IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 39, NO. 2, MARCH/APRIL 2003 485 New Initial Position Detection Technique for Three-Phase Brushless DC Motor Without Position and Current Sensors Yen-Shin Lai, Senior Member, IEEE, Fu-San Shyu, and Shian Shau Tseng Abstract—This paper presents a new detection technique of ini- tial position for a three-phase brushless dc motor which does not require any current and position sensors, and thereby significantly reduces the cost. The fundamental principle of the technique is to determine the initial position of the permanent magnet by the time periods of discharge of stator windings, which are excited before discharge. As compared to previous approaches, the pre- sented technique does not cause any rotation during detection, and it is therefore very promising for particular kinds of applications, which do not allow the motor to rotate potentially in the wrong di- rection during initial position detection, e.g., electrical vehicles. As compared to earlier techniques, the presented technique dramat- ically simplifies the detection procedures and cost. Experimental results derived from a field-programmable gate-array-based con- trol system will be presented to demonstrate the feasibility of the presented technique. Index Terms—Brushless dc motor (BLDCM). I. INTRODUCTION I N GENERAL, a three-phase brushless dc motor (BLDCM) consists of permanent magnet and excitation windings. The initial position of the permanent magnet and excitation decide the rotation direction at the moment of startup. Fig. 1 shows the structure of a particular kind of BLDCM. As shown in Fig. 1, the rotor of motor has 12 poles and the stator has nine slots, and the voltage is fed to the stator via a three-phase inverter as shown in Fig. 2. The dc-link voltage is connected to the stator windings to create a field, which is perpendicular to the rotor field produced by the permanent magnet, in order to derive maximum torque and the specified rotational direction. This feature is achieved by proper commutations of inverter, which acts as a commutator and brush of conventional dc motors, once the position of the permanent magnet is known. Therefore, the initial position of permanent magnet should be clearly identified for proper commutation control to avoid po- tentially wrong direction of rotation at the moment of startup. Paper IPCSD 02–083, presented at the 2002 Industry Applications Society Annual Meeting, Pittsburgh, PA, October 13–18, and approved for publica- tion in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Industrial Drives Committee of the IEEE Industry Applications Society. Manuscript sub- mitted for review June 1, 2002 and released for publication January 4, 2003. This work was supported by Hitachi Micro System Asia (HMSA) Pte. Ltd. Y.-S. Lai and F.-S. Shyu are with the Department of Electrical Engineering, National Taipei University of Technology, Taipei 106, Taiwan, R.O.C. (e-mail: yslai@ntut.edu.tw). S. H. Tseng was with the Department of Electrical Engineering, National Taipei University of Technology, Taipei 106, Taiwan, R.O.C. He is now with Machvision, Inc., Hsin Chu, Taiwan, R.O.C. Digital Object Identifier 10.1109/TIA.2003.809450 Fig. 1. Illustration of a BLDCM. Fig. 2. Block diagram for a three-phase BLDCM drive. Since the initial position detection of the BLDCM is essential for particular kinds of applications, such as an electrical scooter, several techniques [1]–[6] have been presented to detect the ini- tial position of the BLDCM. Some of these techniques either re- quire position sensors (Hall sensors) or current sensors, or may cause backward rotation. To cope with the above-mentioned issues, this paper presents a novel initial position detection technique for BLDCM drives, which does not require any current and position sensors, and thereby significantly reduces the cost. Moreover, the presented technique does not cause any rotation during detection, and it is therefore very promising for particular kinds of applications, which do not allow the motor to rotate potentially in the wrong direction during initial position detection, e.g., electrical vehi- cles. As compared to the techniques shown in [4]–[6], the pre- sented technique dramatically simplifies the 0093-9994/03$17.00 © 2003 IEEE