Design optimisation of the LCsCp resonant inverter to drive 1 kW high-pressure sodium lamps

A novel design optimisation for the half-bridge series-parallel (LC_sC_p) resonant inverter used for high-power high-pressure sodium (HPS) lamp electronic ballasts is presented. A series of analyses and calculations are presented to obtain the ideal values of input DC voltage and resonant components meeting the requirement of approximate zero current switching (ZCS) behaviour over the lamp lifetime, ensuring the optimal design with minimised switching and conduction losses at steady-state operation. A new combined power control method is fulfilled to maintain the desired maximum lamp power under the optimal input voltage. Corresponding illustrations are provided to confirm the analysis result. The developed design optimisation method has been implemented into a 1 kW LC_sC_p resonant inverter prototype. The measured efficiency is about 98.1% for a new lamp and 99% for an ageing lamp.