26-11-2012, 02:05 PM
Dual Winding Method of a BLDC Motor for Large Starting Torque and High Speed
1Dual Winding Method.ppt (Size: 289 KB / Downloads: 25)
Abstract
This paper presents a novel winding method and its inverter circuit to drive a brushless dc (BLDC) motor to high speed with large starting torque.
The proposed winding coils are composed of dual windings, i.e.,
main and auxiliary windings, and the proposed invertercircuit has
nine switches.
In the starting period, it energizes both main and auxiliary windings
in parallel connection to generate large starting torque.
After the motor is accelerated, the proposed inverter circuit is
automatically switched to energize main winding, which generates
small back-electromotive force, to reach high speed.
The proposed method is applied to the spindle motor of a hard disk driveand its effectiveness is verified through experiment.
Introduction
A BRUSHLESS dc (BLDC) motor has been widely used in the driving source of many precision electromechanical devices not only because it has high efficiency but also because it has good controllability.
[1]. The linear torque–speed characteristics of a BLDC motor make it easy to control its speed over the wide range. However, a BLDC motor cannot be run at high speed with large starting torque at the same time because its inherent back-electromotive force (EMF) is proportional to the speed. In order to run a BLDC motor at high speed, back-EMF constant is designed to be small in order to reduce the voltage drop due to back-EMF. However, it generates small
starting torque because back-EMF constant is identical to torque constant, and it consequently results in a long transient period. It is one of the drawbacks of a BLDC motor in high-speed applications.
Several researchers have addressed the driving methods to run the motor at high speed with large starting torque. Jang and Kim proposed a method to drive a BLDC motor at high speed with large starting torque by utilizing a bipolar-starting and unipolar-running algorithm.
DUAL WINDING METHOD AND ITS INVERTER CIRCUIT
Fig. 1 shows the proposed winding method and inverter circuit of the BLDC motor. The winding coils of each phase are composed of dual windings, i.e., main and auxiliary windings in parallel connection. The proposed inverter circuit can be controlled in such a way that the current flows in either main and auxiliary windings or main winding only.
PROTOTYPING AND EXPERIMENTAL VERIFICATION
The proposed BLDC motor and its inverter circuit are prototyped for a spindle motor of a hard disk drive (HDD). The operating speed is 10 000 r/min and the number of coil turns of the main and auxiliary windings are 25 and 50, respectively. The proposed inverter circuit is also developed as shown in Fig. 1, and its switching action is controlled by a TMS320F240 digital signal processor (DSP) from Texas Instruments.
Fig. 6 shows the measured torque–speed curves of the prototyped motor with the operation of dual windings and main winding. The proposed motor with dual windings has a starting torque of 15.9 mN m which is 60% larger than the motor operated by only the main winding. In the speed range lower than 6000 r/min, the main and auxiliary windings are energized to maximize the torque.