弱电网下海上低频风电系统网侧控制和稳定性分析研究

Research on grid-side control and stability analysis of the offshore low-frequency wind power system in weak grid

低频交流输电技术广泛应用于海洋风电的输送,但其送出的电流质量和系统稳定性会受到网侧变流器和弱电网线路阻抗的影响。文章针对海上低频风电系统的网侧控制,研究了αβ坐标系下基于虚拟同步机(Virtual Synchronous Generator,VSG)控制方法,并引入虚拟阻抗环节实现VSG的功率解耦,使得网侧变流器能在电网频率突变时自发调频,提高了其并网电能质量和弱电网下的稳定性。考虑到VSG并网系统与弱电网之间的交互作用,利用谐波线性化方法建立了αβ坐标系下VSG并网系统的序阻抗模型,结合阻抗分析法和Nquist稳定判据分析了并网系统在弱电网下的稳定性。最后,通过仿真验证了分析的正确性。

Low frequency AC transmission technology occupied much offshore wind power transmission market.However,in the offshore low-frequency wind power system,the control of the grid-side converter and the line impedance of the weak grid will affect the grid-side current quality and stability of the system.Aiming at improving the performance of the grid-side control for the offshore low-frequency wind power system,a control method based on Virtual Synchronous Generator(VSG)technology inαβcoordinate system is researched in this paper,and the virtual impedance compensation link is introduced to realize the power decoupling with the VSG control,the grid-connected inverter can support the grid frequency variation when the grid frequency changes suddenly,thus the grid-side power quality and the stability of the system in weak grid is improved.Considering the interaction between the VSG grid-connected system and the weak grid,the sequence impedance model of the VSG grid-connected system inαβcoordinate system is established by harmonic linearization method,and the stability of the system in weak grid is analyzed by combining impedance analysis method and Nyquist stability criterion.Finally,the correctness of the analysis is verified by simulation in this paper.