Distributed Data-Driven Secondary Regulation for the Conflict Between Voltage Recovery and Accurate Current Sharing in DC Microgrids

The problem of voltage restoration and current balancing has been a hot topic in the study of DC microgrids (MGs), and how to engineer a secondary controller to solve the conflict between these two is the concern of this paper. With the above consideration, an optimal distributed data-driven secondary control strategy is proposed, relying entirely on the input and output data of DC MGs. The proposed framework completes the design of a secondary control strategy based on a data model for the first time, which incorporates the physical coupling relationship between voltage and current into the controller design and is independent of the global circuit parameters and topology information. By means of a proposed cost function, the designed control strategy enables DC MGs to achieve better output current quality at steady state. Unlike the existing schemes based on average voltage observer, this paper resorts to a combination of limiting the voltage reference value generated by the secondary controller and a current cooperative strategy based on the data model to achieve an easy-to-use trade-off between the two objectives of voltage regulation and current sharing. Then, an analytical model of a closed-loop DC MG system under the proposed control scheme is developed, and the analysis of stability and consensus of weighted output current is given accordingly. Finally, the proposed control strategy is tested on a hardware DC MG system with solar panels and a maximum power point tracking (MPPT) controller.

I. Introduction

The fact that the penetration of renewable energy sources (RESs) in the power system is growing has led to a strong interest in microgrids (MGs) in various research areas [1]. MGs, as an effective architecture for integrating RESs, are mainly organized in the form of ac MGs [2], dc MGs [3], [4] and hybrid ac/dc MGs [5], [6]. In contrast to the ac characteristics of wind turbine-based power generation systems, the dc nature of emerging RESs, such as solar, and storage units (e.g., batteries and supercapacitors [7], [8]), makes them inherently suited to the dc MG paradigm, thus avoiding redundant inverter procedures [9], [10]. From the demand side, as the equipment of power electronics continues to miniaturize, many new types of loads are also electronic dc loads, such as data centers, etc. Besides, there is no need to consider some factors in dc MG that cannot be ignored in its counterpart, such as transformer inrush current, frequency synchronization, and reactive power flow [11], [12], which makes it highly popular in some critical applications [13], [14]. Although dc MGs are simpler in structure and control than ac ones, there are some challenges to be addressed in their widespread availability, which is the interest of this article.