Optimal vector control of pumping and ventilation induction motor drives

An original speed control for centrifugal pump and fan drives with squirrel-cage induction motors that seeks the maximum energy saving is proposed. The strategy is based on minimizing the motor and converter losses at the steady state and minimizing the transient time that the motor employs in passing from one steady stage to another. The shortest transient time is achieved by applying the Pontriagin's maximum principle taking into account the parabolic load torque-speed dependence of these types of drives. Short-time transients, which take the motor from one point of maximum efficiency to another, contribute to reduce losses and to extend the application of the energy-saving concept to the drives with frequent changes of load torque and speed.