A new control strategy for cascaded H-bridge multilevel converter to operate as a D-STATCOM

In this paper, an indirect current control method is proposed for cascaded H-bridge-based multilevel converter to operate as a STATCOM. As the indirect control approach does not need any current sensor, the system reliability increases. Using the proposed control strategy, dc link voltages are balanced, although the H-bridge cells have different amounts of losses. The reactive power is also equally distributed between the cells, independent of the active power distribution. The proposed STATCOM can be connected directly to a 3.3 kV distribution network, and work as a distribution network STATCOM (D-STATCOM), eliminating the bulky and heavy coupling transformer. Also using multicarrier phase-shifted sinusoidal PWM (MPS-SPWM), low order harmonics from the line side current are eliminated. To verify the feasibility of the control strategy, simulations are carried out on a 7-level cascaded H-bridge converter in PSCAD/EMTDC environment.