PWM-controlled series compensation with low harmonic distortion

The paper describes a pulse width modulation (PWM)-controlled series compensator with continuously variable reactance, employing simple PWM duty ratio control. Each phase of the compensator comprises a switched reactor and parallel capacitor. The duty ratio control gives a wide range of capacitive and inductive compensation. The harmonics created by the switched reactor have been analysed. The switched reactor and parallel capacitor have been simulated with a range of switching frequencies and duty ratios. With appropriate choice of capacitor and reactor. A scaled-down experimental model of the compensator has been simulated and constructed. The harmonics have been found to be small even with the switching frequency of the controlled turn-off switches as low as 400 Hz. A large step change in duty ratio from maximum capacitive compensation to inductive compensation shows the rapid dynamic response of the compensator with a fast settling time. This demonstrates that the proposed compensator should be considered as another useful FACTS controller for series compensation