Design of Optimal Train Speed Profile for PMSM Railway Traction System Using Dynamic Programming with MTPA Control Method

Abstract

Permanent magnet synchronous motor (PMSM) as a railway traction system has begun to be introduced in some commuter lines. In comparison with the common induction motor (IM), PMSM has different loss characteristics. Namely, during coasting, the production of iron loss still exists due to the rotating permanent magnet which increases energy consumption. Conventionally, no traction energy is consumed during coasting and thus, coasting is often exploited to configure optimal train speed profile. However, this feature might not be applied in PMSM. In this paper, the optimal train speed profile for PMSM is configured with dynamic programming (DP). To include the effect of coasting, the train energy consumption is modeled using the Maximum Torque Per Ampere (MTPA) control method. The result shows that the energy is consumed during coasting due to d-axis current flowing to the motor to suppress the back-emf. Moreover, the regenerative braking can achieve an efficiency of more than 88%. In addition, the optimal train speed profile for PMSM utilizes less coasting, and during braking, maximum deceleration is utilized more compared to the conventional model.