Fault Detection and Ride Through of CHB Converter-Based Star-Connected STATCOM Through Exploring the Inherent Information of Multiloop Controllers

A simple detection and ride-through operation approach is proposed for star-connected cascaded H-bridge (CHB) converter-based STATCOMs with a single IGBT open circuit fault. It adopts a modified current regulator with high gains at both dc and fundamental frequencies. Then, the output signals of the current regulator branches and the dc voltage balancing regulator are synthesized as an inherent indicator to quickly determine the position of the open-circuit fault IGBT. With this approach, the controller can also be considered as an inherent system state monitor, but without any additional sensors or computing burdens. Afterwards, in the ride-through operation stage, the faulty H-bridge module can switch to half-bridge operation and the corresponding dc offset voltage is compensated by the remaining healthy modules. It has been validated that the proposed approach is accurate in various conditions, including grid voltage and load disturbances.

I. Introduction

Although with a grid-friendly stair-case output voltage waveform and direct medium voltage integration, a cascaded H-bridge (CHB) converter based STATCOM suffers from a high possibility of power switch faults as a large number of low voltage IGBTs are used in this topology. In various types of switch fault, a single IGBT open circuit fault is the most commonly seen [1], which can happen due to bond wire breaking, missing gating signals, etc. [2]. Accordingly, in the previous research, attention has been focused on the detection of a single IGBT open circuit fault and the ride-through operation of the postfaulty system.