A Medium-Voltage Current Source Inverter for Synchronous Electrostatic Drives

Abstract

Macroscale synchronous electrostatic machines (SEMs) require medium-voltage (5 kV) and high fundamental frequencies (high pole number 96) to be competitive with traditional electromagnetic machines. This article focuses on the design, modeling, and characterization of a medium-voltage current source inverter hardware platform to meet the low current and high-frequency requirements of SEMs. The inverter stage utilizes junction field effect transistor (JFET) supercascodes for the medium-voltage switches. A full-bridge front end regulates the necessary dc-link current and provides some of the voltage gain from the low-voltage dc input. A sensitivity analysis shows that the system losses have a quadratic dependence on the output voltage and a linear dependence on switching frequency and dc-link current. Minimal dependence on output power and fundamental frequency was measured. Averaged modeling shows a right-half-plane (RHP) pole exists for the dc-link control. Two methods for stabilizing the machine drive were proposed and validated. Active damping via virtual resistance on the dc link was used to shift the pole to the left half-plane. The second method utilizes the $q$ -axis voltage decoupling to remove the voltage disturbance of the inverter controller on the dc-link current. The impacts on system stability and disturbance rejection were measured and correlate with modeling.