多光伏发电单元并入弱交流电网系统的站内/站网次同步振荡特性分析

针对多光伏发电单元并入弱交流电网系统的次同步振荡(sub-synchronous oscillation, SSO)问题,建立了3个光伏发电单元并入弱交流电网系统的小信号模型。通过特征值法分析,得出系统中存在的SSO模式,并计算各SSO模式的参与因子。结果表明,系统中存在2个站内SSO模式和1个站网SSO模式。站内SSO模式由光伏电站内部3个发电单元之间交互作用产生,主导因素为直流侧电容、逆变器电流内环控制器参数;站网SSO模式由3个发电单元与交流电网交互作用产生,主导因素为直流侧电容、逆变器电流内环控制器参数和交流电网。同时,通过分析主导因素对站内/站网SSO模式的阻尼耦合特性,得出光伏发电单元的发电容量、直流侧电容、电流内环控制器参数变化对2种SSO模式阻尼的影响趋同。最后,在PSCAD/EMTDC中搭建时域仿真模型,验证了理论分析结果的正确性。

Inside-Plant and Plant-Grid Sub-synchronous Oscillation Characteristics Analysis of Multiple PV Generation Units Connected to a Weak AC Power Grid

Aiming at the problem of sub-synchronous oscillation (SSO) when multiple PV generation units are merged into the weak AC power grid, three small signal models of PV generation units merged into the weak AC power grid system is established in this paper. Through the analysis of eigenvalue method, the SSO mode existing in the system is obtained, and the participation factor of each SSO mode is calculated. The result shows that there are two inside-plant SSO mode and one plant-grid SSO modes in the system. The inside-plant SSO mode is generated by the interaction among the three power generation units inside the PV plant. The dominant factors are the DC-side capacitance and the parameters of the inverter current inner loop controller; the plant-grid SSO mode is generated by the interaction between the three PV generation units and the AC power grid. The dominant factors are the DC-side capacitance, the inverter current inner loop controller parameters and the AC power grid. Meanwile, by analyzing the damping coupling characteristics of the dominant factors in inside-plant and plant-grid SSO mode, it is concluded that the influence of the PV unit’s generating capacity, DC-side capacitance, and current inner loop controller parameter changes on the damping of the two SSO modes is convergent. Finally, a time-domain simulation model was built in PSCAD/EMTDC to verify the correctness of the theoretical analysis results.