基于欠励磁状态运行的虚拟同步发电机低电压穿越控制策略

虚拟同步发电机(VSG)技术可模拟同步发电机(SG)运行特征,有助于并网系统和传统电源在电网中的协调运行。但其电压源特性增加了低电压穿越(LVRT)的运行难度,难以限制电流并提供适当无功支撑。为此,将传统SG并网无功调节原理应用于LVRT控制中,提出一种基于欠励磁状态运行的VSG的LVRT控制新方法。不改变原有VSG控制结构,对下垂特性、无功环和有功环分别进行改进设计,抑制电网故障对VSG的暂态冲击,加速励磁状态的转变过程。并在保持原有VSG特性的基础上改进附加电流环,应用新的定向方法,辅助系统欠励磁状态运行,实现故障穿越。所提方法无需切换控制算法,也无需加入状态平滑切换策略,且能同时应对LVRT和电网不对称跌落问题,简化控制策略,拓展VSG运行优势的适用范围。最后,通过仿真验证了所提方法的正确性和有效性。

Under-excitation Operation of Low Voltage Ride-through Control Strategy for Virtual Synchronous Generator

Virtual synchronous generator(VSG)technology can simulate the operation characteristics of synchronous generator(SG), which is helpful for coordinated operation of grid-connected system and traditional power supply in power grid. However, the nature of voltage source exacerbates the difficulty of low voltage ride-through(LVRT)to limit current and provide proper reactive power support. Thus, learning form the reactive power regulation theory of SG, a new LVRT control strategy is proposed for VSG. The design of droop characteristic, reactive and active power loops are improved respectively without changing the original VSG control structure. This helps to suppress the transient impact of grid faults on the VSG, and accelerate the transient process between excitation states. Moreover, an additional current loop is redesigned in a new orientation method to assist the system running in the under-excitation state to realize LVRT. The proposed control strategy can deal with symmetric and asymmetric grid voltage drop problems without smooth handoff algorithm, which helps to simplify the control strategy and expand the suitable range VSG operation advantages. The simulation results verify the feasibility of proposed LVRT control strategy.