A Phase-Shifted PWM STATCOM Using the Modular Multilevel Cascade Converter (MMCC-SSBC)

—Discussion on the Current Control System—

Abstract

This paper presents a transformerless phase-shifted PWM STATCOM intended for installation on the 6.6-kV power distribution system. The power circuit of this STATCOM is characterized by using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC). This paper designs, constructs, and tests the 140-V, 10-kVA downscaled STATCOM with a per-cluster cascade count of N=6, to verify operating performance in both steady and transient states. The 13-level (line-to-neutral) voltage waveform with low voltage steps yields a nearly sinusoidal current with a current THD (total harmonic distortion) of 1.7%. Modeling and analysis of the phase-shifted PWM STATCOM are carried out, leading to the design of current control gains.