PMSM Vector Control And Modulation Algorithm For Electric Traction

Permanent magnet synchronous motors(PMSM) has the characteristics of high efficiency, high reliability, high power density, high starting torque, and wide speed range. As an electric traction motor, PMSM can improve the efficiency of traction drive system, reduce the failure rate and the weight of the train. This PMSM traction solution can conform to the state’s long-term goal of energy saving and emission reduction. Thus, this work has a great theoretical value and practical significance.In order to increasing the starting torque, expanding speed range, improving the efficiency, reducing the torque ripple, and decreasing the stator current harmonic of electric railway traction PMSM drive system, this paper focuses on the control and modulation algorithm of PMSM. The specific contents are shown as follows.Firstly, an overview of control and modulation strategies for PMSM is introduced. PMSM’s mathematical model in two phase rotating coordinate system is described. On the basis of the adopted PMSM’s mathematical model, the basic principle of vector control is analyzed. In order to satisfy the high speed electric locomotive characteristics for the large starting torque and wide speed range, three specific vector control strategies such as maximum torque per ampere, negative d-axis current compensation for flux weak, and maximum torque per voltage control are discussed. And then the best trajectory of stator current control limited by voltage and current limit circle is shown. Besides, for the PMSM is hard to start smoothly, a speed detection scheme combined with sensorless and traditional relative position sensor technologies is given. The low cost and high precision of PMSM rotor position detection can be realized absolutely.Secondly, the mathematical model of three-phase two level inverter is discussed, and the asynchronous space vector modulation(SVPWM) theory of inverter is discussed. Combined with its voltage vector synthesis and working principle, a synchronous synthesis SVPWM algorithm is analyzed. The main effect factors of PMSM’s torque ripple was discussed. Following the motor stator flux linkage area equivalent principle, a synchronous SVPWM preliminary design scheme is shown. And then, in order to reduce the PMSM’s torque ripple, the parameters of synchronous SVPWM are optimized, based on motor stator flux tending to round shape and reducing its δ angle pulsation principles. The high power traction driving system’s restricted factors such as low switching frequency is analyzed. And a multi-mode modulation strategies is shown, and the switching principles between different modulation strategies are analyzed to reduce torque ripple.Finally, a hardware-in-the-loop(HIL) experiment platform is set up, which consists of TMS320F28335 DSP controller and RT-LAB real-time simulator. Based on this platform, DSP programming and modeling the PMSM’s traction drive system of Electric Multiple-Units (EMU) in RT-LAB simulator are done. And then the adopted PMSM’s full speed vector control and modulation algorithm with low switching frequency are tested in the HIL experimental platform. PMSM can keep low torque ripple and small stator current harmonic in the whole wide speed range. The HIL experimental results verify the effectiveness of the adopted control and modulation algorithm of PMSM.