A Multichannel High-Frequency Current Link Based Isolated Auxiliary Power Supply for Medium-Voltage Applications

Abstract

The auxiliary power supply (APS) is one of the critical components inside medium-voltage (MV) power converters. Besides high insulation capability and small footprint, low common-mode (CM) coupling capacitance and multichannel output are the desired features of APS in the emerging silicon-carbide-based MV converters due to their fast switching speed. This article presents the design and optimization procedure of a high-density isolated APS using an LCCL-LC resonant topology with an operating frequency of 1 MHz. The proposed design procedure attains consistent soft-switching operation under a random number of output channels. The galvanic isolation is realized by a current-fed single-turn 1 MHz transformer that can achieve a breakdown voltage of over 20 kV while maintaining a small size. Design optimization on the insulation system of the current transformer is proposed to obtain both high partial-discharge inception voltage (PDIV) and low coupling capacitance. Finally, two versions of APSs are developed, using air and silicone as dielectric materials, which can reach PDIV of over 5 and 16 kV, respectively. The corresponding coupling capacitances are 1.86 pF and 3.6 pF. Both designs can provide a maximum power of 20 W on the receiving side, and 120 W on the sending side.