Mid Sweden University

Printed electronics is a rapidly developing field where many components can already be manufactured on flexible substrates by printing or by other high speed manufacturing methods. However, the functionality of even the most inexpensive microcontroller or other integrated circuit is, at the present time and for the foreseeable future, out of reach by means of fully printed components. Therefore, it is of interest to investigate hybrid printed electronics, where regular electrical components are mounted on flexible substrates to achieve high functionality at a low cost. Moreover, the use of paper as a substrate for printed electronics is of growing interest because it is an environmentally friendly and renewable material and is, additionally, the main material used for many packages in which electronics functionalities could be integrated. One of the challenges for such hybrid printed electronics is the mounting of the components and the interconnection between layers on flexible substrates with printed conductive tracks that should provide as low a resistance as possible while still being able to be used in a high speed manufacturing process. In this article, several conductive adhesives are evaluated as well as soldering for mounting surface mounted components on a paper circuit board with inkjet printed tracks and, in addition, a double sided Arduino compatible circuit board is manufactured and programmed.

This work describes the development of inkjet printed, low-cost memory cards, and complementary pair of memory card reader and card reader/programmer for PCs. This constitutes a complete system that can be used for various applications. The memory cards are manufactured by inkjet printing nano-silver ink on photo paper substrate. The printed memory structures have an initial high resistance that can later be programmed to specific values representing data on the cards, the so called Write Once Read Many (WORM) memories. The memory card reader measures the resistance values of the memory cells and reads it back to the computer by USB connection. Using multiple resistance levels that represent different states it is possible to have a larger number of selectable combinations with fewer physical bits compared to binary coding. This somewhat counters one of the limitations of resistive memory technology that basically each cell needs one physical contact. The number of possible states is related to the resolution of the reader and the stability of the WORM memory.

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.

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.

The first electric low-voltage vehicles were constructed in the mid-19th century, but by the early 20th century they were progressively replacedby successors with internal combustion engines. As the consequences ofusing fossil fuels are better understood, our society is now transitioning back. The strong driving force towards electric transportation can be traced to several events and trends. The foremost of these is perhaps the rising awareness of climate change and the necessary reduction of the environmental footprint, as well associated political will for change. Alongside this, the pioneering automotive company Tesla, Inc. showed what electric cars are capable of and how to easily charge them along the road. The diesel gate unearthed in 2015, also played a major role. This transition is not without challenges, however. An electric car is expected to be reasonable priced, sustainable, environmentally friendly and electrically safe, even in case of an accident. Overnight charging at home should be possible, as well as the ability to quickly charge while in transit. While the industry has long experience with high-voltage electrical machines, the required battery technology is quite new and low-voltage in nature. Currently, the battery is the most costly part of an electric drivetrain and it has the highest environmental impact. Efficient battery use is therefore key for sustainability and a responsible consumption of the resources available. Nonetheless, most electric vehicles today use lethal high-voltage traction drives which require a considerable isolation effort and complex battery pack. Previous research results showed that a 48 V drivetrain compared to a high-voltage one, increases the drive-cycle efficiency. Hence, similar driving range can be reached with a smaller battery. This thesis provides an introduction to low-voltage, high-current, battery-powered traction drives. With the aim of increasing efficiency, safety and redundancy while reducing cost, a solution that breaks with century-old electric machine design principles is proposed and investigated. An overview and motivation to further investigate 48 V drivetrains with intrinsically safe and redundant machines is provided. The main focus of this work is the practical implementation of multi-phase low-voltage but high-current machines with integrated power electronics as well as components for a 48 V drivetrain. With this work, it is confirmed that today’s MOSFETs are not the limiting factor towards low-voltage, high-current drives. In the first part of this work, two small-scale prototype machines were constructed and tested. The air-cooled, small-scale 1.2 kW proto-type reached a copper fill-factor of 0.84. The machine’s low terminal-to-terminal resistance of 0.23 mΩ, including the MOSFET-based power electronics, allowed continuous driving currents up to 600 A. The resistive MOSFET losses stayed below 21 W. The second part focuses on the key components for a 48 V high-power drivetrain. A W-shaped coil for a multiphase 48 V machine with direct in-conductor cooling was designed and tested. With glycolwater, it reached a current density of 49.5 A/mm2 with 0.312 l/min flowrate. Furthermore, a reconfigurable battery pack for 48 V driving andhigh-voltage charging was investigated.

