Research On Harmonics Suppression Technology Of Photovoltaic Grid-connected Generation System

Grid-connected photovoltaic(GCPV)generation have in the stage of large-scale application,but it can not be utilized fully that limited by illumination condition.With the improvement of the level of urbanization in our country,a large number of nonlinear loads have been poured into the power grid for commercial and residential,harmonics current generate by nonlinear load cause pollution to public grid.This paper research the harmonics suppression technology of GCPV system,to solve the problem caused by harmonics in power grid,also improve the utilization ratio of GCPV system.The main research contents in this paper as follows:(1)Determine the technical scheme.Make comparison analysis of active power filter(APF)and GCPV generation system,to get the harmonics suppression technical scheme based on APF;make sure there are two key point of this scheme,first is the current harmonics in power grid be detected,second is synthesis the harmonics signal with PV signal to the grid-connected control signal.(2)Research on harmonics current detection method.Make detailed analysis of the FBD method and i_p-i_q method;unite the FBD method to improve the i_p-i_q method,the improved method can be applied in GCPV generation system connect to the three phase three wire network,and reduce the amount of computation compared with the traditional i_p-i_q method;simulate the harmonics detection method before and after improved,the simulation results show that the improved detection method can improve the dynamic response speed.Analyze the influence to the detection method of the low-pass filter with different cut-off frequency;the average value filter and second order Butterworth filter are designed,choose the average value filter which get steady state quickly during test.In addition,make analysis of the digital phase locked loop.(3)Research on system control strategy.For the grid-connected control instruction signal,analysis synthesis method based on harmonics detection;considering the current inject to power grid may greater than maximum while generation and harmonics suppression working together,propose a peak current protect measure.Voltage-current double closed-loop control analyzed here: in order to reduce the influence by capacitor in the DC side which it can act nonlinear,bring in PI controller based on power balance in the outer voltage loop;bring in PR controller in the inner current tracking loop;using SVPWM modulation for converter.(4)Designing LCL filter on the side of power grid.Analyze the LCL filter according to its math model,aim at the operation of the system need to combine two working station which involve grid-connected generation and harmonics suppression,conclude parameter design restrain of inductance?capacitance and resonant frequency,and compute parameters for simulation example;for the problem of self-resonance in LCL filter,add damping for resonance peak suppressing in the inner loop capacitor current feedback.(5)Construct GCPV generation system model with the use of Matlab/Simulink software,simulate the grid connected power generation and the harmonics suppression,verifies the correctness of the technology project for harmonics suppression,the rationality of the total structure and control strategy in the system.