A shunt active filter for distorted voltage conditions

The increasing use of power electronic system has led voltage harmonic distortion level to an unacceptable level at point of common coupling (PCC). This ongoing degradation of power quality (PQ) has inspired considerable research interest in the area of power quality improvement. This thesis reports an investigation of some aspects of PQ improvement by using a shunt active filter (SAF) in a case where the source voltage is distorted. The harmonic extraction in distorted cases is obtained by using a modified instantaneous reactive power theory (IRPT). The dynamic model of the SAF is derived in d-q frame and the design of the current controller is explained based on this model. PI controllers are used for the current controller to get desired dynamic response of the SAF. Proper selection of parameters for SAF based on its rating and applied system are explained. Space vector PWM is used to switch the inverter. The ripple in the inverter output is removed with a small filter. The design of ripple filter is discussed. The proposed SAF performance is verified through simulation. Actual industrial conditions are considered where several nonlinear loads are connected at common PCC. Simulations are performed for both current source type and voltage source type nonlinear loads. The SAF is designed for a 1MW thyristor/diode rectifier load. It's steady state and dynamic response is verified for different degree of voltage distorted cases. The proposed SAF can mitigate the load current harmonics properly as well as reduce the voltage distortion at PCC.