Improved Fault Diagnosis Capability in CHBMCs: Counter Design for Multiple OC Switches via an E-SVM Unit
Hongjian Lin, Henry Shu-Hung Chung, Chunxu Lin, Dong Xie, Qingli Deng, Mingcheng Lyu, Stefan M. Goetz, Junyu Chen, Xinglai Ge
Abstract
The cascaded H-bridge multilevel converter (CHBMC) is widely used in medium- and high-voltage applications due to its flexibility and scalability. However, its numerous switches make it prone to open-circuit (OC) faults, which lead to overshoot currents and increased harmonics, while unbalanced DC capacitor voltages can destabilize the system. To resolve the aforementioned issues, this paper proposes an enhanced space vector modulation (E-SVM) unit that uses counters for multiple OC switch fault diagnosis and incorporates DC capacitor voltage balancing capability. In conjunction with the ESVM unit, the zero level per power cell helps identify faulty switches, while redundant space vectors balance DC capacitor voltages. Switching losses are minimized by optimizing the switching transition, and a voltage balancing degree quantifies the boundary of the unbalanced loads. The E-SVM is software-based, level independent, and control-agnostic by the control unit. It ensures seamless CHBMC operation. Its effectiveness is demonstrated by comparing the verification results with theoretical predictions.