Research On Passive Control Strategy Of Three-Phase LCL Type Photovoltaic Grid-Connected Inverter

Photovoltaic power generation is an important direction of new energy research,photovoltaic grid connected inverter is an important part of photovoltaic power generation system.Photovoltaic grid connected inverter adopts traditional PI control scheme,which has the problem of poor output waveform quality in weak grid environment.In order to improve the static and dynamic performance of the system and improve the quality of output waveform,this paper mainly studies the passive control strategy of three-phase LCL photovoltaic grid connected inverter.Based on the review of the current research status of the existing three-phase LCL photovoltaic grid-connected inverter,this paper analyzes the ability of the LCL filter to suppress harmonics in each frequency range and the addition of the filter will cause the system to generate at its resonance frequency.The problem of spikes,and the parameter design of the LCL filter under the strong power grid environment is carried out.The influence of the grid impedance on the performance of the LCL filter is discussed,and the mathematical model of the three-phase LCL photovoltaic grid-connected inverter under the weak grid is established.This paper analyzes the passive control strategy of three-phase LCL photovoltaic grid connected inverter.The mathematical model of PCHD is established for three-phase LCL grid connected inverter in weak current grid.The passive control law is obtained by adding damping dissipation term.Combined with the control law and the system state variable equation,the passive controller for weak current network is designed.In this paper,a hybrid controller based on active damping and passive control is studied.Aiming at the problem that LCL filter has resonance peak at its resonance frequency,the passive damping methods of series resistance of capacitor branch and parallel resistance are compared and analyzed.The passive damping method of series resistance of capacitor branch is selected and applied to traditional controller and passive controller respectively.The results show that better grid current waveform can be obtained when the damping method is applied to passive control.Considering that the passive damping method will increase the extra power consumption of the system,the active damping method based on notch filter is introduced to obtain the improved passive controller.Through the simulation and experimental research,it is observed that the simulation of the passive controller has a more stable and smooth grid current waveform than the traditional controller when the given current value changes.The simulation analysis of the improved passive controller shows that the control strategy of notch filter series passive controller can make the output power quality of the system reach the national standard,and the improved passive controller can effectively suppress the resonant peak of LCL filter while the system responds quickly.