Stator flux oriented asynchronous vector modulation for AC-drives

Abstract

A vector modulation strategy (stator flux-oriented asynchronous vector modulation, of SFAVM) for voltage stiff pulse-width-modulation (PWM)-inverters in three-phase AC drives is presented. Switching between the voltage vectors is achieved on the basis of a desired trajectory for the state flux vector, which determines the airgap torque of the AC machine. This strategy with constant switching periods and duty cycles proportional to the voltage amplitude makes it possible to operate with a one-dimensional look-up table, conventional digital control schemes with constant sampling periods, and full synchronization between controllers and the switching process in the PWM-inverter. The fundamental current component can be obtained directly by sampling twice in each switching period without filtering, and the controller sampling period can be half the switching period, which makes it possible to exploit the maximum torque bandwidth of the AC drive. SFAVM is suited for fully digital fast response control of AC drives.<>