Online Maximum Torque per Ampere Control for Doubly-Fed Induction Machines

This paper introduces a control approach to optimize the ratio of the torque to the total input current in windings of the doubly fed induction machine (DFIM). Essentially, this strategy aims to share the currents more evenly between stator and rotor windings to achieve a specific torque level. Due to constraints imposed by the flux and the frame alignment, the angles of rotor and stator currents are interrelated. Consequently, a fundamental relationship is established between these angles, so the total current magnitude in terms of the rotor current angle is expressed. The optimal angle required to implement the maximum torque per total Ampere (MTPTA) control strategy is then determined using a numerical minimization process. Additionally, the maximum torque per inverter Ampere (MTPIA) strategy is proposed in this paper, which is demonstrated by minimizing the rotor current magnitude while maintaining a constant rotor current angle for a given torque level.