Small signal characterization of fluorescent lamps in dimmed operation

In recent bibliography, several small signal models for fluorescent lamps have been presented. These models are focused in the characterization of the lamp small signal dynamic impedance at nominal power level. This impedance can only be used to analyze the lamp-ballast interaction at nominal power. However, in dimming ballasts, the interaction between lamp and ballast can lead to system instability at reduced power operation. In present paper, the small signal model of a compact fluorescent lamp is obtained at different power levels. At each power level, the parameters of the single-pole, single-zero model are obtained. The static gain, pole and zero frequencies of the model are calculated and fitted to a power dependent polynomial expression. Using the generalized multi-frequency averaging technique the stability of a voltage controlled resonant inverter is analyzed. The stability margin of the system is calculated using the proposed model and verified using an experimental prototype.