Mitigation of Voltage Swells by Static Series Compensator

Swells and overvoltages can cause overheating, tripping or even destruction of industrial equipment such as motor drives and control relays. This paper investigates the possibility of employing the Static Series Compensator (SSC) to mitigate voltage swells/overvoltages. In the case of voltage swells, active power may be drawn from the grid into the energy-storage capacitor (ESC) of the SSC, depending on the load current and the SSC impedance. This active power may overcharge the ESC. Two possibilities to overcome this situation are explored in this paper: 1) if the dc-voltage of the ESC is lower than a predetermined voltage level, the active power is employed to charge the ESC to this voltage level; 2) otherwise, the overvoltage protection of the SSC must operate. This paper also applies an overvoltage protection scheme based on a combination of a dc resistor with a chopper and the valves of the SSC. The design of the dc resistor is discussed. A 10 kV SSC experimental setup is exploited to carry out experiments in the case of balanced and unbalanced voltage swells at the grid side.