Control Of Permanent Magnet Brushless Dc Motor Without Position Sensor

The availability of high performance magnets, like samarium cobalt and neodymium-boron-iron, has made it possible to improve the performance of brushless dc motors significantly. Design engineers now selecting PMBLDC motors over conventional dc or induction motor drives for the following reasons; 1) The absence of brushes results in an essentially maintenance free operation and eliminates the undesirable effects of commutation such as sparks, brush-loss, radio-frequency interference, etc. 2) The low inertia of the rotor enhances the quality of the mechanical response of the motor, shortening the acceleration and deceleration time. 3) Utilizing rare-earth permanent magnet materials with high coercive force results in substantially higher efficiency than their counterpart with brushes of the same size. 4) Because of the absence of commutation segments, the stator construction is simple.For the sake of harsh installation, lower endurability and harsh working environment, the use of BLDCM is limited.In this paper, the theme is the back electromotive force detection. This paper analyzes two EMF methods based on a lot of documents, and point out the errand and compensation of these two methods. Especially for the Integrated phase detection, give an alternative solution which uses the Digital potentiometer to replace the fixed resistor. This solution widen the application of the BLDCM.