Analysis and implementation of a NPC-based DSTATCOM under the abnormal voltage conditions

An inverter-based DSTATCOM is presented and analysis to protect the load voltage against the abnormal voltage conditions. The neutral point diode clamped inverter is used in the system to achieve three-level pulse-width modulation. If the voltage sag or swell is detected at the distribution end, the adopted inverter was operated as a static synchronous compensator (STATCOM) to supply or absorb the reactive power in order to obtain the constant root mean square voltage at the load side (or PCC point). A voltage controller based on root mean square error at the PCC point is used in the control scheme to generate the necessary inverter output currents which are orthogonal to the PCC voltages. Experimental results based on a laboratory scale-down prototype are provided to verify the effectiveness of the control scheme.