Research on Restrat Method of Permanent Magnet Synchronous Traction Motors during Coasting for High-Speed Train

Permanent magnet synchronous motors (PMSMs) have been more and more interesting for railway vehicle traction system because of their high efficiency and light weight. For the existing of permanent magnet material, the back EMF can be generated during coasting. The inverter components may be destroyed without proper control, when the peak value of back EMF is higher than its withstand voltage. Presently, there are two ways to solve the problem: reducing synthesized air-gap flux linkage by adding negative d-axis current during coasting which can reduce the efficiency, or adding some contactors between inverter and PMSM which is commonly used. But when close the contactors, the phase and frequency of the output voltage of inverter should agree with that of the back EMF to ensure system security. In this paper, an integrated control method of PMSMs during coasting when applied to high speed train is proposed. Based on the mathematical model of PMSM in the synchronous rotating reference frame, the relationship between stator currents, stator voltage and back EMF is analyzed. Then a closed-loop restarting control method after coasting is designed: add an gradual voltage to ensure the smooth switching from coasting to traction or brake. As it has turned out by the simulation results, the method is correct and effective.