GB2284104A

GB2284104A - Adjustable flux permanent magnet brushless AC or DC motor

Info

Publication number: GB2284104A
Application number: GB9323677A
Authority: GB
Inventors: Ching Chuen Chan
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-11-17
Filing date: 1993-11-17
Publication date: 1995-05-24
Anticipated expiration: 2013-11-17
Also published as: GB9323677D0; GB2284104B

Abstract

The stator of the motor is similar to that of conventional ac motor, whereas the rotor incorporates magnetic bridge b between circumferentially adjacent pole pieces p. Auxiliary air gaps g may be provided in the bridge b. The magnetic bridges b provide parallel paths for air gap flux so that the airgap flux can be adjusted effectively, efficiently and flexibly. The distinct features of the design lie in: (i) the airgap flux consists of two parallel flux, (ii) the magnetic paths are optimized, (iii) the reluctance of direct axis armature flux is significantly smaller than that of conventional permanent magnet ac motor, (iv) the arrangement of the permanent magnet m is so designed that no magnetic isolation is required at the rotor shaft, and (v) the configuration of the permanent magnets and the construction of the rotor are simple. Therefore, the motor possesses the following major advantages: (i) higher power-to-weight ratio, (ii) higher performance-to-cost ratio and (iii) higher efficiencies over the operating torque-speed range. The motor is suitable for use in an electric vehicle. <IMAGE>

Description

COMPLETE SPECIFICATION A Novel Adjustable Flux Permanent Magnet Brushless DC Motor I, CHING CHUEN CHAN, a professor of Electrical Engineering, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by it is to be performed, to be particularly described in and by the following statement: This invention relates to permanent magnet brushless dc motors or permanent magnet ac motors. The principles of operation of this kind of motors are already known. The magnetic flux of the motor is produced by permanent magnet and the commutation is performed by electronic switches in accordance to the position ofthe rotor. The motor can be fed by sinusoidal or rectangular current. For a sinusoidal-fed motor, vector control can be applied, where the torque component armature current, Iaqs and field component armature current, Iad, can be controlled separately. For a rectangular-fed motor, a hysterics current controller is usually used, the field component of the armature current can be controlled by regulating the commutation angle of the power converter. Therefore, for both sinusoidal-fed motor and rectangular-fed motor, the airgap resultant flux can be regulated in order to control the speed of the motor. However, in conventional permanent magnet brushless dc motors or permanent magnet ac motors, the field control cannot be achieved efficiently since the reluctance ofthe magnetic path ofthe direct axis component of armature flux is large.

This invention deals with a novel adjustable flux permanent magnet burshless dc motor or adjustable flux permanent magnet ac motor. The stator of the motor is similar to that of conventional ac motor. The originality lies in the novel construction of the rotor comprising magnetic bridges which provide parallel path for the airgap flux so that the airgap flux can be adjusted effectively, efficiently and flexibly. Fig. 1 and Fig. 2 (a) (b) show the structure of the two-poles motor and four-poles motor respectively. In the figures, the stator multi-phase winding is only represented by widing "a" for the sake of simplicity, while "m" represents the permanent magnet, and "b" represents the magnetic bridge. The rotor core can be made by solid iron or steel sheet laminations. Qm is the flux produced by the permanent magnet and 4)ad is the flux produced by the direct-axis component of armature current, Iad.

Here, the direct axis is defined as the axis that coincides with the position of the rotor pole, hence Iad is also called the field component of the armature current, Ia. Thus the armature current, Ia, consists of direct axis component or field component, Iad, and quadrature axis component or torque component, Iraq. It can be seen from Fig. 1 and Fig. 2 (a) (b) that the airgap flux consists of the permanent magnet flux, vm, and the direct axis armature current flux, Xad. Iad is adjustable by vector control or other means, hence Xad is adjustable. When vad =0, the major portion of cm will flow across the airgap through the stator, while a partial portion of vm will flow through the magnetic bridge, b, thus the airgap resultant flux is minimum. When ad increases, the airgap resultant flux will increase. Therefore, the airgap resultant flux can be adjusted very effectively, efficiently and flexibly, because: (i) m and vad are parallel, (ii) the magnitude and direction of ad can be controlled by regulating Iad, (iii) the magnetic paths of Xm and Xad are optimum, and (iv) the reluctance of ad of the motor is significantly smaller than that of conventional permanent magnet brushless dc motor or permanent magnet ac motor. If necessary, an auxiliary airgap "g" in the magnetic bridge may be introduced as shown in Fig. 1 and Fig. 2 (a) (b). The purpose of the auxiliary airgap is to linearize the relation between ad and Iad, and hence to improve the performance. It can be seen from Fig. 1 and Fig. 2 (a) (b) that the configuration of the permanent magnet is a simple cuboid, moreover magnetic flux isolation at the rotor-shaft is not necessary, hence the rotor shaft can be made of normal steel. Although Fig. 1 and Fig. 2 (a) (b) show only the two-pole motor and four-pole motor configuration, same principles also can be applied for other number of pole pairs. Fig. 3 shows the stator and rotor stampings of eight-pole motor. The flux lines of m (when Iad = 0) obtained from finite element method is also shown in Fig. 3.

The magnetic flux path can be optimized by employing appropriate shape of rotor slots.

The major advantages ofthis novel design are as follows: 1. Less magnetizing ampere-turns is required due to the magnetic circuit is optimized with minimum reluctance. Thus leading to reduction in copper weight, magnet weight and iron core weight, and increase in efficiency.

2. The efficiencies over the operating torque-speed range can be optimized through controlling the airgap flux by simply regulating Iad and hence ad. Thus leading to significant energy saving. Therefore this invented motor is very suitable for electric vehicle application.

3. The torque-speed characteristic of the motor can be regulated in accordance with the application demand through the control of the airgap flux.

4. The speed range of the motor can be extended through the weakening of the airgap flux.

5. The fabrication is easy due to simple configuration of permanent magnet and simple rotor structure.

6. The power-to-weight ratio, performance-to-cost ratio and overall efficiency are enhanced.

Claims

What I claim is:1. An adjustable flux permanent magnet brushless de motor having a novel construction of the rotor comprising magnetic bridges which provide parallel path for the airgap flux so that the airgap flux can be adjusted effectively, efficiently and flexibly. The abovesaid magnetic bridge(s) may have auxiliary airgap(s) to improve the performance. The arrangement of the permanent magnet is so designed that the magnetic flux path is optimized and no magnetic isolation is required at the rotor shaft part.
2. An adjustable flux permanent magnet brushless dc motor substantially as hereinbefore described with reference to the accompanying drawings. Similar structure can also be applied for higher pole-pairs motors.