An Examination of Inductance Matrices and Winding Factors of Pole-Changing Induction Motor with Pole-Amplitude Modulation

Pole Changing from 8-pole to 6-pole by Pole-Amplitude Modulation

Abstract

A pole-changing induction motor with pole-amplitude modulation (PAM) has a single-winding system, and has a unique speed ratio other than 1: 2. It provides an excellent energy-saving property when used for the flow control system of pumps and blowers. This, therefore, has attracted considerable attention in a field of flow control design.
However the method of conversion from an 8-pole to a 6-pole induction motor by using this PAM becomes complicated compared with the method of conversion to a 10-pole motor. In addition, the induction motor designed by this approach is likely to be affected by large harmonic magnetomotive forces, and therefore needs careful investigation in the design.
This paper describes the harmonic torque prevention approach done by using the unified theory of electrical machinery for the case of 8-pole to 6-pole conversion by PAM. From the result of analysis and speed-torque experiment, it is shown that this induction motor is driven by the negative-phase revolving magnetic field due to the 3rd order harmonic, and that there appear 13th harmonic asynchronous crawling torque in motor region and 11th harmonic asynchronous torque in braking region. It is also shown that a long-pitch winding with a machine angle of 8/24 is recommended for the motor design so that the 11th and the 13th harmonic torques are removed.