Analysis Of Resonance Mechanism Of Distribution Network Under Large-scale Photovoltaic Access

In the neutral ungrounded distribution system,the magnetizing inductance which has the nonlinear characteristics of the electromagnetic voltage transformer When it was been the distributed by the outside will be easily saturated.The ferroresonance will influence the normal operation of the power grid and electrical machines when the magnetizing inductance matches the distributed capacitance of the distribution network.Due to the lack of traditional energy sources and environmental pollution,the large-scale photovoltaic grid-connected power generation has become a major trend around the world.However,the specificity of the photovoltaic power generation will influence the ferroresonance of the distribution networks when access the network.Therefore,this thesis intends to study the mechanism and influential factors of ferroresonance in distribution networks when large-scale photovoltaic access conditions.Firstly,the output characteristics of photovoltaic and arrays is studied,and the basic forms of photovoltaic power generation systems are introduced.The causes of voltage fluctuations in distribution networks which are caused by large-scale photovoltaic generation are analyzed.Based on the Fourier expression of the output voltage of the photovoltaic inverter,the harmonic characteristics when photovoltaic access the distribution network are studied.Secondly,the mechanism of the ferromagnetic resonance of the power distribution system that is not directly grounded at the neutral point has analyzed,and the equivalent circuit of the large-scale photovoltaic power generation when it is access to the distribution network is simplified.According to the simplified circuit,the relationship between the PV output power and the voltage transformer flux linkage is deduced,and the influence of the PV output power on the ferromagnetic resonance of the distribution network is studied.Finally,according to the equivalent circuit of the ferromagnetic resonance in the distribution network,the equation between the harmonic voltage and the voltage transformer flux linkage which is caused by large-scale photovoltaic generation is established,The built-in equations can be used to determine the inductive resistance of excitation inductance of the voltage transformer.Then,the influence of the harmonic voltage caused by photovoltaic power generation on the ferromagneticresonance of the distribution network is studied when using the discrimination conditions of the ferromagnetic resonance in the distribution network.