Weiya Wang

Design and control of a novel spherical permanent magnet actuator with three degrees of freedom

The paper describes the design and control of a new version of a spherical permanent magnet actuator, which is capable of three degrees of freedom and a high specific torque. Based on an analytical magnetic field distribution, the torque vector and back-emf are derived in closed forms. An optimal design procedure is proposed to achieve maximum output torque or maximum acceleration for a given payload. The control of the actuator, whose dynamics are similar to those of robotic manipulators, is facilitated by the establishment of a complete actuation system model and the application of the computed torque control law. The validity of the analysis and design techniques, and the effectiveness of the control strategy, are confirmed by measurements.

A novel spherical permanent magnet actuator with three degrees-of-freedom

The paper describes a new version of spherical actuator, which is capable of three degrees-of-freedom and a high specific torque. The three-dimensional magnetic field distribution is established using an analytical technique formulated in spherical co-ordinates, and enables the torque vector and back-emf to be derived in closed forms. This facilitates the characterisation of the actuator, and provides the foundation for design optimisation, actuator dynamic modelling and servo control development.

Design Considerations for Tubular Flux-Switching Permanent Magnet Machines

This paper describes a tubular, three-phase, flux-switching permanent magnet (PM) brushless machine that combines salient features from switched reluctance (SR) and conventional PM brushless machines. Feasible slot-pole number combinations, which are also applicable to rotary flux-switching machines, are derived. This paper also examines an alternative stator winding configuration, which is unique to the tubular machine topology. It is shown that this yields ~10%-15% higher thrust force capability as compared to a flux-switching machine equipped with a conventional winding.

A Linear Permanent-Magnet Motor for Active Vehicle Suspension

Traditionally, automotive suspension designs with passive components have been a compromise between the three conflicting demands of road holding, load carrying, and passenger comfort. Linear electromagnetic motor-based active suspension has superior controllability and bandwidth, provides shock load isolation between the vehicle chassis and wheel, and, therefore, has great potential. It also has the ability to recover energy that is dissipated in the shock absorber in the passive systems and results in a much more energy-efficient suspension system. This paper describes the issues pertinent to the design of a high force density tubular permanent-magnet (PM) motor for active suspension in terms of performance optimization, the use of a solid stator core for low-cost production and its impact on thrust force, and the assessment of demagnetization risk.

Demagnetization Assessment for Three-Phase Tubular Brushless Permanent-Magnet Machines

We describe an analytical technique for assessing the risk of partial demagnetization in tubular permanent-magnet (PM) machines. The technique establishes analytical expressions for the open-circuit and armature reaction fields in the cylindrical coordinate system and superposes the fields in the permanent-magnet regions to determine the extent to which the magnets may be partially irreversibly demagnetized. We have applied the technique to a quasi-Halbach magnetized tubular PM machine equipped with a modular stator winding, and have validated the predictions by finite-element analysis. We found that partial demagnetization may occur even under an open-circuit operating condition when the machine is operating at high temperature. We propose alternative Halbach magnetization distributions that improve the demagnetization withstand capability. The analytical technique provides a computationally efficient tool for identifying regions that are prone to partial demagnetization and for assessing the consequences. It enables the risk of demagnetization to be fully assessed at the design stage so as to achieve a robust machine, particularly when operating in harsh environments.

Analysis of a Magnetic Screw for High Force Density Linear Electromagnetic Actuators

This paper describes a high force density linear electromagnetic actuator based on the concept of magnetic screw-nut, in which helically disposed, radially magnetised permanent magnets are placed on both the screw and the nut. Magnetic force and torque can be developed between the two parts without direct mechanical contact. Analytical and numerical analysis has been carried to predict the performance of the magnetic screw-nut assembly. It has been shown that a thrust force density in excess of 10 MN/m3 can be achieved for airgap lengths varying from 0.4 mm to 0.8 mm and a lead λ greater than 7 mm. When combined with a naturally cooled permanent magnet brushless machine having a torque density of ~15 kNm/m3, the resulting thrust force density of the combined system, i.e. electrical machine and magnetic screw-nut assembly, is an order of magnitude higher than that of a liquid-cooled tubular permanent magnet brushless machine.

Fractional-Slot Permanent Magnet Brushless Machines with Low Space Harmonic Contents

The paper is concerned with new winding configurations and associated pole-slot combinations for permanent magnet (PM) machines that lead to improved performance and facilitate cost reduction. Compared to the current state of the art, the salient feature of the proposed designs is elimination and/or reduction of undesirable space harmonics which result from the existing fractional-slot per phase per pole permanent magnet machines with concentric windings. This will bring the benefits of significant reduction of the eddy current loss in the rotor permanent magnets, short end-winding and hence reduced copper loss and copper usage, increased power/torque density, reduction in manufacturing cost, and improved energy efficiency. Although the proposed technique is primarily aimed for brushless permanent magnet machines, it is also applicable to synchronous reluctance machines, induction machines and synchronous wound field machines. The proposed technique is applied to the design of an interior mounted permanent magnet machine for electric vehicle traction applications, and demonstrated by the measurements on a prototype machine.

A tubular flux-switching permanent magnet machine

The paper describes a novel tubular, three-phase permanent magnet brushless machine, which combines salient features from both switched reluctance and permanent magnet machine technologies. It has no end windings and zero net radial force and offers a high power density and peak force capability, as well as the potential for low manufacturing cost. It is, therefore, eminently suitable for a variety of applications, ranging from free-piston energy converters to active vehicle suspensions.

A low-power, linear, permanent-magnet generator/energy storage system

This paper describes the design, analysis and characterization of a linear permanent magnet generator and capacitive energy storage system for generating electrical power from a single stroke of a salient-pole armature. It is suitable for applications that require relatively low levels of electrical power, such as remote electronic locks. An electromagnetic analysis of the generator is described, and a design optimization methodology for the system is presented. Finally, the performance of a prototype is validated against measurements.

Design of a miniature permanent-magnet generator and energy storage system

The paper describes a methodology for optimizing the design and performance of a miniature permanent-magnet generator and its associated energy storage system. It combines an analytical field model, a lumped reluctance equivalent magnetic circuit, and an equivalent electrical circuit. Its utility is demonstrated by means of a case study on a 15-mW, 6000-r/min generator, and the analysis techniques are validated by measurements on a prototype system.