Cryogenic Power Electronics

# Electrifying Large Scale Transport
### Cryogenic Power Electronics

.TitleAuthor[Duleepa J Thrimawithana]

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.footer[[D J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer, and Software Engineering, The University of Auckland (June 2023)]

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# New Zealand

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# The University of Auckland

- Highest ranked New Zealand university and 85th in the QS World University Ranking
- Over 5,000 staff members and 40,000 students
- Nine faculties including Medical & Health Sciences, Engineering, Business & Economics and Science

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# Dept. of Electrical, Computer & Software Eng.

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- One of the 5 departments in the Faculty of Engineering
- Offers 3 undergraduate degree programs
 - Electrical & Electronics, Computer Systems and Software
 - Project based teaching
- 35+ full-time academic staff members and 15+ post-doctoral research fellows
- 150+ postgraduate students and 700+ undergraduate students
- Regular visiting research scholars and research students
- Research groups include Power Electronics, Power Systems, Signal Processing, Robotics, Embedded Systems, Parallel Computing, Telecommunications and Control Systems
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# Dept. of Electrical, Computer & Software Eng.

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# Power Electronics Research Group

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# Advanced Energy Technology Program
### An Overview

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.footer[[D J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer, and Software Engineering, The University of Auckland (June 2023)]

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# Program Overview

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# National and International Partners

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# Power Electronics & GaN HEMTs Work Stream

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# System Overview

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# Component Characterization 
### Behavior Under Cryogenic Conditions

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.footer[[D J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer, and Software Engineering, The University of Auckland (June 2023)]

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# GaN HEMTs - RDS(ON) at 77K

- The performance of GaN HEMTs in cryogenic temperatures depends on the gate technology
 - Devices with ohmic p-GaN gates do not perform well 
 - The series Si-FET in a cascode limits improvement in RDS(ON)

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# GaN HEMTs - RDS(ON) Comparison

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# GaN HEMTs - RDS(ON) Variation

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# GaN HEMTs - Threshold Voltage

- The threshold voltage of devices with Schottky p-GaN gates reduces with temperature
 - In contrast the threshold voltage of cascodes and devices with ohmic p-GaN devices increases with reducing temperature

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# Si Switches - RDS(ON) at 77K

- The RDS(ON) of Si MOSFETs improve until about 120K 
- The RDS(ON) of Si-Superjunction MOSFETs improve until about 120K but starts to get worse quite rapidly 
- The RDS(ON) of SiC devices do not deteriorate until about 220K 
- The effective RDS(ON) of Si IGBTs gets worse with reducing temperature

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# Core Loss Measurement

- Used a modified partial cancellation method to extract core losses 
 - Tested laminated steel, iron powder, ferrite and nanocrystalline cores
- Tests were conducted at 295K (room temperature) and 77K (using an LN2 bath)
 - A power amplifier drives the test setup and Cp help reduce VA requirement

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# Core Types

- Many core types were tested to understand changes in magnetic properties at cryogenic temperatures
 - Notable core types tested are summarized in the table

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# Core Losses

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# Nanocrystalline Core Comparison

- Not all nanocrystalline core types behaves the same 
 - Introducing an air-gap in the core increases core loss

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# Nanocrystalline Core Comparison

- Not all nanocrystalline core types behaves the same 
 - Introducing an air-gap in the core increases core loss

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# The Design of a Cryogenic Inductor

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# A GaN Based Cryogenic Converter
### The Design and Performance

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.footer[[D J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer, and Software Engineering, The University of Auckland (June 2023)]

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# A 5kW Cryogenic Converter

- A GaN based synchronous buck converter that can operate in cryogenic temperatures has been built and tested down to 40K
 - All components except the controller were operated at cryogenic temperatures
- Helps identify advantages and drawbacks of operating at cryogenic temperatures  
 - Compared with operation at 295K including a loss breakdown

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# Converter Efficiency at 77K

- Experiments considered nanocrystalline inductor operation in 77K and 295K
 - This enabled comparison with a ferrite inductor that operated at 295K
- As expected the nanocrystalline inductor leads to slightly lower efficiency
 - However, it allows over 70% reduction in weight

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# Loss Breakdown

- An air-core inductor is used to extract switch losses and compare 
 - A significant improvement in switch loss is observed at 77K
- Though a ferrite core inductor is more efficient there is a significant weight penalty 
 - The nanocrystalline core allows over 70% reduction in weight

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# Operation Down to 40K

- The GaN based synchronous buck converter has been tested down to 40K

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# GaN HEMTs for Cryogenic Operation
### Characterization and Optimization

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.footer[[D J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer, and Software Engineering, The University of Auckland (June 2023)]

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# Impact of Thermal Cycling

- Samples with pre-existing surface features were cycled between 340K to 80K
- Atomic force microscopy used to look for evidence of heterostructure degradation
- Proportion of sample area which is occupied by fissures (averaged over 5 scans) used as a metric
 - This was measured using FIJI, by segmenting the atomic force microscopy images
- No significant change which suggests repeated thermal cycling does not damage the heterostructure

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# Active and Logic Devices for Cryogenic Operation
### Characterization and Performance

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.footer[[D J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer, and Software Engineering, The University of Auckland (June 2023)]

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# Active and Logic Devices

- Intel Max 10 CPLD, TI C2000 series F280037 and an Atmel ATtiny1614
 - All 3 devices works at 77K with both the internal RC oscillator as well as an external CMOS oscillator 
 - ADC,PWM and UART peripherals work but ADC require a stable reference 
- OpAmps and isolators that function at 77K have been identified

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# Benchmark Setup
### SiC Based 150kW Motor Driver

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.footer[[D J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer, and Software Engineering, The University of Auckland (June 2023)]

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# A Benchmark System

- A liquid cooled, SiC based benchmark setup is under development to drive a 1MW HTS machine

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# Wireless Power Research
### Stationary and Roadway EV Charging

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.footer[[D J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer, and Software Engineering, The University of Auckland (June 2023)]

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# The Team

- Members from Power Electronics, Centre for Advanced Composites Materials, Transportation, Engineering Science,  Business School, GNS Science, Victoria University, Mahi Maioro and AUT
 - Collaborations with ASPIRE, Utah State University and Cambridge University

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# Current Work

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# Capabilities

- The power electronics team work with the other teams to develop converter, magnetic and controller designs and extensively test them

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# Thank You