Department of Electrical Engineering, Southern Taiwan University Initial Rotor Position Estimation for Sensorless Brushless DC Drives Student: G-E Lin Adviser: Ming-Shyan Wang Date : 25th-Dec-2009 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 4, JULY/AUGUST 2009

Department of Electrical Engineering, Southern Taiwan University 2 Outline Abstract I. INTRODUCTION II. PROPOSED INITIAL ROTOR POSITION ESTIMATION METHOD A. Inductance Comparison Process B. Polarity Determination Process III. EXPERIMENTAL RESULTS IV. CONCLUSION REFERENCES

Department of Electrical Engineering, Southern Taiwan University 3 Abstract This paper presents a method for determining the initial rotor position of a brushless dc machine at standstill without a position sensor. The key principle of the rotor position estimation is based on the simple de tection and comparison of phase voltage and current responses relating to t he stator inductance varied with the position of the rotor magnet. In the proposed method, only three voltage-pulse injections are applied, and a 30 ◦ resolution can be achieved. Moreover, no knowledge of machine parameters is required.

Department of Electrical Engineering, Southern Taiwan University 4 I. INTRODUCTION brushless dc (BLDC) motors are widely used in a number of industrial applications because of their high power density, durability, high efficiency, silent operation, and high starting torque. An inverter-driven three-phase BLDC motor, as shown in Fig. 1, needs rotor position information to ensure stable operation by synchronizing the phase excitation to the rotor position. Startup is one of the major problems in sensorless BLDC drives, which are mostly based on back-electromotive-force (EMF) estimation techniques. The main reason is that the back-EMF voltage disappears at standstill. To solve these startup problems, the initial rotor position should previously be determined. Most popular techniques to estimate the rotor position are based on the inductance variation, varying with the rotor position.

Department of Electrical Engineering, Southern Taiwan University 5 Fig. 1. Inverter-driven three-phase BLDC motor.

Department of Electrical Engineering, Southern Taiwan University 6 II. PROPOSED INITIAL ROTOR POSITION ESTIMATION METHOD The basic principle of estimating rotor position is based on the saturation effect of the stator core. The key principle of the proposed method for detecting the rotor position at standstill is to measure and then compare the stator inductance of each phase. The machine parameters are listed in Table I. Fig. 2 shows the measured current response and calculated inductance against the actual rotor position.

Department of Electrical Engineering, Southern Taiwan University 7 TABLE I PARAMETERS OF THE TESTED BLDC MACHINE

Department of Electrical Engineering, Southern Taiwan University 8 Fig. 2. Measured current response and calculated equivalent inductance versus the actual rotor position of a surface-mounted BLDC machine.

Department of Electrical Engineering, Southern Taiwan University 9 A. Inductance Comparison Process In this process, a sequence of two voltage pulses is injected to a pair of selected windings. As shown in Fig. 3, each voltage-pulse injection consists of two intervals. The first voltage pulse is injected to the phase-A and phase-B windings by turning “on” switches AH and BL, as shown in Fig. 3(a). Therefore, the voltage across the phase-B winding can be detected through the phase-C terminal and the negative dc bus. Its equivalent circuit is simplified, as depicted in Fig. 4(a).

Department of Electrical Engineering, Southern Taiwan University 10 Fig. 3. Switching states for the BLDC drive in Fig. 1 during the first volt agepulse injection. (a) Pulse-injecting interval. (b) Freewheeling interval.

Department of Electrical Engineering, Southern Taiwan University 11 Fig. 4. Terminal voltage detection. (a) Pulse-inj ecting interval of the first voltage-pulse injection. (b) Freewheeling interv al of the first voltage-pulse injection. (c) Pulse-injecting interval of the sec ond voltage-pulse injection. (d) Freewheeling interval of the second voltage -pulse injection.

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Department of Electrical Engineering, Southern Taiwan University 18 B. Polarity Determination Process

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Department of Electrical Engineering, Southern Taiwan University 22 IV. CONCLUSION A simple initial rotor position estimation method at standstill has been introduced in this paper. It is based on the stator inductance variation due to the influences of the saturation of the stator iron and the flux due to the position of the rotormagnets. In the proposed method, only three narrow voltage pulses have been applied to the phase windings to determine the rotor position, and a 30 ◦ resolution has been achieved. Additionally, only one sensing resistor has been added into a typical BLDC drive. It is particularly suitable for sensorless BLDC drive applications in which low cost is the major requirement.Moreover, no machine parameters are required.

Department of Electrical Engineering, Southern Taiwan University 23 References [1] STMicroelectronics, Application Note AN1276 BLDC Motor Start Routine for the ST72141 Microcontroller. [Online]. Available: [2] S. Ogasawara and H. Agaki, “An approach to position sensorless drives for brushless DC motors,” IEEE Trans. Ind. Appl., vol. 27, no. 5, pp. 928–933,Sep./ Oct [3] P. B. Schmidt, M. L. Gasperi, G. Ray, and A. H. Wijenayake, “Initial rotor angle detection of a non-salient pole permanent magnet synchronous machine,” in Conf. Rec. IEEE IAS Annu. Meeting, New Orleans, LA, 1997,pp. 459–46 3. [4] G. H. Jang, J. H. Park, and J. H. Chang, “Position detection and startup algorithm of a rotor in a sensorless BLDC motor utilizing inductance variation,” Proc. Inst. Elect. Eng.—Elect. Power Appl., vol. 149, no. 2,pp. 137–142, Mar [5] W.-J. Lee and S.-K. Sul, “A new starting method of BLDC motors without position sensor,” IEEE Trans. Ind. Appl., vol. 42, no. 6, pp. 1532–1538, Nov./Dec [6] Y.-S. Lai, F.-S. Shyu, and S. S. Tseng, “New initial position detection for three-phase brushless DC motor without position and current sensors,” IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 485–491, Mar./Apr [7] J. Sugawara, T. Kaimori, and S. Nichikata, “A novel and simple initial rotor position detecting method for PMSMs,” in Proc. IEEE PEDS, 2005,pp. 612–61 7.

Department of Electrical Engineering, Southern Taiwan University 24 Thank you for your attention.