LV converters : improving efficiency and EMI using Si MOSFET MMC and experimentally exploring slowed switching

Roscoe, Nina M. and Holliday, Derrick and McNeill, Neville and Finney, Stephen J. (2018) LV converters : improving efficiency and EMI using Si MOSFET MMC and experimentally exploring slowed switching. IEEE Journal of Emerging and Selected Topics in Power Electronics. ISSN 2168-6777

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    Abstract

    Widespread adoption of electric vehicles will require AC power distribution systems to accommodate high penetrations of power electronic loads, placing increasing demands on the power quality of grid-connected converters. Recent developments in devices and circuit topologies have potential to improve the intrinsic power quality of these grid interface inverters, reducing the need for passive filters and associated reactive power consumption. Wide bandgap devices, such as SiC, have recently gained much attention due to their low switching losses facilitating raised PWM frequencies. However the high cost of SiC together with electromagnetic interference (EMI) resulting from very rapid switching transitions necessary to realize low switching losses cause concern. Previous research in Si MOSFET modular multilevel converters (MMC) suggests a high efficiency alternative with potential for lower EMI. Si MOSFET MMC benefits are enhanced with parallel-connected devices and slowed switching, made possible by low effective switching frequency. This paper uses experimental results to explore the impact of parallel connection and slowed switching on Si MOSFET MMC losses, and presents improved Si MOSFET switching loss models to resolve inaccuracies observed with conventional Si MOSFET models. EMI is then compared between SiC and Si MMC using carefully controlled relative measurements of radiated EMI.