Research On Harmonic Current Detection And Elimination Method For Grid-connected PV

With the contradiction between fossil energy and the environment emerged,solar energy as new green energy is attracted more and more attention.The proportion of photovoltaic systems is growing in the power industry,but the output of photovoltaic power generation system is affected by the external environment,so the certain condition must be meet,of which is current harmonic content.The photovoltaic grid-connected current detection and suppression technology research is main topic in the paper,background and significance of the subject and the existing current detection and suppression method is introduced.The simulation model and output characteristics of photovoltaic cells,maximum power point tracking and control strategy for grid-connected system are described.The reasons of harmonics produced by grid-connected PV are analyzed.By mathematical and simulation analysis of SPWM,the effect of output harmonic spectrum is obtained under different amplitude modulation ratio and frequency modulation ratio.The shortcoming of ip-iq,harmonic detection algorithm based on instantaneous reactive power theory is analyzed.In order to solve the problem of the low-pass filter delay in the presence of the conventional method,variable step size LMS adaptive filter algorithm instead of the fixed step LMS for filtering function is proposed,the step size is updated by coherence average estimation of adaptive feedback amount.Simulation results show that the detection algorithm based on variable step size LMS filter has higher precision tracking speed and stability compared to the detection algorithm based on low-pass filter.In the last,contrary to traditional PI control only can be achieved unsteady-state error under DC signal,however,the command signal of active filter is multiple set of sinusoidal signals,single PI control can not guarantee that steady-state error is zero.Thus the use of complex control that combine PI control with repetitive control to achieve the two complement of each other and make up for deficiencies of two control strategy,meanwhile,parameters of the PI control and repetitive control are designed.Simulation results show that PI-repetitive control method has more effectively suppress harmonic than single PI control,so the control strategy can meet the requirements of grid-connected PV.