Optimal power split ratio of a distributed electric vehicle traction system

This paper investigate the potential efficiency improvement by optimising the power split ratio between the front-axle and rear-axle tractions in a two-motor distributed traction electric vehicle based on finite element methods. The drive train employs asymmetrical motor topologies with a surfacemounted or interior permanent magnet (PM) machine and a synchronous reluctance machines (SynRM) or permanent magnet assisted synchronous reluctance machines (PMaSynRM). The results show that the optimal power split ratio always assign more torque to the PM machine in the low torque region, thus increasing the system´ efficiency in the low-torque high-speed area by 1-3%. By using optimal power split ratios, the asymmetrical traction system efficiency over the New European Driving Cycle can be improved by 1-2%, compared to the cases with equal split ratio, i.e., 50% to 50%. And it is also shown that both the PM/PMa-SynRM combination and the PM/SynRM combination yield better efficiency than the PM/PM combination when optimal power split ratios are employed with improved robustness and lower cost.