The control of a static var compensator and active power filter

Abstract

In an AC supply system, good management of reactive power plays an important role in ensuring a good quality of supply. A solid-state static VAr compensator enables precise and continuous reactive power control to be achieved. A leading and lagging VAr can be compensated to give a system with unity power factor. This thesis describes a solid- state static VAr compensator which utilises a deadband PWM switching pattern. By using simulation as well as experimental results, a comparison is made with conventional sinusoidal PWM. The use of deadband PWM enables higher modulation indices to be achieved hence facilitating a smaller size of reactive component on the DC side. Deadbanding reduces the effective switching frequency thus minimising the switching losses and resulting stresses. Power quality is also affected by harmonic distortion which originates from the non- linear characteristics of electrical devices and loads. The use of an active power filter to provide harmonic compensation as well as power factor correction is described in this thesis. Modified delta modulation is proposed to control the switching of an active power filter. Compensation is achieved with a reduction in switching losses. The application of a variable structure control system is considered. Sliding mode switching control is used to ensure good tracking of the reference current, thus providing the required compensation.