To meet the fast-growing energy demand and, at the same time, tackle environmental concerns resulting from conventional energy sources, renewable energy sources are getting integrated in power networks to ensure reliable and affordable energy for the public and industrial sectors However, the integration of renewable energy in the ageing electrical grids can result in new risks/challenges, such as security of supply, base load energy capacity, seasonal effects, and so on Recent research and development in microgrids have proved that microgrids, which are fueled by renewable energy sources and managed by smart grids (use of smart sensors and smart energy management system), can offer higher reliability and more efficient energy systems in a cost-effective manner Further improvement in the reliability and efficiency of electrical grids can be achieved by utilizing dc distribution in microgrid systems DC microgrid is an attractive technology in the modern electrical grid system because of its natural interface with renewable energy sources, electric loads, and energy storage systems In the recent past, an increase in research work has been observed in the area of dc microgrid, which brings this technology closer to practical implementation This paper presents the state-of-the-art dc microgrid technology that covers ac interfaces, architectures, possible grounding schemes, power quality issues, and communication systems The advantages of dc grids can be harvested in many applications to improve their reliability and efficiency This paper also discusses benefits and challenges of using dc grid systems in several applications This paper highlights the urgent need of standardizations for dc microgrid technology and presents recent updates in this area

DC Microgrid Technology: System Architectures, AC Grid Interfaces, Grounding Schemes, Power Quality, Communication Networks, Applications, and Standardizations Aspects

DC microgrids have attracted significant attention over the last decade in both academia and industry. DC microgrids have demonstrated superiority over AC microgrids with respect to reliability, efficiency, control simplicity, integration of renewable energy sources, and connection of dc loads. Despite these numerous advantages, designing and implementing an appropriate protection system for dc microgrids remains a significant challenge. The challenge stems from the rapid rise of dc fault current which must be extinguished in the absence of naturally occurring zero crossings, potentially leading to sustained arcs. In this paper, the challenges of DC microgrid protection are investigated from various aspects including, dc fault current characteristics, ground systems, fault detection methods, protective devices, and fault location methods. In each part, a comprehensive review has been carried out. Finally, future trends in the protection of DC microgrids are briefly discussed.

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DC Microgrid Protection: A Comprehensive Review

Due to inherent advantages of DC system over AC system such as compatibility with renewable energy sources, storage devices and modern loads, Direct Current Microgrid (DCMG) has been one of the key research areas from last few years. The power and energy management in the DCMG system has been a challenge for the researchers. MG structure and control strategies are the integrated part of the power and energy management system. This paper covers all the aspects of the control of DCMG, whether it is DC bus voltage, power or energy related. Different MG Structures with their comparative analysis has been given in this paper. Various control schemes: Basic control schemes like centralized, decentralized and distributed control and multilevel control scheme such as hierarchal control has been discussed. The Power management in grid-connected, Islanded mode and transition mode has been presented. Different energy management strategies have been presented as energy management plays very important role in optimizing the size and rating of energy storage system and their maximum utilization. The energy management of a battery and super capacitor based HESS in all configurations has also been discussed and finally, future trends in further research are presented.

A review on overall control of DC microgrids

Low-voltage, low-power solar photovoltaic (PV) based dc microgrids are becoming very popular in nonelectrified regions of developing countries due to lower upfront costs compared to utility grid alternatives and limited power needs of rural occupants The optimal planning of distribution architecture along with sizing of various system components such as solar panels, batteries, and distribution conductors is essential for minimizing the system cost and enhance its utilization In this paper, we develop a framework for optimal planning and design of low-power low-voltage dc microgrids for minimum upfront cost The analysis is based on region-specific irradiance and temperature profiles; constraints in storage and distributions; distribution loss analysis; and optimum component sizing (storage, conductor, and PV panel) requirements based upon an energy balance model for a 24-h operation We further analyze the merits of tailoring distribution architecture for maximizing the system utility in the planning of future microgrid deployments

Optimal Planning and Design of Low-Voltage Low-Power Solar DC Microgrids

This work presents an extensive review of hierarchical control strategies that provide effective and robust control for a DC microgrid. DC microgrid is an efficient, scalable and reliable solution for electrification in remote areas and needs a reliable control scheme such as hierarchical control. The hierarchical control strategy is divided into three layers namely primary, secondary and tertiary based on their functionality. In this study, different methods of primary control for current and voltage regulation, secondary control for error-correction in voltage and current, power sharing in a microgrid and microgrid clusters and tertiary control for power and energy management with a primary focus on minimal power loss and operational cost in a DC microgrid system are reviewed in-depth. Along with this, the advantages and limitations of various control structures like centralised, decentralised, distributed are discussed in this study. After a comparative study of all control strategies, the optimum control schemes from the author's point of view are also presented.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-rpg.2019.1136

Review of hierarchical control strategies for DC microgrid

It is well established that access to energy is closely linked with socioeconomic development. India houses the largest share of the world's population deprived of electricity with about 237 million people lacking access (International Energy Agency). At the same time, in India, many households that do have access to electricity lack an uninterrupted and quality power supply. A recent study conducted by the Council for Energy, Environment, and Water (CEEW) across six states (Bihar, Jharkhand, Madhya Pradesh, Uttar Pradesh, West Bengal, and Odisha), found that about 50% of the households had no electricity despite having a grid connection. This indicates that there is an immediate need to address the quality, affordability, and reliability of the power supply in addition to extending the grid footprint.

Solar-dc Microgrid for Indian Homes: A Transforming Power Scenario

The Uninterrupted Direct Current (UDC) solution has been developed by IIT Madras with a view to provide 24 X 7 power to all homes of India and alleviate power deficit situation prevalent in the country. This concept is being piloted and tested for practical viability in Sasaram, India. This paper discusses the necessary interventions needed at the sub-station end and the consumer end. The design details of the Brown-Out Feeder Energization Automation System (BOFEAS) commissioned in various feeders at Sasaram are also presented in this paper. The new efficient resonant switching power converter design has proven to be critical in developing Uninterrupted DC Power Module (UDPM), which is required to make in-home DC power line and DC power distribution possible. Various implementation challenges while executing UDC solution in Sasaram are also elaborated in this paper. Furthermore, the key role the local DISCOMs have to play in order to ensure UDC solution is implemented effectively is stressed upon. The learnings from Sasaram presented in this paper could be leveraged to ensure 24X7 good quality power supply across India.

Aditya Lolla

Papers

Solar-dc Microgrid for Indian Homes: A Transforming Power Scenario

Bringing Uninterrupted DC power to Indian homes: The Sasaram experience