Current control of a phase-shifted-PWM STATCOM using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC)

This paper presents and discusses a phase-shifted-PWM STATCOM using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC). A three-phase 140-V, 10-kVA downscaled experimental system with a cascade count N =6 is designed, constructed and tested for verifying the performance and functionality of the STATCOM on both steady and transient states. The 13-level line-to-neutral (25-level line-to-line) voltage at the ac side yields an almost sinusoidal line current with a THD of 1.7%. An analytical model for the phase-shifted PWM is proposed, leading to the design of current control gains. Two phase-shifted PWM methods named as one-cell and all-cells update methods are compared theoretically and experimentally. The all-cells update method can reduce the inherent delay time, thus resulting in a faster and more stable system response than the one-cell update method.