Thrust Force Density Research Articles

A Primary Permanent-Magnet Linear Motor for Urban Rail Transit

In this paper, a new permanent-magnet (PM) linear motor is proposed, in which both the magnets and armature windings are placed in the short mover, while the long stator consists of iron core only. Hence, this new PM linear motor can be called a primary permanent-magnet linear motor. It exhibits the advantages of robustness, low cost, high efficiency, high power factor, and high thrust force density. It is especially suitable for long stator applications such as urban rail transit. In this paper, the topology and operation principle of this motor are discussed in detail. The steady-state characteristics including field distributions, flux-linkage, back-EMF, phase inductance and thrust force are investigated. In addition, the technique of skewing stator teeth is adopted to improve the electromagnetic performance. Results from finite element method (FEM) verified the theoretical analysis results.

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/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> 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/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , 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.

Performance Analysis of a Novel Magnetic-Geared Tubular Linear Permanent Magnet Machine

This paper presents a novel tubular linear permanent magnet machine for direct-drive applications, in which a magnetic gear is integrated with a tubular linear machine, aiming to improve the thrust force density and enhance the machine efficiency. The operating principle of the proposed machine is introduced and the machine design with improved thrust force density is presented and discussed. By using circuit-field-motion coupled time-stepping axisymmetric finite element method (FEM), the steady-state as well as transient performances of the machine are simulated. The FEM computation results are consistent with those obtained theoretically, hence verifying the validity of the machine design.

Thrust Force of Novel PM Transverse Flux Linear Oscillating Actuators With Moving Magnet

This paper investigates the thrust forces of two novel permanent magnet transverse flux linear oscillating actuators (TFLOAs), one with moving magnet and the other moving both magnet and iron core, for pump and compressor drives. Different from the conventional linear actuators, the lamination construction of the TFLOAs is similar to that of a normal rotating motor, which is easy to stack. Based on a simple magnetic circuit model taking into account the interpole leakage flux, the thrust forces are deduced analytically. The predicted results are verified by the finite element analyses and validated by experiments. It is shown that the thrust force performances of both TFLOAs are similar, whereas the former has a lower thrust force density and higher resonant frequency.

Finite element analysis of load characterisitic and parameters in permanent magnet linear synchronous motor with structure slots per phase per pole less than 1

By stability achievement of permanent magnet linear synchronous motor(PMLSM) with slots per phase per pole less than 1(q1) fractional slot, thrust force density becomes the key point in analysis and design of the motor. To analyze the load characteristics, a finite element method(FEM) model of PMLSM is set up based on 2D electromagnetic field equations. Taking influence of end-leakage to PMLSM into account, open-boundary condition is used to improve the precision of analysis. With fixed three-phase winding current of fractional slot from space-time vectogram, relaxation factor method is used to adjust angle α. By iterating the normal rated thrust, load characteristic and parameters are obtained by instantaneous current method. Experimental prototype is used for parameter measurement. Comparing the FEM calculation with actual measurements, results show that FEM based model can confirm the load characteristic and obtain the parameters and power-angle characteristic of PMLSM. Direct-quadrature axis inductances give a good reference to the motion control of PMLSM.

Increasing of thrust force in transverse flux machine by permanent-magnet screen

This paper proposes a basic model and an analytical study of the transverse flux machines using permanent-magnet (PM) shields to increase the thrust force. By improving the magnetic field distribution in the electrically excited transverse flux linear motor (TFE-LM), the rare-earth PM shields provide an increase of the thrust force. Analytical equations are developed to predict the thrust force and to guide the design of TFE-LM. The thrust force and the thrust force density of TFE-LM with PM shields are calculated also by a 3D-Finite Network Method program. The presence of PM shields in a TFE-LM having a current linkage of 2 kA and the air-gap length of 1 mm leads to the increase of thrust force by approximately 160%. This result reveals a great potential in reducing the mass of the TFE-LM by inserting PM shields in the teeth.

Static Characteristics of Linear BLDC Motor Using Equivalent Magnetic Circuit and Finite Element Method

This paper presents the static characteristics of the linear BLDC motor. An equivalent magnetic circuit model is derived for the prototype motor. The air-gap flux density is calculated using the equivalent magnetic circuit and compared with results from finite element analysis. The thrust force is measured for the prototype motor and is also compared with those from derived circuit model and FEA. These values agree well to show the validity of the equivalent circuit model. Using this equivalent circuit model, the thrust force density variation according to change of coil width to pole pitch can be expected at the design stage.