Research On Prediction Function And Compound Repetitive Control Strategy Based On LCL Active Filter

In recent years,the economy has developed at a high speed,and different fields need to provide different forms of electric energy.Power electronic devices are widely used in power systems,which brings convenience and also causes a large number of harmonics in the power grid.The active power filter is a power electronic device that can dynamically compensate harmonics and plays an important role in improving power quality.In this paper,LCL filter is taken as the research object,and the problems of harmonic current detection based on prediction function,command current tracking of compound repetitive control and parameter design of LCL output filter are deeply studied.Firstly,for the problem of unavoidable digital sampling delay in the process of harmonic current detection of active power filter,a predictive function model is constructed for functions with continuity,first-order and second-order derivatives at a certain point.The prediction function is discretized,and an expression that predicts the next time value using the current value and the recent historical time value is derived.In order to reduce the error caused by the function model parameters,the least squares method is used for optimization.Secondly,in order to achieve accurate tracking of the command current signal,a repetitive control method can be realized for the periodic signal without static tracking.Since the method has a defect of periodic delay,the compound repetitive control method combining PI control and repetitive control is adopted.The circuit topology and working principle of LCL type APF are introduced.The influence of each parameter in the LCL output filter on the filtering effect of the filter is deeply studied,and the parameter design method suitable for the output current of the active filter is given.In order to eliminate the inherent delay of the system,a combination of prediction function and compound repetitive control is proposed to effectively compensate,improve the tracking ability of the system to command current,and improve the harmonic compensation accuracy of the system.Finally,the MATLAB/simulink module is used to build the prediction function based on LCL active filter and the simulation model of compound repetitive control system.It is proved that the proposed method is feasible and correct in reducing system delay and command current tracking.The simulation results show that the prediction function and compound repetitive control can accurately predict the load current and track the instruction current signal with very low error,which can obviously improve the compensation effect of the system for harmonics.