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© EVS-25 Shenzhen, China, Nov. 5-9, 2010 The 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition Development of a Switched Reluctance Motor for Automotive Traction Applications Saphir Faid 1 , Patrick Debal 1 , and Steven Bervoets 1 1 Punch Powertrain, R&D Department, Schurhovenveld 4 125, BE3800 Sint-Truiden, Belgium E-mail: [email protected] Abstract— This paper presents an advanced development of a switched reluctance motor/generator for automotive traction applications. The performance, efficiency and peak torque characteristics of switched reluctance machines, combined with its typical robust, low cost construction make this technology an attractive alternative to other motor types typically chosen for traction applications. In this research, a combined optimization was conducted on the design and control for a compact high torque assist motor/generator aimed at application in full hybrid vehicles. From the early design stage, known challenges related to switched reluctance motors such as torque ripple, vibrations and acoustic noise were addressed by a combined approach of innovative mechanical design features and state of the art control of the motor excitation. The motor was manufactured and characterized, with resulting characteristics covering the application requirements and matching simulated performance and efficiency. The motor was integrated into hybrid- and battery electric test vehicles where performance, NVH levels and durability are assessed while demonstrating the potential of this motor for automotive traction applications. Copyright 2010 EVS25. Keywords— Switched Reluctance Motor, Hybrid, EV, torque ripple, acoustic noise 1 Introduction Punch Powertrain develops hybrid and electric drivetrains for passenger cars. The electric traction motor is a crucial component as it impacts the vehicle’s performance and because the cost of batteries related to range requirements urges for a highly efficient but cost- effective drivetrain. For the projects under development, several options for electric traction motors were investigated, namely permanent magnet motors, induction motors and switched reluctance motors (SRM). Induction motors are the most widely used type in industrial applications as well as heavy traction applications (railway, electric buses,…). Permanent magnet synchronous motors offer significantly better efficiency and power density, which has led to increasing popularity in hybrid and electric passenger cars, electric bicycles, scooters,… However, cost and supply concerns regarding the limited reserves of rare earth magnets are a limiting factor for application of permanent magnet motors in a scenario of serious worldwide electrification of mobility [1]. The topic on the most suitable electric machine remains open, and because of some particular advantages, switched reluctance motors may offer an interesting solution for applications requiring a highly performing but cost-effective solution. 2 SRM Properties A switched reluctance motor produces torque purely through interaction of the stator field with rotor saliency. In figure 1 the basic operation of a switched reluctance motor is illustrated. The stator consists of laminated iron with stator poles and windings. The rotor is just laminated iron. By exciting a pair of opposing stator windings, the principle of reluctance will cause a torque to align the rotor poles with the stator poles. The simplest design can be a single phase motor, but this would not allow total control of the motor. The shown design is an 8/6 configuration with 8 stator poles and 6 rotor poles which is a typical four phase motor. The four phase operation offers the possibility to achieve full torque in each rotor position and allows smoothening of torque ripple at low speeds as demonstrated in this paper. Figure 1: SRM Operation Switched reluctance motors boast advantageous properties such as a simple, robust and low-cost construction, lack of permanent magnets, high efficiency in wide speed range and intrinsically safe operation. In case of sudden short-circuit of a sudden open circuit or even short circuit of the motor phases, current will fade out quickly and the motor can keep Unaligned Position Aligned Position
