Research On Detection And Control Method Of Unified Power Quality Conditioner

With the new changes of load components,power quality problems become more and more prominent.Unified Power Quality Regulator(UPQC)can solve many kinds of voltage and current problems,which can not only improve the current quality problems on the grid side and avoid the pollution of load current,but also improve the voltage quality problems on the load side to meet the load requirements.In this paper,the three-phase UPQC system is studied.Firstly,the main circuit topology of three-phase UPQC system is introduced.Indirect control is selected as the compensation method of the system,and its working principle is described in detail.Aiming at the problem of coordinated control between series and parallel converters,the internal power flow in the compensation process is analyzed,and the compensation capacity of the system is designed.In the aspect of signal detection,several commonly used signal detection methods are compared.Aiming at the problem of spectrum leakage and phase error when system voltage frequency offset occurs in DFT algorithm based on sliding window,an improved sliding window DFT signal detection method is proposed,which reduces the error caused by frequency offset and shortens the transition time.In the aspect of control,the tracking control mode and control strategy of UPQC system are analyzed.The SPWM method is used as the PWM control method in this paper.Because the signal detection method in this paper does not need decoupling of the signal,and the PI control method can't achieve zero steady-state error control for AC signal,so an improved quasi-PR control based voltage-current double-loop control method is adopted to improve the steady-state precision.Then the series part and parallel part of the system are analyzed separately,and their respective mathematical models are established.The simulation model of MATLAB/Simulink is built.The simulation results show that the detection method and control method adopted in this paper are effective.Finally,the parameters of UPQC system components are optimized.Damping resistance is added to the AC side of the converter.Then the system simulation model is built and simulated.The compensations of grid voltage and load current under six different operating conditions are simulated and analyzed,and the corresponding waveforms are given.The simulation results verify the correctness of the power flow theory in the system,and show that the proposed signal detection method and compensation control strategy are feasible,which can effectively make system compensate some power quality problems,such as the three-phase unbalance voltage,voltage and current distortion,voltage rise and fall,thus obtaining a good compensation effect of grid voltage and load current.