Statcom Operation of Hybrid Series Converter and DC Capacitor Voltage Balance Technique

The hybrid-series-converter-(HSC) has enhanced operating modulation-index-(MI) range as compared to the parallel-hybrid-converter-(PHC). However, the HSC is underutilized when employed for high-voltage-direct-current-(HVDC) applications, HSC-HVDC. The parallel-chain-links-(PCLs) of HSC-HVDC generate fixed voltage and the series-chain-links(SCLs) of HSC-HVDC serves only as voltage wave-shaping circuit and does not increasing the output voltage levels. Thus, energy storage requirement of HSC-HVDC is higher than PHC. The switches of HSC-HVDC undergo forced commutation and increase losses. This paper intends to extract all the advantages inherent with the HSC and utilize it to its maximum capability by operating it as a static-compensator-(STATCOM), HSCSTATCOM. The proposed HSC-STATCOM requires lesser switching devices, capacitors besides having reduced energy storage requirements and zero-voltage-switching-(ZVS) nature. A new capacitor voltage control technique during unbalanced grid conditions is also proposed in this paper. The operating principle of the proposed STATCOM and proposed control technique is validated using different simulation case studies.