Research On Low Frequency Oscillation Suppression Of Vehicle-grid System Based On Sliding Mode Control And Its Improved Algorithm

With the development of electrified railway,the complexity of traction power supply system increases,and the low frequency oscillation(LFO)of vehicle-grid coupling system has occurred many times in the global range,which seriously affects the safe and stable operation of trains.It is generally believed that the LFO is caused by the mismatch between the electrical parameters of traction network and the control parameters of line-side converter(LSC).The suppression methods can be carried out from two aspects of improving traction network and improving the control stratefy of EMU’s LSC.However,improving the traction network means improving the quality of power supply,which is difficult to realize in practice.Therefore,this paper improves the control strategy of EMU’s LSC to suppress the occurrence of LFO: combined with the theory of sliding mode control(SMC),the SMC control strategy of EMU’s LSC is designed,and combined with the theory of extended state observer(ESO),the sliding mode control method based on extended state observer(ESO+SMC)is designed.Both control strategies are validated and analyzed in Matlab/Simulink simulation platform,RTLAB full-digital on-line simulation platform and d SPACE hardware-in-loop experiment platform.Firstly,based on the principle of reduced-order and the parameters of multi conductor transmission line,the reduced order simulation model of traction network is built,and the mathematical model of CRH5 EMU traction drive system is also built.The topological structure of EMU’s LSC is introduced,and the mathematical model of EMU’s LSC in dq reference frame is deduced.The simulation model of CRH5 EMU traction power unit is built according to the traditional current decoupling control principle of CRH5 EMU’s LSC in dq reference frame.Then,since the sliding mode of SMC control can be changed according to the system structure,and the SMC is a variable structure system,which is the same as power electronic devices.Based on above advantages,a control strategy based on SMC of EMU’s LSC is proposed to suppress LFO by combining with SMC theory and the topological structure of CRH5 EMU’s LSC.The traditional proportional integral(PI)control,predictive control and SMC control strategies are respectively connected to the Matlab/Simulink simulation model of CRH5 EMU traction power unit,and the control performances are discussed and analyzed.In order to further verify the suppressing effect of the proposed strategy,the control strategies of EMU’s LSC based on PI control and SMC control are verified in RTLAB full-digital online simulation platform and d SPACE hardware-in-loop experiment platform,and the results show that the SMC control strategy can effectively suppress the occurrence of LFO,but there are still some defects.Finally,because of some defects of SMC,while the ESO is an effective disturbance observer,which can be combined with the existing control methods to ensure the robustness of the control loop and achieve better control effect.Therefore,based on the theory of ESO,an ESO+SMC control strategy is proposed to improve the performances of SMC and effectiveness of LFO suppression.The control performances of ESO+SMC control strategy are verified in many aspects.The results show that the proposed strategy can not only improve the defects of SMC,but also successfully suppress LFO.