Optimized control of high-performance servo-motor drives in the field-weakening region

Magnetic saturation may cause the inductance of a servo motor to deviate from values defined during the design of a drive's control system. Modern servo-drives are equipped with field-weakening strategies that control the trajectory of the motor's current vectors to produce the optimum levels of torque within the defined limit of current and voltage. The objective of this paper is to develop a 'plug and play' control scheme to integrate industrial inverters and machines without extensive characterization of the matched set, while operating within the operating specifications of the drive components. In this paper, an approach to torque optimization is presented in which the motor-terminal voltage-vector magnitude is regulated at high motor speeds while producing torque-optimizing current-vector commands. This method differs from other field-weakening solutions due to the active control of the voltage vector trajectory on the dq-voltage plane across an extended motor speed range. In a decoupled cascaded control strategy, the voltage-control loops produce current-vector trajectory commands in order to realize the voltage set points. The resulting current vector continuously conforms to the defined voltage and current limits of the servo drive without characterization of magnetic saturation. Results of the successful hardware implementation of the method in an industrial drive are presented.