Reliable starting method for sensorless brushless dc motor drive

With features such as high power density, high efficiency and reliability, speed controllability over a wide range, maintenance-free, etc., brushless dc motors driven by sensorless drive are extensively used in industrial equipments, automotive parts, and domestic appliances. The techniques of open-loop starting and the transfer from open-loop to closed-loop commutation are key issues for the design of highly reliable sensorless drives. This paper presents two cost effective and highly reliable methods which can successfully transfer from open-loop starting to closed-loop commutation. Theoretical analyses and various experiments reveal that the proposed methods can effectively solve problems such as time-consuming trial and error tuning during open-loop starting interval, common-mode noise of neutral point, complex phase shift computation, and influence by external load, which often happen in sensorless drives of brushless dc motors.