| The design and control parameters tuning of grid-connected photovoltaicinverter was based on ideal conditions, but did not consider the impact of the gridimpedance. For the photovoltaic generation system connected to local grid by longtransmission line or multi-level booster, at this point the grid impedance can not beignored, how to analyze the grid impedance impact on the operating performance ofgrid-connected photovoltaic inverter and improve the stability of grid-connectedphotovoltaic inverter system connected to the weak grid are important issues inresearch areas of photovoltaic generation.This paper respectively analyzes the external characteristics of photovoltaic cellsarray equivalent method, the mathematical model of grid-connected photovoltaicinverter system, the control strategy and design of controller parameters, based on this,the simulation model of single-stage three-phase photovoltaic inverter system wasbuilt by using PSCAD/EMTDC simulation software. This research provides anempirical basis for further study.This paper established the contact between grid impedance, control strategy,control parameters and control performance, a stability analysis method ofgrid-connected photovoltaic inverter system based on Nyquist stability criterion wasestablished to analyze the grid impedance impact on the phase margin and gainmargin of grid-connected photovoltaic inverter control system under existing controlstrategies and control parameters.For performance deterioration and even instability problems occur when thegrid-connected photovoltaic inverter which control system designed under the idealgrid conditions connected to a weak grid, a control parameters tuning method toimproved control system gain according to grid impedance has been proposed toimprove the stability of grid-connected photovoltaic inverter system. The design example and simulation have verified the practicability and availability of thetheoretical analysis and proposed control parameter tuning. |
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