Control scheme for cascaded H-bridge converter-based distribution network static compensator

In this study, a new control scheme is proposed for cascaded H-bridge (CHB)-based static compensator (STATCOM). The new indirect current control method does not require any current sensors, so the total system has enhanced reliability. Using the proposed control approach, dc-link voltages across dc-link capacitors are regulated to the reference value, even if the H-bridge cells dissipate different amounts of losses. However, regardless of the active power distribution, the reactive power is equally shared between the cells. The proposed scheme is investigated on distribution network STATCOM, but is not restricted to that and can be applied to STATCOMs at any voltage and power level. Multicarrier phase-shifted sinusoidal pulse-width modulation is used for modulation purpose, since it is naturally the best option for CHB converter. In this way, low-order harmonics are eliminated from the line side current and the current THD is below 5%, which satisfies IEEE-519 standard. To verify the feasibility of the control strategy, simulations as well as experimental implementations are carried out on a CHB converter having three cells in each phase.