Research On Vector Control Technology Of High Power And Low Switching Frequency Traction Converter

Vector control is widely used in traction drive of electric locomotive because of its simple control structure,fast dynamic response and large electromagnetic torque at low frequency.In the increasing capacity of the AC motor traction drive system,in order to reduce the device switching losses and improve the device output power,it is necessary to reduce the switching frequency of the device.The dynamic performance of the vector control system is reduced at low switching frequency.How to enhance the dynamic response capability of vector control system at low switching frequency is the content of this paper.The main work of this paper are as follows:This paper introduces the mathematical model of asynchronous motor and the basic working principle of vector control.The source and mathematical model of digital control delay under low switching frequency are analyzed,and the coupling effect of digital control delay in rotating coordinate system is deduced.The concept of complex vector is introduced,and the complex vector model of induction motor is established.Based on the complex vector model,the coupling problem of induction motor at low switching frequency is analyzed.A delay compensation strategy based on amplitude and phase correction of voltage vector is proposed for digital control delay under low switching frequency.Based on the delay compensation,an improved complex vector current decoupling control strategy is proposed.Compared with the complete complex vector controller,the strategy simplifies the algorithm while implementing effective decoupling.A motor stator fundamental current observer based on complex vector model is designed.The observer can observe the fundamental component of the stator current in the full speed range of the motor operation,so as to realize the smoothing transition of linear region to the nonlinear region of SVPWM modulation.An improved currentsampling method is proposed.The method used in conjunction with fundamental current observation can significantly enhance the dynamic performance of the control system.The simulation scheme of this paper is simulated by Matlab/Simulink simulation tool,and the asynchronous control platform is designed to verify part of the control target mentioned in this paper.