This paper presents the latest comprehensive literature review of AC and DC microgrid (MG) systems in connection with distributed generation (DG) units using renewable energy sources (RESs), energy storage systems (ESS) and loads. A survey on the alternative DG units' configurations in the low voltage AC (LVAC) and DC (LVDC) distribution networks with several applications of microgrid systems in the viewpoint of the current and the future consumer equipments energy market is extensively discussed. Based on the economical, technical and environmental benefits of the renewable energy related DG units, a thorough comparison between the two types of microgrid systems is provided. The paper also investigates the feasibility, control and energy management strategies of the two microgrid systems relying on the most current research works. Finally, the generalized relay tripping currents are derived and the protection strategies in microgrid systems are addressed in detail. From this literature survey, it can be revealed that the AC and DC microgrid systems with multiconverter devices are intrinsically potential for the future energy systems to achieve reliability, efficiency and quality power supply.

AC-microgrids versus DC-microgrids with distributed energy resources: A review

This paper presents a comprehensive review on the unified power quality conditioner (UPQC) to enhance the electric power quality at distribution levels. This is intended to present a broad overview on the different possible UPQC system configurations for single-phase (two-wire) and three-phase (three-wire and four-wire) networks, different compensation approaches, and recent developments in the field. It is noticed that several researchers have used different names for the UPQC based on the unique function, task, application, or topology under consideration. Therefore, an acronymic list is developed and presented to highlight the distinguishing feature offered by a particular UPQC. In all 12 acronyms are listed, namely, UPQC-D, UPQC-DG, UPQC-I, UPQC-L, UPQC-MC, UPQC-MD, UPQC-ML, UPQC-P, UPQC-Q, UPQC-R, UPQC-S, and UPQC-VA. More than 150 papers on the topic are rigorously studied and meticulously classified to form these acronyms and are discussed in the paper.

Enhancing Electric Power Quality Using UPQC: A Comprehensive Overview

A microgrid (MG) is a local entity that consists of distributed energy resources (DERs) to achieve local power reliability and sustainable energy utilization. The MG concept or renewable energy technologies integrated with energy storage systems (ESS) have gained increasing interest and popularity because it can store energy at off-peak hours and supply energy at peak hours. However, existing ESS technology faces challenges in storing energy due to various issues, such as charging/discharging, safety, reliability, size, cost, life cycle, and overall management. Thus, an advanced ESS is required with regard to capacity, protection, control interface, energy management, and characteristics to enhance the performance of ESS in MG applications. This paper comprehensively reviews the types of ESS technologies, ESS structures along with their configurations, classifications, features, energy conversion, and evaluation process. Moreover, details on the advantages and disadvantages of ESS in MG applications have been analyzed based on the process of energy formations, material selection, power transfer mechanism, capacity, efficiency, and cycle period. Existing reviews critically demonstrate the current technologies for ESS in MG applications. However, the optimum management of ESSs for efficient MG operation remains a challenge in modern power system networks. This review also highlights the key factors, issues, and challenges with possible recommendations for the further development of ESS in future MG applications. All the highlighted insights of this review significantly contribute to the increasing effort toward the development of a cost-effective and efficient ESS model with a prolonged life cycle for sustainable MG implementation.

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Review of Energy Storage System Technologies in Microgrid Applications: Issues and Challenges

Critical review of energy storage systems

Demand response programs offer efficient solutions for many power system problems, such as high generation cost, high demand’s peak to average ratio, high emissions, reliability issues and congestion in generation, transmission and distribution systems. Their main function is to assist power systems during peak demand hours and also during contingencies. They are a subcategory of the family of demand side management (DSM) strategies. DR programs are classified into two broad categories; price-based DR programs and incentive-based DR programs. In order to exploit their full potential, DR programs must be implemented optimally. Such a problem, which here is referred to as “DR optimisation problem”, is a hot research topic and has been frequently researched in the literature. This paper aims to review different research works on DR optimisation problems. Based on the conducted review, some directions for future research are proposed.

Optimisation of demand response in electric power systems, a review

This article describes the current state of development and future direction in the market for electric vehicles in Poland, with respect to the charging infrastructure. The authors have concentrated above all on the assumptions and results of ventures to-date in this field. There has also been conducted an analysis of the influence of electric vehicle development, in part concerning the charging infrastructure, on the Polish power system. In addition, this article outlines the potential for using electric vehicle charging terminals, in developing Semi Smart systems at the level of low-voltage distribution grids.

Electric vehicle charging infrastructure in Poland

The basic idea of decentralized demand response systems is not new, however, material presented in the subject matter literature is usually limited to general ideas and possible system services. In this paper, the original stochastic decentralized active demand response (DADR) system is presented in the form of an application-ready control algorithm. The results of simulation investigations have confirmed that the proposed stochastic DADR solution, because of its high dynamic response in dealing with disturbance phenomena, might be used as part of both the primary and the secondary load frequency control in electrical power systems. The applicability of the proposed algorithm for control of refrigerators has been numerically tested for various system parameters. Fulfillment of all assumed DADR system requirements concerning high dynamic, “soft” operation, fair share in service as well as minimization of degradation in comfort of use of DADR controlled devices have been confirmed in numerical evaluations.

Application of Stochastic Decentralized Active Demand Response (DADR) System for Load Frequency Control

The parameters of electrical energy, such as supply voltage amplitude, are very important, especially from the viewpoint of the final consumer with respect to sensitive loads connected to the grid. Dynamic states in the power grid?voltage sags and swells?might cause faults and defects to develop in sensitive loads. To mitigate unwanted effects, many topologies of ac/ac converters are implemented as voltage compensators. This article presents a review of hybrid ac/ac converters designed to compensate voltage sags and swells with the aim of protecting sensitive loads against sudden and severe changes in supply voltage amplitude. In this article, only solutions without galvanic separation between source and load are described. To assess the properties and to compare different topologies of voltage compensators, some common parameters, such as range of voltage sag and swell compensation, reliability, quantity of switches and transformers, and required power ratings of power electronic units in relation to power of load, are introduced. In addition, we discuss possibilities for compensation of voltage interruption, time of compensation, the efficiency, and the effect on the supply network of the described circuits. The results of the analysis have been collected and compared in tabular form and represented in graphical form. Furthermore, we show potential areas of application for particular solutions of ac voltage compensators.

Hybrid Voltage Sag\/Swell Compensators: A Review of Hybrid AC\/AC Converters

With the rising penetration of intermittent renewable energy sources (RES) and their variable nature it has become a challenge for distribution grid operators to maintain voltage quality inside the permissible range. It requires the involvement of new distributed resources, such as energy storage devices, to smooth power fluctuations of RES and to avoid long-term voltage rises. To achieve the best results such devices should be located as close to the micro source as possible – behind the meter. Small, distributed energy storage devices could be used to increase self-consumption of generated energy inside microgrids, helping also to flatten the daily load curve of the electrical power system (EPS). This paper discusses the properties of selected energy storage technologies suitable for small-scale microgrids containing renewable energy sources. The properties of small Zinc Bromine (ZnBr) flow batteries obtained in experimental research have been presented and compared to the properties of other energy storage devices similarly classified but at a different level of development. The simple equivalent model of the ZnBr battery has also been developed and described.

Marcin Jarnut

Papers

Electric vehicle charging infrastructure in Poland

Application of Stochastic Decentralized Active Demand Response (DADR) System for Load Frequency Control

Hybrid Voltage Sag\/Swell Compensators: A Review of Hybrid AC\/AC Converters

Comparative analysis of selected energy storage technologies for prosumer-owned microgrids

AC–AC power electronic converters without DC energy storage: A review