Cascaded multilevel control of DSTATCOM using multiband hysteresis modulation

In this paper a cascaded H-bridge inverter topology is used in a distribution static compensator (DSTATCOM). A new multiband hysteresis algorithm is used to control the switches of the cascaded H-bridges leading to multilevel output of the inverter. The algorithm requires hierarchal switching of each H-bridge. Sequential change in the hierarchy facilitates equal charging and discharging of each capacitor. This leads to self-balancing of voltage across the capacitors. The multiband hysteresis algorithm is robust even under unequal capacitor voltages due to the dissimilarity in the H-bridge and capacitor units. The use of a resonant controller provides good tracking of the fundamental component of reference current. Discrete sampling of the switching function limits the switching frequency of the semiconductor devices. A 7-level cascaded inverter topology is considered for shunt compensation of an 11-kV distribution system. The results are validated through PSCAD/EMTDC simulation software