A Novel Technique for a DC Brushless Motor Having No Position Sensors

Abstract

A DC brushless motor is a kind of a synchronous motor driven by the inverter and needs sensors to detect the rotor position. As one of the methods, the induced voltages of a brushless motor have been utilized practically. However, there are some problems in this method, such as the motor can get insufficient torque on account of the low induced voltages in a low-speed range.
This paper proposes a new method which controls the inverter angular frequency ω₁, by using inherent characteristics that the torque current i_r, is almost proportional to the internal phase angle φ where the primary flux of a synchronous motor is controlled to be constant.
If the parameters of a motor are given exactly, the speed regulation is quite little and the transient characteristics with high response and high starting torque are obtained. Furthermore, it is possible to operate a synchronous motor in the field weakening range.
Here, the principle of the control method and the performance characteristics of a DC brushless motor having no position sensors are discussed. The simulation and the experimental results of the tested machine show that the proposed method is very useful for practical applications.