditional technology are totally limited by parasitics. Two different approaches to reduce the parasitics in the vertical MESFET are proposed where f(T) increases significantly.

  • 31.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Optimization of 2H, 4H and 6H-SiC MESFETs for High Frequency Applications2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 101, s. 75-77Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Silicon carbide MESFET devices are well suited for high speed, high power and high temperature electronics due to high saturation velocity, high critical electrical field, good thermal conductivity and large band-gap. Optimization of a high performance device demands a substantial number of numerical simulations, where several different design parameters have to be investigated thoroughly. In this work, we optimize the geometry of lateral MESFETs for maximal unity current-gain frequency (fT) using iterative 2-dimensional simulations. We also present a comparison of performance for individually optimized devices, realized with lithographic resolutions ranging from 0.2 to 2 μm in different SiC polytypes.

  • 32.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    The power of using automatic device optimization, based on iterative device simulation, in design of high-performance devices2004Inngår i: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 48, nr 10-11, s. 1721-1725Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An automatic optimization tool for semiconductor devices based on iterative device simulations is developed. The tool is used for optimization of different kinds of semiconductor devices using various performance measures. High performance optimization algorithms, both local and global, are used to achieve an efficient design in shortest possible time. In this paper the effects of different optimization algorithms, performance measures, and number of variables in the optimization are studied. Both the computational efficiency and the devices achieved with different performance measures are studied. We give a demonstration of the usefulness of this method in a comparison between different device topologies, which have been optimized for best performance.

  • 33.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    The power of using automatic device optimization, based on iterative device simulations, in design of high-performance devices2003Inngår i: 2003 International Semiconductor Device Research Symposium, ISDRS 2003 - Proceedings, 2003, s. 152-153, artikkel-id 1272038Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Device design is a time consuming work, where the influence of many design parameters has to be investigated carefully. In advanced devices optimal performance is often achieved taking multiple trade-off into consideration, and manual device optimization is often insufficient. In this paper we present the feasibility of using device optimization for design on electronic devices. An optimization tool is developed, which runs device simulations and automatically changes the design parameters, searching for optimal performance according to a specified performance measure. This has been shown to be a very time and cost efficient way for device design, as the search for optimal performance is fuily automatic working in a systematic way 24 hours 7 days a week. From an industrial point of view this is very important as it can reduce the evaluation and optimization cost for new devices considerably. It is impossible to give a fair comparison between different devices unless these are designed to give optimal performance. We give a demonstration of the usefulness of this method in a comparison between different device topologies which individually have been optimized for best performance.

  • 34.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Hjelm, Mats
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Petersson, Sture
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Käckell, P.
    Persson, C.
    The Effect of Different Transport Models in Simulation of High Frequency 4H-SiC and 6H-SiC Vertical MESFETs2001Inngår i: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 45, nr 5, s. 645-653Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A full band Monte Carlo (MC) study of the high frequency performance of a 4H-SiC Short channel vertical MESFET is presented. The MC model used is based on data from a full potential band structure calculation using the local density approximation to the density functional theory. The MC results have been compared with simulations using state of the art drift-diffusion and hydrodynamic transport models. Transport parameters such as mobility, saturation velocity and energy relaxation time are extracted from MC simulations

  • 35.
    Bertilsson, Kent
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Petersson, Sture
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Simulation of anisotropic Breakdown in 4H-SiC Diodes2000Inngår i: IEEE Workshop on Computers in Power Electronics: COMPEL 2000, IEEE , 2000, s. 118-120Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The breakdown characteristics of two-dimensional 4H-SiC diode structures have been studied using an anisotropic drift-diffusion model. The degree of anisotropy was estimated from recent full band Monte Carlo simulations. Identical diode structures have previously been used in the literature to measure the hole impact ionization coefficients of 4H-SiC. The reported measurements from different research groups show large differences in the impact ionization coefficients. Our numerical simulations show that the differences in these measurements can be explained by the difference in device geometry used by the research teams if one considers an anisotropic impact ionization process. This indicates that it is very important to consider anisotropic impact ionization in design and characterization of 4H-SiC power devices.

