The Researches On A Maximum Power Point Tracking Technique For PV System And Droop Control Of Inverters

Increasingly along with the traditional fossil energy depletion,renewable energy sources such as solar energy,wind energy are becoming more and more get attention.Meanwhile micro-grid using power electronic transform device makes more renewable energy sources be used more efficiently.The questions about a maximum power point tracking technique for PV system and droop control of inverters are discussed in this paper.Firstly,the PV system needs to use DC/DC converter find maximum power point in order to improve the efficiency of the photovoltaic system.Aiming at the unimodal output characteristic of the PV array,this paper introduces several kinds of commonly used control algorithms,such as constant voltage,conductance increment,P&O method.Meanwhile the paper analyzes the advantages and disadvantages between the algorithms.Using Matlab/Simulink,the control models of the traditional conductance increment method and P&O method are given.According to the simulation results,this paper analyzes the shock and misjudgment defects of traditional algorithm.In the end,an adaptive hysteresis comparison method is put forward.This method can be adaptive to change the search step length according to the volume of the slope.The simulation results show that the method can restrain the shock and misjudgment defects of traditional algorithms.The output characteristic of photovoltaic array under the condition of partial shadow is multimodal,but the traditional MPPT control algorithms are easy to fall into local optimal value and reduce power generation efficiency.This paper analyzes characteristic curve of the photovoltaic array output and infer the general law of multi-peak P-U curve.In combination with dynamic differential evolution algorithm,a MPPT control method based on an improved DDE algorithm is proposed.In order to improve the precision of the algorithm,the last part of the algorithm uses the small step disturbance.The S-function functions of the perturbation and observation method,the initial dynamic differential evolution algorithm and the improved DDE algorithm are written.The simulation shows that the dynamic differential evolution algorithm has the very good stability and accuracy.Finally,this paper discusses the problems of the droop control of inverters.This paper introduces the principle of traditional droop control algorithm and gives P-f,Q-U droop control model.Through analyzing the power circulation of the micro-grid,this paper describes tvoltage and reactive power droop coefficient and impedance have a certain influence on the precise distribution of reactive power.The new method that it uses the virtual impedance and increase reactive power droop coefficient is put forward.The simulation results prove the effectiveness of the algorithm.