Research On Control Strategy Of LCL Photovoltaic Grid-connected Inverte

As a crucial component of photovoltaic power generation systems,grid-connected inverters serve as the bridge between solar energy and the power grid,and are the absolute core of "green energy conversion".They are capable of both feeding power into the distribution network and supplying local loads with power when operating in island mode.The quality of the control strategy directly affects the grid-connected efficiency and power quality of the system,making the inverter control strategy a hot topic of current research.In this paper,LCLtype photovoltaic grid-connected inverters are studied,and a systematic research on the control strategy of LCL-type photovoltaic grid-connected inverters is conducted from the perspectives of passive and active damping,aiming to address the inherent harmonic resonance peak problem.The specific research content is as follows:(1)The mathematical model of photovoltaic cells is introduced,and their operating characteristics are analyzed.Photovoltaic grid-connected inverters are classified,and singlestage photovoltaic grid-connected inverters are selected as the main research object of this paper.By comparing the filtering performance of L-type,LC-type,and LCL-type filters using the Bode diagram,it is found that the LCL-type filter has stronger high-frequency harmonic suppression ability and higher research value.The limiting conditions of each parameter of the LCL-type filter are analyzed,and the method and calculation process of LCL-type filter parameter design in this paper are given.The mathematical models of LCL-type photovoltaic grid-connected inverters under different coordinate systems are derived,and the advantages and disadvantages of control under different coordinate systems are analyzed.(2)The causes of resonance peak in LCL-type filters and the control methods to suppress resonance are analyzed,and the working principles of several passive damping and active damping methods are described in detail.In response to the additional damping power loss and calculation complexity of traditional passive damping control strategies,an active damping control strategy is proposed,which adopts a capacitor current proportional feedback control scheme with PQ control for the outer loop and AQPR-HC(adaptive proportional resonantharmonic compensation)control for the inner loop in the two-phase stationary coordinate system.Multiple harmonic compensators are paralleled with the QPR controller,enabling the provision of both larger fundamental frequency gain and harmonic compensation for specific harmonic components,which is conducive to suppressing grid-connected current harmonics and improving system stability.(3)Simulation and comparative analysis are performed using the simulation model built in MATLAB/Simulink,and the experimental platform of LCL-type grid-connected inverters is constructed to verify the designed grid-connected control strategy.The simulation and experimental results show that the newly proposed active damping control strategy in this paper not only avoids additional damping power loss,but also has stronger ability to suppress gridconnected current harmonics,which is conducive to improving system stability compared to the traditional passive damping control strategy.