On the drivability of DC brushless motors with faulty hall sensors during braking maneuvers

Brushless DC motors are now a standard for many engineering applications. To work properly, they need to be controlled based on rotor angle position, usually retrieved by a set of three Hall sensors. Their breakdown can be detrimental, not only in all the cases in which maintenance stops result in economic losses but especially for safety critical applications, where functionality must be always ensured. This paper investigates the drivability of such motors with a reduced number of Hall sensors for vehicles equipped with electronic brakes. A drivability bound is mathematically derived for a three-phase Brushless DC motor, whose phase voltages and currents are not known. An angle estimation algorithm, merging electrical measurements and available Hall sensors, is proposed. Experimental results are finally provided on bicycles braking maneuvers to further support the proposed study.