  • 36.
    Das, Moumita
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Barg, Sobhi
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Haller, Stefan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bakar, Muhammad Abu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Rezaee, Ali
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    State of Art of Designing Power Electronics Converter for Low Voltage Motor Drives for Electric Vehicle2020Inngår i: 2020 IEEE International Conference on Power Electronics, Smart Grid and Renewable Energy (PESGRE2020), IEEE, 2020Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In recent times, the boom in electric vehicle (EV) is increasing due to the development of highly efficient power converters and to reduce the fossil fuel dependency. Hence, the progress in both electric and hybrid vehicles are rising. However, the safety become an issue in EVs for operating at high voltage level. Therefore, the application of the low voltage motor in EVs is proposed. This helps to increase the safety in the vehicle and reliability of the system. The proposed voltage for such low voltage motor drives is 48V. This voltage level is also beneficial for integration of battery and ultra-capacitors (UCs). This paper proposes the state of art of designing power converters for low voltage motor drives. Additionally, a novel bi-directional DC-DC converter with reconfigurable transformer is proposed for driving low voltage motors. The proposed bi-directional converter can operate with wide input (12V-4SV) and wide output voltage (1.5V-24V) ranges for power level of 1. 2kW. Analysis of this system and operating principle of the novel converter are also included for different output voltage and current levels. The presence of UCs in the system helps to improve the control response required during accelerating and braking. The simulation results of the system are included in the paper for different voltage and speed levels. The preliminary experiment result is included in the paper.

  • 37.
    Das, Moumita
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    GaN Based Converters for Battery Charging Application of Electric Vehicle2019Inngår i: IECON2019: 45th Annual Conference of the IEEE Industrial Electronics Society, IEEE, 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The high frequency capability and low on-state losses of Gallium Nitride (GaN) transistors offer the potential to increase converter efficiency and/or reduce heatsink and passive component size. This paper investigates the use of GaN technology to enhance the performance of power factor correction (PFC) and LLC converters for battery charging applications. First the efficiency performance of non-isolated PFC converters using GaN transistors is compared by simulation, the asymmetric bridgeless PFC converter is shown to achieve the best efficiency, with a predicted figure of 99% in a 1MHz, 200W design. The predictions are validated by an experimental prototype using a GS66502B, GaN Systems E-mode GaN transistor. Then the efficiency comparison of the PFC and LLC converter using GaN devices for battery charging applications is included in the paper. The experimental results of the PFC converter with GaN devices are also included. Additionally, this paper includes the analysis and design of a common mode input filter for the GaN-based high frequency converters for battery charging application. The size of both the converters using GaN devices is reduced by 40% than the converters based on Si devices. The switching loss comparison of GaN and Si devices are also included in the paper.

  • 38.
    Dubaric, Ervin
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Simulations of Submicron MOSFETs in 2H, 4H and 6H-SiC2002Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 101, s. 14-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we present numerical studies of the high frequency performance of a submicron MOSFET in 2H-, 4H- and 6H-SiC. The studies are based on simulations where commercial two-dimensional drift-diffusion and hydrodynamic carrier transport models have been used. The results have been compared with those obtained from full band Monte Carlo simulations. The Monte Carlo carrier transport model is based on data from a full potential band structure calculation using the Local Density Approximation to the Density Functional Theory. In 6H-SiC the bulk transport properties in the direction perpendicular to the c-axis, are slightly lower than in 2H- and 4H-SiC. However, in the direction parallel to the c-axis the transport properties are considerably less favourable than in the other two polytypes. The effects of these differences, on surface mobility device performance and carrier energy, have been studied.

