并网逆变器复合电流环引起次/超同步振荡机理研究

Mechanism Research of Subsynchronous and Supersynchronous Oscillations Caused by Compound Current Loop of Grid-Connected Inverter

针对我国电力系统中的并网逆变器引起的次/超同步振荡现象,以单逆变器经阻抗并理想电源的典型系统为例进行分析。由于锁相环动态和较大电网电抗的存在,单逆变器并网系统电流环存在dq轴耦合。将dq轴统一考虑,建立了单逆变器并网系统的复合电流环模型。复合电流环中存在正反馈作用,该反馈与锁相环、电流控制器、系统运行点、电网电抗和滤波电抗等多个因素相关,若匹配不当则可能造成振荡或失稳。使用根轨迹法对上述因素对系统稳定性的影响进行分析,探讨了通过适当调整并网逆变器控制参数来抑制振荡的方法。通过时域仿真验证了复合电流环的准确性,同时验证了调整电流环控制参数抑制次/超同步振荡的效果。最后,对复合电流环模型的应用进行了展望。

To analyse subsynchronous and supersynchronous oscillations in power systems in China caused by grid-connected inverters, a single inverter connected to an ideal electric source via a reactance was built as a typical system. D-axis and q-axis current loops of the grid-connected inverter system were coupled due to existence of dynamics of phase-lock loop and large grid reactance. A compound current loop model of this system was built up considering both d-and q-axis models. The compound current loop had positive feedback effect, related to phase-lock loop, current controller, system operating point, grid reactance and filter reactance. The oscillations would happen if these factors were not properly matched. Root locus method was used to analyze influence of these factors on system stability. An oscillation damping method is discussed by properly adjusting control parameters of the grid-connected inverter. With time domain simulation, accuracy of the compound current loop model and effect of subsynchronous and supersynchronous oscillation damping by adjusting current controller parameter are verified. Finally, application prospect of the compound current loop is explored.