Research On The Harmonic Characteristics Of PV Grid Under Non-ideal Grid Conditions

With the rapid development of modern industry and environmental pollution continue to intensify,timely and vigorously promoting photovoltaic(PV)renewable energy is an important measure to alleviate social contradictions while human survival pressure gradually increases.It is expected that the development scale of China's photovoltaic which is belonging to renewable energy will reach to 105 million kW.h until 2020 according to the forecasting of ? '13th Five-Year' Plan for Social Developmentof?.PV system has a wide range of promotion and practicality because of it's strong adaptability,low noise,environmental protection and growing technology.But what will be challenged is the continued capacity increase and the very cooperation to power system.This paper is of great significance to further expand the scale and increase capacity of PV industry.When focuses on the background harmonic injection and the three-phase imbalance,and studies the response mechanism of the PV grid-connected system Of the power quality.At first,this paper studies the influence of the power grid background harmonic condition on the power quality at the point of common coupling(PCC).It will cause voltage and current fluctuating abnormally at the DC side when the grid voltage contains harmonics.An impedance analysis method based on small signal model of grid-connected system is proposed to analyze the PCC current harmonic characteristics quantitatively.In the grid-connected system built by Matlab/Simulink the correctness of the analysis method is verified in terms of comparison between the detection of specific harmonics and theoretical derivation.Then,a 12.24 k W PV grid-connected system on rooftop is established to monitor and analyze the characteristics.Finally,the PCC power quality is studied through the experimental platform to simulate the power grid background harmonic conditions.Moreover,the AC/DC side interaction mechanism of PV grid-connected system is studied when the voltage is three-phase unbalanced.Then the effect on two times wave of the DC side is derived by the the instantaneous power theory.And considering theamplitude and phase sequence,which is combined with the switch function of Fourier expression harmonic characteristic at PCC is derived.finally,the scientificity of the relevant inference is verified by simulation and experiment similarly.At last,a new hybrid power filter(HPF)is proposed which is composed of active power filter(PPF)and passive power filter(APF)based on harmonic characteristics of PV grid-connected system under non-ideal conditions.Using the simulink software to build the filter module,and confirmed that HPF has advantages in improving the power quality of the grid system.