A Multiple Fault-Tolerant Topology of Cascaded H-Bridge Converter for Motor Drives Using Existing Precharge Windings

In this article, a fault-tolerant topology of a cascaded H-bridge (CHB) converter is proposed for motor drive applications. Usually, multiwinding transformer fed CHB converters are provided with pre-charge windings for precharging the dc-link capacitors. The windings become inactive after the precharging process. The proposed topology contains redundant cells connected to the precharge windings. After faults in the converter, when the faulty cells are bypassed, the redundant cells can substitute the faulty cells with their power fed from the precharge windings. The aim is to obtain prefault rated line voltages during postfault conditions using the redundant cells. In addition, multiple faulty cells in the same leg or different legs of the converter can be tolerated with the proposed topology. The available power factor range for the proposed topology during most of the multiple fault conditions is improved. The impact of the dc-link voltage of the redundant cells on fault-tolerant capability of the proposed converter is also discussed. To maintain the rated line voltage during postfault conditions, a pulsewidth modulation (PWM) clamping technique is proposed and analyzed in this article. The proposed fault-tolerant topology is verified using computer simulation and experimental results.