Digital average current-mode controller for dc-dc converters in physical vapor deposition applications

A dc power supply in physical vapor deposition (PVD) applications operates as a constant power source during normal operation or as a constant current source during fast micro arcs in the plasma. A two-loop control is usually applied: an external (slower) loop controls the output power, while an internal (fast) loop controls the current. This paper introduces a digital average current mode controller for de power supplies in PVD applications. The controller provides a current source response to fast disturbances, and enables equal current sharing among buck converter modules operating in parallel. Adaptive adjustments of the compensator gain in the digital current control loop enable operation over wide ranges of output power and voltage. The proposed control strategy is robust and noise insensitive. The current and power control algorithms are implemented on a digital signal processor/field-programmable gate array-based digital control platform using a low-cost 10-bit 500 kS/s analog-to-digital converter. The performance is verified on a 25 kW experimental prototype.