Simplified power quality conditioner for dynamic voltage restoration and fault current limitation

Power quality improvement has become one of the important issues because of increasing sensitive loads. For example, dynamic voltage restoration is one of the major issues about the power quality. On the other hand, a large current caused by some system fault may be unwillingly large because of many interconnections of distributed generators. A Unified Power Quality Conditioner (UPQC) is well known apparatus, which consists of two self-commutated converters. This paper proposes a simplified power quality conditioner by replacing the shunt converter of the UPQC by two diode-bridge rectifiers. By the simplification of the UPQC, the overall system reliability is increased and installation cost is reduced. Power conditioning is provided by the series converter, while the d.c. voltage control is realized by the diode bridge rectifier. Although the active power flow through the rectifier must be only one direction, the amount of active power can be regulated by the d.c. voltage control of the series converter. In case some excessive energy is stored in the d.c. capacitor, it can be returned to the power system by an appropriate control of the series converter. In this paper, the effectiveness of the Simplified Power Quality Conditioner (SPQC) as a dynamic voltage restorer and a fault current limiter is verified by simulation.