Patent ID: 7956637

Claim:
A motor efficiency monitoring system comprising: a processor programmed to: determine an instantaneous efficiency of an electric motor under load while the electric motor is online, wherein the instantaneous efficiency is based on a determination of stator winding resistance and an input voltage and an input current; and wherein the determination of motor efficiency is independent of a rotor speed measurement, and wherein the determination of the stator winding resistance occurs while the electric motor under load is online; wherein the input voltage and current are determined at least two different load points; and wherein the processor is further programmed to: acquire a set of parameters based on the at least two different load points, wherein the set of parameters comprise a core resistance, a rotor resistance, one of a magnetizing inductance and a magnetizing reactance, and one of a stator leakage inductance and a stator leakage reactance; determine an equivalent circuit based on the acquired set of parameters, wherein the equivalent circuit has a stray-load resistor; and estimate an output power from the equivalent circuit.