Power Electronics plays a very important role in the electrical power conversion and is widely used in transportation, renewable energy and utility applications. By 2020, 80% of electrical power will go through power electronics converters somewhere between generation, transmission, distribution and consumption. So high-efficiency, high-power-density and high-reliability are very important for power electronics converters. The conventional power electronics devices are based on silicon materials and have reached the limit of their potential. The emergence of wide-bandgap (WBG) material such as silicon-carbide (SiC) and Gallium-Nitride (GaN) based devices has brought in clear opportunities enabling compact, more efficient power converters, operating at higher voltages, frequencies and powers to meet the increasing demand by a range of existing and emerging applications. For example, more/full electric aircrafts with hybrid propulsion requires 10s of MW efficient power conversion with high frequency drives, higher voltage levels as well as higher power density. Wireless power charging is pushing the frequency from 100s of kHz to MHz at kW power level to minimise passive elements such as inductors and capacitors. Transformerless, compact, high-efficiency medium-voltage (1kV~10kV) power conversion enabled by high voltage SiC devices is critical for the realisation of power electronics based distribution networks (including energy storage interfacing) for smart grid as well as future transportation systems. Whilst WBG devices offer the possibility to operate at higher voltages with lower on-state losses, and faster switching speeds than Si devices, maximising the performance benefits at a converter level creates a range of interrelated challenges. For example, high voltage and current changing rates of WBG devices will generate significant electro-magnetic-interference (EMI) and affect the running of other equipment. Identifying the most effective circuit topologies, passive component technologies and control methods, and managing the very high switching rates to extend the frequency/voltage/power envelope present great challenges to power electronic engineers, but are vital if the true potential of WBG circuits is to be achieved. They therefore form the main motivation for this project. This Converter Architecture (CA) project brings together the UK's best academic and industrial expertise to investigate optimal converter architectures, advanced passive components design methods, fast speed control techniques and holistic optimisation to realise the full potential of WBG devices in achieving higher efficiency, high power density with extended voltage, frequency and power handling capability.

Power electronics reduces our carbon footprint and contributes nearly £50bn per year to the UK economy and supports 82,000 skilled jobs in over 400 UK-based companies. Power electronic converters regulate the flow of power in most electrical devices, in electric vehicles etc. They do so by switching currents on and off, 10s of thousands of times per second, and the ratio of on-time to off-time determines the power flow. The efficiency, size, and weight of these converters are determined by the amount of waste heat generated. For example, the size of laptop power adapters has shrunk over the years, due to their increase in efficiency. In an electric car, waste heat causes power converters to be typically larger than the motors they are feeding. This heat is mostly produced in the instances when the transistors are switching. The power electronics industry is about to undergo significant change, as ultra-fast-transition transistors made from silicon carbide (SiC) or gallium nitride (GaN) have recently emerged. Their switching transitions are so short (below 10 nanoseconds) that, in principle, efficiency can be pushed to levels never achieved before. This could lead to a ten-fold miniaturisation, leading to converters that are much smaller than the motor being driven, or credit-card-sized laptop power adapters. The fast switching, however, comes with the downside of extreme electromagnetic noise, and industry is struggling to adopt these new technologies. Our project will provide answers to key uncertainties for adoption of these new technologies, namely how to drive the SiC and GaN power devices quickly, safely and quietly. The electromagnetic noise (EMI) is seen on an oscilloscope as sharp corners, rapid oscillations, and overshoot spikes, during the switching transitions. In this project, we are developing solutions to achieve clean switching, without these undesirable features, to quieten the EMI. These features are countered by feeding specially-shaped signals into the transistors' gates. The switching transition is too fast for any known signal generators and closed-loop control methods, or passive switching-aid (filtering) circuits to provide the required shaping of gate signals. Therefore, an alternative approach is adopted. We recently developed a chip that can adjust its current output every 100 picoseconds, i.e. the time it takes light to travel 3 cm. It is the only known driver chip that can interact frequently enough with a gate signal to shape these short sub-10 nanosecond switching transitions. We will create improved versions of this driver to drive gallium nitride and silicon carbide transistor gates with signals that are designed to soften the switching and cancel out unwanted high-frequency effects. The signals need to be changed automatically as the converter temperature changes, and when changes to its output power are requested. Also, each type of circuit requires slightly different signals. Therefore, automatic adaptation will be developed to simplify the use of this technology by industry. An interesting challenge is the safe generation of optimised gate signals, as the wrong signal can cause a power converter to fail. Another challenge is the regeneration of energy put into the gate, so that it can be used for the next switching event. The project develops microelectronics (high-speed, EMI-quietening gate drivers) and power electronics (converters and control systems). Industry advisors from 8 partner companies will steer the development for three years. In Year 4, the research is scaled down, and trials in UK-based industry set up to transfer knowhow, test the research, and provide new avenues for fundamental research. This research will help maintain the compatibility between emerging high-efficiency power electronics and modern ultra-low-power microelectronics that is increasingly susceptible to electromagnetic noise, and simplify and expedite industry adoption of SiC & GaN.

