Fault-Tolerant Control and Isolation Method for NPC-Based AFEC Using Series-Connected 10kV SiC MOSFETs

Abstract

Power Conditioning Systems (PCS) based on three-level converters with series-connected 10kV SiC MOSFETs have gained popularity for medium voltage applications with the increase in distributed energy sources. With the use of Silicon Carbide (SiC), a wide bandgap semiconductor composed of Silicon (Si) and Carbon (C), MOSFET increases in power electronics application due to higher switching frequency operations. A high switching frequency such as 10 kHz or more leads to a reduction in magnetic components’ size and the PCS structure’s size. Therefore, the smaller, modular, and lightweight PCS can be attained for micro-grid integration, EV charging, or high inertia-dominated power grid applications. The three-level NPC (3L-NPC) inverter using series-connected 10kV SiC MOSFET is a suitable topology for coupling the PCS with the medium-voltage utility grid. The converter’s pole sustainability increases with the two series-connected switches, yet the switches are still sensitive and prone to malfunction under various environmental and mechanical causes. Therefore, a meticulous fault isolation and coordination design may be necessary for the front-end converter for possible switch faults in the converter poles. A well-designed fault-tolerant controller may sustain the converter operation under fault conditions while protecting the healthy parts of the converter. Besides, it minimizes the harmful effects of fault on the grid side and increases the system availability. This paper analyzes short and open circuit switch faults that might occur in the PCS. Accordingly, a fault-tolerant method and a fault isolation method are proposed. The proposed methods are verified with Saber™ and the Real-Time Digital Simulator simulation platforms.