基于改进虚拟同步发电机算法的微网逆变器二次调频方案

Secondary Frequency Regulation for Microgrid Inverters Based on Improving Virtual Synchronous Generator

传统的虚拟同步发电机控制方案可帮助微网逆变器实现一次调频功能,为微网提供频率支撑,然而一次调频属于有差调节。通过改进虚拟同步发电机的控制结构,可使逆变器根据工作模式在一次调频和二次调频之间切换。二次调频适用于孤岛模式的微电网,可实现微网频率的无差控制,同时利用小信号等效以及根轨迹分析方法对二次调频控制策略进行了稳定性分析,并给出了相关参数的选取范围。该方案可使多台逆变器参与调频并按容量均分缺额功率,有利于总调频容量以及微电网容量的扩展。此外,二次调频对频率额定值的追踪功能还可辅助完成微网孤岛模式到并网模式的预同步环节,保证了预同步过程的顺利实行。最后,通过微网仿真平台验证了所提控制方案的有效性。

Traditional virtual synchronous generator control scheme can help inverters to realize primary frequency regulation and provide frequency support for microgrid. However, steady-state error exists by using this method. With improved control structure of virtual synchronous generator, function of secondary frequency regulation for island mode can be obtained to stabilize microgrid frequency. System stability is discussed through small signal equivalent analysis and root-locus method, and selection range of related parameters is confirmed. Simultaneously, active power sharing according to inverter capacity can be implemented by changing related parameters. It helps several inverters to participate in secondary frequency regulation together, conducive to extend total capacity of frequency regulation and microgrid. Furthermore, the proposed secondary frequency regulation can assist implementation of pre-synchronization function. Simulation results verify effectiveness of the proposed method.