Optimal Power Flow And Sensitivity Analysis For Power System With DFIGs Integrated Through VSC-HVDC Lines

Due to the good operating characteristics and controllability of the voltage source converter based high voltage direct current(VSC-HVDC),it has the great advantages in the integration of the doubly-fed induction generator(DFIG).The optimal power flow(OPF)model of the DFIG integrated through the AC/VSC-HVDC transmission is established to optimize the control variables of the DFIG and VSC-HVDC,where the detailed configuration of the DFIG and the VSC-HVDC is included.The sensitivities of the objective function to the constraints of the DFIG and VSC-HVDC are newly proposed based on the analytical expressions of the Lagrange multipliers to quantify the power flow control capability of the DFIG and VSC-HVDC.The main contents and the innovation points of the dissertation are as follows:(1)Considering the limitation of the droop control of the VSC,it is described by the sensitivity method that the direct current power flow controller(DCPFC)may reduce the voltage deviation.An optimal control strategy for the VSC and the DCPFC to adjust the power flow of the DC grid is applied.(2)The multi-target optimization model with the objective function of the minimum power loss and the minimum voltage deviation is derived.The analytical expressions of the grid loss and the voltage deviation under various conditions(power disturbance,overload or outage of the VSC)are proposed.(3)For the DFIG integrated through the AC/VSC-HVDC lines,the detailed model of the DFIG,the detailed model of the VSC-HVDC,the detailed range of the active and the reactive power of the DFIG are established.Considering the wind speed fluctuation and the control mode switch of the VSC,the DCPFC is added to the power system to increase the power flow control capability.The detailed OPF model is established.(4)The sensitivities of the objective function to the constraints of the DFIG and VSC-HVDC are newly proposed based on the analytical expressions of the Lagrange multipliers to quantify the power flow control capability of the DFIG and VSC-HVDC.The relationship between the required adjustments of the DFIG and the VSC-HVDC(the coordination of the sensitivities)is proposed under the same adjustments of the objective function to adjust conveniently.