Research On Harmonic Suppression Method For Large-Scale Grid Connected Photovoltaic Power Station

Large grid connected photovoltaic power station has the advantage of concentrating solar energy,and is conducive to expanding the scale of photovoltaic power generation.It has become the key planning and construction goal of new energy power generation in recent years.With the increase of network capacity of large-scale photovoltaic power plants,most countries have established strict standards to ensure that the power grid safety,so as to ensure the safe and stable operation of photovoltaic power plants,it is important to research photovoltaic power grid power quality.In this paper,to carry out basic research of photovoltaic grid connected inverter,based on the theoretical analysis and simulation,the harmony of large photovoltaic power grid harmonic detection method of wave suppression strategy is studied;the specific contents are as follows:(1)Harmonic Mechanism of Grid-connected InverterIn this paper,the common three-phase photovoltaic grid connected inverter is taken as the object of study,and the basic structure and working principle are studied.This paper analyzes two common grid connected control strategies of grid connected photovoltaic power station,and verifies the disturbance suppression effect of the grid connected control method on the background harmonic of power grid;Finally,the influence factors of the output harmonic of the inverter under SPWM modulation mode are studied,and the output harmonic distribution probability of the grid connected inverter is summarized.(2)Harmonic Current DetectionThe principles of harmonic detection method baesd on synchronous rotating coordinate system(dq method)and Discrete Fourier Transform(DFT)are analyzed,there simulation models are built using Matlab-Simulink,and the harmonic detection simulation are performed respectively.The results indicates,as a kind of full harmonic detection method,dq method is not ideal for the detection of special order harmonic,DFT can precisely detect any order of harmonic,but its accuracy is lower than dq method in full harmonic detection.This paper studied the artificial neural network(ANN)adaptive harmonic detection model,detection of the basic principle and mathematical model are analyzed.(3)Harmonic suppressionTo improve current quality of LCL-type grid-connected inverter,accurate equivalent impdance network model is proposed by incorporating dead-time effectsand digital control delay into the model.Based on the developed model,harmonic suppression mechanism and performance of grid voltage feed-forward and multi-resonant control schemes is analyzed and compared from the standpoint of output impedance and current gain characteristics of closed-loop system.Then a combined harmonic suppression scheme is proposed.Simulation results are presented to demonstrate the effectiveness of the proposed low-order harmonic suppression strategies.