Model-Free Energy Management System for Hybrid Alternating Current/Direct Current Microgrids

A hybrid ac/dc microgrid combines the benefits of ac and dc power systems. It provides high efficiency and is compatible with conventional ac distribution network. This article proposes a centralized energy management approach to perform coordinated control on a hybrid ac/dc microgrid as a single-controllable entity. The central controller relies on low-bandwidth communication channels and is aimed at achieving 1) proportional power sharing among energy storage units located in both dc and ac sides of the microgrid, 2) state-of-charge equalization of the energy storage units, 3) grid power flow control, 4) plug-and-play capability, and 5) operation in grid-connected and islanded modes through an interlinking utility interface converter. The state-of-charge equalization method guarantees uniform operation of the energy storage units during both charge and discharge modes considering typical operational transients. Finally, the proposed model-free approach is evaluated experimentally through a laboratory-scale hybrid ac/dc microgrid in different operational conditions in both grid-connected and islanded operating modes.

I. Introduction

The growth of renewable energy sources (RESs), energy storage units (ESUs), and modern loads as electric vehicles into the distribution power systems has challenged the grid interconnection in terms of efficiency, reliability, and power quality. Regarding the power quality issues, the typical limits of hosting capacity are overvoltage, overload of conductors, and voltage unbalance [1], [2]. In this context, a microgrid (MG) shows itself as a feasible model to enable the interconnection of multiple RESs, ESUs, and loads in a same cluster ensuring dispatchability, reliability, and stability of the overall system contributing to enhance the hosting capacity of distribution grids and then increasing the amount of distributed energy resources (DERs) integrated into the power system [3].