Research On Harmonic Current Detection Algorithm And Compensation Technology In Shunt Active Power Fitter

In recent decades, with the continuous development of industrial technology,harmonic contamination become more and more serious because of the extensive use of power electronic devices and other nonlinear loads.The result of harmonic contanmination makes a serious threat to the safe operation of power system. Active power filter(APF), a power electronic device, as a kind of high efficient solution, has been followed with wider and wider interest.This paper presents the background of harmonics apperance and the harm to power supply system, the ways to restrain the harmonics,the development situation of APF both at home and abroad,the classification of APF, the basic principle of shunt APF, and also introduces some harmonic current detection algorithm and compensation current tracking control strategy.The real-time and accuracy of harmonie current detection algorithm is one of the critical factors to the working performance of the APF. Based on the detailed analysis and comparison of several commonly used harmonic current detection algorithm, decide to adopt the adaptive harmonic current detection algorithm. In view of the feedback signal mixed with a large number of harmonics in traditional variable step size adaptive harmonic current detection algorithm,reducing the detection accuracy. To overcome this shortcoming, this paper uses the error feedback filter to filter the feedback error and improves the steady state accuracy of the system.In addition, in order to make the system can converge quickly, this paper uses2order iterative variable step-size algorithm, and the error of load current values with the same phase in two adjacent fundamental wave cycles is used as one part of the feedback amount to adjust step size, makes the algorithm also have a fast tracking speed when the load sudden changs.The model of harmonic current detection is built in the MatLab/Simulink, The simulation shows the validity of the method.A brief analysis of the advantages and disadvantages of hysteresis current control and the Space Vector Pulse Width Modulation(SVPWM) control, combine the advantages of the both, this paper adopts the strategy of double hysteresis current control based on SVPWM. In view of the harmonic current detection algorithm has about a unit delay of sample time, this paper adopts Lagrange interpolation algorithm, according to the previous harmonic current values to predict the the next sampling cycle harmonic current value.This algorithm is very simple and is conducive to the realization the deadbeat control of APF.At last, the model of the whole APF system is built in the Matlab/Simulink,comparison of three different control strategies of the compensation effect,the simulation shows the strategy of double hysteresis current control based on SVPWM has the advantage of lower switching frequency and high precision,this strategy can suppress the harmonic currents very well and have a good performance of dynamic compensation.