Study of New Start Method for Position Sensorless Brushless DC Motor

Abstract

A lot of brushless DC motors are adopted in the compressor of the air conditioner and the refrigerator because of the maintenance-free and highly effective. And, sensorless drive using back electromotive force (EMF) is widely used for these motor controls.However, it is very difficult to apply the sensorless drive at the start sequence because the EMF is too low to detect. Therefore, an open loop drive that controlled by fixed switching pattern is used at the start sequence. After acceleration up to the appropriate speed, the drive method switches to the sensorless drive from the open loop drive.This start sequence has some problems. The motor output torque and the rotational speed change greatly when the motor is driven by an open loop control, and it causes the vibration. Furthermore, it is important to adjust the switching patterns of the open loop appropriately. If it is not adjusted appropriately, the switch to the sensorless drive may fail.In this paper, we propose new start method suitable for sensorless brushless DC motor drive systems. The proposed method introduces new switching patterns at the start point. The switching patterns are determined by motor parameters. Using this method, the open loop drive sequence can be eliminated. Fig. 1 shows the simulation result of the motor output torque and the rotational speed of conventional open loop start method.The motor output torque and rotational speed change greatly and the vibration occurs after the start. Fig. 2 shows the simulation result of the motor torque output and the rotational speed of new start method.The motor output torque and the rotational speed are smooth from the start. Fig. 3 shows the experimental result that shows applied voltage and the motor current waveform at the start. The smooth acceleration is obtained using the proposed method. As mentioned above, we has proposed new start method for brushless DC motors. Rapid acceleration and high performance can be achieved. The simulation and experimental results demonstrated the validity of the proposed method.

Position-sensorless control method at low speed for permanent magnet synchronous motors using induced voltage caused by magnetic saturation

“…The position sensorless drive methods based on the back electromotive force (EMF) have been widely used for permanent magnet synchronous motors (PMSMs) (1) (2). However, these methods cannot detect the rotor position at low speed.…”