Decentralized Adaptive Nonlinear Controller for Voltage Regulation of Output-Constrained DC Microgrids With ZIP Loads

In this article, a decentralized adaptive nonlinear controller is designed for islanded DC microgrids (DCmGs) containing several distributed generation units (DGUs). DGUs are connected by distribution lines represented by a general resistive-inductive-capacitive dynamic model. It is assumed 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). The proposed controller ensures voltage adjustment in the large signal sense in the presence of unknown ZIP loads and DC input voltages, unknown topological changes, and plug-and-play (PnP) operations of DGUs. The current of P-load, as a function of the inverse of the DGU's output voltage, to remain bounded requires that the output voltage never cross zero. To fulfill this requirement, a Barrier Lyapunov Function (BLF) is employed, which gets to infinity when the output voltage becomes zero. Then, the local controller of each DGU is designed based on the adaptive backstepping procedure such that for the closed-loop system, the adopted BLF remains bounded. The boundedness of this BLF ensures that the output voltage never becomes zero, and thus the mentioned singularity is prevented. Each local controller is synthesized independently of the distribution lines and by employing only the values of the local measurements and parameters of the DGU. The efficiency of the proposed nonlinear controller is evaluated by simulating a DCmG system under different scenarios in MATLAB/Simscape Electrical environment.