A Novel Technique to Arrest Unbalanced Magnetic Pull due to Conical Motion in Three Phase Induction Motor using Feedforward Control

All rotating electrical machines have air gap between their stator and rotor, the length of which is usually kept very small, to facilitate a better flux path. However this aggravates problem of unbalance magnetic pull (UMP) due to rotor eccentricity which in course of time may lead to rotor-stator rub contact. This paper discusses a numerical technique of determining UMP in a three phase induction motor with rotor static eccentricity. A multi-slice method is also detailed whereby the cumbersome task of 3D finite element (FE) analysis can be simplified, while handling conical motion of rotor. FE analysis is utilised to determine the UMP developed under various static eccentricity conditions, the values of which are further used to design a feedforward controller to minimize conical rotor eccentricity of the rotor. The proposed control scheme can be implemented by incorporating Active Magnetic Bearings (AMB) for the machine. The control scheme of a three phase induction motor with a PID and feedforward controllers along with AMB is detailed in the paper.