Envelope impedance: Theory and applications

Various power electronics systems, such as resonant converters, motor drives, and electronic ballasts for fluorescent lamps, are driven by carriers of relatively high frequency as compared to the control bandwidth. In these cases, the small signal response relevant to the feedback network design is embedded in the envelope of the signals rather then in the carrier. In this study, a systematic procedure for deriving the Envelope Impedances (EI) of elements and sub systems was developed. The proposed method is based on phasor transformation by which the carrier is eliminated, leaving only the low frequency components. It is demonstrated, by analyzing passive elements and sub circuits, that the EI parameter could help to better understand and analyze carrier driven systems and may lead to new applications. The predictions of proposed method were verified against experimental measurements.