Patent ID: 7668690
Filing Date: 2010-02-23
Classification: G01P,H02P

Abstract:
1. A method for determining rotational position or speed of a mechanically commutated DC motor from motor current ripple due to commutation for controlling a motor driven power device, said method comprising the steps of: monitoring motor current of a mechanically commutated DC motor with a current sensor; detecting ripples in the motor current with a processor; calculating a ripple frequency based on time between two successive ripples with the processor; determining a ripple count between two successive frequencies with the processor; comparing the ripple count to a threshold value with the processor; determining an estimated ripple frequency from a motor model stored in a memory when the ripple count exceeds the threshold value; calculating a corrected ripple count from a ratio of the calculated ripple frequency and the estimated ripple frequency with the processor; and determining, with the processor, at least one of the motor position and the motor speed based on the corrected ripple count.