Permanent magnet utilization criteria in a DC motor

Author

Gould, J.E.

Author_Institution

Permanent Magnet Association, Central Research Laboratory, Sheffield, England

Volume

7

Issue

2

fYear

1971

fDate

6/1/1971 12:00:00 AM

Firstpage

295

Lastpage

297

Abstract

In a dc motor with permanent magnet stator, the mean no-load working point of the magnet material can, after stabilization by stall current, be represented by a point $B_{m},H_{m}$ on a recoil line inside the demagnetization curve. The point results from the application during stall of an effective mean field Hadue to armature reaction in addition to the self-demagnetizing field due to circuit reluctance. It is shown that the motor specification and sizes lead to a specific value for $H_{m}/H_{a}$ . The limiting values of this ratio (Hmzero or Hazero) imply that the corresponding optimum magnet designs for minimum magnet volume should be based either on maximum recoil energy or on $(BH)_{\\max }$ . In practice, the best extreme working point during stall should lie between the points for these two criteria, dependent on the actual $H_{m}/H_{a}$ . In some existing motors $H_{m}/H_{a}$ has been found to be between 0.5 and 1.5. For such values of $H_{m}/H_{a}$ , the variation of Bmand of $B_{m},H_{m}$ with working point is illustrated for high coercivity ferrite and for two grades of cast alnico alloy. A note on design methods is appended

Keywords

DC motors; Permanent magnets; Armature; Circuits; Coercive force; DC motors; Demagnetization; Design methodology; Ferrites; Magnetic materials; Reluctance motors; Stators;

fLanguage

English

Journal_Title

Magnetics, IEEE Transactions on

Publisher

ieee

ISSN

0018-9464

Type

jour

DOI

10.1109/TMAG.1971.1067031

Filename

1067031