This paper reviews the relative merits of induction, switched reluctance, and permanent-magnet (PM) brushless machines and drives for application in electric, hybrid, and fuel cell vehicles, with particular emphasis on PM brushless machines. The basic operational characteristics and design requirements, viz. a high torque/power density, high efficiency over a wide operating range, and a high maximum speed capability, as well as the latest developments, are described. Permanent-magnet brushless dc and ac machines and drives are compared in terms of their constant torque and constant power capabilities, and various PM machine topologies and their performance are reviewed. Finally, methods for enhancing the PM excitation torque and reluctance torque components and, thereby, improving the torque and power capability, are described

Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles

This paper reviews the relative merits of induction, switched reluctance, and permanent-magnet (PM) brushless machines and drives for application in electric, hybrid, and fuel cellvehicles,withparticularemphasisonPMbrushlessmachines. The basic operational characteristics and design requirements, viz. a high torque/power density, high efficiency over a wide operatingrange,andahighmaximumspeedcapability,aswell as the latest developments, are described. Permanent-magnet brushless dc and ac machines and drives are compared in terms of their constant torque and constant power capabilities, and various PM machine topologies and their performance are reviewed. Finally, methods for enhancing the PM excitation torque and reluctance torque components and, thereby, improv- ing the torque and power capability, are described.

Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Induction and switched-reluctance machines can provide the needed characteristics, but permanent magnet brushless machines offer a higher efficiency and torque density.

Switched reluctance (SR) motors have an intrinsic simplicity and low cost that make them well suited to many applications. However the motor's doubly salient structure and highly nonuniform torque and magnetization characteristics lead to the inability to excite the motor using conventional AC motor waveforms, or apply established AC motor rotating field theory to the motor. Furthermore, high torque ripple is inherent in the motor unless a torque ripple reduction strategy is employed. Thus, control of the motor is difficult and complex compared to other machines. Previous methods of control have fallen into two main categories: those which use a simplified linear model and those which account for the motor saturation. The simplified linear model schemes have the advantage of simplicity and tractability but are inaccurate in most practical SR drives, whereas the nonlinear schemes have the problem of high complexity and computational expensiveness which makes real-time implementation difficult. To overcome these problems, in this paper, a novel control method for the SR motor is derived from analysis of the nonuniform torque characteristics of the motor. The control method applies the philosophy of direct torque control (DTC). Unlike previous direct torque control schemes for the SR motor drive, the new method does not involve short flux patterns, a change of the motor winding configuration, or the use of a bipolar current drive. Thus, the scheme can be conveniently implemented on any normal type of SR motor drive. In addition, the scheme overcomes the problems associated with torque ripple control in the SR motor by regulating the torque output of the motor within a hysteresis band. Furthermore, the scheme is very simple and can be implemented in real-time with low cost microprocessor hardware.

A new torque and flux control method for switched reluctance motor drives

This paper describes the results of an extensive study into the production and reduction of acoustic noise and vibration in the switched reluctance drive. Time domain analysis has been used to draw conclusions about the effects of changing the operating parameters of the power electronic controller on the vibration and acoustic noise. Experimental results have been taken from a four-phase switched reluctance drive with one-, two-, or four-phase excitation. The results of this time domain study reveal important information about the stator vibration which would not be apparent from frequency spectra. The results have been used to derive operational concepts for the power electronic controller to reduce the acoustic noise and vibration produced by the drive. A new control technique has been developed to cancel the stator vibration. Using this novel control method, experimental results show that the vibration and acoustic noise produced by a switched reluctance drive can be reduced dramatically without affecting the performance of the drive.

