20-kV Insulated Auxiliary Power Supply for Medium Voltage Converter
Currently, building medium voltage (MV) converter with high voltage SiC devices is being investigated to promote the integration of distributed energy resources (DER), such as wind and solar. Medium voltage converters can serve as an energy transactive hub that is capable of interfacing, controlling and coordinating DERs as well as new loads such as electric vehicle chargers, smart homes, and server farms. It is one of the fundamental technologies that would make the grid more sustainable, reliable and flexible, which ultimately improves overall energy efficiency and cuts carbon emissions. A reliable auxiliary power supply that powers gate driver and control circuits is indispensable in the proper function of the new generation SiC devices in MV converters .
Medium Voltage H-Bridge Power Module
The auxiliary power supply (APS) is required to withstand high insulation voltage of 20 kV. Different topologies for the power supply are examined. Transformer design and insulation material that offers reliable insulation voltage are compared. The goal is to build a compact and standardized APS with high power density so that it can be easily placed with the power electronic submodule in MV converter. The APS will be built and then tested under hi-pot and partial discharge test to validate its insulation voltage. Another target of the APS is to achieve a interwinding capacitance smaller than 5 pF, which reduces the common mode current imposed by the high dv/dt during device switching. The capacitance can be calculated and simulated using ANSYS Maxwell. Finally, the capacitance is tested using impedance analyzer.
How WBG Can Help
High voltage SiC MOSFET is one type of WBG device implemented in the MV converter. Its high breakdown voltage greatly reduces the number of devices, passive components used in the overall converter design, but requires an auxiliary power supply to offer comparable insulation voltage. The device is capable of switching at high speed, which provides the MV converter with higher control bandwidth and faster dynamic response. For example, the grid-connected MV converter using WBG device performs better in low voltage ride through, fault clearance and black start than a converter built with conventional Si device. On the other hand, the high switching speed generates high dv/dt, which demands low parasitic capacitance of the auxiliary power supply.
 L. Zhang, S. Ji, S. Gu, X. Huang, J. Palmer, W. Giewont, F. Wang, L. M. Tolbert, "Design Considerations for High-Voltage-Insulated Gate Drive Power Supply for 10-kV SiC MOSFET Applied in Medium-Voltage Converter," IEEE Transactions on Industrial Electronics, 2020.