88 CES TRANSACTIONS ON ELECTRICAL MACHINES AND SYSTEMS, VOL. 3, NO. 1, MARCH 2019 Abstract—There has been a growing need for high specific power electrical machines for a wide range of applications. These include hybrid/electric traction applications, and aerospace applications. A lot of work has been done to accomplish significantly higher specific power electrical machines especially for aerospace applications. Several machine topologies as well as thermal management schemes have been proposed. Even though there has been a few publications that provided an overview of high-speed and high specific power electrical machines [1-3], the goal of this paper is to provide a more comprehensive review of high specific power electrical machines with special focus on machines that have been built and tested and are considered the leading candidates defining the state-of-the art. Another key objective of this paper is to highlight the key “system-level” tradeoffs involved in pushing electrical machines to higher specific power. Focusing solely on the machine specific power can lead to a sub-optimal solution at the system-level. Index Terms— Density, Electrical, High, Machines, Perspective, Power, Specific. I. INTRODUCTION There has been growing and continued interest in high-speed and high specific power electrical machines. In [1], a survey of high-speed machines based on various application and machine topologies is reported as shown in Fig 1 and 2. Another survey has been presented in [2] highlighting the key technologies that go into high-speed machines, as well as some performance figure-of-merit (FoM). For example, RPM kW is used to identify the safe limits for tip speeds to avoid running into mechanical and rotor dynamics issues. In [3], a survey of high high-specific power electrical machines is disclosed. The focus in [3] is on the electric machine specific power and a general comparison between different machine topologies is presented. This paper will provide a more comprehensive survey of high specific power machines in terms of highlighting specific Manuscript was submitted for review on 31, August, 2018. Ayman EL-Refaie is with Marquette University, Milwaukee, WI 53233 USA (e-mail: Ayman.EL-Refaie@Marquette.edu). Mohamed Osama is with GE Aviation, Munich, Germany (e-mail: Ayman.EL-Refaie@Marquette.edu). Digital Object Identifier 10.30941/CESTEMS.2019.00012 examples that are considered the state-of-the art. More performance details for these specific examples will be reported. Key “system” tradeoffs and considerations will also be discussed. The paper will mainly focus on electrical machines for land vehicles, and aerospace applications. Fig. 1. Survey of high-speed machines by application[1]. Fig. 2. Survey of high-speed machines by topology [1]. II. MACHINES FOR LAND VEHICLES In this section, high-specific power electrical machines designed for hybrid/electric vehicles is covered. The focus will be on machines that stand out in terms of having significantly higher power density and/or torque density compared to many other machines in that crowded space. In this paper, the focus will be on electrical machines used in light-duty vehicles (since they usually target the highest specific power) while a comprehensive review of electrical machines used in other types of vehicles has been presented in [4]. In [5] a comprehensive summary of the teardown and test results of several mainstream central traction motors in light duty vehicles was disclosed. These include: 2004 Prius, 2006 Accord, 2007 Camry, 2008 LS 600h, 2010 Prius, 2011 Sonata, High Specific Power Electrical Machines: A System Perspective Ayman EL-Refaie, Fellow, IEEE, Mohamed Osama, Member, IEEE