A Decentralized Nonlinear Control Strategy for a Robust Voltage Regulation in Islanded DC Microgrids with ZIP Loads

Abstract

In this article, a decentralized nonlinear voltage controller for islanded DC microgrids (DCmGs) containing several distributed generation units (DGUs) is developed. DGUs are connected to each other by resistive-inductive (RL) distribution lines. Each DGU feeds an unknown nonlinear ZIP (constant impedance 'Z', constant current 'I' and constant power 'P') load at its point of common coupling (PCC). By applying the existing voltage controllers on the DCmGs with unknown ZIP loads, convergence to the voltage setpoints is guaranteed only around the system operating point, while the proposed decentralized controller in this paper ensures voltage adjustment in a large signal sense in the presence of unknown ZIP loads, unknown DC input voltages, unknown topological changes, and plug-and-play (PnP) operations of DGUs. The local nonlinear controllers of DGUs are developed based on the adaptive backstepping procedure. Each local nonlinear controller is synthesized independently of the distribution lines and by employing only the values of the local measurements and parameters of the DGU. This leads to the stability preservation of the system under PnP operations of DGUs without the need to retune the design parameters of the local controllers. The efficiency of the proposed nonlinear controller is evaluated by simulating a DCmG system under different scenarios in MATLAB/Simscape Electrical environment.