Design optimization of inverter fed 3-phase squirrel cage induction motor

Static inverter fed induction motor drive is an important competitor in the field of variable speed drives. Design optimization of a six-stepped three-phase inverter fed squirrel cage induction motor for minimum cost and maximum frequency operation is presented in this paper. Additional winding loss, core loss, stray loss and torque pulsations produced by harmonic voltages over a frequency-range that influence the design parameters are considered as constraints. In addition many important constraints at minimum frequency such as no-load power factor, locked rotor current and at maximum frequency pullout torque etc., are imposed to satisfy the performance characteristics. Nonlinear programming technique (NLP) employing Powell's unconstrained optimization method together with Zangwill's exterior penalty function formulation is applied to a mathematical model of an inverter fed 3-phase squirrel-cage induction motor with 11 design variables and a number of performance constraints. The optimal solution by this method efficiently proved the design optimization procedure adopted in this paper satisfying the constraints to predict the machine performance.