弱电网下构网型双馈风电机组直流动态分析及优化控制策略

DC-link Dynamics Analysis and Optimal Control Strategy for Grid-forming DFIG-based Wind Turbines in Weak Grid

当双馈风电机组接入弱交流电网时,转子侧和网侧变流器均采用无锁相环的构网型控制策略可以提高发电系统的并网稳定性。然而,对直流端口而言,网侧变流器在构网型控制下的直流电压抗扰能力有所降低,机组出力波动时直流电压的动态特征不容忽视。为此,文中首先建立了考虑交直流侧动态耦合特征的构网型双馈风电机组的小信号模型。基于系统模型研究了不同电网强度和风机转速下直流电压控制的稳定性,根据耦合传递函数矩阵分析了不同条件下定子功率变化对直流电压的耦合影响。利用小信号模型分析了定子功率对直流电压的交、直流耦合路径,并分别设计了解耦优化策略。理论分析表明,所提策略可以降低有功功率加载对直流电压的耦合作用,优化直流侧动态特性。最后,利用硬件在环实验平台验证了理论分析的正确性及所提控制策略的有效性。

When the doubly-fed induction generator(DFIG)based wind turbines are connected to the weak AC power grid,the grid-forming(GFM)control strategy without the phase-locked loop for both the rotor-side converter(RSC)and the grid-side converter(GSC)can improve the grid-connection stability of the power generation system.However,for the DC-link port,the antidisturbance ability of the DC-link voltage of GSC under GFM control is reduced,and the dynamic characteristics of the DC-link voltage cannot be ignored when the unit output power fluctuates.Therefore,this paper establishes a small-signal model for the gridforming DFIG-based wind turbines considering the dynamic coupling characteristics of the AC and DC sides.The stability of the DC-link voltage control with different power grid strengths and wind turbine rotor speeds is studied based on the system model.According to the coupled transfer function matrix,the coupling influences of the stator power on the DC-link voltage in different conditions are analyzed.The AC/DC coupling path of stator power to the DC-link voltage is analyzed by using the small-signal model,and the decoupling optimization strategies are designed.Theoretical analysis shows that the proposed strategy can reduce the coupling influence of active power loading on DC-link voltage,and optimize the dynamic characteristics of the DC side.Finally,the correctness of the theoretical analysis and the effectiveness of the proposed control strategy are verified on the hardware-in-loop experiment platform.