The active power filter (APF) is mainly composed of controller, isolation switch (circuit breaker), contactor, IGBT, driving circuit, protection system, fuse, connection reactor, DC capacitor, etc. The controller measures phase A, C reactive power(current), produces control signal, drives IGBT on/off and produces harmonic and reactive current same as system harmonic current but in opposite phase to filter system harmonic, reduce reactive power and keep system power factor approximately at 1.