Nonsmooth Decentralized Voltage Controller for Constrained Regulation of DC Microgrids with Constant Power Loads

This paper presents a novel decentralized voltage controller that enforces state constrains at all times and significantly enhances the transient response of DC Microgrid networks with constant power loads. The structure of the proposed controller ensures the existence of a positive invariant set under the solution of the dynamics, enforcing boundedness of each nodal voltage around a rated value. A rigorous analysis is presented to formulate sufficient conditions on the controller tuning parameters such that the boundedness property is guaranteed despite the time-varying nature of the nonlinear load demand. Closed-loop stability of the entire DC Microgrid with respect to desired reference points is analytically proven by employing a suitable Lyapunov function. This allows us to estimate the region of attraction of the desired equilibrium and obtain conditions under which system stability is ensured at all times. Furthermore, the structure of the proposed controller significantly improves the convergence rate of the closed loop system when compared with similar approaches in the literature. The theoretic results are verified in both experimental and power hardware-in-the-loop testing scenarios, while demonstrating fast voltage restoration in cases of load demand fluctuations and constrained regulation to the desired voltage references.