Research On Harmonic Detection And Control Strategy Of Active Power Filter

With the extensive use of power electronic nonlinear devices, the problem of harmonic pollution in electric power system becomes more and more serious. Because of its good performance in harmonic compensation, active power filter has been widely concerned and studied. The key research contents of APF include:load current harmonic detection algorithm and tracking control of harmonic compensation. This paper offers all the methods and theories based on the three-phase shunt active power filter.p-q and ip-iq harmonic detection methods based on instantaneous reactive power theory have been widely used in harmonic detection, p-q detection can accurately detect the harmonic and reactive current only in the ideal three-phase voltage. ip-iq methods can accurately detect the fundamental positive sequence current in the unbalanced and distorted three-phase voltage, but when it detects the fundamental positive sequence active current, error appears. This paper presents an improved method for fundamental positive sequence active current detection based on the rotation factor. Obtaining the error vector information of traditional ip-iq detection by the theory of rotation vector. By the error correction, thus obtaining the accurate fundamental positive sequence active current.The grid side current control mode is not necessary to detect the load current harmonics. it has feedback effects on current compensation instruction, belonging to the closed-loop control, so it has higher compensation precision. But the grid side current control method regulate the active power output only through the voltage loop. It is easy to cause the DC side capacitor voltage a large fluctuation and the dynamic performance is poor when the load is abrupted. This paper proposed an improved method for grid side current control of active power filter based on deadbeat control. The deadbeat control is carried out in the αβ coordinate system to avoid the serious coupling. In this paper, the linear prediction method, the repeated prediction method and the adaptive prediction method are introduced. Combining them with deadbeat control respectively to improve the dynamic performance of APF.Finally, the APF simulation model is built in the Matlab/Simulink environment. Simulation experimental results show that the improved detection method proposed in this paper can accurately detect the fundamental positive sequence active current under unbalanced three-phase voltages. The grid side current control method based on the deadbeat control proposed in this paper improve the compensation precision of the APF, and it has good dynamic characteristic under the load change condition.