Reactive Power Compensation of Modular Multilevel Cascaded Converter STATCOM using Average Power Inter-Cluster Control Method under Unbalanced Voltage Conditions

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This presents a reactive power control strategy for the single delta bridge cell modular multilevel cascaded converter (SDBC-MMCC) for static synchronous compensator (STATCOM) under asymmetric voltage conditions. An average power balancing method is proposed to support continuous injection of reactive power under grid voltage fault conditions, considering sub-module capacitor voltage balancing and STATCOM maximum phase current protection. Analytical solutions of the STATCOM phase currents are presented. A maximum current limit control scheme is proposed to ensure continuous reactive power injection and STATCOM operation under unbalanced voltage condition. The fault-ride through capability of the SDBC STATCOM under asymmetrical condition is analyzed using the proposed method. A comparative analysis shows that the current requirement of the proposed strategy is superior to the zero-sequence current balancing technique.