Combining direct compensation current and DC-link voltage controls in a multilevel cascade STATCOM for fast response requirement

This paper proposes a combination control scheme for direct compensation current and dc-link voltage balance in a multilevel cascade static synchronous compensator (STATCOM). A cascade full H-bridge (FHB) based-converter with modular structure is employed as the main circuit of the STATCOM, which is suitable for high-power and high-voltage applications. For achieving reactive power compensation and power factor correction (PFC), a direct compensation current control is applied to provide or absorb reactive power. For maintaining the dc-link voltage balance between FHB cells in the converter, a voltage balance control is developed. A phase-shift pulse width modulation (PS-PWM) is applied as the modulation scheme of the FHB converter for fast compensation response. Finally, the STATCOM is constructed and simulated with MatLab/Simulink program. Simulation results verify that the proposed STATCOM not only maintains the dc-link voltages balance between FHB cells, but also regulates the needed reactive power currents with a fast response time during the system compensations.