Research On Robust Control Algorithm For Grid-Side Converter In Railway Electrical Traction

The electric traction systems of high-speed trains operate in extremely complicated environments,such as large output power,frequent load fluctuations,severe disturbance of traction network voltage,and strong electromagnetic interference,which results in a great challenge for the control of the grid-side converter.To improve the control performance and robust performance of the single-phase two-level pulse width modulation(PWM)rectifier,current control algorithms based on robust control and model predictive control(MPC)theory are studied in detail.The specific contents are as follows:Firstly,The operation principle and digital control method are analyzed for the singlephase two-level PWM rectifier.Secondly,grid-side mathematical models and the closed-loop control model of the dq decoupling control framework are established.Thirdly,PI-based instantaneous current control(ICC),deadbeat ICC(DB-ICC),PI-based direct current control(DCC),and model predictive DCC(MP-DCC)are introduced.These works lay a solid foundation for subsequent study.To solve the shortcomings of PI-based DCC,such as slow dynamic response and complex multi-PI parameter tuning,an H_∞ mixed sensitivity(H_∞-MS)DCC scheme is proposed in this paper.Firstly,the frequency domain analysis method of the feedback system is introduced.The analysis idea of the H_∞ standard control problem and the solution method of the controller is given.Secondly,the grid-side inductance parameter perturbation is incorporated into the system output multiplicative uncertainty for analysis.Weighting functions are selected to plan the control performance and robust performance.From this,the grid-side generalized feedback system of the single-phase PWM rectifier is constructed to solve the H_∞ optimal controllers.The proposed scheme can improve the dynamic and robust performance of the current loop.Considering the imaginary(β)-axis current estimation error,a current loop incomplete decoupling model of the single-phase PWM rectifier is established in the d-q frame.According to this model,the influence of the β-axis current estimation error on the dynamic performance of the current loop is analyzed in detail.Based on the characteristic of theβ-axis equivalent closed-loop without transient process,a reference-input-based imaginary axis current estimation(RI-based IACE)method is proposed to improve the dynamic performance of control schemes based on the dq current decoupling control framework.To solve the problem of poor robustness of MPC and strong conservativeness of traditional H_∞ control,a Generalized internal model control(GIMC)-based model predictive(MP)-DCC is proposed in this paper.Firstly,the basic principle and control structure of GIMC is analyzed.The significant advantage of GIMC is that the control performance and robust performance of the system can be planned by the nominal controller and robust control,respectively.Secondly,the nominal controller is designed by the MP-DCC principle.Finally,the nominal controller is substituted into the GIMC structure.The β-axis current estimation error and grid-side inductance parameter perturbation are incorporated into the input and output disturbances for analysis and processing,respectively.According to the analysis of the characteristics of the closed-loop transfer function,the structure of the robust controller is given,and the parameter selection principle is determined.The proposed GIMC-based MPDCC scheme can enhance the robustness of the system with maintaining the good control performance of MP-DCC.Traditional PI-based current control either has steady-state error or has slow dynamic response.Traditional DB-ICC improves the control accuracy,but it is still unable to fully realize zero-steady-state error due to the approximate error generated by the linear extrapolation method.Compared with stationary-reference frame control schemes,MPC based on d-q frame for single-phase PWM rectifiers has slower dynamic response.To solve the above problem,a model prediction instantaneous current control(MP-ICC)scheme in the stationary-reference frame is proposed.Firstly,the grid-side instantaneous current prediction model of the single-phase two-level PWM rectifier is given.Then,according to the principle of continuous-control-set MPC,the cost function is selected to minimize the instantaneous current error.Finally,the optimal modulation function is obtained by minimizing the cost function.To solve the problem that MPC is sensitive to grid-side inductance parameters,the influence of grid-side inductance parameter mismatch on current loop stability and control performance is analyzed.Based on the characteristic that the grid-side loop can quickly enter the steady state,an online estimation method of inductance parameters based on the phasor method is proposed to enhance the robust performance of the system.To verify the effectiveness and correctness of proposed schemes,the comparison and analysis with traditional schemes are carried out on the hardware-in-loop experimental platform and low-power prototype,respectively.