基于双馈风电机组控制参数优化的电网功角振荡控制

Power Angle Oscillation Control of Power Grid Based on Control Parameter Optimization of Doubly-Fed Wind Turbine Generator

随着大量风电并网,双馈感应发电机(DFIG)与同步发电机(SG)间的动态交互,将加剧SG功角振荡。基于特征值分析的控制参数优化,未考虑非线性元件和大扰动场景。该文从抑制功角振荡出发,以SG转速为DFIG电力系统稳定器(PSS)输入信号,建立风电并网电力系统动态模型。在微分方程中引入中间变量,以解耦状态变量轨迹灵敏度。区分状态变量与代数变量对应的雅可比矩阵,推导DFIG并网电力系统轨迹灵敏度的解析表达。设定目标函数为SG功角偏差相对值二次方对时间积分,按时间顺序累加功角对控制参数的轨迹灵敏度,得到目标函数对控制参数的梯度信息。考虑DFIG-PSS可能弱化转子侧变流器(RSC)控制效果,提出基于轨迹灵敏度的RSC和DFIG-PSS参数协调优化方法。给出4机2区域系统仿真结果,验证了所提方法对DFIG并网系统功角振荡的阻尼效果。

With the increasing wind turbine generators integrated partially or completely through the converters,the damping capability of the power system is decreased,which will intensify the dynamic interaction among the doubly-fed induction generators(DFIGs)and the synchronous generators(SGs),and yield the power angle oscillation among the SGs.The angular oscillation is usually suppressed by the power system stabilizer(PSS)installed at the SGs.It may also be suppressed by the PSS at the DFIGs,i.e.DFIG-PSS,or by adjusting the control parameters of the DFIGs.The DFIG-PSS is often installed at the outer loop of the rotor-side converter(RSC).The control effect of the RSC may be weakened by the DFIG-PSS.Hence the control parameters of the DFIG-PSS and the RSC are to be optimized together.The parameter optimization based on the eigenvalue analysis is for small disturbances.It does not consider the system nonlinearity and large disturbance,hence is incompetent to suppress the oscillation which is usually quantified by a period of dynamic process.In this paper,a coordinated optimization model to the parameters of the DFIG-PSS and the RSC based on the trajectory sensitivity is newly proposed.The DFIG-PSS is designed to suppress the power angle oscillation by controlling the DFIGs to absorb or release the energy.The dynamic model of power system with the control strategy of the DFIG including the DFIG-PSS is derived.The intermediate variables are introduced to the differential equations to decouple the trajectory sensitivities.The Jacobian matrices of the state variables and the algebraic variables are distinguished to derive the analytical expression of the trajectory sensitivities,which is computationally efficient than deriving the trajectory sensitivities from the parameter perturbation method.Then the gradient information of the objective function with respect to the control parameters is obtained.Based on the location of the DFIG-PSS and the relation of the PI parameters,the control parameters to be optimized are decided.With the gradients,the interior-point method is applied to optimize the parameters of both the DFIG-PSS and the RSC.Based on above algorithm,the Matlab program for the dynamic control and the angular oscillation of the power system with the DFIGs is written by the authors.The simulation results on the 4-SG 2-area test system are given to verify the control effect.It is shown that the relation between the control parameters and the power angle oscillation is quantified by the gradient derived from the analytical expression of the trajectory sensitivity with desirable accuracy.After the optimization,the gain of the outer active power loop of the RSC increases,and the gain of the inner current loop decreases,which help to regulate the output of the DFIG and reduce the risk of the angular oscillation.It is also found that the parameter optimization to both the DFIG-PSS and the RSC has better effect on reducing the amplitude of the power angle difference and accelerating the convergence than optimizing the DFIG-PSS only.The proposed algorithm is beneficial to the wind turbine generators,e.g.the DFIGs,functioning similarly as the SGs and participating into the system stability control.With more and more SGs displaced by the wind turbine generators,the proposed algorithm may be applied to improve the angular and oscillational stability of the power systems.