A Capacitor-Voltage-Balancing Method Based on Optimal Zero-Sequence Voltage Injection in Stacked Multicell Converter

This article introduces a capacitor-voltage-balancing method based on optimal zero-sequence voltage injection in a stacked multicell converter (SMC). The proposed method is implemented using hybrid carrier pulsewidth modulation and is capable of balancing and regulating the voltages of dc-link capacitors and floating capacitors in the topology. The dynamic model of voltage fluctuation and the coupling relationship of voltage-balancing control between dc-link capacitors and floating capacitors are analyzed. The optimal zero-sequence voltage selection method is presented to address the voltage deviations of dc-link capacitors with the maximal regulation ability for floating capacitor-voltage-balancing control. Compared with the active capacitor-voltage-balancing (ACVB) method, the proposed method calculates the compensation current of the neutral point (NP) and chooses the optimal zero-sequence voltage in the whole available range. As a result, the low-frequency voltage ripples in NP can be suppressed with excellent dynamic performance under wider load conditions. Simulation and experimental results are presented to verify the effectiveness of the proposed method.