DC Link Capacitor Loss Minimization for Medium Voltage High Power Railway Traction Converter

Railway propulsion system deploys three induction motors, each rated at 850 kW, on a single bogey. These motors are operated from three-phase two-level voltage source converters (VSI) connected across the same DC bus of traction converter. DC bus is usually regulated at a fixed voltage through parallel-connected single-phase front end converters. Switching frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(f_{sw})$</tex> of these motor drives is usually restricted below 500 Hz due to significant switching energy losses. Operation at low fsw results into high current ripple on DC link current which increases the loss in the DC link capacitors. Temperature rise on account of power loss in capacitor bank is curtailed by increasing the size of the DC bus capacitance. This paper proposes an interleaved carrier based method to minimize the ripple in DC link current for a multi motor drive operated traction system. Proposed method is validated on a 3 MW traction converter having 3600 V DC link which feeds three IM drive each rated at 850 kW, 2.2 kV and 65 Hz over simulation in PLECs software.