Abstract
Electric power quality is one of the most important indicators of power distribution systems. Since the causes of power quality problems are generally complex and difficult to detect, applications of power electronics in power transmission and distribution systems become a new trend in power engineering practice. Unified Power Quality Conditioner (UPQC) is a new power electronic equipment with excellent performance, which can synthetically compensate familiar voltage and current quality problems of power system. However, there’s no control method which is very suitable for UPQC. Among all existing power electronics apparatus, the Unified Power Quality Conditioner (UPQC) seems to be the most advanced and effective way for power quality enhancement. In this thesis, we will focus on the UPQC. Generally speaking, the UPQC and UPFC (Unified Power Flow Controller) have a power circuit the same which is based on series and shunt power converters that share a single DC link. The shunt controller is implemented for load current compensations under harmonic distortion conditions while the series controller is designed for voltage sourced compensations. By applying the (SRF) theory, an improved UPQC control configuration will be developed in this thesis with the following new features: (1) a voltage sag/swell compensator is implemented in the series controller for dynamical voltage restoring, and (2) a reactive power compensation scheme is developed for the shunt controller with considering power ratings of the shunt converter. Practical considerations about UPQC modules and parameters settings are also discussed in details. The proposed control configuration has been validated under the PSCAD simulation environments. Simulation results on various operating conditions have been performed to verify the effectiveness of the proposed control configuration.