Adaptive Voltage Tuning Based Load Sharing in DC Microgrid

The distributed control of dc microgrid requires communication of the voltage or per-unit current data between the neighboring nodes. This data is processed by the secondary controller to generate a reference for the primary controller. Any uncertainty in the communicated data leads to the oscillations in the dc bus voltage, disproportionate load sharing, or instability due to erroneous references generated. In this work, an ISMC based secondary controller is proposed, which tunes the voltage reference within the regulation range and also mitigates the bounded uncertainties in the communicated microgrid load data. The ISMC has the advantage of elimination of the reaching phase, as the desired node trajectories start from sliding manifold. This makes the secondary control robust throughout the operating range and facilitates proportional load sharing in uncertain operating conditions. The proposed secondary control compares the actual node parameters with the desired global reference values and generates the control signal, which is added with the primary controller's control signals. The proposed control methodology requires only local parameters for formulation. This eases the control design process. Further, a sliding mode control based primary control (SMPC) is proposed to regulate the voltage of a node and facilitate plug and play among the microgrid interfacing converters. The proposed robust SMPC has excellent control during load transients and plug-in and out of nodes from the dc bus. The proposed control is verified using simulations and experiments on a three-node dc microgrid.