New form of composite-rotor induction motor for fan drives

A new form of composite-rotor induction motor for variable-voltage fan drives is described. The rotor incorporates a section of unlaminated steel and a conventional cage winding, and is of very simple constructional form. It is designed to achieve reduced values of maximum input current and losses, by virtue of the variation of its effective rotor impedance as a function of applied voltage. The principle of its design and operation is explained and theoretical analyses of its performance are presented. Results are given for a prototype fan drive delivering 2.25 kW output at 1400rev/min, showing stable operation and acceptable maximum losses. Computed results correlate well with those measured.