Indirect Maximum Torque per Ampere control of induction motor drives

A novel control technique is proposed aimed to efficiency optimization in scalar controlled induction motor drives. The proposed approach consists in modulating of the value of the magnetizing flux according to the load. Differently from other optimization methods, the proposed approach is based on a constant-optimal slip control, and then the model of the machine is not required to evaluate the power losses, avoiding any inaccuracy due to imperfect tuning of the motor parameters. The algorithm is based on an intuitive adaptation of the well known maximum torque per ampere (MTA) control into a proper scalar control scheme able to ensure a constant-optimal slip value for efficiency optimization. The proposed control scheme is implemented using the same hardware resources as those required by conventional constant V/f or slip control implementation. An experimental evaluation has been accomplished on a 5 Hp induction motor drive in order to evaluate the efficiency improvement and dynamic response of the proposed method.