Quietening ultra-low-loss SiC & GaN waveforms

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.

We aim to enable the UK to gain a competitive advantage by successful early deployment of recently emerged SiC and GaN power conversion devices. The impact of this project can be summarised as follows:

Economy and UK companies:
1. Significant miniaturisation of power technology, helping UK industry reduce size, weight, and power of products and systems.

2. Improved knowledge for utilisation of GaN & SiC devices, resulting in lowering costs by avoiding expensive EMI mitigation, and in speeding up time to market.

3. Access to state-of-the-art facilities and knowledge.

4. Increased market demand as power electronic system capability increases.

5. UK to maintain its position as a major player in GaN & SiC power electronics.

6. Increased IP residing in the UK.

7. Attract high-value activities such in areas of electric vehicles, robotics, consumer products, and renewables, to the UK.

Society:
1. Reduced greenhouse emissions and enhanced opportunity for meeting future targets (CO2 reduction 2020 and 2050 goals) through more efficient power conversion, miniaturisation of electrical systems in electric vehicles, and adoption of renewables through use of smart grid technologies.

2. Cleaner urban environment due to enhanced impact of clean transportation (electric/hybrid vehicles, rail, 'more electric' aircraft systems, ship propulsion).

3. Skilled young researchers and PhD students helping to address skill shortage.

4. Improved knowledge of industry engineers.