The paper reviews different approaches, technologies, and strategies to manage large-scale schemes of variable renewable electricity such as solar and wind power. We consider both supply and demand side measures. In addition to presenting energy system flexibility measures, their importance to renewable electricity is discussed. The flexibility measures available range from traditional ones such as grid extension or pumped hydro storage to more advanced strategies such as demand side management and demand side linked approaches, e.g. the use of electric vehicles for storing excess electricity, but also providing grid support services. Advanced batteries may offer new solutions in the future, though the high costs associated with batteries may restrict their use to smaller scale applications. Different “P2Y”-type of strategies, where P stands for surplus renewable power and Y for the energy form or energy service to which this excess in converted to, e.g. thermal energy, hydrogen, gas or mobility are receiving much attention as potential flexibility solutions, making use of the energy system as a whole. To “functionalize” or to assess the value of the various energy system flexibility measures, these need often be put into an electricity/energy market or utility service context. Summarizing, the outlook for managing large amounts of RE power in terms of options available seems to be promising.

https://research.aalto.fi/files/6557604/lund_et_al_review.pdf

Review of energy system flexibility measures to enable high levels of variable renewable electricity

Energy storage systems (ESSs) are enabling technologies for well-established and new applications such as power peak shaving, electric vehicles, integration of renewable energies, etc. This paper presents a review of ESSs for transport and grid applications, covering several aspects as the storage technology, the main applications, and the power converters used to operate some of the energy storage technologies. Special attention is given to the different applications, providing a deep description of the system and addressing the most suitable storage technology. The main objective of this paper is to introduce the subject and to give an updated reference to nonspecialist, academic, and engineers in the field of power electronics.

Energy Storage Systems for Transport and Grid Applications

Advances and trends of energy storage technology in Microgrid

Demand-side management, together with the integration of distributed energy generation and storage, are considered increasingly essential elements for implementing the smart grid concept and balancing massive energy production from renewable sources. We focus on a smart grid in which the demand-side comprises traditional users as well as users owning some kind of distributed energy sources and/or energy storage devices. By means of a day-ahead optimization process regulated by an independent central unit, the latter users intend to reduce their monetary energy expense by producing or storing energy rather than just purchasing their energy needs from the grid. In this paper, we formulate the resulting grid optimization problem as a noncooperative game and analyze the existence of optimal strategies. Furthermore, we present a distributed algorithm to be run on the users' smart meters, which provides the optimal production and/or storage strategies, while preserving the privacy of the users and minimizing the required signaling with the central unit. Finally, the proposed day-ahead optimization is tested in a realistic situation.

Demand-Side Management via Distributed Energy Generation and Storage Optimization

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.

/pdf/review-of-energy-storage-system-technologies-in-microgrid-13f9i4hnhx.pdf

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

Distributed energy storage systems in combination with advanced power electronics have a great technical role to play and will have a huge impact on future electrical supply systems and lead to many financial benefits. So far, when Energy storage systems (ESSs) are integrated into conventional electric grids, special designed topologies and/or control for almost each particular case is required. This means costly design and debugging time of each individual component/control system every time the utility decides to add an energy storage system. However, our present and future power network situation requires extra flexibility in the integration more than ever. Mainly for small and medium storage systems in both (customers and suppliers) side as the storage moves from central generation to distributed one (including intelligent control and advanced power electronics conversion systems). Nevertheless, storage devices, standardized architectures and techniques for distributed intelligence and smart power systems as well as planning tools and models to aid the integration of energy storage systems are still lagging behind.

Challenges in integrating distributed Energy storage systems into future smart grid

This paper demonstrates that the introduction of a Flywheel Energy Storage System (FESS) into a isolated hybrid grid increases the renewable energy penetration. The isolated power system studied includes diesel and hydro generators and wind turbines. The simulated and measured results clearly show the positive influence of the energy storage on the system performance. The system has been operating with the FESS for 1 year and has demonstrated improvements in renewable energy penetration, reduced diesel fuel usage, and improved power system stability and power quality.

Increasing Renewable Energy Penetration in Isolated Grids Using a Flywheel Energy Storage System

One of the desirable characteristics of inverters in three-phase systems is the ability to feed unbalanced/non-linear loads with voltage and frequency nominal values. Therefore three-leg four-wire inverters are expected to play an essential role in future power systems because of their ability to handle the neutral current caused by unbalanced or non-linear loads. This study introduces an original control method in combination with three-dimensional space-vector modulation (3D-SVM) strategy. The steps for the 3D-SVM implementation are identified. The switching vectors, 3D-SVM diagrams and the boundary planes equations, as well as the matrices for the duty cycles and symmetric switching sequences are discussed in detail. Experimental results including different loads are presented to validate the proposed SVM control strategy for three-leg four-wire voltage source inverters. The experimental results of this study show that the developed control scheme in combination with three-leg four-wire inverters can carry out the grid feeding requirements and supply good power quality to loads under extreme unbalanced conditions efficiently.

Control strategy and space vector modulation for three-leg four-wire voltage source inverters under unbalanced load conditions

Future power distribution requires advanced expandability and flexibility in the integration of distributed energy resources which normally require interfacing units to provide the necessary crossing point to the grid. The core of these interfacing units is power-electronics grid front end, namely, inverters. The inverter is the primary interface that provides not only their principal interfacing control function but also various utility functions. This paper presents the flexible control methodology of inverters as grid front end using an isochronous control function which is used by synchronous generators in conventional power systems to provide load sharing and control.

Control Strategy for Three-/Four-Wire-Inverter-Based Distributed Generation

A key component at the grid side of a PV/hybrid power system (HPS) is the inverter. One of the desirable characteristics of inverters in three-phase systems is the ability to feed unbalanced loads with voltage and frequency nominal values. This paper introduces innovative three-phase inverter topologies in combination with an advanced control function able to feed isolated grids with unbalanced loads. Therefore, standardized advanced control functions based on symmetrical components will be used. In this paper a four leg power electronics topology in combination with the developed control algorithm is used to perform a three-phase symmetrical voltage source with a controlled neutral point. The advantages of the developed control function will be introduced and discussed by a simulation study.

N. Hamsic

Papers

Challenges in integrating distributed Energy storage systems into future smart grid

Increasing Renewable Energy Penetration in Isolated Grids Using a Flywheel Energy Storage System

Control strategy and space vector modulation for three-leg four-wire voltage source inverters under unbalanced load conditions

Control Strategy for Three-/Four-Wire-Inverter-Based Distributed Generation

Grid-Forming Three-Phase Inverters for Unbalanced Loads in Hybrid Power Systems