I. Introduction
Interior permanent-magnet (IPM) machines have been extensively studied in recent years because of their good torque density, efficiency, and inherent suitability to zero-speed sensorless control due to rotor saliency [1]–[9]. Moreover, it is shown in the literature that enhancing the rotor saliency is beneficial when a large constant power speed range (CPSR) is required [10]. In fact, a large saliency conversely means a relatively low permanent magnet (PM) flux linkage, with the additional advantages of a lower magnet quantity and cost, a lower overvoltage in case of inverter fault, and a larger overload capability [11]. The latter characteristic is very welcome in up-to-date applications, such as electric and hybrid traction [12]. PM-assisted synchronous reluctance (PMASR) machines are basically multilayer IPM machines showing a high saliency and a small per-unit PM flux or, in other words, synchronous reluctance (SyR) machines with PMs inserted into the rotor layers.