48 V is emerging as a safe-to-touch alternative voltage level for electric vehicles (EVs). Using a low- instead of a high-voltage drive train reduces isolation efforts, eliminates the risk of electric shock, and thus increases the system safety. In contrast, fast charging of a 48 V battery would require very high currents and is incompatible with the widely established high-voltage electric vehicle charging infrastructure. Instead of employing additional on board power converters for fast charging, the concept of a reconfigurable battery is presented. A small-scale prototype system is designed consisting of eight 48 V lithium iron phosphate battery modules. In series configuration, they can be charged at 460 V with up to 25 A. In 48 V parallel configuration, the peak discharge current is up to 800 A. The MOSFET-based reconfiguration system also operates as a module charge balancer during high-voltage charging. The cost overhead for the reconfiguration system is estimated to 3% for a scaled-up full size EV. Due to the additional reconfiguration switch resistances, the simulation of a 48 V 75 kW electric vehicle in the World harmonized Light-duty vehicles Test Procedure showed a performance reduction of 0.24%.

The development of recent high-efficient power converters leads to novel multi-switch topologies. To allow precise control of multiple switches, high-resolution PWM signals are required. Today, DSCs already provide PWM signal generation with 250 ps resolution. Nevertheless, limitations prevent them from meeting new converter topologies. Still, they are a promising choice for prototyping compared to FPGAs in terms of cost, footprint and complexity. To overcome these limitations, a hybrid-controller with a dual core dsPIC DSC and a CPLD was designed. The presented controller is optimized for a wide-range converter with reconfigurable transformer configuration. Since it is very versatile, easy to configure and fabricate, it can also be used for prototyping of many other converter topologies. In addition to the regular DSC features, it adds dynamic signal routing, logic and synchronization capabilities. The proposed hybrid-controller is described, experimentally verified and compared to a purely DSC based controller when driving a phase-shifted full-bridge with reconfigurable transformer. To estimate the component stress, the generated PWM waveforms were captured and fed into a spice simulation of the converter. 

A high copper fill factor allows reducing the resistive losses responsible for more than 50 % of the losses in today's most commonly used electrical motors. Single-turn windings achieve a copper fill factor close to one. Furthermore, they do not suffer from turn to turn faults and provide a low thermal resistance between winding and stator. The reduced EMF of single-turn winding configurations promotes the use of extra-low voltage high current MOSFETs. Rapid development of these MOSFETs allows reversing common design principles to explore new applications, such as battery electric traction drives. This paper presents a 2.5 V 1 kW MOSFET driven 13-phase permanent magnet DC motor with a single-turn winding configuration. The motor prototype with a copper fill factor of 0.84 was tested with continuous drive currents up to 600 A. The measured torque-efficiency map shows that such a high-current concept with voltages below 60 V is feasible using today's extremely low-voltage high current semiconductors. Due to the rapid development of such switches, there is great potential in this concept for further improvements. This work presents a small-scale version of the high-current drive, which is part of the development of an extra-low voltage traction drive concept. 

To verify the FEM simulation of the air-gap flux density, it is necessary to measure the flux density distribution as function of the angular machine position. This paper presents a scalable 3-D direct air-gap flux density magnitude measurement system for rotating electrical machines. A combination of eight linear Hall effect flux sensors and a rotary encoder is used to measure the flux density magnitude as function of the angular machine position. The system is designed for permanent magnet motors with an air gap of at least 1 mm, but can also be used for other types of machines. The miniaturized sensor array with the flux sensors is 0.7 mm thick, and measures the distribution of the air-gap flux density magnitude in a range of ±2 T along the rotor axis. The design of the measurement system is described and tested on a prototype of an electronically commutated permanent magnet DC motor. The obtained measurement results are compared with the FEM simulation results of the prototype motor. A good match between the simulated and measured flux density magnitude is shown. The conclusions presented in this study, are used to further optimize the simulation model and the prototype motor.

Rapid development of extremely-low voltage high current MOSFETs allows reversing common design principles to explore new applications, such as battery powered traction drives. This enables the usage of multi-phase single-turn stator windings which can achieve a copper fill factor close to one. This paper briefly describes the proposed 2V, 1.1kW MOSFET commutated 13-phase permanent magnet DC motor and presents the efficiency and resistive loss measurements of the first prototype. The motor was successfully run with drive currents up to 520 A. Most of the obtained losses were resistive contact losses due to the flexible winding connections, less than 6% are dedicated to the MOSFETs. The results show that such a high current drive system is feasible and has great potential for further improvements, which is supported by the rapid development of extremely-low voltage high current semiconductors.

