High-Frequency Power Conversion for Machine Drive Applications Dr Niall Oswald Electrical Energy Management Group University of Bristol

Introduction Presently working on two projects: EPSRC ‘Centre for Power Electronics’ components theme Focus is on wound passive components – performance and lifetime when subjected to high speed switching waveforms. TSB ‘Power Module Validation’ (PoMoVal) Development, test and analysis of a high-power, high-frequency power module for Electric Engine Start functionality. Safran Power UK, Raytheon Systems Ltd, UoB. These projects have similar objectives – enabling compact, efficient power conversion for machine drive applications, using new device technologies.

Opportunities… Low per-cycle switching loss of new devices (WBG) allows high switching frequency operation, in turn enabling: High output frequency High speed, torque-dense machines (e.g. 10 pole traction 12k rpm – 1 kHz fundamental). High switching frequency  reduced current waveform distortion. Compact, lightweight output filtering Sinusoidal output voltage, low harmonic distortion output current waveform – reduced losses in driven machine. Possibility of eliminating screened cables – desirable in many applications, reduces installation cost. Filter cut-off frequency can be placed outside controller bandwidth. However…

…and Challenges Low per-cycle switching loss is largely due to increased switching speed – dominant DC-AC power conversion topologies (2L-VSI, 3L-NPC) are hard-switched. ‘Slow’ IGBT-based drives already require significant EMC countermeasures to achieve compliance. SiC MOSFETs capable of switching at 10s of kV/μs. Neither practical nor desirable to have this level of dv/dt present at inverter output terminals – essentially mandates use of output filtering! Filter components must withstand switching stress and provide sufficient attenuation of increased high- frequency spectral content. Filter topology selection and parasitic circuit elements important in determining overall performance. Oswald, N.; Anthony, P.; McNeill, N.; Stark, B.H., "An Experimental Investigation of the Tradeoff between Switching Losses and EMI Generation With Hard-Switched All-Si, Si-SiC, and All-SiC Device Combinations," IEEE Transactions on Power Electronics, May V, 10 A +40 dB above 16 MHz

Project Plans & Objectives Key objectives: Development of wound component high frequency electrical behavioural models. Investigation of aging effects of high dv/dt on wound components. Exemplary application – 40 kVA all-SiC 2L-VSI. Consideration of application requirements provides representative basis for filter design (cut-off frequency, voltage drop, etc.). Based around commercially-available 1200 V, 100 A SiC MOSFET module (CREE CAS100H12AM1). Single phase inductor test-bed circuit under construction.

Project Plans & Objectives Test-bed circuit designed to maximise switching performance (not cost/size optimised!) Draws on previous experience (PhD research, PoMoVal test circuits). Loss analysis used to determine capabilities of CREE all-SiC module. 100 A 40 kHz 50 A 100 kHz 30 A 200 kHz Initial tests will use existing UoB- designed high-performance inductor.

Potential Outcomes & Exploitation Plans Improved understanding of trade-offs between total filter volume and switching frequency, subject to EMC limitations. Development of improved (compact, low-loss, low-EMI) output filtering topologies using models developed by this research. Construction of demonstration high-frequency inverter?