Operation of the SDBC based STATCOM integrated with one Single-Phase Converter allowing Active Power Control under Unbalanced Grid Conditions

Even though the modular multilevel cascaded converter with single-delta bridge-cells (MMCC-SDBC or SDBC) has been widely discussed for static synchronous compensators (STATCOM), it is essentially for the reactive power compensation. In order to simultaneously compensate for the reactive power and regulate the active power, this paper integrates the SDBC based STATCOM with one single-phase converter through one medium-frequency transformer operating at three times the fundamental frequency. This paper especially focuses on the operation of the developed system under unbalanced grid conditions because it is relatively critical compared to the SDBC based STATCOM. Further investigation shows that the developed system is almost impossible to operate under unbalanced grid conditions with only the circulating current control due to the considerable magnetizing inductance. Experimental results are preliminarily provided to confirm the performance of the developed system under unbalanced grid conditions.