弱电网下基于虚拟同步机的并网逆变器短路电流抑制研究

Research on short circuit current suppression of grid connected inverter based on VSG generators in weak grid

随着电力系统中新能源发电渗透率的提高,电网逐渐趋于弱电网,导致发电系统中低惯量、弱阻尼现象日益严重。虚拟同步机(VSG)技术可以提高惯量增加阻尼,保证系统在小扰动下的动态稳定性。然而高渗透率的电网系统为非无穷大系统,当网侧发生短路故障时,故障瞬间产生因非周期分量引起的暂态冲击电流,仅依靠传统的VSG控制无法有效地抑制短路电流,难以保证系统在大扰动下的暂态稳定性。针对以上问题,本文基于VSG暂态功角特性,提出了适用于弱电网的单位圆混合相量分析法,并结合提出的动态调节控制策略能够在电网阻抗波动时有效地抑制短路电流的稳态值和暂态冲击峰值,保证了系统的暂态稳定性。仿真和实验结果验证了本文所提控制方法的正确性和可行性。

With the increase of the permeability of new energy in the power system, the power grid tends to be weak, which leads to the phenomenon of low inertia and weak damping in the distributed generation system. The virtual synchronous generator(VSG) technology can improve the inertia and increase the damping, so as to ensure the dynamic stability of the system under small disturbance. However, the high permeability grid system is a non-infinite system, and when a short-circuit fault occurs on the network side, the fault instantaneously generates transient inrush currents caused by non-periodic components, which cannot be effectively suppressed by traditional VSG control alone, making it difficult to ensure the transient stability of the system under large disturbances. In view of the above problems, this paper proposes a unit-circle hybrid vector analysis method based on the transient power angle characteristics of VSG for weak power grids, and combined with the proposed dynamic regulation control strategy the steady-state value of short-circuit current and transient impact peak can be effectively suppressed when the grid impedance fluctuates, ensuring the transient stability of the system. Simulation and experimental results verify the correctness and feasibility of the proposed control method.