Parallel operation of charge-controlled DC-DC converters

In this paper, a charge control applied to parallel-connected DC-DC converters is proposed. Charge control is a kind of current-mode control, in which the integral of the inductor current in the on state of each switching cycle reaches a reference value. This value is the feedback output signal of a pole placement block, which fixes the poles of the output-voltage. Firstly, a charge controller is designed for a single DC-DC converter in order to show the benefits of this technique. Although the controller introduces a nonlinearity, the close-loop system output-voltage is near-linear under some conditions. The controller is studied for two different power distributed schemes: master-slave and democratic approaches. This control technique provides the following performances: tight output voltage regulation, robustness against external disturbances, and uniform distributed current sharing among modules. Besides, a fixed-frequency operation is achieved, being useful for active ripple cancellation methods, as the interleaving technique. On the other hand, the controller response against load current and line voltage step changes within one switching-cycle. The features of the proposed control scheme are verified through simulation results, confirming the theoretical analysis done.