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There is a great demand for efficient, quiet, reliable, and cost-effective motor drives for propulsion systems in hybrid and plug-in hybrid electric vehicles. Owing to a rigid structure and the absence of magnetic source on the rotor, a switched reluctance machine (SRM) is inherently robust and cost effective. In spite of these advantages, several challenges in the control of this machine remain an issue, including high levels of torque ripple, acoustic noise, and a relatively low torque density. This paper presents a new family of SRMs which have higher number of rotor poles than stator poles. Using a newly defined pole design formula, several novel combinations of the stator-rotor poles have been proposed. From the simulation and experimental analysis of a prototype 6/10 configuration, it has been observed that this machine produces higher torque per unit volume and comparable torque ripple when compared to a conventional 6/4 SRM with similar number of phases and constraints in volume. The results presented in this paper make this family of machines a strong contender for survivable high-performance applications for automotive propulsion systems. The simulation and experimental results for the prototype 6/10 configuration have been presented and compared to a conventional 6/4 design for verification.Index Terms-High torque density, low cost, low torque ripple, propulsion, switched reluctance machine (SRM).

Electric machines have broadly been used in many industries including the transportation industry. With the evolving trend of electrification in transportation, electric machines with higher power density and higher efficiency are demanded and, thus, more stringent thermal management requirements are needed for electrified vehicle applications. This study comprehensively presents various important aspects of thermal management in electric machines with the main focus on transportation applications. Design considerations, challenges, and methods for enhanced thermal management are discussed. Fundamental thermal properties of common materials are presented and sources of losses in various parts of machines are explained. Furthermore, typical cooling techniques and thermal analysis approaches for electric machines are reviewed in detail. This study will serve as a reference guideline for machine designers, who are interested in thermal management, and for thermal researchers working on electric machines.