Stuart D. Calverley

A Novel Magnetic Harmonic Gear

Magnetic gears offer several advantages compared to mechanical gears in terms of reduced maintenance, improved reliability, and inherent overload protection while having a high efficiency. This paper describes the principle of operation of a novel form of magnetic gear, which is particularly suited to applications for which a high gear ratio is required. The performance capability of such a magnetic gear is investigated, and it is shown that it transmits a ripple-free torque and that an active torque density of up to 150 kN · m/m3 per stage can be achieved when high-energy permanent magnets are employed. Simulation results on this novel gear are verified by experimental measurements on a prototype.

Design and Operation of a Magnetic Continuously Variable Transmission

This paper describes a magnetic power split device integrated with a brushless permanent-magnet machine, which acts as a magnetic continuously variable transmission. It employs an atypical configuration of magnetic gear which facilitates integration. Nevertheless, 2-D and 3-D finite-element analyses and tests on a prototype have shown that such a device can exhibit a high torque density and a high efficiency. Furthermore, potential applications in hybrid vehicles and wind turbines are also discussed.

Prediction and measurement of core losses in a high-speed switched-reluctance Machine

We describe a procedure for calculating the core loss in high-speed switched-reluctance machines. The technique calculates core losses within a switched-reluctance machine to a high degree of spatial resolution over a wide range of operating conditions. We confirmed the calculations experimentally, using a loss segregation method, and found good correlation.

A novel magnetic harmonic gear

Magnetic gears offer several advantages compared to mechanical gears, in terms of reduced maintenance, improved reliability and inherent overload protection, whilst having a high efficiency. The paper describes the principle of operation of a novel form of magnetic gear, which is particularly suited to applications for which a high gear ratio is required. The performance capability of such a magnetic gear is investigated, and it is shown that it transmits a ripple-free torque, and that a torque density of up to 110 kNm/m can be achieved when high- energy permanent magnets are employed.

Design, analysis and realization of a novel magnetic harmonic gear

High performance magnetic gears are competitive with mechanical gears in terms of their torque transmission capability, and they offer significant operational benefits. Various topologies of magnetic gear have been developed, the one which is described in this paper being particularly appropriate for use in applications for which a high gear ratio is required. It is the magnetic equivalent of a mechanical harmonic gear, and can transmit ripple-free torque at a torque density of up to ~110 kNm/m3 when high energy permanent magnets are employed. The paper will describe the operating principle, design and analysis of a harmonic magnetic gear, including a dual-stage configuration which enables much higher gear ratios to be achieved. Finally, the practical realization of such a magnetic gear will be described.

Design of a high-speed switched reluctance machine for automotive turbo-generator applications.

The efficient generation of relatively large quantities of electrical energy in vehicles is becoming an increasingly important issue, as a result of increasing demands of ancillary equipment and the emergence of hybrid power-train vehicles. An attractive solution to meeting these demands is to extract the electrical energy by means of a generator driven by a high-speed exhaust mounted turbine, a technology that is beginning to emerge commercially. This thesis is concerned with the design of a system, which extends this concept to enable both electrical generation and highly flexible air-management. The heart of the system is a high-speed switched reluctance machine, the rotor of which is located on a common shaft with the turbine and compressor wheels of a standard commercial turbocharger. The design synthesis of a -switched reluctance machine capable of meeting the required performance specification is particularly onerous given the harsh environment in which it operates, specifically in terms of the restricted space envelope, the high ambient temperature and the very high rotational speeds. This thesis describes the design of a switched reluctance machine for a prototype system, a procedure that encompasses the detailed analysis of centrifugal stress in the rotor, aerodynamic losses, iron loss, rotordynainic performance and dynamic performance. The design and analysis of the system is supported by experimental evaluation at both component and system level.

Operating Strategies of Switched Reluctance Machines for Exhaust Gas Energy Recovery Systems

This paper presents an operating strategy for high-speed switched reluctance (SR) generators employed in exhaust gas energy recovery systems. The machine is operated in “single pulse” mode, and a parametric study of the control angles is performed to analyze the machine operation. It is shown that, for given speed and power, optimum sets of control angles exist, which achieve maximum machine efficiency and minimum thermal stress. This study is undertaken using a coupled nonlinear modeling approach, combining magnetostatic finite-element analysis with time-domain circuit simulation. The results are compared with measurements performed on an SR generator designed for a prototype exhaust gas energy recovery system, showing overall good agreement.

Switched Reluctance Turbo-Generator for Exhaust Gas Energy Recovery

The paper describes a comparative study of low voltage and high voltage SR machines for use in an automotive turbo-generator exhaust gas energy recovery system. Their relative merits, in terms of the total machine loss and the loss distribution, are quantified. It is shown that the requirement for an integer number of turns imposes severe restrictions on the design of the low voltage system, whereas the flexibility to employ various winding designs in the high voltage system can be exploited to advantage. A comprehensive analysis of both the winding design and the operating control angles is presented. While the magnitude of the total machine loss is relatively insensitive to the operating voltage, the copper loss at full load is significantly lower in the high voltage system. The merits of operating the system at high voltage, in terms of the thermal rating of the electric machine, are also discussed.

Dynamic model of a switched reluctance machine for use in a SABER based vehicular system simulation

This paper describes a flexible modelling technique for the dynamic simulation of a switched reluctance machine employed in an automotive turbo-electric application to recuperate electrical energy. Due to the increasing numbers of electrically driven ancillaries and associated electrical load on the vehicle, a model which can be readily employed in a hierarchical system simulation of the vehicle electrical architecture, realised within the SABER environment, is required. The model allows comprehensive modelling of an extensive range of control strategies to be performed and appropriate switching control angles to be identified. Trade-off studies are performed in order to minimise global system losses while ensuring RMS and peak currents, and hence component ratings, are not excessive. The simulation is complemented using accurate iron loss calculations performed on a range of control conditions. A case study of a 70,000 rpm, 2.3 kW switched reluctance machine is presented.

Design and operation of a magnetic Continuously Variable Transmission

This paper describes a magnetic power split device integrated with a brushless permanent-magnet machine, which acts as a magnetic continuously variable transmission. It employs an atypical configuration of magnetic gear which facilitates integration. Nevertheless, 2-D and 3-D finite-element analyses and tests on a prototype have shown that such a device can exhibit a high torque density and a high efficiency. Furthermore, potential applications in hybrid vehicles and wind turbines are also discussed.