J.F. Eastham

Optimum design of brushless tubular linear machines

A method which uses finite-element techniques for designing linear tubular brushless DC machines is described. The design technique makes use of approximate calculations to decide the machine dimensions. Finite-element analysis is then employed to calculate a series of designs and determine the optimum one. The effects of variation in slot depth and pole pitch are illustrated. The finite-element analysis is supported by analytical results from using a simple method of calculating electromagnetic force. >

Modelling electromagnetic rail launchers at speed using 3D finite elements

A formulation which allows the simulation of railguns and other devices incorporating moving conductors which are of constant cross-section in the direction of motion has been described. The formulation is believed to be as economic in terms of computer resources as possible. One important feature is that the final set of equations which has to be solved appears to be well-conditioned, and can be solved efficiently using the preconditioned biconjugate gradient technique. It is important that the mesh used in the moving region does not contain any large jumps in element size in the direction of motion. The application of the method to railgun launchers is illustrated. >

Analysis of the performance of tubular pulsed coil induction launchers

The authors present a scheme for modeling coil guns using finite elements. The relative motion between the coils and the projectile is modeled by using two distinct meshes which are coupled using Lagrange multipliers which depend on the relative position of the two meshes. This scheme allows the inner mesh to slide during the transient simulation without the need to remesh the problem. Results are presented for a simple experiment involving a single coil and aluminum projectile. >

Dynamic performance of a brushless DC tubular drive system

The authors describe the computer-aided analysis of the dynamic performance of a tubular linear machine system with permanent magnetic cogging forces. These forces include not only the conventional tooth cogging force apparent in both linear and rotary machines but also a force unique to permanent magnet linear machines that is due to the finite length of the stator. System equations which describe both the machine and the inverter supply are solved by a step-to-step numerical method to find the dynamic performance of the machine in an oscillator mode. The work is verified by experimental results obtained for a practical model. >

Finite element analysis of an interior-magnet brushless DC machine, with a step-skewed rotor

The use of finite-element (FE) analysis as a tool for optimising the design of a new form of permanent-magnet electrical machine is described. In order to reduce unwanted torque and generated voltage pulsations, the rotor is divided into a number of separate sections that have both axial separation and different radial positions. FE analysis is employed to optimise: (i) spacer width between the rotor sections, and (ii) radial positioning of sections, in order to give minimum torque and voltage pulsation. In comparison with a single-section rotor, it was found that a 3-section rotor gave an 89% reduction in peak-to-peak torque pulsation. Where possible, the accuracy of the PE method was confirmed by comparison with experimental measurements.

Finite element analysis of brushless DC motors for flux weakening operation

Finite element analysis is used to obtain the non-linear variation of axis and cross-axis flux-linkages for a dq model of an interior magnet, brushless DC motor (BLDC). The model is used to compare competing designs of the conventional form of BLDC with designs of a novel type that has q-axis flux barriers. It is shown that the flux-barrier motor will give (i) equal rated performance, and (ii) better over-rating performance.

EFFECTS OF SLOT CLOSURE BY SOFT MAGNETIC POWDER WEDGE MATERIAL IN AXIAL-FIELD PERMANENT MAGNET BRUSHLESS MACHINES

The article reports on a study of the effects of slot closure in axial‐field permanent magnet brushless machines by a two‐dimensional finite element method (2D FEM) of analysis. The closure of the slots is made by using soft magnetic powder wedge material. Parameter values and machine performance for the open and closed slot configuration are computed. In order to test the 2D FEM model, calculated results are compared with measurements and favorable agreement is shown.

Full-scale testing of a high speed linear synchronous motor and calculation of end-effects

A description is given of apparatus constructed to perform full-scale tests on linear synchronous motor (LSM) designs suitable for 100-passenger vehicles, traveling at speeds up to 400 km/hr. Test results are presented that illustrate the terminal characteristics of the machine, which are shown to be predictable using a simple mathematical model. In all forms of linear machine the air-gap flux takes time to develop at the entry end of the stator and a further time to decay at the exit end. This effect, which is due to induced secondary currents, is known as the longitudinal end effect. A simple method is described for predicting the effect, and the results are confirmed by measurements on a full-scale test rig. >

Automatic treatment of multiple wound coils in 3D finite element problems including multiply connected regions

This paper describes an efficient scheme for incorporating multiple wire wound coils into 3D finite element electric machine models. The scheme is based on the magnetic scaler representation with an additional basis for each coil. There are no restrictions on the topology of coils with respect to ferromagnetic and conductor regions. Reduced scaler regions and cuts are automatically generated.

Finite element analysis of a novel brushless DC motor with flux barriers

The paper describes the finite-element modelling of a novel form of brushless DC machine, which is of the interior magnet type, and uses radial flux barriers in the q-axis. It is shown that the machine can give more torque than its conventional interior magnet counterpart if the magnetic saturation of the machine is the same in both cases. The work is supported by results taken from an 11 kW prototype machine.