Study On Harmonic Suppression In Microgrid Based On Active Power Filter Control Study On Harmonic Suppression In Microgrid Based On Active Power Filter Control

With the increasing complexity of the energy structure and electric load,micro-grid technology has been researching in many countries.However,harmonic currents are generated by microsource and a number of non-linear loads in the micro-grid,which has a serious impact on the stable operation of the system.Effective measures should be taken to provide a stable environment of micro-grid power supply and improve the power quality of micro-grid.In this thesis,the harmonic problem generated by the non-linear load in the micro-grid is studied.The three-phase three-wire shunt active power filter(APF)is used for harmonic suppression,which has important research significance to improve the power quality of the micro-grid and ensure the stable operation of the system.Firstly,the basic structure of micro-grid and the harmonic problems in micro-grid are analyzed in this thesis.Secondly,several commonly harmonic detection methods are introduced and the method of instantaneous reactive power is emphasized.The method of i_p-i_q based on instantaneous reactive power is adopted to avoid the influence of voltage fluctuation in the micro-grid.Then,the active power filter is adopted to suppress the harmonic generated by the non-linear load.The working principle of APF is expounded and the mathematical model of the main circuit is established.In order to reduce the system delay,the control method of deadbeat current predictive is adopted to predict the next instruction current in the current loop of APF.So as to ensure the real-time and accuracy of current tracking in the all-digital system,the method of SVPWM is used to convert the current control into voltage control.In order to maintain the stability of the system,the method of PI is adopted to ensure that the DC-side voltage is stable at the reference in the value voltage loop.Finally,passive power filter(PPF)is connected to the APF AC side circuit to improve the harmonic suppression effect and reduce the investment costs.In this thesis,the models of p-q and i_p-i_q harmonic detection method are established by using Matlab/Simulink software.The simulation is performed under the condition that the power supply voltage is symmetric and distortion-free and the power supply voltage is asymmetric and distorted.The results show that i_p-i_q method can avoid the influence of power supply voltage distortion.The harmonic current component can be accurately separated.In addition,the model of APF is established.The SVPWM control strategy of the deadbeat current prediction is verified in the conditions of three-phase voltage symmetry,sudden load and power supply voltage distortion.The results show that the harmonic current can be quickly suppressed by the active power filter under three conditions.The APF+PPF model is established.Under three-phase voltage symmetry condition,the simulation results show that the method can improve the harmonic suppression effect and reduce the capacity of the active power filter effectively.Moreover,the cost is reduced considerably.