Discrete-time Analysis and Use of CVCR and SFBD type Current Regulators in Saturated Salient AC Machines

This paper analyzes the behavior of complex vector (CVCR) and state feedback (SFBD) type current regulators in discrete-domain that are commonly used in AC machines. This paper aims to: 1) provide an accurate discrete-time model of AC machine considering the effects of resistance, salient inductance, and stationary frame latched voltage, 2) provide unique insights into differences in command tracking, and dynamic stiffness properties of CVCR and SFBD type regulator structures in the discrete domain, 3) provide guidelines and a methodology to set virtual damping resistance, 4) provide an analysis of different current observer structures to mitigate the inherent delay in the control system and allow for noise immunity, 5) provide a method to use both CVCR and SFBD simultaneously to leverage the strengths of each regulator structure, 6) define and analyze a new metric, noise immunity, for CVCR and SFBD type regulator structures. Finally, the proposed controller is easy to tune, robust against parameter errors, well suited for saturated machines, well suited for low fundamental to sampling ratios, and has improved command tracking, dynamic stiffness, and noise immunity properties.