Electronic Ballast for High Pressure Sodium Lamps without Acoustic Resonance via Controlled Harmonic Injection Synthesized with PWM

This paper presents a study and analysis of a electronic ballast for high pressure sodium lamps followed by simulation and experimental results. The acoustic resonance control technique consists in the injection of current harmonics fed to the lamp, which are synthesized by the full bridge inverter via PWM through an LC filter. The controlled harmonic spectrum of current supplied has been used in order to avoid acoustic resonance. Another interesting feature of this approach is the reduction of the crest factor of the lamp current. Acoustic resonance happens when the inverter is operating in high frequency, which has certain advantages as the use of smaller and less costly passive elements, although the switching losses increase and acoustic resonance may occur. The use of currents with harmonics is a way of avoiding the excitation of this resonance due to the frequency spread. The LC filter design is also presented, which allows the desired harmonics to pass with controlled amplitudes, while filtering undesired high frequency components. Furthermore, simulation and experimental results of the proposed electronic ballast are presented to verify the analytical discussions and the design specifications