Power-Mode Control of Multiphase Resonant Electronic Ballast

A wide-bandwidth power-mode-controlled triple LCpCs resonant inverter is proposed for minimizing the light flicker caused by utility voltage fluctuation in industrial environments and compensating the dc bus ripple as an alternative rather than increasing the dc bus capacitance. To keep its efficiency, the inverter is controlled at a constant switching frequency by the phase displacement Ψ of the output voltage of one class-D section referred to the others. An approximate explicit form of the small-signal transfer function from the control angle Ψ to the output power is obtained by using a reduced-order model. This transfer function presents the main pole at a frequency high enough for the loop gain to exhibit wide bandwidth with a simple integral control action that compensates the voltage fluctuations in the frequency range where human perception is sensitive to light flicker. Experimental results are given using a 400-W high-pressure sodium lamp as the load.