Negative-sequence reactive-power control by the modular multilevel cascade converter based on double-star chopper-cells (MMCC-DSCC)

This paper presents a modular multilevel cascade converter based on double-star chopper-cells (MMCC-DSCC) intended for its applications to a STATic synchronous COMpensator (STATCOM). The DSCC is characterized by cascade connection of multiple bidirectional chopper-cells per leg, thus leading to flexible circuit design, low voltage steps, low voltage harmonics, and low EMI emissions. However, no paper has been published on its application to STATCOMs with experimental verification. This paper designs, constructs, and tests a 200-V 10-kVA STATCOM based on the DSCC with focus on steady-state and transient-state performance as well as startup performance. Experimental results verify that it can start up by itself without using any auxiliary circuit, and that it achieves controlling the same amount of negative-sequence reactive power as the converter capacity.