Cost effective voltage sag mitigation using square-wave Series Compensators

Voltage series compensators typically insert a sinusoidal voltage to compensate voltage sags. In order to achieve a sinusoidal waveform, the output circuitry is formed by a PWM inverter with a sinusoidal filter. However, the sag disturbance is a phenomenon that typically occurs during hundreds of milliseconds. Instead of injecting a sinusoidal voltage, this paper proposes a series compensator that injects a square-wave voltage to protect the sensitive loads. The proposed compensator does not need the high switching frequency PWM inverter, thyristor by-pass switches and sinusoidal output filter, reducing the overall cost and volume of the final equipment. This paper presents the proposed series compensator topologies and control. Experimental results are also included to demonstrate the compensator performance when protecting microcomputer and PLC loads.