Melanie Michon

Effect of Rotor Eccentricity in Large Synchronous Machines

This paper addresses the effects of rotor eccentricity on the unbalanced magnetic pull (UMP) and induced electromotive forces (EMFs) in permanent magnet and wound field machines with particular emphasis on wind applications. It is shown that in both machines, the UMP can be of similar or greater magnitude than the gravitational force acting on the rotor. It is also shown that although rotor eccentricity may have a noticeable effect on the induced EMF in individual coils, albeit the effects on the phase EMF may depend on the coil connections. Furthermore, the mechanical deflections and forces on the bearings are determined using Euler-Bernoulli beam theory taking into account the UMP and gravitational forces as well as the non-linear stiffness characteristics of the bearings. It is shown that the UMP could have a significant effect on bearing forces.

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.

Effects of unbalanced magnetic pull in large permanent magnet machines

In addition to the circumferential shear stresses which produce torque, radial attractive stresses between the rotor and stator also exist. Although, the forces between the rotor and stator are normally negligible when they are concentric, an unbalanced magnetic pull (UMP) occurs when the rotor axis is displaced from the stator axis. In the paper, the magnitude of UMP in large permanent magnet machines and its effects on bearing forces/life are investigated. It is shown that UMP can have a significant effect on bearing life.

Dynamic behaviour of a multi-MW wind turbine

The paper presents an investigation into the effects of wind and grid conditions on the dynamic behaviours and the interactions between the electrical, mechanical and control components of a 3MW variable-speed wind turbine. All the components of the drivetrain have been modelled with sufficiently high fidelity, and it has been shown that extreme wind and grid conditions, such wind turbulence and grid voltage sag, can have significant effects on the conditions exhibited by the gearbox, for example. Furthermore, it has also been shown, that despite the fact that the turbine is connected to the grid through a full power converters, a grid voltage sag can expose the mechanical components of the drivetrain to load reversals and oscillations.

Operating strategies for Switched Reluctance generators in exhaust gas energy recovery systems

The 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 analyse 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, non-linear modeling approach, combining magneto-static finite element analysis with time-domain circuit simulation. The results are compared with measurements performed on a SR generator designed for a prototype exhaust gas energy recovery system showing overall good agreement.