Circuit Simulation for Preventing Saturation of Commonmode Chokes in Railway Traction Inverters

Abstract

Railway vehicle traction systems generate several ten amperes of common-mode (CM) current. For suppressing the CM current, the traction inverters equip nanocrystalline cores through the motor cables to act as a CM choke. However, the cores sometimes become saturated due to the large CM current. In this paper, we will describe a circuit simulation to verify saturation of cores at the design stage of the traction system. For Cauer I type equivalent circuit, we derive the circuit constants using only AL values and corner frequencies as circuit parameters, which can be derived from the magnetic field inside the core. The simulation results using the equivalent circuit and the CM circuit of an actual railway traction motor reproduce the core saturation.