This paper proposes an extremely-low voltage high current MOSFET-based drive architecture. A single-turn multiphase winding design allows a copper fill factor approaching one. The single-turn coil design leads to a low EMF voltage and high current design which requires a matched drive system. To identify the technical design obstacles and verify the feasibility of the proposed architecture, a small scale prototype is built and successfully tested. The described prototype consists of an extremely-low voltage 13-phase single-turn coil permanent magnet DC motor and MOSFET-based commutator. The prototype's locked rotor-torque and no-load power consumption, as well as the EMF voltage measurements are presented and the DC motor constants are extracted. The experimental results from the prototype measurements indicate a promising potential for cost-effective extremely-low voltage high current MOSFET-based drive systems.

Traction drive applications demand high power density motors with a good stator cooling design. We propose a novel multi-phase winding for a 48 V traction drive design having identical preformed hollow copper conductors with in-conductor direct cooling capability. This paper studies the cooling performance of an individual conductor phase using either EGW50/50 or water as coolant. Analytical calculations and experiments are conducted on a straight conductor of the same length using 20°C water as coolant. The results are then cross verified with those from the FEM simulations to validate the simulation setup. Then a final simulation is conducted at a current of 700A and a current density of 49.5 A/mm 2 on the preformed conductor using 65 CEGW50/50 as coolant at a pressure of 140kPa. The results highlight the exceptional performance of the cooling design which enables a power dissipation of 71OW at a maximum conductor temperature rise of only 56. 9 C. 

The significant problems in increasing the switching frequency of isolated converters to achieve low cost and high power density are increased magnetic and switching losses. This paper presents solution with the investigation of newly designed high frequency, low profile, hybrid power transformer together with commercially available GaN MOSFETs. For achieving stringent power converters, a center tapped 4:1:1 half bridge transformer was designed in a multilayered PCB laminate with a total height of transformer as 4.2mm. The maximum obtained energy efficiency of transformer is 98% in the frequency region of 1 – 5MHz. The designed transformer possesses better high frequency characteristics in the frequency range of 3 - 5MHz with tested power density of 47W/cm³ at an operating frequency of 3MHz. This transformer has been utilized in the multi resonant zero voltage switching (ZVS) half bridge converter with synchronous rectification using GaN MOSFETs and then evaluated. The maximum achieved efficiency of multi resonant ZVS half bridge converter with this transformer is 92% in 3 – 4.5 MHz switching frequency range with characterized output power of 40W. This is to the author’s knowledge, the best energy efficiency ever reported for an isolated DC-DC converter in this frequency range and power levels. At a specified input voltage, the converter has been regulated to 15V within 1% for both line and wide load variations. This work provides considerable step for the development of next generation ultra flat low profile isolated DC-DC/AC-DC converters operating in MHz frequency region.

This paper introduces high frequencyhalf bridgeDC-DC converter, using multilayered coreless Printed Circuit Board (PCB) step down power transformer. The converter is simulated and then implemented on a PCB. Complementary Pulse Width Modulated (PWM) signals are generated to turn on high and low side Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) alternately by a micro-controller. The isolated gate drive signals are provided to the high side MOSFET by using high frequency coreless PCB isolation transformer. We tested the converter for switching frequency range of 2 to 3 MHz, and for maximum input voltage up-to 170 V. The maximum output power achieved is 40 W and the maximum energy efficiency is approximately 82 %. © 2011 IEEE.

Power supply is an inevitable component for all electronic instruments as a constant DC source. Almost all power supplies use feedback loop to achieve constant DC output voltage. In a feedback loop, the galvanic isolation is required between input and output. It can be achieved either by implementation of opto-coupler feedback on the secondary side or magnetic feedback. In this paper both opto-coupler and auxiliary feed-back techniques are implemented and analyzed in a high frequency half bridge converter using coreless Printed Circuit Board (PCB) power transformer. The implementation of opto-coupler feedback is temperature sensitive and has relatively high cost. The auxiliary winding of transformer can also be used to provide feedback signals as alternate to opto-coupler. Auxiliary feedback implementation is cheaper, temperature stable and insensitive to temperature variations. In this paper, the feasibility of feedback using auxiliary winding of coreless PCB power transformer is investigated. It is observed that this technique can be used as an alternative to opto-coupler feedback.

Inverter drive resistance spot welding machines are becoming a good choice of welding because of the increased machine efficiency and output power. The DC link capacitors in spot welding equipment store a large amount of energy. In case of any failure, the IGBT in the inverter has a risk of exhibiting a violent rupture. This rupture can damage the converter, drive down time and personal injury which may lead to the machinery certification problems. IGBT failure detection and solution for protection of these failures in resistance welding machines have not been reported in literature. Literature study of the IGBT failure, rupture, fault detection and protection has been carried out for inverter drives in power applications. On the basis of the findings some protection schemes and important measures in the design of the machine have been adopted which have resulted in the reduced risk of IGBT failure.