Study On Double-loop Control Strategy Of Three-phase Shunt Active Power Filter

Due to the development of power electronics technology, many high-powerelectronic non-linear devices are applied to the mine grid. As these devices areconstantly connected to the grid, it was resulted in the distortion of coal grid currentand voltage waveforms. The amount of harmonic was increased significantly, andcaused pollution. All of these lead to decline in the quality of power supply, andimpact coal mine safety production. Therefore, harmonic suppressioncoal of the minegrid has important significance and practical needs.This thesis has selected Active Power Filter (Active Power Filter, APF) as amethod that suppress coal power grid harmonic, and described its basic principles andstructure briefly. Then, the three-phase three-wire shunt active power filtermathematical model was established, while doing the coordinatetransformation and decoupling control provided the basis for the control of the currentloop. Selected FBD (Fryze-Buchholz-Dpenbrock) power theory as APF harmoniccurrent detection algorithm, which compared with the instantaneous reactive powertheory, FBD had many advantages such as real-time, high precision and implementedeasily so on.On the basis of measuring the harmonic current accurately, the parameters of thetraditional PI control double-loop control system that is consist of current loop andvoltage loop, were setted in detail. Using Matlab to simulate the entire system, and theresults showed that the compensation effect of the system is not ideal. Due to thecurrent loop exsit interference signal with high frequency and periodic, PI control cannot track changing signals without error. Voltage loop was affected by the capacitoraverage voltage and ripple voltage variations, and it can not establish a precisemathematical model. Under PI control, voltage curve had overshoot, long responsetime, and steady-state error.Since the PI control had problems, this thesis proposes the new control strategythat added repetitive control into current control loop, and added fuzzy control intovoltage loop to compensate PI control insufficient. The paper designed each parameterof repetitive controller and fuzzy rules of fuzzy PID control in detial. The simulationmodel of SAPF double-loop control system using new composite controller in Matlab/Simulink. The simulation results showed that the control effect is better than theoriginal PI control method. The total harmonic distortion (THD) of supply current hasfallen by half after compensated. High-frequency periodic signal reduced significantly. The DC voltage waveform response fast, have high steady-state accuracy withoutovershoot. These simulation data proved that the correctness and feasibility ofdouble-loop control system under the new composite control strategy.