  • 39. Harris, Christopher
    et al.
    Basceri, Cem
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Schottky diode with incorporated pn- junctions2007Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    A semiconductor device of unpopular type has Schottky-contacts (6) laterally separated by regions in the form of additional layers (7, 7') of semiconductor material on top of a drift layer (3). Said additional layers being doped according to a conductivity type being opposite to the one of the drift layer. At least one (7') of the additional layers has a substantially larger lateral extension and thereby larger area of the interface to the drift layer than adjacent such layers (7) for facilitating the building-up of a sufficient voltage between that layer and the drift layer for injecting minority charge carriers into the drift layer upon surge for surge protection.

  • 40. Harris, Christopher
    et al.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Konstantinov, Andrei
    Method of manufacturing silicon carbide self-aligned epitaxial MOSFET for high powered device applications2010Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    A self-aligned, silicon carbide power metal oxide semiconductor field effect transistor includes a trench formed in a first layer, with a base region and then a source region epitaxially regrown within the trench. A window is formed through the source region and into the base region within a middle area of the trench. A source contact is formed within the window in contact with a base and source regions. The gate oxide layer is formed on the source and base regions at a peripheral area of the trench and on a surface of the first layer. A gate electrode is formed on the gate oxide layer above the base region at the peripheral area of the trench, and a drain electrode is formed over a second surface of the first layer.

  • 41. Harris, Christopher
    et al.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Konstantinov, Andrei
    Silicon carbide self-aligned epitaxial MOSFET for high powered device applications2008Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    A self-aligned, silicon carbide power metal oxide semiconductor field effect transistor includes a trench formed in a first layer, with a base region and then a source region epitaxially regrown within the trench. A window is formed through the source region and into the base region within a middle area of the trench. A source contact is formed within the window in contact with a base and source regions. The gate oxide layer is formed on the source and base regions at a peripheral area of the trench and on a surface of the first layer. A gate electrode is formed on the gate oxide layer above the base region at the peripheral area of the trench, and a drain electrode is formed over a second surface of the first layer.

  • 42.
    Hjelm, Mats
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Full Band Monte Carlo Study of Bulk and Surface Transport Properties in 4H and 6H-SiC2001Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 184, nr 1-4, s. 194-198Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The bulk and surface electron transport properties of the 4H and 6H polytypes of silicon carbide (SiC) are studied using a full band Monte Carlo (MC) program. The model for the electrons is based on data from a full potential band structure calculation using the density functional theory (DFT) in the local density approximation (LDA). Both SiC polytypes have anisotropic transport properties, but the degree and characteristics of the anisotropy is different. In this study, we show how the anisotropy affects the bulk mobility for intermediate angles between the crystal axis and the plane perpendicular to it. Simulations of surface transport properties have also been performed for semiconductor-interface angles up to 15 degrees from the plane perpendicular to the c-axis. We present results for surface mobility and velocity as a function of the electric field component parallel to the interface plane. In the surface mobility simulations, a semi-empirical model for the semiconductor-insulator interface has been used, where it is assumed that the electrons are reflected in two perpendicular planes.

  • 43. Intarasiri, S.
    et al.
    Hallén, A.
    Lu, J.
    Jensen, J.
    Yu, L.D.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Wolborski, M.
    Singkarat, S.
    Possnert, G.
    Crystalline quality of 3C-SiC formed by high-fluence C+-implanted Si2007Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 253, nr 11, s. 4836-4842Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Carbon ions at 40 keV were implanted into (100) high-purity p-type silicon wafers at 400 oC to a fluence of 6.5×1017 ions/cm2. Subsequent thermal annealing of the implanted samples was performed in a diffusion furnace at atmospheric pressure with inert nitrogen ambient at 1100 oC. Time-of-flight energy elastic recoil detection analysis (ToF-E ERDA) was used to investigate depth distributions of the implanted ions. Infrared transmittance (IR) and Raman scattering measurements were used to characterize the formation of SiC in the implanted Si substrate. X-ray diffraction analysis (XRD) was used to characterize the crystalline quality in the surface layer of the sample. The formation of 3C-SiC and its crystalline structure obtained from the above mentioned techniques was finally confirmed by transmission electron microscopy (TEM). The 1 results show that 3C-SiC is directly formed during implantation, and that the subsequent high-temperature annealing enhances the quality of the poly-crystalline SiC.

