Research On Detection And Control Method Of Unified Power Quality Conditioner

The Unified Power Quality Conditioner (UPQC) is an important represent in the active power filter family. It combines the advantages of both the series active filter and the parallel active filter, which provides comprehensive power quality compensations. For this reason, it is considered to have extensive prospect nowadays when power quality problem is more seriously concerned. By introducing the associated content of active power filter, the system configuration and the function of UPQC are explained in the thesis at first. Then, the detection method and the control strategy, which are the important parts affecting the compensation effect of the UPQC, are discussed and investigated in detail in the thesis. In order to overcome the deficiencies of the existing UPQC detection method, a combinational harmonic voltage-current detection method for UPQC based on the Park transformation is proposed in the thesis. In the proposed method, the positive fundamental frequency component of voltages can be measured quickly from the unbalanced and distorted three-phase system voltages, and the results of voltage detection are used in the current detection. As a result, the phase of the reference currents can follow the phase of positive fundamental frequency voltage, which again guarantees the simultaneous detection of the harmonic currents and reactive currents. The advantage of the proposed method is that neither the phase-locked loop nor the band filter is needed for the three-phase power system voltages. Thereby, the corresponding detection errors can be avoided. The control strategy of UPQC used in the thesis includes two parts, a series control and a parallel control. The parallel part control consists of a Proportion-Integral (PI) control and a regular time hysteresis PWM control. The Series part control adopts a triangle wine-linear PWM control. In order to overcome the drawback of the compensation of such kind control for series part during the voltage sag and voltage surge, an improved adaptive PWM control is developed which can automatically adjust the amplitude of the triangle wave during voltage sag and voltage surge. Simulation results given in the thesis verify the correctness of the harmonic detection method and the control strategy proposed in the thesis.