Research On Unified Power Quality Conditioner

At present, due to the widespread use of power electronic devices and the increase ofnon-linear loads, power quality problems is prominent in modern power system. It is effectivemeans that power electronic devices solve the problems. Therefore, research on UPQC(Unified Power Quality controller)has theoretical significance and practical value.To solve power quality problems comprehensively, working principle of UPQC isstudied. The topological structure of UPQC for three-phase three-fire distribution system isgiven, and meanwhile the mathematic model of UPQC is established.For the error of existing detection method with PLL, an improved detection method ofthree-phase voltage fluctuation without the PLL is presented in this thesis, which is based oninstantaneous reactive power theory. Simplified transform matrix by abc static coordinates toαβ static coordinates is given in the method. The variables of rotational transform matrix isobtained by calculation method to replace variables which is obtained by PLL. Thus, the errorcaused by PLL is reduced.On the basis of the analysis and comparison among triangular carrier PWM controlmethod, hysteresis tracking control method and voltage space vector control method, ahysteresis tracking control method based on space vector control is presented in the thesis,which takes space vector control in combination with hysteresis tracking control. Optimalvoltage vector according to the output value of hysteresis comparator is selected in themethod, which has characteristics of fast speed, good results and simple realization.For the proposed detection method and control strategy, the simulation model of UPQCis built based on MATLAB/simulink to analyze the compensation performance of UPQC. Thesimulation results show the correctness and effectiveness of improved detection method andcontrol strategy of the thesis.