A Novel Fault-Tolerant Operation Approach for Cascaded H-Bridge Converter-Based Battery Energy Storage Systems to Avoid Overcharge

Conventional fundamental frequency zero-sequence voltage (FFZSV) injection-based fault-tolerant operation methods cause power reversion under submodule (SM) failure conditions with low-power factor, which leads to overcharge risk in the cascaded H-bridge converter-based battery energy storage system (CHB-BESS). To solve this issue, a novel fault-tolerant operation approach has been proposed for the CHB-BESS. First, the power reversion mechanism and overcharge risk are analyzed with the conventional FFZSV injection-based methods. On this basis, the operation conditions of the CHB-BESS are divided into three stages according to the safe FFZSV injection region, the FFZSV is modified, and the negative sequence current is injected when necessary. As a result, the power flow of battery packs among the three phases can maintain the same direction, and the power reversion and overcharge risk can be avoided. Experimental results under various conditions verify that the proposed fault-tolerant operation approach of the CHB-BESS can achieve uninterrupted operation and avoid overcharge risk.