where τ ref e is the torque reference, τmax e is the maximum torque, and sgn(・) is the signum function.
The selection of τmax e depends on the converter rating. Unlike motors, converters generally do not have a short-term overload capability. Consequently, to permit short-term overload and faster transient response, a converter with a higher rating than the motor is often selected, which allows τmax e to be set up to 3τnom during transients [33]. Above base speed, i.e., in the field-weakening region, τmax e is reduced approximately as the inverse of the speed [6], [34], [35].