Sensorless Control Of BLDC Motor Based On The Variation Behavior Of Winding Inductance

In brushless DC motor (BLDCM), rotor position sensor is used to detect the rotor position to realize the commutation of three-phase currents. However, because of some disadvantages of the position sensor itself, the application of BLDCM is somewhat limited in some special occasions. Therefore, more and more attention is paid to sensorless control technology of BLDCM.According to the disadvantages of sensorless control technology, some intensive research has been done in the paper which is based on the variation characteristics of winding inductance. This strategy can help estimate the commutation moments precisely when the motor runs at low speeds. The proposed method is also combined with core saturation effect, which presents a novel method which can be used to estimate the rotor position range in the stationary state.The research in this paper starts from the effects of rotor’s saliency and core saturation on winding inductance, analyzes the variation characteristics of winding self inductance and mutual inductance. Meanwhile, the particular equivalent relationships between self inductance and mutual inductance and consequently voltage relationships, caused by the symmetrical characteristic of motor structure, parameter and distribution of magnetic field, are expounds at some special electrical angles according to the approximate expression of winding self inductance and mutual inductance. Also, the principles and derivation of the proposed method are given. In addition, core saturation effect, combined with the proposed theory, is applied into the initial rotor position estimation. In the new method, four PWM pulses are orderly injected to the windings and the rotor position can be determined within the range of 30 electrical degrees. This method can not only estimate the rotor position in the stationary state and at low speeds, but also reduce the requirements for the processor and transducer.In this paper, the experimental prototype is built, and the experiment is performed to verify the effectiveness of the proposed method. The experimental results show that the novel method can estimate the rotor position in the stationary state. In addition, the commutation signals can be obtained within low speed range. The error between the estimated and actual values is very small, which verifies the availability and feasibility of the proposed method.