Current and flux regulation in field-weakening operation [of induction motors]

Field-weakening techniques have been developed which provide maximum torque capability above rated speed. Unfortunately, most of these techniques are valid only for steady-state operation and show significant sensitivity to DC-bus voltage and machine parameters. This paper analyzes the requirements of dynamically providing maximum torque under field-weakening operation. Three major issues are addressed: current regulator design; saturation techniques for current regulators in order to ensure best performance under voltage constraints; and flux regulator design to minimize transient errors when varying flux. Maximum DC-bus utilization through the proper use of saturation techniques, dynamic response and reduced sensitivity are the advantages of the proposed solution.