The Study On The Effect Of Large-scale Photovoltaic Grid-connected On System Stability And Countermeasures

As one of the important forms of new energy development and utilization,photovoltaic power generation is developing rapidly in recent years.Photovoltaic power generation has characteristics that are different from the regular power sources such as random output,connecting to grid with power electronic inverters,no mechanical rotary inertia.The stability characteristic of power system will be effected significantly after large-scale photovoltaic connecting to power.grid.The effect of large-scale photovoltaic grid-connected on system stability has become a research hotspot.The effect of large-scale photovoltaic grid-connected on system transient angle stability,thermal power unit subsynchronous oscillation characteristics are maintly studied in this paper.The effect of photovoltaic power change on voltage fluctuations is also researched.To address the the effect of large-scale photovoltaic grid-connected on system transient angle stability,on the basis of transient angle characteristic,combined with the ransient power characteristic of photovoltaic power,the mechanism of large-scale photovoltaic grid-connected on system transient angle stability is analyzed,including the effect of the overall inertia of photovoltaic and thermal interconnection system,the scale of the photovoltaic grid-connected,the photovoltaic reactive power control measures on system transient angle stability.The measures that improves the system transient angle stability is proposed inluding keeping the proportions of regular units,controlling the scale of photovoltaic power and adopting the constant voltage control pattern and so on.Taking Hetian Power Grid in the south of Xinjiang as exam ple,the effectiveness of the proposed measures are verified.To address the the effect of large-scale photovoltaic grid-connected on nearby thermal power unit subsynchronous oscillation characteristics.The photovoltaic electromagnetic transient model is built.By using test signal method,the unit electrical damping characteristic is analyzed with or without the photovoltaic grid-connected.The effect of the reactance of photovoltaic collection lines,the photovoltaic connection location on damping characteristic is studied.The damping will be improved with the photovoltaic grid-connected.If the connection location is far from the photovoltaic grid-connected,the increase amplitude of damping is smaller.The threat of subsynchronous oscillation still exists if the photovoltaic and thermal poewr units are connected to the AC system through series compensation lines.The subsynchronous oscillation will be suppressed by configuring supplementary subsynchronous oscillation damping controller at the photovoltaic stations dynamic reactive power compensation device.To address theeffect of high permeability of the photovoltaic`s power change on the voltage fluctuation.On the basis of power characteristic s of the photovoltaic power station,a typical photovoltaic grid-connected system is built to study the mechanism of voltage fluctuations affected by photovoltaic output fluctuation.The voltage fluctuations under different solar penetration is researched.If the photovoltaic permeability is higher,the larger the system voltage fluctuation range is.In order to improve the situation,magnification and the oil motor open time constant of thermal power units can be optimized to suppress the voltage fluctuation and promote PV acceptance ability.Taking Xinjiang Kashgar Power Grid as example,the effectiveness of the proposed measures are verified.