Characteristics Measurement of Electric Motors by Contactless Eddy-Current Magnetic Coupler

Torque-speed characteristics measurements are essential in the design and manufacture of electric motors. Dynamometers have been widely used in motor characteristics measurements, and the coupling between the motor under test and dynamometer is a critical issue for high-power electric motors. This paper develops a contactless measurement system, which consists of a permanent magnet (PM) coupler and requires no dynamometer. The torque of the PM coupler is transmitted by the eddy-current and controlled by the air gap inside the coupler. An equivalent circuit model of the magnetic coupler is derived theoretically and then verified experimentally under different operating conditions. The capacity of the proposed measurement system can also be determined in order to provide sufficient and accurate measurement information for the tested motors. A 1.5 kW dc motor with a maximum torque of 8.15 N-m was tested as an illustrated example. The experimental results are given to show the effectiveness of the proposed approach.