Fault-Tolerant Control of Cascaded H-Bridge Converters Using Double Zero-Sequence Voltage Injection and DC Voltage Optimization
- Resource Type
- Academic Journal
- Authors
- Zhendong Ji; Jianfeng Zhao; Yichao Sun; Xiaojun Yao; Zean Zhu
- Source
- JOURNAL OF POWER ELECTRONICS. 2014-09 14(5):946-956
- Subject
- Cascaded H-bridge converter
DC voltage balancing
DC voltage optimization
Fault-tolerant control
Star connection
Zero-sequence voltage
- Language
- Korean
- ISSN
- 1598-2092
2093-4718
Cascaded H-Bridge (CHB) converters can be directly connected to medium-voltage grids without using transformers and they possess the advantages of large capacity and low harmonics. They are significant tools for providing grid connections in large-capacity renewable energy systems. However, the reliability of a grid-connected CHB converter can be seriously influenced by the number of power switching devices that exist in the structure. This paper proposes a fault-tolerant control strategy based on double zero-sequence voltage injection and DC voltage optimization to improve the reliability of star-connected CHB converters after one or more power units have been bypassed. By injecting double zero-sequence voltages into each phase cluster, the DC voltages of the healthy units can be rapidly balanced after the faulty units are bypassed. In addition, optimizing the DC voltage increases the number of faulty units that can be tolerated and improves the reliability of the converter. Simulations and experimental results are shown for a seven-level three-phase CHB converter to validate the efficiency and feasibility of this strategy.