Electric Traction System Design for a Hybrid Delivery Vehicle

A hybrid-electric powertrain for a 7.5 tonne goods delivery vehicle can offer an improvement in efficiency over the conventional powertrain if the urban element of the duty cycle can be satisfied by electric-only driving, with conventional driving and electric-assist elsewhere [1]. Performance demands and unit cost of the electric powertrain mean the traction system must be designed to exploit efficiency benefits.

The system analyzed here features a new Permanent Magnet (PM) Motor-Generator. This is fed via a voltage-source inverter, commutated by Pulse Width Modulation, from a Nickel Metal Hydride (Ni-MH) battery system. Assessment is made here of the overall system including the new Motor-Generator. This explicitly considers the electrical losses throughout the traction powertrain, which are closely dependent on current levels in various components. Minimization of the electrical system power losses under the electric-only driving regime through design or operation is considered in this paper.