Magnetic Pole Position Detection Method and Control of Brushless DC Servomotor with Incremental Encoder

On startup of a brushless DC servomotor, it is necessary to detect of its magnetic pole position, to generate the torque effectively. Numerous brushless DC servomotors provide a high angle resolution encoder for the speed control and position control. It can use as a magnetic pole position detection, too. There are the absolute encoder and the incremental encoder. If a brushless DC servomotor provides an absolute encoder, the motor can startup, because it is necessary to detect of its absolute position for the magnetic pole position detection. However, it is not used except uses of demands for high accuracy because the encoder is expensive. The incremental encoder in general use cannot detect the magnetic pole position when the motor starts, and so it demands an exclusive magnetic pole position sensor till a standard signal output of the encoder.This paper describes a method of the magnetic pole position detection of a brushless DC servomotor with an incremental encoder only use the encoder without an exclusive magnetic pole position sensor. The feature of this method is that can detect the magnetic pole position with very little revolutions in a matter of minutes during the motor starts.