Design Approaches and Control Strategies for Energy-Efficient Electric Machines for Electric Vehicles—A Review

Shao, Lingyun; Karci, Ahu Ece Hartavi; Tavernini, Davide; Sorniotti, Aldo; Cheng, Ming · 2020 · Crossref

DOI: 10.1109/access.2020.2993235

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Summary

This review paper addresses the critical need for improving the energy efficiency of electric machines (EMs) in electric vehicles (EVs) to extend driving range and support market penetration. As EMs are the primary source of power loss in electric powertrains, the authors survey design parameters, control strategies, and novel topologies that minimize energy consumption. The study is motivated by governmental roadmaps from the UK, US, and China, which set aggressive targets for power density, efficiency, and cost reduction for next-generation traction motors. The authors analyze four dominant machine types: induction machines (IMs), permanent magnet synchronous machines (SPM and IPM), switched reluctance (SR) machines, and PM-assisted synchronous reluctance (PMaSynR) machines. The review details how specific design choices impact efficiency. For IMs, it highlights the shift from deep slots to shallow, wide, or closed slots to reduce rotor resistance and harmonic losses, noting that die-cast copper rotors offer 1–2% efficiency gains over aluminum. For PM machines, the paper examines how rotor magnet arrangements (V-shaped, tangential, delta-shaped) and flux barrier designs influence torque ripple and high-speed efficiency. It also discusses the adoption of bar-wound (hairpin) windings to increase slot fill factor and reduce copper losses, despite potential high-frequency skin effects. For SR and PMaSynR machines, the review covers the use of high-saturation iron materials and optimized pole geometries to enhance torque density and reduce acoustic noise. Regarding control strategies, the paper categorizes loss minimization control (LMC) methods into model-based, adaptive search, and hybrid approaches. Model-based methods offer fast convergence but rely on accurate parameter identification, while search-based methods are robust to parameter variations but converge slowly. The review emphasizes that dynamic efficiency evaluation along actual driving cycles is superior to steady-state testing for predicting real-world energy consumption. Furthermore, it notes that advanced thermal management systems are essential for maintaining high efficiency and enabling compact motor designs. The significance of this work lies in its comprehensive synthesis of how geometric design, material selection, and control algorithms interact to optimize EM performance. The authors conclude that while IPM machines currently offer high efficiency and torque density, ongoing research into PMaSynR and advanced IM designs aims to reduce reliance on rare-earth materials and lower costs. The review provides actionable guidelines for engineers to balance trade-offs between efficiency, power density, and manufacturability, supporting the development of commercially viable, high-performance EV powertrains.

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