Design and FEM Validation for an Axial Single Stator Dual Rotor PMSM Lucian Nicolae Tutelea 1 , Sorin Ioan Deaconu 2 , Ion Boldea 1 1 Electrical Engineering Department 2 Electrical Engineering and Industrial Informatics Department Politehnica University of Timisoara sorin.deaconu@fih.upt.ro Abstract-A novel synchronous machine-the single stator dual PM rotor brushless, axial-flux, concentrated double layer fractional tooth winding, single inverter with dual frequency PWM independent control for two shafts – has been proven in previous papers of these authors to be able to improve the machine efficiency and boost the torque density. This paper will present the key design equations and design procedure of the Single Stator Dual Rotor PMSM by the equivalent magnetic circuit method , analyze skewed PM angle effects on machine performance and give design guidelines to achieve specific design objectives. A quasi-3D finite-element analysis with specialized software is given to prove the effectiveness of the design equations and find the main characteristics of the machine. I. INTRODUCTION The axial flux permanent magnet (AFPM) machine, also called the disc-type machine, is an attractive alternative due to its pancake shape, compact construction and high power density. AFPM motors are particularly suitable for electrical vehicles, pumps, fans, valve control, centrifuges, machine tools, robots etc [1], [2]. Axial flux machines appeared in the technical literature in the early ‘70s and trading of axial flux induction motors started few years later [3]-[6]. Nowadays, direct drive applications that require actuators or generators capable of operating at low speeds with large torques have revived the attention towards Axial Flux Machines, especially for the PM type, as they are capable of larger torque density and efficiency [3], [7]-[11]. However, AFPM Synchronous Machines become advantageous whenever a number of design prescriptions are fulfilled. Most notably, it is widely accepted that the number of pole pairs must be conveniently high [3], [12]. Fractional slot windings can be often realized in concentrated layouts: this happens when windings overhangs are not overlapped and the coils are wound individually around the stator teeth. Fractional Slot Concentrated Windings offer remarkable advantages both on the end user and to the manufacturer. In fact, they allow the physical separation of the phases and of the magnetic circuits of the phases, thus reducing the risk of phase-to-phase faults and minimizing the mutual inductance among the phases [3], [13]. The features of Single Stator Dual Rotor PMSM are summarized as the following: greatly shortened end windings, high ratio of diameter to length, high efficiency, high torque density and low material costs [14], [15]. II. DESIGN EQUATIONS This paper will derive the main design equation and a design procedure for these machines, but provided with two rotors. In addition, quasi 3D finite-element analysis is employed to prove the effectiveness of the design equations and the main machine characteristics. In fig. 1 a drawing of longitudinal section is shown. The single stator dual PM rotor axial synchronous machine has in centre the stator assembly (1) with the two three-phase windings (2) placed in open slots, fixed rigid in the casing (3), provided with two side covers (4), (5) in which the two ball bearings supports (6), (7), one radial and one axial, are introduced. The ball bearings allow the two shafts (8), (9) to rotate independently, each shaft having in the side towards the stator a disk of solid steel on which the permanent magnet poles are placed in circular and symmetric manner . The other end of the shaft is inserted into a half-coupling which is connected to the thermal engine (10), respectively, to the gears towards the drive wheels (11). Many unknown parameters are involved in the design of the Single Stator Dual Rotor PMSM. As a result, it is necessary to assign some description to these parameters. They will be further explored in the design equations. Table I gives a list of the parameters used in the design approach. 8 2 3 1 10 6 4 5 7 11 9 Fig.1. Longitudinal section through the dual PM rotors machine.