Analysis and reduction of vibration and acoustic noise in the switched reluctance drive

Acoustic noise in the switched reluctance motor (SRM) is caused primarily by the deformation of the stator lamination stack. Acoustic noise is most severe when the periodic excitation of the SRM phases excites a natural vibration mode of the stack. The natural vibration modes and frequencies of a four-phase, 8/6 SRM are examined. Structural finite element analysis is used to compute the natural modes and frequencies. Impulse tests on the stator stack verify the calculations and show which modes are excited. Heuristic arguments are developed to predict the operating conditions that will excite the natural modes. Measurement of vibration while the machine is under load shows which operating conditions excite the natural modes and verifies the predictions. An approximate formula is derived to predict the frequency of the fundamental vibration mode in terms of lamination dimensions and material properties. The formula is validated by comparison with finite element calculations for several laminations, and hence is shown to be useful in design trade-off studies.

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Vibration modes and acoustic noise in a four-phase switched reluctance motor

This paper describes the results of an extensive study into the production of acoustic noise and vibration in the switched reluctance motor drive. Time domain analysis has been used to draw conclusions about the effects of changing the operating parameters of the power electronic controller on the vibration and acoustic noise. Experimental results have been taken from a four phase switched reluctance motor drive with one, two or four phase excitation. The results of this time domain study reveal important information which would not be apparent from frequency spectra. The results can be used to derive control laws for the power electronic controller to reduce the acoustic noise and vibration produced by the motor.

Time domain analysis of vibration and acoustic noise in the switched reluctance drive

This paper describes the electromagnetic design, construction and testing of a prototype 5-phase switched reluctance motor that exploits the short flux path concept If the phase windings are arranged so that neighbouring poles have opposite magnetic polarity then the B-field associated with any two consecutive phase windings forms a short flux loop linking adjacent excited stator poles via the rotor teeth The MMF required to produce a given flux in the airgap is reduced, resulting in a drop in copper losses Furthermore, the volume of iron in which hysteresis and eddy current losses are generated is reduced, thus resulting in a drop in iron losses This paper reviews aspects of the 5-phase motor design, dynamic simulation and construction Test results from a prototype drive rated at over 4 kW are given

Design and performance of a high efficiency 5-phase switched reluctance motor

Electrically powered thruster units are widely used for the propulsion of a variety of small vessels. In craft powered this way, one or more thrusters mounted externally to the vessel are employed to provide both propulsion and a means of steering. This paper describes some of the aspects of the design of a prototype switched reluctance motor for use in an integrated motor/propeller unit. The motor is a three phase sector design with a six pole stator and twenty pole rotor. The paper addresses the factors which influenced the choice of phase and pole numbers and considers some of the trade-offs between the mechanical and electromagnetic requirements. Motor control is also discussed.

Design of a switched reluctance sector motor for an integrated motor/propeller unit

This paper describes the analysis of a switched reluctance motor in which the windings are arranged to provide short flux path excitation. This winding arrangement decreases the current required to establish the flux in the airgap, thus improving the efficiency of the motor. The paper provides some insight into modelling of switched reluctance motors with two phases simultaneously energised, as this is fundamental to the operation of the proposed machine. Finite element analysis was used to model the performance of a prototype machine configured for long or short flux path excitation. Computer predictions show good agreement with test results and indicate the improvements in performance offered by the new winding configuration.

Modelling of a new winding arrangement to improve performance in the switched reluctance motor

This paper describes the implementation and performance of the rotor position sensing system used in an integrated switched reluctance marine propulsion unit. Factors which influence the design of the drive system, including choice of operating point, selection of commutation angles and the effect of the rotor position sensing system on winding design are addressed. The performance of the propulsion unit under bollard-pull test conditions (zero speed of propeller advance) is reported.

C. Pollock

Papers

Time domain analysis of vibration and acoustic noise in the switched reluctance drive

Design and performance of a high efficiency 5-phase switched reluctance motor

Design of a switched reluctance sector motor for an integrated motor/propeller unit

Modelling of a new winding arrangement to improve performance in the switched reluctance motor

Design and performance of a rotor position sensing system for a switched reluctance marine propulsion unit