Single Current Loop Control Strategy Of High Speed Train For Induction Traction Motor In Six-step Mode

In high power traction drive system,in order to reduce the switching loss,inverter will usually use single pulse modulation to make full use of the DC bus voltage and reduce the switching frequency,after the traction motor enters the field-weakening region.The traditional vector control algorithm is limited by the single degree of freedom in six-step mode.At the same time,the accurate field orientation of the motor control in the whole speed range has a great influence on the control performance.In view of the above problems,this thesis studies the motor control in six-step mode and the field orientation correction of the motor in the full speed range.First of all,this thesis establishes the mathematical model of asynchronous motor,considering the limitation of current and voltage in the six-step mode,the current distribution strategy for maximizing the torque output of the motor is derived,which gives the reasonable reference value of d-q axis current according to different operating conditions.Furthermore,the limitation of the traditional double current loop vector control in six-step mode is analyzed.The motor voltage is limited to the DC side voltage in six-step mode,and the current controller is unable to adjust because of the adjustable voltage margin.Secondly,a single current closed loop control strategy is proposed,which only retains the d axis current loop,and the q axis voltage is calculated by the d axis voltage.This method solves the problem that traditional vector control can not operate in six-step mode.Based on this,a dual-mode motor control method suitable for mixed multi-mode pulse width modulation is proposed,which realizes the full speed domain control of the asynchronous traction motor.According to the difference of control strategy,the influence of the rotor time constant on the variables in the motor control is analyzed,and then the corresponding field orientation correction strategy is proposed,based on the full domain dual mode control method.In the middle and low speed domain,the correction strategy based on torque observation is adopted.In six-step mode,the single current closed-loop control can self-correct the field orientation to ensure the accurate output of the motor torque.Finally,the proposed control strategy is verified in dSPACE platform of CRH5 EMU provided by CRRC Qingdao sifang rolling stock research institute,and verified on the laboratory of the 5.5kW asynchronous motor on the laboratory.Meanwhile,the proposed control strategy is verified in 5.5kW asynchronous motor experimental platform.The experimental results verify the effectiveness and feasibility of the proposed method of single current closed loop control and the correction method based on torque observation.