A variable inductor MATLAB/Simulink behavioral model for application in magnetically-controlled electronic ballasts

In magnetically-controlled electronic ballasts, in order to perform the lamp start and dimming, the typical resonant inductor is substituted by a variable inductor. This variable inductor is controlled by a dc current, which modifies the resonant tank in order to vary the rms value of the lamp current and thereby the luminous output. In order to perform optimization studies, computational models, which accurately simulate the real behavior of the fluorescent lamp and the variable inductor, in magnetically-controlled electronic ballasts, are extremely necessary. Traditionally, they are implemented in circuit-simulation programs, such as SPICE-based programs. In this paper it is demonstrated how a MATLAB/Simulink compatible behavioral model of a variable inductor can be developed easily using simple laboratory measurements. The resulting model includes coil losses but not temperature effects. Design criteria and practical verifications are included to confirm this model. Theoretical predictions are verified with the experimental results for a 36 W TLD Philips fluorescent lamp which has also been previously tested and modeled experimentally, in order to derive the dimming characteristics.