光伏经LCC-HVDC外送系统的次同步振荡特性分析

Analysis of Subsynchronous Oscillation Characteristics of Photovoltaic Power Station Integrated with LCC-HVDC System

随着我国西北地区光伏发电的持续增长,大规模光伏经电网换相型高压直流输电(LCC-HVDC)外送成为重要的外送方式。当光伏电站位于LCC-HVDC送端近区时,系统的次同步振荡(SSO)特性尚不明确,目前相关研究处于空白。针对上述问题,首先采用模块化建模方法,建立光伏经LCC-HVDC外送系统的状态空间模型;然后基于特征值分析法分析系统振荡模式,研究LCC-HVDC对系统SSO阻尼的影响;最后根据特征值根轨迹,分析系统参数对SSO特性的影响。研究结果表明,存在光伏电站和LCC-HVDC状态变量共同参与的SSO模式,且LCC-HVDC的接入会削弱光伏并网系统阻尼,增大发生SSO的风险;在光伏经LCC-HVDC外送系统中,光伏并网逆变器外环、LCC-HVDC整流器的比例系数减小或LCC-HVDC整流器的积分系数增大时,SSO对系统的威胁增加。研究结果可为实际工程提供理论参考。

With the continuous growth of the photovoltaic power plants capacity in northwest of China,large-scale photovoltaic power via line-commutated-converter based high-voltage direct current(LCC-HVDC)has become an important transmission method in the grid.When the photovoltaic power station is located at the sending-end of the LCC-HVDC,sub-synchronous oscillation(SSO)characteristics of the system are not clear,and related research is currently in a gap.To address the above problems,we first adopted the modular modeling method to establish the state space model of the photovoltaic power via LCC-HVDC system.Based on the eigenvalue analysis method,the oscillation mode of the system was analyzed to study the influence of LCC-HVDC on the SSO damping of the system.Finally,according to the root locus of the eigenvalue,the influence of system factor on the characteristic of SSO was analyzed.The research results show that there is a SSO mode in which photovoltaic power station and LCC-HVDC state variables participate together,and the access of LCC-HVDC weakens the photovoltaic grid-connected system damping and increases the risk of SSO.When the proportional coefficient of the outer loop of the photovoltaic power station and the LCC-HVDC rectifier decreases or the integral coefficient of the outer loop of the LCC-HVDC rectifier increases,the risk of SSO in the photovoltaic power station integrated with LCC-HVDC system increases.The research results can provide a theoretical reference for the operation and control design of such photovoltaic transmission projects.