Energy-Release Strategy for Permanent Magnet Traction System with Onboard Energy Storage System for Subway Applications

This paper proposes a novel energy-release strategy for permanent magnet traction system with on board supercapacitor for subway applications, in which the flux-weakening region is used. The stored energy is not released until the flux-weakening region is approaching. Compared with the conventional energy-release strategy, the proposed strategy is realized by raising the dc bus voltage instead of reducing the dc bus voltage drop. Two simulations are carried out to verify the effectiveness of the proposed strategy. Reduced flux-weakening region and less copper loss are shown in the simulation results. Even though the energy-saving ratio 80.9% is small, the saved energy is still significant since the subway is the high power electrical system.