Abstract: The three-rotor single phase variable voltage and speed motor possess the advantages of simple control, low price, and a wide range of variable speed, particularly good condition for heat scatter in lower speed running. The stator of the motor is similar to that of general three phase induction motor, whereas the rotor adopts the compound strucuture including main, cup, and fan rotors. Therefore, magnetic circuit in stator side is common, and divided into two in rotor side, thus making analysis calculation uncommon. This paper describes the running principles, the structures of the motor, the magnetic circuit structure, equivalent eletric circuit, the finite element analysis of a cup-rotor resistance and the calculation of T-S curve. Thus, the calculation and measurement of a test motor are proceeded with a satisfactory result.

Key words: variable voltage and speed motor, equivalent electric circuit, cup-rotor, T-S