Control Strategy Research On Three Phase Four Wire System Active Power Filter

In recent years, a large number of Nonlinear load using in power grid, resulting in harmonic problems to power system which can’t be ignored,More and more harmonic compensation devices is using into the power system. Active power filter is considered to be the final solution of harmonic governance; it’s dynamic management of harmonic pollution overcome the inherent defects of the traditional passive filter. However, most of residential load with three phase four wire system absorption energy from power system, what’s more, as the application of intelligent micro power grid, the low voltage level harmonic pollution and three-phase unbalanced problem become more and more serious, the traditional three-phase three-wire system active power filter has limitations. the main research content is as follows:1. Established the mathematical model based on ABC coordinate switch state, at the same time make the mathematical model of ABC coordinates transform to dq0 coordinates to facilitate analysis.2. This article considers the neutral point in dc side is not balanced, analysis different current flow’s impact on the fluctuation of capacitor voltage under different working condition.The topology structure interpretation the voltage unbalance of capacitors on the mechanism. this article put forward impact factor which according to the midline current and capacitor voltage, calculates reasonable injected current according to the up and down the centerline of the capacitor voltage difference value. Define the appropriate sampling time, impact factor according to the inverter carrier comparison signal. Simulations show that using the method of neutral point control strategy can effectively suppress the neutral point offset.3. Established state space model of three phase four wire system APF in dq0 coordinatesl, based on the modeling design a first-order linear ADRC forcurrent tracking control of APF. Linear ADRC can comprehensive estimation and compensation the inner disturbance and outside disturbance of system, achieve the dq axis decoupling control, offers Parameter setting method,make the output current tracking the change of the command signal well. Simulation shows APF output current can tracking instruction current well and is superior to the traditional PID control in same conditions. The LADRC can replace PID to make the whole system control performance achieves good result.4 、 This article establishes a three phase four wire system active power filter comprehensive simulation system, analyzes the APF system filtering performance on the condition of three-phase load balancing, sudden load and three-phase unbalanced load. The results show that three phase four wire system APF has good filtering performance, and load line current is under control. The control system achieves an excellent performance, three phase four wire system APF has better adaptability.