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3-PHASE BRUSHLESS DC MOTOR USING A SINGLE SENSOR

IP.com Disclosure Number: IPCOM000005795D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2001-Nov-07
Document File: 2 page(s) / 66K

Publishing Venue

Motorola

Related People

John Babico: AUTHOR

Abstract

In a 3-phase brushless DC motor three sensors are required to determine the rotor position and the infor- mation from each sensor specifies the commutation of each winding. The two major problems in a 3-sensor system are cost and mechanical orientation/mounting of these sensors with respect to the stator windings. Fig. (1) shows a single sensor system with a 4.pole rotor and 3 phase windings. The SZ and SI sensors which are normally inside the motor are not used in the present system, but the SI and SS information is generated electronically using the S signal as shown in Fig. (2).

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MOzoRoLA Technical Developments Volume 9 August 1989

3.PHASE BRUSHLESS DC MOTOR USING A SINGLE SENSOR

by John Babico

   In a 3-phase brushless DC motor three sensors are required to determine the rotor position and the infor- mation from each sensor specifies the commutation of each winding. The two major problems in a 3-sensor system are cost and mechanical orientation/mounting of these sensors with respect to the stator windings. Fig. (1) shows a single sensor system with a 4.pole rotor and 3 phase windings. The SZ and SI sensors which are normally inside the motor are not used in the present system, but the SI and SS information is generated electronically using the S signal as shown in Fig. (2).

   Two constant angle (S,) generators are used to electronically create a constant phase shift angle between signals Sr, SI and SS representative of the same signals provided by the sensors Sr, SI and St in prior systems. However, only one sensor (S,) is used. The time diagrams in Fig. (3) show this relationship.

   The present invention was implemented in a breadboard built to prove the concept. A 25.watt 3.phase brushless DC motor was controlled using the Motorola MC33034P60 DC brushless motor controller IC. The motor had 3 Hall sensors separated by 30" (mechanical) but only one Hall sensor was utilized. The rotor had 4 permanent magnet poles which meant that 1 mechanical degree = 2 electrical degrees. The spacing between the sensor signals SI, SI and S3 was 8, and equal...