Advanced Switched Reluctance Machines for Electrified Vehicles

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Electrified vehicles are emerging as the next generation of vehicles because electrification is an effective long-term solution for the transportation system to improve sustainability, efficiency, emissions, performance, and safety. Electrified vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), utilize one or more electric machines in their powertrains. ***Electrified vehicles' traction motors are expected to have a wide constant-power speed range and short overloading capability in order to match with the driving conditions. They also need to meet critical industry requirements such as reliability, low cost and weight, low maintenance, and quiet operation. Traction motors should deliver high torque at low speed for starting and hill-climbing conditions and high power to achieve high cruising speeds. Interior permanent magnet (IPM) synchronous machines are employed in most of the currently available hybrid and electric vehicles on the market. With the use of high-energy and high-coercivity rare-earth magnets, permanent magnet machines can provide high torque density and smooth operation. However, permanent magnets are sensitive to temperature. This causes a significant limitation on the operation of the machine in harsh environments. In addition, rare-earth magnets take up a significant portion of the total cost of the traction motor. When compared with the conventional vehicles, the high cost of the traction motors for electrified vehicles currently presents a challenge for their mass-production and increased market penetration. ***Switched reluctance machines (SRMs) do not employ any permanent magnets or conductors on the rotor. Therefore, they can operate in harsh environmental conditions and at high-speeds and high temperatures. The structure of SRMs enables a wide constant-power speed range, which matches very well with the traction requirements. Due to its simple construction, manufacturing cost of SRMs is significantly lower than the permanent magnet machines. Most significant challenges in SRMs are high torque ripple and high levels of acoustic noise and vibration. In addition, the machine demonstrates a highly nonlinear behavior due to saturation in various parts of the stator and rotor cores. This creates a challenge in terms of torque control and state estimation. Furthermore, highly saturated operating conditions can affect the efficiency of the motor. ***This proposed research program is focused on a novel family of SRMs with improved power density, efficiency, and performance for electrified vehicles. The proposed family of SRMs involves novel motor configurations with various stator and rotor pole combinations and advanced control techniques to improve the torque- and power-density and performance of the motor with reduced torque ripples, acoustic noise, and vibration. **