Variable frequency drives (VFDs) completely change the power conditions and efficiency of connected motors. Due to insufficient data, energy simulation programs, such as EnergyP/us, directly use manufacturer efficiency data by ignoring VFD impacts. The paper is to validate an approach to convert manufacture efficiency data to actual motor efficiency with VFDs using the equivalent circuit method. First the motor circuit parameters are estimated based on manufacturer data; and then applied to simulate the motor efficiency with VFDs, which is validated by the measured efficiency. The result shows the approach can effectively calculate the motor efficiency with VFDs using manufacture data.