Priority-driven self-optimizing power control scheme for interlinking converters of hybrid AC/DC microgrid clusters in decentralized manner

Hybrid AC/DC microgrid clusters are key building blocks of smart grid to support sustainable and resilient urban power systems. In microgrid clusters, the subgrid load-priorities and power quality requirements for different areas vary significantly. To realize optimal power exchanges among microgrid clusters, this paper proposes a decentralized self-optimizing power control scheme for interlinking converters (ILC) of hybrid microgrid clusters. A priority-driven optimal power exchange model of ILCs is built considering the priorities and capacities in subgrids. The optimization objective is to minimize the total DC-voltage/AC-frequency state deviations of subgrids. To realize the decentralized power flow control, an optimal-oriented quasi-droop control strategy of ILCs is introduced to not only achieve a flexible self-optimizing power flow management, but also provide an ancillary function of voltage support. Consequently, as each of ILCs only monitors the local AC-side frequency and DC-side voltage signals, the whole optimal power control of the wide-area microgrid clusters is achieved in a decentralized manner without any communication link. Thus, the proposed control algorithm has the features of decreased cost, increased scalability, reduced geographic restrictions and high resilience in terms of communication faults. Finally, the proposed method is validated by case studies with four interconnected microgrids through hardware-in-loop tests

A review of networked microgrid protection: Architectures, challenges, solutions, and future trends

The design and selection of advanced protection schemes have become essential for the reliable and secure operation of networked microgrids. Various protection schemes that allow the correct operation of microgrids have been proposed for individual systems in different topologies and connections. Nevertheless, the protection schemes for networked microgrids are still in development, and further research is required to design and operate advanced protection in interconnected systems. The interconnection of these microgrids in different nodes with various interconnection technologies increases the fault occurrence and complicates the protection operation. This paper aims to point out the challenges in developing protection for networked microgrids, potential solutions, and research areas that need to be addressed for their development. First, this article presents a systematic analysis of the different microgrid clusters proposed since 2016, including several architectures of networked microgrids, operation modes, components, and utilization of renewable sources, which have not been widely explored in previous review papers. Second, the paper presents a discussion on the protection systems currently available for microgrid clusters, current challenges, and solutions that have been proposed for these systems. Finally, it discusses the trend of protection schemes in networked microgrids and presents some conclusions related to implementation

The Role of Power Electronic Converters in Microgrid Technology: A Review of Challenges, Solutions, and Research Directions

The paper is on the role of power electronic converters in microgrid technology: A review of challenges, solutions and research directions. The objective of the paper is to perform a comprehensive overview of the role of power electronic converters in microgrid technology, focusing on challenges, solutions, and research directions. Findings revealed that major challenges of power electronic converters integration in microgrid technology are voltage and frequency regulation issues, power quality issues, creative management and coordination challenges, and Integration of renewable energy sources. The solutions to these problems are advanced control algorithms such as Model Predictive Control (MPC); deployment of active power filters or harmonic compensators to reduce harmonic distortion and improve power quality; iimplement a centralized control system with centralized monitoring controllers to coordinate the operation of several converters and ensure consistent operation; and combining multiple renewable energy sources in a hybrid energy system to diversify generation sources and reduce the gap. The future research directions include, among others, advanced control strategies, grid-forming converters, wideband semiconductor, and cyber-security and Resilience. The paper concludes that the integration of power electronic converters into microgrid technology presents both opportunities and challenges. Although these converters play an important role in the efficient conversion, distribution and utilization of energy in microgrids, they face various technical and practical challenges. To mitigate these challenges, the implementation of advanced control strategies, grid-forming converters, etc., is inevitable.&nbsp

Control Strategies of DC Microgrids Cluster:A Comprehensive Review

Multiple microgrids (MGs) close to each other can be interconnected to construct a cluster to enhance reliability and flexibility. This paper presents a comprehensive and comparative review of recent studies on DC MG clusters’ control strategies. Different schemes regarding the two significant control aspects of networked DC MGs, namely DC-link voltage control and power flow control between MGs, are investigated. A discussion about the architecture configuration of DC MG clusters is also provided. All advantages and limitations of various control strategies of recent studies are discussed in this paper. Furthermore, this paper discusses three types of consensus protocol with different time boundaries, including linear, finite, and fixed. Based on the main findings from the reviewed studies, future research recommendations are proposed

