A Phase-Shifted PWM D-STATCOM Using a Modular Multilevel Cascade Converter (SSBC)—Part II: Zero-Voltage-Ride-Through Capability

This paper provides an experimental discussion on zero-voltage-ride-through (ZVRT) capability of a phase-shifted pulsewidth-modulation distribution static synchronous compensator (D-STATCOM) using the modular multilevel cascade converter based on single-star bridge cells (SSBC). The cluster-balancing control producing a significant effect on the ZVRT capability is modeled and analyzed with focus on either a low-pass filter (LPF) or a moving-average filter (MAF) to attenuate the 100-Hz (double the line frequency) component inherent in each dc capacitor voltage. The cluster-balancing control using the MAF is better in transient performance than that using the LPF. A three-phase downscaled SSBC-based D-STATCOM rated at 150 V and 10 kVA is designed, constructed, and tested to verify the ZVRT capability under the severest single-, two-, and three-phase voltage sags with a voltage depth of 100%. Experimental waveforms show that the STATCOM continues operating stably as if no voltage sag occurred.