With the widely use of Permanent Magnet Brushless DC Motor (BLDCM) in many fields, the superiority in the control method of position sensor-less is more and more obvious. In this paper several control methods of position sensor-less for BLDCM are presents, and a novel technique, the method of speed-independent position function, is introduced to detect the rotor position of BLDCM. This method may detect the rotor position from almost zero speed to high speed, and may also give the commutation time.
The principles and characteristics of the sensorless brushless DC motor rotor position detection were analyzed by using inductive method and third harmonic back-EMF detection method. A composite rotor position detection method was proposed in full speed range (including zero speed). At zero speed (static state) inductive method was used to determine the initial rotor position, and it was bases of starting and controlling for the brushless DC motor; at low speed third harmonic back EMF detection method was used. Analysis shows that the composite test method can estimate the rotor position, and it is to achieve the position sensorless brushless DC motor to run a viable method.
Combined Discrete Space Voltage Vector with Direct Torque Control for Bearingless Brushless DC Motor and Closed-Loop Suspended Force Control