Variable frequency drive system apparatus and method for reduced ground leakage current and transistor protection

Abstract

As applications of variable frequency drives (VFD) () continue to grow so do challenges to provide VFD () systems meeting application specific requirements. For multiple reasons to include safety standards and electromagnetic interference, reduced ground leakage current is desirable. Building high output voltage VFDs () using transistors rated at voltages lower than the VFD output voltage is desireable for economic reasons. The apparatus and method described herein meet these challenges and others, in part by placing an electrically insulating plate (cp) having high thermal conductivity, a low dielectric constant, and high dielectric strength between the heat sink plate of a VFD power semiconductor module and a grounded cooling plate (TE). The positive effects of this plate installation include reducing ground leakage current induced by system capacitances to ground upon high frequency voltage steps and increasing the effective dielectric strength of the VFD's () transistor modules engaging in high reliable VFD () voltage output for a given transistor rating.