Patent ID: 8326502

Claim:
A method for estimating electric motor RPM based on a computed Back Electromotive Force (BEMF) of the electric motor, the method comprising: obtaining RPM versus the BEMF data for the electric motor comprising: rotating the motor shaft of the electric motor over an RPM range covering the normal operating range of the electric motor; measuring BEMF versus RPM over the RPM range; and recording the BEMF versus RPM data for later real time use; estimating a real time BEMF of the electric motor during the later use of the electric motor, comprising: measuring a motor voltage at electric motor terminals; measuring a motor current through the electric motor corresponding to the motor voltage measurement; computing IR loss by multiplying the motor current times a dynamic internal resistance of the electric motor; and computing the BEMF by subtracting the IR loss from the motor voltage; estimating the electric motor RPM by comparing the real time BEMF to the recorded BEMF versus RPM data; and providing the estimated RPM to an intelligent controller to optimally control the motor.