Model-based NPC converter regulation for synchronous rectifier applications

This paper deals with the regulation of the three-level neutral-point-clamped (NPC) converter operating as synchronous rectifier connected to the ac mains. The regulation of the rectifier, whose primary application is to derive dc power from the utility grid, is based on a dynamic model of the system. This model includes the dynamics of the instantaneous powers as well as those of the total dc-link voltage and of the voltage difference of the dc-link capacitors, which are the state variables of the system and should be controlled. In this way, a direct power control (DPC) strategy and a proportional-integral (PI) cascade controller are considered for the regulation, respectively, of the instantaneous powers and of the total dc-link voltage. Regarding the balancing of the capacitor voltages, a novel and simple controller is proposed. This model-based controller can be considered as a non-conventional form of a PI controller. Simulations are performed in PSCAD environment to evaluate the performance of the closed-loop rectifier system under the proposed controllers.