Controlled HID Lamp-Ballast Interaction for Low-Frequency Square-Wave Drivers

High intensity discharge lamps are typically operated at low frequency to avoid damage from acoustic resonance. Accordingly, an electronic ballast normally comprises a buck converter to control the lamp current magnitude and a full-bridge to commutate the lamp current at a low frequency. In such a system, the negative dynamic lamp characteristic may interact with the power electronic driver may give a poorly damped response, sometimes resulting in an oscillatory lamp current. Furthermore, lamp aging and reduced power mode operation both tend to increase re-ignition voltage overshoot, which in turn may lead to reduced lifetime, or prematurely extinguishing lamps. In the present paper, a procedure for obtaining the small-signal dynamic characteristics of metal halide lamps is proposed. Using this dynamic model, the lamp-ballast interaction is simulated and analyzed. A fuzzy-logic control method is presented to cope with nonlinear behavior and improve the lamp-ballast performance. The simulation results are verified with practical measurements on a laboratory prototype