  • 44.
    Kotte, Hari Babu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Ambatipudi, Radhika
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    A 45W LLC resonant Converter in MHz Frequency Region for Laptop Adapter Application using GaN HEMTs2013Inngår i: PCIM Europe Conference Proceedings, Berlin: Mesago PCIM GmbH , 2013, s. 1029-1035Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The authors report the feasibility of low profile, high power density and energy efficient isolated DC/DC converter in 3 – 4 MHz frequency region corresponding to low line input voltage of 90 – 110 Vac suitable for 45W laptop adapter application. Using novel hybrid power transformer, GaN HEMTs, the simulation and experimental results of LLC resonant converter for DC input voltage range of 127 – 155Vdc with a regulated output voltage of 22Vdc was presented. The maximum energy efficiency of converter at the full load condition is reported to be approximately 91% whereas light load efficiency was improved using pulse skip modulation technique.

  • 45.
    Kotte, Hari Babu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Ambatipudi, Radhika
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    A ZVS Flyback DC-DC Converter using Multilayered Coreless Printed Circuit Board (PCB) Step Down Power Transformer2010Inngår i: World Academy of Science, Engineering and technology, Paris: World Academy of Science,Engineering and Technology , 2010, s. 148-155Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The experimental and theoretical results of a ZVS (Zero Voltage Switching) isolated flyback DC-DC converter using multilayered coreless PCB step down 2:1 transformer are presented.The performance characteristics of the transformer are shown which are useful for the parameters extraction. The measured energy efficiency of the transformer is found to be more than 94% with the sinusoidal input voltage xcitation. The designed flyback converter has been tested successfully upto the output power level of 10W,with a switching frequency in the range of 2.7MHz-4.3MHz. The input voltage of the converter is varied from 25V-40V DC.Frequency modulation technique is employed by maintaining constant off time to regulate the output voltage of the converter. The energy efficiency of the isolated flyback Converter circuit under ZVS condition in the MHz frequency region is found to be approximately in the range of 72-84%. This paper gives the comparative results in terms of the energy efficiency of the hard switched and soft switched flyback Converter in the MHz frequency region.

  • 46.
    Kotte, Hari Babu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Ambatipudi, Radhika
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Comparative Results of GaN and Si MOSFET in a ZVS Flyback Converter using Multilayered Coreless Printed Circuit Board Step-Down Transformer2010Inngår i: Proceedings of 2010 3rd International Conference on Power Electronics and Intelligent Transportation System, Shenzhen: IEEE conference proceedings, 2010, s. 318-321Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of this paper is to compare two different material MOSFETs performance namely GaN (Gallium Nitride) and conventional Si (Silicon) in Zero Voltage Switching (ZVS) flyback converter circuit with Coreless PCB step down transformers. The switching frequency of the regulated converter is in the range of 3.2-5MHz. In high frequency circuits, proper selection of MOSFETs is required in order to have low gate drive power consumption so that high energy efficiency of the converter can be achieved. Even though Si MOSFET has already known for its popularity in low to medium power converters and high frequency applications, GaN MOSFET device could produce better results.  This can be done by reducing the total switching loss, conduction loss because of its low Rds-on and gate drive power consumption of the converter as a result of low gate charge, Qg. From the experimental results, it can be observed that GaN MOSFET can produce higher energy savings including gate drive power by gaining approximately 8%-10% efficiency compared to its counterpart, Si MOSFET in a regulated 45-15V isolated DC-DC converter.

