Research Of Double Closed Loop Control Strategy On Three-Phase Four Wire Shunt Active Power Filter

A lot of power electronic equipment is used in production and living with the development of science and technology. On one hand people benefit from power electronic devices, on the other hand power grid is polluted by grid harmonic because of the characteristics of a non-linear. So it is very important to improve the quality of power network. Active power filter is also more and more effective in reducing harmonics of power grid. Compared with passive filter, active power filter has the characteristics of on-line real-time, and can effectively compensate the variation of harmonics.This paper selects the three-phase four wire active power filter capacitor in fractional system as the research object, the device generally used in low voltage system. In this paper, the topology structure and working principle of the model are introduced, and the harmonic detection algorithm based on p-q method and ip-iq method is introduced in this paper. By comparing the two algorithms, the improved ip-iq harmonic detection algorithm which is suitable for the three-phase four wire system is selected, and the mathematical model of the active filter is established. In the aspect of current loop control strategy, the three-dimensional space vector control strategy is analyzed, which can effectively solve the problem of the middle line current, but it can improve the accuracy and the transient performance of the system. Based on three dimensional space vector control, deadbeat control is proposed. The double PI control strategy is adopted to stabilize the DC side voltage in the voltage loop.The control strategy combining fuzzy control and PI control strategy in the whole voltage control is selected, this method can further adjust the parameters based on conventional PI parameters.In this paper, a simulation model of capacitor in active filter is built in MATLAB. The simulation results show that the proposed ip-iq harmonic detection algorithm can effectively detect harmonics, and has good dynamic performance. The accuracy of the harmonic compensation is greatly improved and the steady-state and transient performance are improved effectively by the improved control strategy. The response time of the whole voltage is accelerated, the overshoot is decreased, the steady state error is improved, and the upper and lower capacitance voltage is effectively controlled with double PI in the voltage loop.