Improved Stability of DC Catenary Fed Traction Drives Using Two-Stage Predictive Control

Control of the main propulsion drive of a traction vehicle must secure excellent drive dynamics, but it also has to consider properties of the dc catenary. Specifically, the catenary voltage is subject to short circuits, fast changes, harmonics, and other disturbances that can vary in a wide range. Therefore, the drive is equipped by the catenary input LC filter. The filter is almost undamped by design in order to achieve maximum efficiency, and the control strategy needs to secure active damping of the filter to guarantee stability of the drive. Existing solutions for active damping usually introduce some drawback in dynamic properties of the drive. In this paper, we study the use of two-stage predictive control. Damping of the filter will be solved on a long horizon using a linear controller. Dynamic properties of the drive will be guaranteed by optimization on a short horizon using the finite control set model predictive control (FCS-MPC). These two approaches can be elegantly combined via approximate dynamic programming. The resulting algorithm can be interpreted as a standard FCS-MPC with a model-based designed cost function. Performance of the resulting controller was verified in simulations on a prototype of a main permanent-magnet synchronous motor drive of a tram and experimentally on a developed laboratory prototype of 10.7 kW.