Control and Energy Management of Standalone Interconnected AC Microgrids

This thesis considered microgrids as local area distribution mini-power grids formed by distributed generation sources, energy storage systems and loads. They are reliable and can operate at different voltages and frequencies to meet the requirements of the load. Microgrids have limited renewable energy source (RES) capacity, which can only supply a limited load and increasing the load beyond a specifically designed limit can lead to stability issues. Irrespective of its limited capacity, there has been an increased widespread deployment of renewable energy-based microgrids worldwide orchestrated by the 2015 Paris Agreement and the war in Ukraine and as a solution to meet the global demand for energy in electricity deficit zones aimed to achieve universal access to affordable, reliable, and sustainable energy. Fast forward to the future, flooded singly operated microgrids face the problem of more curtailing of RES and load shedding. Multiple microgrids can be interconnected to mitigate the limitations of single microgrids and improve supply reliability, enhance power supply availability, stability, reserve capacity, reduce investment in new generating capacity and control flexibility. As a result, this thesis proposes a new structure and control technique for interconnecting multiple standalone AC microgrids to a common alternating current (AC) bus using a back-to-back power electronic converter and a traditional transformer. Each microgrid considered in this thesis comprises a renewable energy source (RES), battery, auxiliary unit, and load. The battery maintains the AC bus voltage and frequency and balances the difference in power generated by the RES and that consumed by the load. Each microgrid battery’s charge/discharge is maintained within the safest operating limit to maximise the RES power utilisation. The back-to-back converters are used to decouple the connecting standalone microgrid frequencies and facilitate power exchange between microgrids. The transformer is used to transmit electric power over long distances efficiently. The control technique for all the connecting bidirectional back-to-back converters is developed to manage the bidirectional power flow between each microgrid and other microgrids in the network and to balance the energy in the global bus of the interconnected microgrid with no communication. The control strategy uses a frequency signalling mechanism to limit the power demand of individual global converters and adjusts its droop coefficients accordingly and in proportion to deviation in frequency. The global droop controllers of the global connecting converters receive information about the status of the frequencies of individual microgrids using a low bandwidth communication link to enhance network power flow. MATLAB/Simulink results validate the performance of the proposed structure and control strategy. A decentralised control scheme is further proposed for the standalone interconnected AC microgrid structure. This thesis presented a high-level global droop controller that exchanges power between the interconnected microgrids. Renewable power curtailment and auxiliary power supplement mechanisms are designed based on the bus frequency signalling technique to achieve balance and continuity of supply. In case of power shortage in one microgrid, priority will first be given to power import from other microgrids. A power supplement is used if the power imported is insufficient to control the battery state of charge (SOC). Similarly, in case of a power surplus, priority will be given to power export, and if this is not enough, power from RES will be curtailed. Performance evaluation shows that the proposed controller maximises renewable power utilisation and minimises auxiliary power usage while providing better load support. The performance validation of the proposed structure and control strategy has been tested using MATLAB/Simulink. Furthermore, this thesis investigated a centralised control and energy management of multiple interconnected standalone AC microgrids using the Nelder-Mead simplex algorithm (Fminsearch optimisation toolbox in MATLAB) based on the new proposed model. The main objective is to minimise the total cost of energy from the auxiliary unit produced from gas. The results obtained are compared with those obtained from an unoptimised system. The performance evaluation investigation results are compared with the unoptimised results to determine the percentage optimal performance of the system. The comparison outcome shows that the proposed optimisation method minimises the total auxiliary energy cost by about 9% compared with the results of the unoptimised benchmark

A survey on power management strategies of hybrid energy systems in microgrid

The power generation through renewable energy resources is increasing vastly, Solar energy and Wind Energy are the most abundantly available renewable energy resources. The growth of small scale distributed grid networks increasing rapidly in the modern power systems and Distributed Generation (DG) plays a predominant role. Microgrid is one among the emerging techniques in power systems. Power Management is mainly required to have control over the real and reactive power of individual DG and for smooth operation, maintaining stability and reliability. This paper presents a survey of the research works already reported focusing on power management of hybrid energy systems such as mainly solar and wind systems in microgrid. Six different approaches have been studied in detail for AC,DC and hybrid AC/DC microgrid

Next-Generation Shipboard DC Power System: Introduction Smart Grid and dc Microgrid Technologies into Maritime Electrical Networks

In recent years, evidence has suggested that the global energy system is on the verge of a drastic revolution. The evolutionary development in power electronic technologies, the emergence of high-performance energy storage devices, and the ever-increasing penetration of renewable energy sources (RESs) are commonly recognized as the major driving forces of the revolution. The explosion in consumer electronics is also powering this change. In this context, dc power distribution technologies have made a comeback and keep gaining a commendable increase in research interest and industrial applications. In addition, the concept of flexible and smart distribution has also been proposed, which tends to exploit distributed generation and pack together the distributed RESs and local electrical loads as an independent and self-sustainable entity, namely a microgrid. At present, research in the area of dc microgrids has investigated and developed a series of advanced methods in control, management, and objective-oriented optimization that would establish the technical interface enabling future applications in multiple industrial areas, such as smart buildings, electric vehicles, aerospace/aircraft power systems, and maritime power systems