Research On Optimization Of Vehicle-grid Operating Performance Under Multiple Conditions Based On Sliding Mode Control And Its Improved Algorithm

With the rapid development of high-speed railways,a large number of AC-DC-AC EMUs have been put into use,and the complexity of the traction power supply system has greatly increased.In addition,the operating conditions of EMUs are very complicated,which results in poor performance of the vehicle-grid coupling system,such as large starting overshoot,increased total harmonic distortion of the traction grid side current during braking condition,large fluctuations in DC side voltage during braking condition,more sensitive to parameter changes and large DC voltage fluctuations when the load changes suddenly,etc.Therefore,the improvement of the control strategy of the rectifier side of the EMU is tried,in order to improve the dynamic and static performance of EMUs under multiple operation conditions.Firstly,a traction network chain network simulation model is built based on the theory of multi-conductor transmission,and the mathematical model of the CRH3 EMUs in the dq rotating coordinate system is derived according to the topological structure of the traction drive system.A simulation model of an electric traction drive unit of the CRH3 EMUs based on traditional transient direct current control is built on the MATLAB/ Simulink platform.Secondly,sliding mode control(SMC)is used as the control strategy on the rectifier side of the CRH3 EMUs,the dynamic and static performance of EMUs is improved when EMUs are operating under different conditions,and it is compared with the dynamic and static performance of the system under Proportional Integral(PI)control in detail;the experiment is verified on the small step size real-time simulation test platform based on hardware in the loop(HIL),and the effect of SMC on improving the performance of the vehicle-network coupling system under multiple operating conditions has been further analyzed.The simulation and experimental results show that the dynamic and static performances of the system under SMC are better than those under PI control,but the SMC cannot stabilize the DC side output voltage of the rectifier at the expected value when the load of the traction motor changes suddenly.Next,in order to improve the control defect of the SMC when the given load torque of the traction motor changes suddenly,the SMC is combined with a sliding mode observer to improve the robustness of the system.The design equation of the sliding mode observer is derived according to the mathematical model of the single traction drive unit of the CRH3 EMU in the dq coordinate system;the sliding mode observer is used to observe the output power of the traction motor in real time and supply it to the SMC outer loop voltage controller to realize the combination of the observer and SMC;PI,SMC,and sliding mode control based on sliding mode observer(SMO+SMC)strategies are connected to CRH3 EMUs simulation model respectively,and then the control effect of the rectifier side of the vehicle-network coupling system under multiple operating conditions is analyzed and verified;based on the HIL small step size real-time simulation test platform,semi-physical experiments are carried out;the simulation and experimental results show that SMO+SMC strategy can improve the control defect of SMC on the rectifier side,and has better control performance in other aspects at the same time.In summary,this article attempts to use the SMO+SMC strategy to improve the dynamic and static performance of the vehicle-network coupling system under different operating conditions,which can provide a reference for future research on the control strategy of the rectifier of the electrified railway EMUs and the improvement of the power quality of the traction network.