This project develops new sensing technology for use in power electronic systems, helping the UK to better compete with global leaders in power electronics. Power electronics is a key electrification technology: it is needed in electric vehicles, renewable energy generation, our electricity grid, and anywhere where the flow of power needs to be accurately dosed. This dosing is carried out by rapidly switching currents on and off to create the desired average. This technology reduces our carbon footprint and contributes nearly £50bn per year to the UK economy and supports 82,000 skilled jobs in over 400 UK-based companies (2016 data). The power electronics industry is undergoing significant change, as ultra-fast transistors made from silicon carbide (SiC) or gallium nitride (GaN) have recently emerged, to replace silicon transistors. These new transistors switch 10x faster, which results in 75% less energy being lost in power converters, and enables converters to be shrunk to less than half their previous size. This makes it much easier to build them into other systems, e.g. electric vehicles, resulting in lighter cars with more space for batteries. This project is about helping to maximise the potential of the new transistors. Many companies are struggling to adopt them, because whilst the very fast switching provides the benefits of improved efficiency and radically smaller system size, it also creates problems with electromagnetic interference, and device and system reliability. The transistors switch current on or off so fast (in less than ten nanoseconds, the time it takes light to travel 3 meters), that engineers cannot accurately measure how the voltages and currents change during this time, even with their best equipment, which means it is difficult to fix problems such as interference. Because of this, even the leading companies are slowing down these new transistors, and losing some of their efficiency potential. Our project develops small, low-cost sensors, that make these nanosecond-scale changes visible. They will allow engineers to see exactly how the transistors are switching, helping them develop better, smaller, lighter, and more reliable power electronics. They will allow computer-controlled SiC and GaN power converters to sense when they are creating too much electromagnetic noise, and reduce this by switching more intelligently. It will allow power circuits to detect external short circuits and isolate these before they damage the power converter. We are also developing sensors that provide engineers, or control systems, directly with information that they need (e.g. device temperature), rather than having to infer this indirectly from volts and amps, making the measurements faster and more efficient. The sensors work by detecting electric or magnetic fields via coils, conductive plates, or antennas. The received signal is fed into a chip inside the sensor that computes the required parameter. These new SiC and GaN transistors have made small field sensors on circuit boards viable for the first time, because as signal speeds increase, the wavelengths of these signals become shorter (cm-scale), meaning that their fields can be picked up with millimetre-size coils or antennas. In order to ensure that we develop what industry needs, we are working with 12 partners across automotive, renewable energy, semiconductors, commercial R&D organisations with deep sector experience, and we are accepting new collaborators on request. Our project provides partners and other UK companies and universities with sample sensors. Their feedback, and discussions with partners helps us prioritise our research, and ensures that we are using our research funds to solve the most important problems. We are providing workshops to help keep engineers up-to-date with advanced measurement techniques, and keeping our results online (publications and a dedicated website) for companies to use as desired.