Quietening ultra-low-loss SiC & GaN waveforms

Lead Research Organisation: University of Bristol
Department Name: Electrical and Electronic Engineering

Abstract

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.

Planned Impact

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.
 
Description This 4-year award is now in its 2nd year.

In discussions and workshops with around 20 power electronics companies (UK companies, and global corporations with a UK R&D base) we have established some of the hurdles facing industry in adoption new more-efficient power electronic technologies, such as SiC and GaN to replace silicon power transistors.

We have learned what is necessary to be able to create power electronics that automatically adapts its gate driving signals to reduce electromagnetic emissions whist increasing power efficiency.

We have created new measurement techniques to help industry work on SiC and GaN.

We are working towards energy recycling in power electronic circuits, and adaptive gate driving to quieten converters.
have been captured and key application constraints have been identified, in part due to the holding of two industry workshops.

We have managed to reduce the cost and size of the underpinning gate driving technology so that the equipment can more easily be transferred to all partners, and used in radiated emissions test facilities.

We have discovered new driving techniques for SiC power devices, and built a test rig to refine these.

We have applied for a patent on generating driving profiles for power semiconductor devices in systems where the operating conditions such as temperature and torque change (as is the case in most electrical drives).
Exploitation Route To early to say. We are running an industry workshop start of 2021 to establish this.
Sectors Aerospace, Defence and Marine,Electronics,Energy,Environment,Healthcare,Manufacturing, including Industrial Biotechology,Security and Diplomacy,Transport

 
Description After two technical workshops attended by Engineering Directors, CTO's Chief Engineers etc. we are seeing take-up of measurement methods, and some collaborative projects starting to exchange design skills.
First Year Of Impact 2020
Sector Aerospace, Defence and Marine,Electronics,Energy,Transport
 
Description Design collaboration with Nidec Control Techniques 
Organisation Control Techniques Drives Ltd
Country United Kingdom 
Sector Private 
PI Contribution Two contracts for a co-design collaboration between Nidec Control Techniques and the University have been carried out.
Collaborator Contribution There was a financial contribution (confidential), and exchange of valuable expertise.
Impact Outcomes Knowledge and design expertise transferred to company. Application and product design expertise transferred to university. Research and development roadmap of the company has been influenced.
Start Year 2019
 
Description Design collaboration with Toshiba Bristol Research and Innovation Lab 
Organisation Toshiba Research Europe Ltd
Country United Kingdom 
Sector Private 
PI Contribution The University of Bristol provides training and prototyping facilities, and design expertise.
Collaborator Contribution Toshiba have contributed financially, and provided semiconductor design and application expertise.
Impact Too soon to tell.
Start Year 2019
 
Description Design for Electromagnetic Compatibility Course 2019 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Study participants or study members
Results and Impact The Universities of Edinburgh and Bristol organised a course for all project members in Bristol, with an open invitation to wider research group members.
The course was led by an internationally renowned EMC expert.
Year(s) Of Engagement Activity 2019
 
Description Printed circuit board design workshop 2019 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Study participants or study members
Results and Impact A one-day workshop organised by University of Bristol, and hosted at the University of Strathclyde, to advance the skills of project
researchers, in the area of PCB design, using Altium for schematic capture, and producing circuit layouts.
May 13, 2019.
Year(s) Of Engagement Activity 2019
 
Description Quietening Waveforms Technical Workshop 2019 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Technical Workshop 1: Challenges of adopting SiC and GaN
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Engineering Directors, Chief Engineers, Managing Directors, and other senior decision makers from 11 Power Electronics companies (global corporations with a strong UK presence, or UK companies) made 5 minute presentations on their technical and commercial challenges of adopting new power semiconductor technologies. Each presentation was followed by 20-40 minutes of discussion amongst the companies and research groups present.

The outcomes of the workshop were:
- Increased common understanding of the technical and commercial hurdles facing the UK power electronics industry.
- Increased understanding of the application domain of power electronics research, and the future needs of industry.
- Increased mutual understanding between industry and academic research groups.
- Increased ability for research groups to create productive roadmaps for their research, and to gain collaboration partners.

A follow-up workshop was requested and duly offered.
Year(s) Of Engagement Activity 2019
 
Description Quietening Waveforms Technical Workshop 2020 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Engineering Directors, Chief Engineers, and other senior decision makers from 10 Power Electronics companies (global corporations with a strong UK presence, or UK companies) took part in an interactive workshop with 4 sessions. The first, on high-bandwidth measurement of high-performance power electronics had been requested at the previous workshop. The other sessions opened up research questions faced by the research groups at Imperial, Edinburgh, Strathclyde, and Bristol. The sessions contained on average 5 questions, and industry and academia discussed possible methods and pitfalls for about 2/3 of the time.
The workshop was ended with a discussion on how universities can enhance their support of industry with courses, knowledge exchange and other types of interaction. The attendees requested a follow-up workshop, and a course for graduate engineers. Two representatives from EPSRC were present at the workshop.

Outcomes:
This workshop furthered the common understanding between industry and university research groups, and led to new relationships between engineers and researchers.
The Quietening Waveforms project benefited from the wealth of experience of the industry attendees, who were very active and forthcoming with advice and ideas. Generally everyone felt they had learned new things, and were supportive of continuing this workshop series in the same discussion-based format. The EPSRC reps commented on the collaborative nature and openness of discussion of this event.
Year(s) Of Engagement Activity 2020