A Real-Time PHIL Implementation of a Novel Nonlinear Distributed Control Strategy for a Multi-Terminal DC Microgrid

Multi-terminal DC Microgrids have great potential for integrating Renewable Energy Sources, Storage Technologies, and modern loads more efficiently because most of them operate on DC power. Besides the reduced conversion steps between the components, which avoids considerable losses, multi-terminal DC MicroGrids offer advantages due to the lack of skin effects and reactive power. Nevertheless, stabilizing such a DC network by controlling its power converters is a very challenging task in view of the fact that the classical solution, to use PI controllers based on linearized models, may lead to stable behavior only in a small region around the respective equilibrium point. In this paper, we present a real-time PHIL implementation of a novel nonlinear control scheme for a multi-terminal DC MicroGrid. The amount of needed capacitors is reduced significantly concerning previous approaches. The proposed nonlinear controller is compared with a cascaded PI controller based on a linearized model, the so-called vector control. Both approaches, nonlinear and linear, are implemented and validated on a real PHIL multi-terminal DC MicroGrid consisting of a battery, a PV, and two load ports. The real-time experimental results of PI-based and nonlinear control-based DC Microgrids are then compared. They show that the nonlinear control allows to better deal with disturbances and nonlinearities of the system, for several points of operation without re-tuning.