Distributed Data-Driven Control for Adjustable Current Sharing and Secure Voltage Restoration in DC Microgrids

For DC microgrids (MGs), real-time adjustment of current sharing ratios and secure voltage restoration are paramount for optimizing load allocation and enhancing dynamic performance. In this paper, a dual-objective distributed model-free adaptive control (MFAC) scheme is designed for the first time to guarantee voltage transient performance and adjustable current sharing. First, an output-constrained nonlinear MG model with ZIP (constant impedance, constant current and constant power) load is established, and subsequently it is converted into an equivalent unconstrained data model using system transformation and dynamic linearization techniques. Second, a new prescribed performance control algorithm with asymmetrical preset boundaries is proposed to restrict voltage transient responses. This algorithm is updated with real-time input and output data at discrete instants, making it independent of line resistance and ZIP load measurements. To enhance the robustness of the control method, an internal observer is designed to actively compensate for the unknown nonlinear dynamics generated by time-varying system parameters. The stability conditions of the transformed systems in the presence of ZIP loads and time-varying line resistance are derived, which can indirectly ensure the prescribed voltage performance of the original system. Finally, the effectiveness of the proposed control method is validated through some simulations and hardware experiments. Note to Practitioners - Current sharing and voltage restoration are two main control tasks in the DC microgrid. With the increasing penetration of renewable energy, real-time adjustment of the current sharing ratio according to the capacity of distributed generators (DGs) can prevent overload. When the system suffering large disturbances, perfect voltage transient response can protect sensitive loads and avoid malfunctions of protection equipment. However, the existing secondary control strategies cannot deal with these problems in a unified distributed MFAC framework. Therefore, this paper propose a new distributed MFAPPC method to achieve adjustable current sharing and secure voltage restoration for the DC MG. This data-driven approach can ensure the stability of the MG system in the presence of ZIP loads and time-varying line resistance, even if the model and load information are unavailable.