Envelope Impedance Modeling of Line Frequency Rectifiers

Abstract

This article examines a powerful way to analyze the interactions between ac-side and dc-side impedances interfaced by a rectifier: envelope impedance. Envelope impedance has allowed for the application of traditional stability analysis techniques to industrially-relevant power electronic systems, such as power-factor-corrected constant-power-loads, where complex nonlinear dynamics prevent the use of other common methods like small-signal approximations. Questions persist regarding when envelope impedance should be used for stability analysis as opposed to traditional single-frequency perturbation methods. This article provides a comprehensive analytical formula for mapping the dc-side impedance of a rectified load to the ac-side input envelope impedance of the rectifier. This formula is validated against the predictions of time-domain simulations and experimental measurements. A practical and measurable definition of envelope impedance and justification for its use over traditional single-frequency small-signal approaches in stability analysis are provided.