DC link voltage swinging and load current unbalance in fault tolerant VSI. Overview and compensation strategies

The topic of this paper is the discussion on the performance of a three-phase fault tolerant inverter with particular attention to the underrated aspect of current unbalances occurring due to the DC link voltage fluctuates after the inverter reconfiguration. Capacitor voltage unbalance affects not only the average output voltage of the inverter, but also its performance. In fact, the inverter performance depends on the fluctuating DC-link voltage components rather than on the average DC-link voltage. After a brief analysis of the voltage fluctuation phenomena resulting from fault tolerant configuration and their effect on load current unbalance, the Authors consider different compensating preventive or repressive strategies in different application scenarios. These strategies can operate both in open and closed loop control. The paper highlights their advantages, drawbacks and analyzes their different behavior.