Research On The Sliding Mode Control Of Rotor-side And Grid-side Power Converters In DFIG

The double-fed induction generator(DFIG)is widely used in wind power generation because of its high efficiency,low cost and flexible control.However,DFIG are usually operated in harsh environments and wind speed variations,and they are essentially a nonlinear,strongly coupled,high-order complex system with uncertainties such as system model misalignment,parameter uptake,and external disturbances.To address the above problems,this paper takes the rotor-side and grid-side power converters in DFIG as the research object,and combines sliding mode control(SMC)and extended state observer(ESO)to carry out the research of related control methods,as follows:(1)The composition of current mainstream wind turbines and their operating principles are introduced,and the mathematical models of DFIG rotor-side and grid-side converters based on direct power control structure in αβ stationary coordinate system are analyzed.(2)In order to weaken the influence of motor parameter uptake and external disturbances on the control effect of DFIG rotor-side converter,a direct power control method of rotor-side converter combining second-order sliding mode control and ESO is proposed.Firstly,ESO is used to estimate the system state variables and the set total uncertainty terms including a large number of coupling terms and auxiliary excitation variable terms,etc.Secondly,based on this,a second-order sliding mode control method based on the super-twisting algorithm is designed and stability analysis is performed using Lyapunov’s second method;Finally,a comparison is made with the second-order sliding mode control through simulation.The simulation results show that the proposed control method further weakens the power and electromagnetic torque jitter during the motor parameter ingestion and external disturbances,and enhances the robustness of the system.(3)A dual closed-loop control method for the grid-side converter combining SMC and ESO is proposed to address the problem of poor control of the grid-side converter due to load variation and filter parameter uptake.The method is designed with ESO-based sliding-mode direct power control with power as the state variable in the inner loop and ESO-based slidingmode control with voltage squared as the state variable in the outer loop.The ESO is used to estimate the system state variables with the set of total uncertainty terms containing the unmodeled dynamics of the system,load variation and filter parameter uptake,etc.,so that the sliding mode control method can be designed without an accurate mathematical model of the system.In addition,the introduction of a power differential feedforward link reduces the impact of the outer-loop sliding mode control nonlinearity when the load changes.The simulation is compared with two cases of load variation and filter parameter ingestion.The results show that the proposed control method has stronger robustness compared with the traditional vector control and sliding mode control.