In this paper a novel hysteresis voltage control for a series active power filter is proposed to improve the Power Quality (PQ), which is one of the most important issues of modern electrical distribution. The active filter controller is based on a new control strategy related to hysteresis band voltage controlmethod, where the band is modulated with the system parameters to maintain the modulation frequency nearly constant. The new hystersis voltage control is presented and tested. This method has a good voltage tracking accuracy and a nearly constant switching frequency. Therefore, it is efficientand safe in operation. Simulation results show that this voltage control method improves the series active power filter performances noticeably. The determination of voltage references for series active power filter is based on a robust three-phase digital locked loop (PLL) system using RST regulator