A control strategy based on extended p-q theory usable in parallel active filters

The combination of extended p-q theory and quasi-instantaneous positive sequence extraction of utility voltages for controlling of parallel active filters (PAFs) is presented. The implementation of this method is very easy and it does not need phase lock loop (PLL). Operation of PAF using this method compensates for reactive power, current harmonics and imbalance currents of a non-linear load in three-phase three-wire harmonic polluted and/or imbalance utility voltage case. Problem of generating three phase balanced reference currents of extended p-q theory has been solved. Analytical calculations have been used to explain the dynamic response of presented control strategy and simulation and experimental results have been used to confirm the validity of its operation.