MPC based Current Sharing for Maximum Torque Dynamics in Efficiency Optimized Field Oriented Induction Machine Control

Efficiency optimized induction machine control is achieved by reduction of the flux linkage at light loads. This has negative effect during torque transients. Before an increased torque can be produced, flux linkage has to be built up which is limited by the rotor time constant. Transient torque response can be improved by boosting the flux linkage with a high current for a short time. However, a maximum inverter current limit exists which is a mutual constraint for the flux-producing and torque producing current components. Known current sharing methods usually apply a constant flux-boosting current or only consider the next controller sampling time instant for optimization which leads to a non-optimal current trajectory. Aim of this paper is a full optimization of the current trajectory considering the whole transient process between two steady-state operating points. This is achieved by a model predictive approach with a prediction horizon in the range of the rotor time constant. The optimal trajectories are calculated offline and are analyzed to formulate a general optimization function which can be implemented on a microcontroller for real-time operation.