Research On Resonance Analysis And Suppression In Photovoltaic Cluster System

With the development of distributed photovoltaic(PV)power generation and grid connection technology,the PV cluster structure which is formed by multiple photovoltaic inverters connect in parallel at point of common coupling(PCC)are widely used.LCL filters are widely used in PV cluster system,resulting in inherent resonance points in the system.Besides,multiple inverters will also couple through the line impedance and the grid impedance to form a complex high-order electrical network,which can easily induce resonance of the PV cluster system,resulting in a decline in power quality and endangering the safe and stability of the system.Therefore,although the development of the PV power generation industry is in full swing,the resonance problem in the photovoltaic cluster system needs further research urgently.This thesis conducts research on photovoltaic cluster systems.Firstly,for the power generation part of the PV cluster system,a maximum power point tracking(MPPT)strategy combining fuzzy control and automatic adjustment step method is proposed.The method not only improves the speed of tracking the maximum power point,but also reduces the power oscillation near the maximum power,thereby reducing the harmonic effect of the front-end power fluctuation on the PV cluster system.Secondly,based on the grid-connected filter model,the characteristics of commonly used LCL filters and several new types of grid-connected filters are analyzed.Besides,the corresponding passive and active damping strategies are analyzed.Furthermore,the idea of modeling the output impedance model of single-phase and three-phase PV grid-connected inverters with LCL filters is unified,which greatly simplifies the process of modeling.And the nonlinear factors in the system are taken into account to improve the accuracy of modeling.Then,on the basis of the above,the equivalent model of the PV cluster system is established.And taking the main factors affecting the resonance characteristics of the PV cluster system as variables,the resonance characteristics are analyzed.Besides,the suppression strategy for the main harmonic source components in the system are proposed to reduce the risk of resonance.Finally,in order to effectively suppress the resonance problem in the PV cluster system,based on theoretical analysis,from the inverter side,a suppression strategy based on output impedance enhancement is proposed and the control loop is optimized;in addition,from the grid side,an impedance reshaping strategy based on the cascaded second-order generalized integrator frequency-locked loop combined with virtual admittance is proposed.And the simulation in MATLAB verifies the effectiveness of proposed strategies.