Voltage Control of a Bi-Directional Isolated DC/DC Converter for Medium-Voltage Motor Drives

This paper describes a next-generation 6.6-kV motor drive employing a bi-directional isolated dc/dc converter instead of a line-frequency transformer. It consists of cascaded six "converter cells" in each phase. Each converter cell includes a bi-directional isolated dc/dc converter and two single-phase PWM converters. On the focus is dc voltage control by the bidirectional isolated dc/dc converter, together with the implementation of the dc/dc converter. Small-signal analysis reveals that the control system can be described as a second-order system. The control scheme is confirmed by both computer simulation and experiment based on a dc/dc converter rated at 360 V, 10 kW, and 20 kHz. Simulation and experimental results verify effectiveness of the control method in both steady-state and transient characteristics.