Commutation point estimation for sensorless brushless DC motor using back-electromagnetic force change rate by least-square method

A new commutation point (CP) estimation method for a high-speed sensorless brushless motor using the back-electromagnetic force (EMF) change rate is proposed. Typical CP estimation methods may not work correctly either at high speed when the number of sampled data is not enough or at low speed when the back-EMF voltage is weak. In the proposed method, the back-EMF voltages are measured using an analogue-to-digital converter. The back-EMF voltage change rate is calculated from the measured values and utilised to estimate the CP by employing the least-square method. The experimental results show that the proposed estimation method works correctly over a wide speed-range operation.