| With the increasing use of power electronic equipment in power system,the harmonic problem of power system is becoming more and more prominent.Active power filter(APF)has the advantages of flexible,real-time harmonic compensation and good dynamic performance in harmonic control,and has attracted wide attention in the field of harmonic control.Due to the existence of harmonic detection link in the APF of traditional harmonic current injection method,the detection error caused by the low-pass filter will affect the tracking control accuracy of the current.Aiming at this problem,this paper proposes a control principle based on fundamental voltage detection method,which avoids the error caused by harmonic detection,and studies the voltage tracking control strategy.Based on the analysis of the structure and principle of traditional harmonic injection APF,this paper proposes a control method based on fundamental voltage detection for the inherent detection error of harmonic detection.Through the analysis of its control principle,it is concluded that the fundamental voltage detection method meets the conditions.The APF control system adopts a double closed-loop control strategy.Taking the current inner-loop proportional controller and the voltage outer-loop proportional integral(PI)controller as examples,through the analysis of the equivalent harmonic transfer function,the conditions for the fundamental voltage detection method under fixed load conditions are obtained,and the value range of the inner-loop proportional controller parameters is obtained.The effectiveness of the proposed method is verified by simulation.Aiming at the problem that the designed APF has poor robustness when the load changes under PI control,repetitive control is introduced to further study the tracking control of voltage.The internal model stability of the basic repetitive control is not high,and it can not adapt to the change of load.This paper proposes an improved repetitive control method,which increases the stability of the system by connecting the feedback gain coefficient Q(z)in series with the internal model feedback path.Aiming at the problem that the repetitive control itself has a fundamental period delay,a composite control strategy composed of PI control and improved repetitive control in series is used to track the fundamental voltage.The design of control parameters meets the adaptive requirements when the load changes.Finally,a simulation model is built in MATLAB/Simulink and PSCAD/EMTDC to verify the feasibility of the fundamental voltage detection control method,and the filtering effectiveness of the composite control strategy under three different load characteristics of resistance,resistance inductance and resistance capacitance is realized.The adaptability of the control scheme is verified by analyzing the transition process of load change.Finally,the simulation results show that the composite control method has good frequency adaptability. |
