Research On Resonance Mitigation Method Of Distributed PV Clusters

In recent years,solar energy exhibits a remarkable characteristic that more and more distributed PVs connect to the main grid in the form of clusters.There exist a large number of LCL filters in PV clusters,making distributed network as a complicated higher-order network which includes many inh erent resonance points.When output voltage and current harmonic frequency of PV cluster matches the system natural resonant frequency,resonance happen.Therefore,in the condition of weak electricity grid,research on the resonance characteristics of multi-paralleled inverters and its suppression strategy have important significance for the realization of the safe and stable operation of clean energy system.In this paper,a multi-paralleled inverters system is studied.Firstly,this paper investigates multi input and output transfer function of parallel LCL system.Then,the transfer function of multi-parallel inverters is established,Finally,this paper investigates resonant characteristics from aspects of composition ratio,parallel inverter quantity and the grid impedance.Aiming at the resonance issue of the LCL inverter,the research of the passive damping and active damping of resonance suppression method is carried out.The passive damping method and the active damping mechanism are studied,and the influence of the grid impedance on the passive damping and active damping method is analyzed.On the basis of this investigation,a notch filter control method is proposed.Taking into account the resonance suppression method of the inverter need change hardware structure and control algorithm of the inverter,this paper proposes two centralized resonance suppression methods.According to the principle of resonance suppression,the two resonance suppression methods are passive switching impedance resonance suppression technology and active virtual damping resonance suppression method,which are all install a resonance suppression device in the point of commom coupling for resonance suppression.Finally,matlab simulation verifies the correctness of the two methods.