Constant-Frequency Model Predictive Direct Power Control for Fault-Tolerant Bidirectional Voltage-Source Converter with Balanced Capacitor Voltage

This paper proposes a constant-frequency model predictive direct power control (CF-MPDPC) method for a fault-tolerant bidirectional voltage-source converter (BVSC). The method can enhance the reliability and fault-tolerant operation capability of BVSCs in the condition of bridge-arm fault. Through the analysis of a fault-tolerant three-phase four-switch (TPFS) structure and the voltage vectors in the αβ stationary frame, the predictive power model and DC-link midpoint voltage offset suppression are established. According to model-predictive theory, fault-tolerant TPFS, and multivector control, the CF-MPDPC method for fault-tolerant BVSC is presented. The method realizes direct power control based on three output vectors with constant frequency, which can track the optimal vector more accurately and reduce current harmonics. Furthermore, the balanced control of DC-link capacitor voltages is also achieved by adding the term of DC-link midpoint voltage offset into the cost function. The balanced capacitor voltages protect the converter against the second faults caused by over-voltage operation of electrolytic capacitor. The simulation and experimental results prove that the fault-tolerant BVSC controlled by proposed method can maintain the continuous operation when the switching devices have fault. Low current harmonic content and stable output power exhibit good reliability and dynamic performance of the proposed CF-MPDPC for a fault-tolerant BVSC with a phase fault.