Symmetric DQ Control of Saturated Salient AC Machines - Utilizing Targeted Time Constant Virtual Resistance and Complex Vector Flux-Linkage Regulation

Abstract

This paper presents a high-performance discretetime current and flux-linkage regulator for control of salient (i.e., asymmetric) AC machines. First, a linearized operating point model of an asymmetric AC machine is presented. Then, the operating point model is used to derived closed-form solutions for the virtual damping resistances required to modify the asymmetric plant of the AC machine to be virtually equivalent to that of a symmetric machine. Next, the obtained virtual damping resistances are paired with a symmetric complex vector style flux-linkage regulator for closed-loop control of current and flux- linkage. Finally, an intuitive flux-weakening regulator is proposed to ensure controlled operation of the flux-linkage regulator at the voltage limits of the system. When compared to existing current regulators for asymmetric AC machines, the regulator developed in this paper: 1) is less parameter sensitive, 2) has improved dynamic stiffness properties, 3) is easier to implement and tune, 4) is well-suited for all levels of machine saturation, 5) is well-suited for low sampling-to-fundamental frequency ratios, and 6) lends itself to complex vector and discrete-domain analysis.