Azizi M. Energy Router for Hybrid Microgrids for efficient and robust energy and power management

Dissertation for a double degree of Doctor of Philosophy in specialty 141 - " Electric Power Engineering, Electrotechnics and Electromechanics." Department of Electrical Engineering and Information Measuring Technologies, Chernihiv Polytechnic National University, Ministry of Education and Science of Ukraine; and R024 - Doctorate in Industrial Engineering, University of Extremadura, Department of Electric, Electronic and Automation Engineering, Badajoz, Spain. Electric energy consumption is increasing much faster than the predicted growth in energy generation. Although the installed capacity of renewable energy sources is also expanding, grid congestion remains unavoidable without adopting smart energy management systems and flexible power electronics structures. Therefore, the rise of electric energy consumption and electric energy congestion is leading to the necessity of autonomous residential buildings. With the increase of domestic generation resources (mainly photovoltaic), and the use of storage systems in many buildings, moving towards zero-emission buildings (ZEBs) and the utilization of the dc system along with ac system is being developed. For this purpose, a new technology, called an energy router (ER) with ac and dc ports, was proposed in recent years. Researchers have already proposed various topologies and control strategies for ER; however, there are still research gaps and challenges that should be addressed. Safety and protection issues and the control response in dynamic conditions are among these challenges. Chapter one provides a general review of power electronics solutions for ZEBs. By exploring the promising future of the low-voltage dc industry in ZEBs, the study presents and compares different configurations for ER and grid-connected scenarios, evaluating their overall efficiencies across hybrid, dc, and ac technologies. Chapter two comprehensively deals with the integration of dc systems and related challenges. Dc microgrids, along with existing ac grids, are a future trend in energy distribution systems. However, there are not yet sufficient standards to integrate dc systems into the ac grid, and safety considerations remain a problem. At the same time, many related issues are still undefined and unsolved. In particular, uncertainty prevails in isolation requirements between ac grids and novel microgrids, as well as in the grounding approaches. This chapter first deals with different integration solutions and then investigates leakage currents and different grounding types and configurations, both on ac and dc sides. It provides an overview of possible grounding approaches at the connection points and the feasibility of avoiding isolation between ac grid and dc systems. Furthermore, it proposes solutions for challenges related to protection, grounding, and leakage currents. Finally, considering the importance of grounding and protecting personnel and equipment on both ac and dc sides, the use of common-ground structures is introduced as an effective method. Regarding the integration challenges and scenarios, chapter three introduces the proposed structure of a single-cell three-phase ER based on the common-ground inverter. In this topology, dc link can access all three phases and balance them without the complexities and costs associated with conventional three-phase systems. Common-ground structure creates the same ground on both ac and dc sides that not only provides safety and protection on both sides, but also decreases the cost and weight since it eliminates isolation. Inverter operating mode and modulation, component design of different parts, and then protection and dc circuit breaker are also described in detail. Chapter four focuses on control strategy and describes different control levels in an ER. The ER system integrates multiple power sources and sinks, and any sudden change in a subsystem can introduce dynamic conditions across the entire system. To enhance the dynamic performance of a multiport ER, flatness-based control (FBC) theory is applied to the low-level control (inner loops) of the ER, ensuring a fast and robust control response in dynamic conditions. The presented method guarantees a robust dc-link in any dynamic conditions. At the end, this chapter examines the high-level energy management system solutions from a simple local-based to a high-tech solution, emphasizing the shift to full digitalization through a combination of cloud-based and edge-computing platforms. Finally, chapter five presents simulation and experimental results. Simulation results are provided to validate the proposed control solution and compare the control response and quality with conventional control solutions. In the experimental part, the general operating modes are analyzed, and the controller response in dynamic conditions is also investigated. At the end, general conclusions are discussed and highlighted.