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Design considerations for fractional-slot winding configurations of synchronous machines

This paper presents some design considerations for synchronous machines characterized by a fractional number of slots per pole per phase. The main advantage of this configuration is a smooth torque, which is due to the elimination of periodicity between slots and poles. A second advantage is a higher fault-tolerant capability, making the machine able to work even in faulty conditions. However, the fractional-slot configuration presents a high content of MMF harmonics that may cause an unbalanced saturation and thus an unbearable torque ripple. A method to design fractional-slot machines is illustrated in this paper, including double-layer and single-layer windings. The analytical computation is extended to determine the harmonics of MMF distribution. Their effect is highlighted in isotropic as well as anisotropic machines. Finally, some considerations are reported to avoid unsuitable configurations

Strategies for the Fault-Tolerant Current Control of a Five-Phase Permanent-Magnet Motor

This paper deals with the postfault current control strategies of a five-phase permanent-magnet (PM) motor. The analysis covers both the open circuit of one and two phases and the short circuit at the machine terminal of one phase. The proposed control guarantees safe drive operation after any fault occurrence. For the sake of generality, an analytical model has been used to investigate the properties of each postfault strategy. The results are general, and they apply to PM motor of any power rating. Simulations and experimental results validate the theoretical predictions.

Impact of Stator Winding of a Five-Phase Permanent-Magnet Motor on Postfault Operations

The performance of a five-phase permanent-magnet (PM) motor is analyzed under postfault conditions. Proper current control strategies are adopted so as to guarantee safe drive operation after any fault occurrence. This paper covers three fault types: the open circuit condition of a single phase, the open circuit condition of two nonadjacent phases, and the open circuit condition of two adjacent phases. Two motors with two different windings (with double and single layers, respectively) are compared under each fault type. This paper aims to highlight the difference in the motor performance of motors adopting these two different windings. A further novelty of this paper is that the proper current control strategies are derived analytically, including not only the fundamental harmonic of the flux-density distribution but also the higher harmonics. It is shown that these harmonics cause high torque oscillations. Owing to this analytical approach, the strategy can be applied to a variety of PM motors. In addition, the postfault current waveforms remain sinusoidal, making the current control easier. For each fault type, the results of both simulations and experimental tests are included. A good match between analytical predictions and experimental tests validates the proposed current control strategies.

Design considerations on fractional-slot fault-tolerant synchronous motors

This paper presents some design considerations of fault-tolerant synchronous motors, characterized by a fractional number of slots per pole per phase. The first advantage of this configuration is a smooth torque, because of the elimination of the periodicity between slots and poles. The second one is a higher fault-tolerant capability making the machine able to work even in faulty conditions. However, the fractional-slot configuration presents a high contents of M.M.F. harmonics that may cause an unbalanced saturation and thus an unbearable torque ripple. A method to design fractional-slot motors is illustrated in the paper, including double-layer and single-layer winding. The analytical computation is extended to determine the harmonics of M.M.F. distribution. Their effect is highlighted in isotropic as well as anisotropic motors. Finally some considerations are reported to avoid unsuitable configurations

Rotor flux-barrier design for torque ripple reduction in synchronous reluctance motors

The torque produced by a synchronous reluctance machine (including the PM assisted configuration) is studied analytically, to the aim of characterizing the effect of the position of the flux-barriers on the torque ripple. It is verified that the position of the flux-barrier ends highly influences the torque waveform. To the aim of reducing the torque harmonic contents, a new strategy is proposed based on the choice of couples of flux-barriers of different shapes. The couples of the flux-barriers are chosen so as to obtain compensation between the torque harmonics produced by each couple of them. Experimental results on two prototypes confirm the analytical prediction

IPM Machine Drive Design and Tests for an Integrated Starter-Alternator Application

This paper deals with an integrated starter-alternator (ISA) drive which exhibits a high torque for the engine start, a wide constant-power speed range for the engine speedup, and a high-speed generator mode operation for electric energy generation. Peculiarities of this ISA drive are thus its flux-weakening capability and the possibility to large torque overload at low speed. The focus on the design, analysis, and test of an interior permanent-magnet motor and drive for a prototype of ISA is given in this paper. In details, this paper reports on the design of stator and rotor geometries, the results of finite-element computations, the description of control system, and the experimental results of prototype tests.

IPM Machine Drive Design and Tests for an Integrated Starter–Alternator Application

This paper deals with an integrated starter-alternator (ISA) drive which exhibits a high torque for the engine start, a wide constant-power speed range for the engine speedup, and a high-speed generator mode operation for electric energy generation. Peculiarities of this ISA drive are thus its flux-weakening capability and the possibility to large torque overload at low speed. The focus on the design, analysis, and test of an interior permanent-magnet motor and drive for a prototype of ISA is given in this paper. In details, this paper reports on the design of stator and rotor geometries, the results of finite-element computations, the description of control system, and the experimental results of prototype tests.

The steering effect PM motor drives for automotive systems

The steer-by-wire (SBW) system requires the use of enhanced fuel economy, assist action given two motor drives, the first for the mechanical steering system and the second for the torque feedback to the steering wheel. An interior permanent magnet (IPM) synchronous motor is used for the steering actuator whereas a fractional-slot surface-mounted permanent magnet (SPM) synchronous motor is used for the torque feedback.

PM motor drives for steer-by-wire applications

This paper presents the analysis and design of the motor and control of a steer-by-wire system, developed in the frame of a two-year inter-university research project. The key requirements of the application are fault-tolerance capability, effective steering control, and torque feedback control. The study mainly deals with the PM motor used in the steering mechanism, because of some innovative aspects. Design criteria and experimental results are included in the paper.

Experimental tests on a 12-slot 8-pole Integrated Starter-Alternator

In modern vehicles, the integrated starter-alternator (ISA) is an electrical machine that has to crank up the internal combustion engine, and to generate electric power during normal driving. Therefore, the ISA has to exhibit high torque and a wide constant-power speed range. This paper reports some design criteria, analysis and test results of an ISA that has been developed using a fractional-slot interior permanent magnet motor.