Control Strategy Of Three-phase Four-wire Active Power Filter Using Multiple Converters

Active power filter (APF) is a kind of power electronic devices used for grid harmonic control and power compensation to improve the power quality of grid power supply system. In recent years, on the one hand, with the rapid development of power electronics technology, a large number of power electronic devices are widely used in social life and the industrial field, its nonlinear characteristics inject in a large number of harmonics to the grid, resulting in the power quality deterioration of power supply system; On the other hand, the continuous progress of science and technology, more and more sophisticated precision equipments have become increasingly demanding. With the contradiction more and more prominent, active power filter will be broad prospects for development. This thesis focuses on the three-phase four-wire shunt Active Power Filter using multiple converters to study.The thesis summarizes the research background of the active power filter of previous work, including research status, the harmonic current detection algorithm and the main circuit control algorithm; and summarizes the development trend of the active power filter. Through the comparative analysis of several types topology of three-phase four-wire shunt active power filter, the thesis uses four-leg converter of the main multiple circuits. Based on a certain compensation capacity of active power filter, the advantage of this topology can reduce the switching frequency of power devices, exponentially increases the equivalent switching frequency of the overall system.The thesis analyzes the iv-iq harmonic current detection algorithm based on instantaneous power theory and the random harmonic current detection algorithm. Then, the thesis uses an improved instantaneous power ip-iq harmonic current detection algorithm. Compared the traditional ip-iq method, this control algorithm has higher harmonic current detection accuracy, and can better control the active component in the active power filter; and compared to the random harmonic detection algorithm, this detection algorithm has little calculated amount, can improve the computation speed and better detection of real-time.The thesis analyzes the carrier phase shifted SPWM control technique in the multiple main circuits, and analyzes the characteristics of the LCL output filter. Then introduce the voltage control of APF DC bus, and present a soft-starting to avoid the grid current impact when APF starting. On this basis, the thesis presents a dual closed-loop control strategy of the multiple main circuits with the LCL-filter. This control strategy can not only improve the equivalent switching frequency, reduce the pollution of the high frequency switching ripple current, but also inhibit the circulating current between the converters of multiple main circuits, improve the compensation effect of the whole system.Finally, develop a three-phase four-wire shunt active power filter using multiple converters, and describe the device hardware circuit design and system software design Set up a simulation model and an experimental prototype of the system, and the results show that the control strategy is correct and feasible, and the harmonic compensation effect of the system is well.