独立电力系统中基于模式切换的虚拟同步发电机控制方法

Virtual Synchronous Generator Control Method Based on Mode Switching in Isolated Power System

同步发电机组-虚拟同步发电机并联供电系统中,两种异构电源的物理结构和控制结构迥异,在负载突变时两种电源的暂态功率难以均分,尤其是在突加负载时,虚拟同步发电机因调节快在暂态过程中会承担过多负荷,甚至短时过载,这使得虚拟同步发电机容量不能充分利用。针对该问题,首先分别从调频、调压和输出阻抗特性差异上,阐明了两者暂态功率分配不均的机理。其次,在传统虚拟同步发电机控制中增加虚拟调速、虚拟励磁、动态虚拟阻抗等环节,以模拟同步发电机组的调速特性和电磁暂态特性,实现与同步发电机组并联运行时的暂态和稳态功率均分。再次,为保证虚拟同步发电机独立运行时的快速动态响应特性,在独立运行模式下仍保持传统虚拟同步发电机控制算法,设计了基于状态跟踪的模式切换环节,实现两种模式之间的平滑切换。最后,基于PSCAD/EMTDC的时域仿真结果和基于RT-LAB的控制器硬件在环试验结果表明,提出的控制方法能够实现虚拟同步发电机与同步发电机组并联运行时的暂态和稳态功率均分,且能够保持虚拟同步发电机独立运行时的快速调压和调频能力,独立、并联运行模式之间能够实现平滑切换,方法可应用于工程实际。

Significant differences of physical and control structures between virtual synchronous generator(VSG) and synchronous generator(SG) lead to the poor transient power sharing in the isolated power system with SGs and VSGs.VSG will take the majority of the load and even short-time overload in the transient process due to faster regulation,which causes the insufficient utilization of inverter capacity and poor economy. To solve this problem, firstly, the reasons of poor transient power sharing are analyzed from the differences of frequency regulation, voltage regulation and output impedance between VSG and SG. Secondly, virtual speed regulation, virtual excitation and dynamic virtual impedance are added to traditional VSG control, so that the VSG can simulate the speed regulation characteristics, electromagnetic transient characteristics and output impedance of SG, and the transient power sharing between SG and VSG can be realized.Then, to ensure the fast transient response, traditional VSG control algorithm is remained in an independent operation mode. And the two modes can be switched smoothly by designing state tracking loop. Finally, simulations in PSCAD/EMTDC and Hardware-in-the-loop experiments based on RT-LAB verify that the proposed control strategy can effectively improve the transient power sharing in parallel with SG and maintain fast dynamic characteristics in an independent operation mode, the modes can be switched smoothly, and the method can be used in engineering.