Magnetic saturation effect in the achievement of wide speed range control for induction machine

The problem of induction machine speed control is considered. Most previous works considered the machine magnetic characteristic to be linear and the flux reference to be constant. Generally, the constant flux reference is given the flux nominal value located in elbow zone of the magnetic characteristic. Doing so, the machine operation mode is not optimal in presence of small load torques. Similarly, if the flux reference is given a small value, the machine operation is again not optimal in presence of large load torques. As a matter of fact, an optimal operation mode can not be achieved with a constant flux reference. But, varying flux control strategies can not be designed without accounting for the nonlinearity of the machine magnetic characteristic. In the present work, we precisely develop a speed control strategy based on a machine model that accounts for the magnetic characteristic saturation. A speed controller is designed using a nonlinear design technique. The performances of the developed control strategy are formally analysed and their supremacy with respect to standard control solutions (assuming linear magnetic characteristic) is illustrated through simulation.