Distributed Controller for the Parallel Operation of Power Converters With Small Output Filters

This study addresses the design of a distributed controller, mostly intended for modular applications where parallel-connected voltage-source converters (VSCs) operate loads in conditions of current continuity. The only requirement is that the modules are based on half-bridge architectures, possibly synchronous, such as buck, boost, half-bridge, full-bridge and three-phase bridges. The proposed controller can work with small (few microhenries) series inductors, mostly comparable with the stray inductance already existing in the wiring. Each regulator adjusts the pulse-width modulation (PWM) of a given converter based only on its own output current. Each PWM pattern is shifted on the nanosecond time scale using a peculiarly inexpensive software modulator. The overall control action allows achieving the synchronous operation of all converters at modulation frequency, thus suppressing the circulating current. The control strategy is mathematically designed through novel models, and experimentally validated employing three DC-DC converters. The study demonstrates (i) the feasibility and robustness of the method to compensate for both phase and frequency errors among the units, (ii) the capability of the controller to cope with the inherent parameter mismatch among the modules, and (iii) its ability to operate in tandem with a load balancing regulator.