Sub Line-Frequency Stability Analysis of Single-Phase Constant Power Loads Using Envelope Impedance

Regulated constant power loads present an incremental negative input impedance that can destabilize the interconnected system. With ac, power-factor corrected (PFC) constant power loads, instabilities can arise from a dynamic instability between the source and load impedance. The dynamics involving a rectifying interface are nonlinear and evade classical impedance and stability analysis. Several efforts have been made to understand and characterize the important dynamic interaction between ac PFC converters and ac sources. This article unravels this work to present a useful model for an ac PFC converter and a tunable controller that can stabilize source–load interactions. Specifically, an envelope impedance technique is developed for analyzing ac source and PFC load. This article also demonstrates an instability arising from incompatible source and load envelope impedance in hardware, and a variable bandwidth constant power load that can correct the instability.