The APF Control Methodresearchbasedon PI Andrepetitive Control In Parallel And Research Of Suppresing Circulation Current In Parallel APFs

The improvement of the level of modern industrialization leads to the rapid development of power electronic technology and power electronic equipment with large number of high frequency switching devices lead to the serious power grid harmonic pollution.Active power filter(APF)has become the main research point of power grid harmonic control technology.In this paper,the optimization control method of three-phase four wire system APF based on repetitive control and PI control in parallel is studied,and current suppression of circulating current in multi APFs parallel operating is on the research.In the research of control method optimization,the improved i_d-i_q detection method is used to solve the problem that the traditional i_d-i_q detection method can't detect harmonic current,when a large amount of unbalanced current exists in the system.Aiming at the problem that the traditional PI control is not good for the tracking of periodic signals,and the steady state accuracy is not high,a parallel control method for repetitive control and conventional PI control is proposed.In the method,the characteristics of high precision and high precision of repetitive control are used to restrain the periodic disturbance,which improves the overall compensation effect of the device.And the proposed hybrid control method is modeled and simulated in Matlab/Simulink,and the experimental results are verified on the experimental platform.The control effect of the compound control is compared with the traditional PI control effect,and the superiority of the compound control is verified by the experimental results.In the research of current suppression of circulating current in multi APFs parallel operating,we start from the definition of circulation,and the causes of circulation are analyzed.The modeling of multi APF parallel connection,the analysis of the circulation loop and the derivation of the formula of the circulation are carried out.Aiming at the circulating current which is generated from the difference in the magnitude of the current in the devices,the coordination control strategy of positive,negative and zero sequence circulation is put forward.In the case of the whole device output unchanged,the coordination control strategy adjusts the device output current,which eliminates the difference in current magnitude and eliminates the circulation current of the system;Aiming at the circulating current which is generated from the difference in the phase of the current in the devices,predictive control strategy is proposed,which has the lead characteristic used to eliminate the phase difference of signal delay so as to achieve the purpose of eliminating the circulation.