  • 47.
    Kotte, Hari Babu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Ambatipudi, Radhika
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Design and Analysis of 45W Multi Resonant Half Bridge Converter in MHz Frequency Region using GaN HEMTsManuskript (preprint) (Annet vitenskapelig)
  • 48.
    Kotte, Hari Babu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Ambatipudi, Radhika
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    High Speed Cascode Flyback Converter Using Multilayered Coreless Printed Circuit Board (PCB) Step-Down Power Transformer2011Inngår i: Proceedings of 8th International Conference on Power Electronics-ECCE Asia, IEEE conference proceedings, 2011, s. 1856-1862Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, design and analysis of the high speed isolated cascode flyback converter using multilayered coreless PCB step down power transformer is presented. The converter is tested for the input voltage variation of 60-120V with a nominal DC input voltage of 90V. The designed converter was simulated and tested successfully up to the output power level of 30W within the switching frequency range of 2.6-3.7MHz. The cascode flyback converter is compared with the single switch flyback converter in terms of operating frequency, gate drive power consumption, conduction losses and stresses on MOSFETs. The maximum energy efficiency of the cascode converter is approximately 81% with a significant improvement of about 3-4% compared to single switch flyback converter. The gate drive power consumption which is more dominant compared to conduction losses of the cascode converter using GaN MOSFET is found to be negligible compared to single switch flyback converter.

  • 49.
    Kotte, Hari Babu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Ambatipudi, Radhika
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    High Speed (MHz) Series Resonant Converter (SRC) Using Multilayered Coreless Printed Circuit Board (PCB) Step-Down Power Transformer2013Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 28, nr 3, s. 1253-1264Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, design and analysis of an isolated low profile, series resonant converter (SRC) using multilayered coreless printed circuit board (PCB) power transformer was presented. For obtaining the stringent height switch mode power supplies (SMPS), a multilayered coreless PCB power transformer of approximately 4:1 turn’s ratio was designed in a four layered PCB laminate which can be operated in MHz switching frequency. The outermost radius of the transformer is 10mm with achieved power density of 16W/cm2. The energy efficiency of the power transformer is found to be in the range of 87-96% with the output power level of 0.1-50W operated at a frequency of 2.6MHz. This designed step-down transformer was utilized in SRC and evaluated. The supply voltage of converter is varied from 60-120V DC with a nominal input voltage of 90V and has been tested up to the power level of 34.5W. The energy efficiency of converter under Zero Voltage Switching (ZVS) condition is found to be in the range of 80-86.5% with the switching frequency range of 2.4-2.75MHz. By using constant off-time frequency modulation technique, the converter was regulated to 20V DC for different load conditions. Thermal profile with converter loss at nominal voltage is presented.

  • 50.
    Kotte, Hari Babu
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Ambatipudi, Radhika
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Bertilsson, Kent
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    High Speed Series Resonant Converter (SRC) Using Multilayered Coreless Printed Circuit Board (PCB) Step-Down Power Transformer2011Inngår i: Proceedings of 33rd International Telecommunications Energy Conference (INTELEC 2011), Amsterdam: IEEE conference proceedings, 2011, s. Art. no. 6099785-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, simulation and experimental results of an isolated low profile, series resonant converter (SRC) using multilayered coreless printed circuit board (PCB) step-down power transformer are described. The designed converter prototype was operated in MHz switching frequency region. For obtaining the stringent height switch mode power supplies (SMPS), a new multilayered coreless PCB power transformer of approximately 4:1 turn’s ratio was designed in a four layered PCB laminate. The outermost radius of the step-down power transformer is 10mm with achieved power density of 16W/cm2. The energy efficiency of the power transformer is found to be in the range of approximately 87-96% with the output power level of 0.1-50W in the frequency range of 1.5-4MHz. This designed step-down power transformer was utilized in SRC and evaluated.The supply voltage of converter is varied from 60-120V DC with a nominal input voltage of 90V. The SRC has been tested successfully upto the output power level of 34.5W. The energy efficiency from the converter prototype under Zero Voltage Switching (ZVS) condition is found to be in the range of 80-86.5% with the switching frequency range of 2.4-2.75MHz. By using constant off-time frequency modulation technique the output voltage of converter is regulated to 20V DC for different load conditions. Thermal profile and the loss estimation of SRC at nominal voltage are also presented.

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