Negative incremental impedance and stability of fluorescent lamps

Fluorescent lamps have a special V-I characteristic. Their incremental impedance is defined and studied in the frequency domain. It is found that the negative incremental impedance of a fluorescent lamp can be characterized by a right half plane zero. The existence of such a result is explained by the modified Francis equation. Two ballasting approaches, series impedance and close-loop operation, are proposed to stabilize lamp operation. Stability criteria based on the Nyquist criterion are developed for both approaches.