Research On Low Voltage Ride-Through Of Front-End Speed Controlled Wind Turbine Based On Robust Control

As a new type of wind turbine,the front-end speed controlled wind turbine(FSCWT)has the advantages of good output power quality and strong reactive power output.It is a development trend of wind turbine in the future.Moreover,in order to improve the reliability of the power system,the "Technical Rule for connecting wind farm into power grid" clearly states that the wind turbine connected to the grid must have a low voltage ride-through(LVRT)capability.Therefore,it is of great significance to study the low voltage ride-through control of the FSCWT.Based on the analysis of the structure and principle of FSCWT,the mathematical model of the FSCWT was established.In addition,four common grid faults and the operating mechanism of FSCWT during the grid-connected voltage dip were studied.At the same time,the transient characteristics of the EESG were analyzed under different grid faults.Aiming at the off-grid problem of FSCWT during the grid-connected voltage dip,the support capability of the FSCWT output current to the grid-connected voltage was analyzed,and a control method was proposed for low voltage ride-through based on a nonlinear robust control from the point of view of excitation system control of the EESG.In this method,a single machine system mathematical model of FSCWT was established.The nonlinear object of mathematical model was linearized by constructing an extended state observer.And then,angle speed deviation of generator rotor,deviations of angle of attack,deviations of active power,and generator terminal voltage were taken as state variables.Robust controller was designed for the linearized system.Finally,the single machine grid-connected model of FSCWT was established on the Matlab/simulink platform,and simulation experiments were conducted.Simulation results show that the control method proposed can ensure that FSCWT is connected to the grid during fault.Meanwhile,it can also improve the transient stability of the system.Aiming at the problem that the uncertainty of the generator parameters under the grid-connected voltage deep dip will increase the difficulty of low voltage ride-through for FSCWT,a control method of LVRT based on adaptive robust control of excitation system was proposed.In this method,the Lyapunov function for three sub-systems and energy function of the system were constructed by use of back-stepping method,and make the energy function satisfy the dissipation inequality to guarantee interference suppression capability of the system.Introducing the error compensation term and additional control variable,the excitation control law and parameter adaptive law of the system were designed.Finally,the simulation model was established.Under the condition of grid symmetry and asymmetry fault,the proposed method was verified by simulation and compared with the nonlinear robust control method.Simulation results show that this method can not only enhance the robustness of the system,but also improve the low voltage ride-through performance of the FSCWT during the grid-connected voltage dip.