Recent proliferation of non-linear loads such as adjustable-speed motor drives, power supplies and inverters have raised serious concerns on the quality and reliability of electrical distribution networks. These loads draw excessive harmonic currents which interact with a wide range of power system components, causing significant deterioration in the power quality. Although traditional passive filtering has been commonly used to mitigate these problems, recent advances in power electronic converters have sparked the interest in active power filter (APF) approach. This book describes the design, analysis and implementation of a hybrid APF connected to a photovoltaic system. The integration improves the harmonic filtering performance of a basic shunt APF while simultaneously supplying power from the photovoltaic array to the load. The compensation current reference for the APF is derived from the extension instantaneous reactive-power theorem. It simplifies the current reference estimation, leading to a more efficient implementation using digital signal processor.