Research On Control System Of Three-Phase Shunt Active Power Filter

With the wide use of various nonlinear loads and power electronic devices in the power grid,a large number of harmonics are generated,which cause serious pollution to the power grid.Active power filter(APF)has become a hot spot in electrical engineering research due to its strong dynamic real-time compensation capability,fast speed and difficulty in resonance with the system.Taking the three-phase three-wire parallel APF as the research object,the harmonic current detection method and the optimal control of DC capacitor voltage are studied,with emphasis on harmonic current control.The mathematical models of parallel active power filter(SAPF)are introduced in??and d-q coordinate systems respectively.Under the condition of phase shift caused by grid voltage fluctuation,three-phase i_p-i_q harmonic current detection with error angle calculation is studied.Aiming at the influence caused by DC side capacitor voltage fluctuation,droop controller is adopted to optimize the reference value of DC side capacitor voltage to make it change linearly with grid fluctuation,thus realizing SAPF optimization of system power loss.For harmonic current control,firstly,because there is error delay in deadbeat control,the control has the defect of deadbeat,thus predictive control is introduced.Secondly,on the basis of linear prediction and adaptive prediction based on LMS algorithm,deadbeat control based on adaptive prediction of LMS/LMF hybrid algorithm is designed.The proposed control method can adaptively adjust the proportion of LMS algorithm and LMF algorithm in weight coefficient updating according to the change of system state,which can fully embody the advantages of high steady-state tracking accuracy of LMS algorithm and high dynamic response speed of LMF algorithm.Finally,compared with traditional PWM modulation,space voltage vector pulse width(SVPWM)modulation has smaller switching loss and higher voltage utilization rate,and can make switching mode more flexible by switching different modulation modes.Therefore,the proposed control method is combined with SVPWM modulation to obtain harmonic current control.Its control advantages are that the compensation current has higher tracking accuracy for harmonic currents with higher low harmonic content,faster tracking speed of harmonic compensation current,and less switching loss of system power devices.MATLAB/Simulink simulation software and developed prototype are used for simulation and experimental verification.Simulation results and experimental results show that compared with the deadbeat control method based on linear prediction and LMS algorithm for APF adaptive prediction,SAPF system adopting the proposed adaptive prediction deadbeat control method based on LMS/LMF hybrid algorithm has higher dynamic response speed,higher compensation accuracy,grid current is closer to sine wave,and THD of grid current is significantly lower;Therefore,the proposed control method has higher control performance.