A Quasi-Resonant Bidirectional Converter with Soft-Switching Operation for Energy Storage Applications

The increased penetration of renewable energy power systems to produce clean and sustainable energy has led to the increased usage of various types of energy storage devices, such as high power density battery technologies, flywheel energy storage and super-capacitors. Energy storage devices are essential in any renewable generation systems to ensure providing uninterruptible and reliable power. Typically, a power electronic converter is required to serve as the intermediary between the common grid in a renewable energy system and the energy storage device. To be specific, the power converter must be able to facilitate bidirectional power flow between the grid and the energy storage device. Since the voltage level of the energy storage device is often much lower than the grid voltage level, the bidirectional converter must ensure that the voltage level can be stepped up or down efficiently as per the system requirements depending on the direction of the power flow. In this thesis, a unique quasi-resonant bidirectional converter topology is proposed for energy storage application. The proposed circuit only requires two switches to achieve bidirectional power flow. Hence, compared to the conventional dual-active bridge (DAB) based bidirectional converter topologies that require 8 switches, the total number of active switching devices required the proposed topology is greatly reduced. In addition, both switches in the proposed topology are able to achieve zero voltage switching (ZVS) turn-on and zero current switching (ZCS) turn-off to minimize the switching power losses without using additional auxiliary circuits. The operating principles and design equations of the proposed circuit will be discussed in details in this thesis. An extended version of the proposed topology that employs a modular design structure for high power application is also presented and discussed. Simulation results and experimental works on a proof-of-concept hardware prototype are given to highlight the performance of the proposed bidirectional converter

Hydrogen Energy Storage

The dominating trend of variable renewable energy sources (RES) continues to underpin the early retirement of baseload power generating sources such as coal, nuclear, and natural gas steam generators; however, the need to maintain system reliability remains the challenge. Implementing energy storage with conventional power plants provides a method for load leveling, peak shaving, and time shifting allowing power quality improvement and reduction in grid energy management issues, implementing energy storage with RES smooth their intermittency, by storing the surplus in their generation for later use during their shortfall, thus enabling their high penetration into the electricity grid. Energy storage technologies (EST) can be classified according to many criteria like their application (permanent or portable), capacity, storage duration (short or long), and size (weight and volume). EST suited for short duration storage and low-to-medium power outputs are seen performing better in improving power quality, while those providing medium-to-high power outputs with long durations are seen better suited for energy management of electrical networks. With the growing deployment of renewable energy systems, EST must be utilized to allow the grid to absorb the increased integration of RES generation. The recent advances in hydrogen energy storage technologies (HEST) have unlocked their potential for use with constrained renewable generation. HEST combines hydrogen production, storage, and end use technologies with the renewable generation either in a directly connected configuration or in an indirectly connected configuration via the existing power network. This chapter introduces the hydrogen energy storage technology and its implementation in conjunction with renewable energy sources. The efficiency of renewable hydrogen energy storage systems (RHESS) will be explored with a techno-economic assessment. A levelized cost (LC) model that identifies the financial competitiveness of HEST in different application scenarios is given, where five scenarios are investigated to demonstrate the most financially competitive configuration. To address the absence of a commercial software tool that can quickly size an energy system incorporating HEST while using limited data, a deterministic modeling approach that enables a quick initial sizing of hybrid renewable hydrogen energy systems (HRHES) is given in this chapter. This modeling approach can achieve the initial sizing of a HRHES using only two input data, namely the available renewable energy resource and the load profile. A modeling of the effect of the electrolyzer thermal transients at start-up, when operated in conjunction with an intermittent renewable generation, on the quantity of hydrogen produced is also given in this chapter

Optimal Operation of a Northwest Grid of Saudi Arabia Including Renewable Resources

The use of fossil fuel, which has been one of the major sources of energy of the modern world, has led to environmental concerns. One solution to these issues is the application of renewable energy, which can also address the fluctuation in fuel prices. The Kingdom of Saudi Arabia (KSA) faces a demand of energy expected to exceed 120 GW by 2032. The government is taking appropriate actions, introducing sustainable renewable energy not only to meet the demand with clean energy sources but also to reduce the Kingdom’s consumption of fuel and gas. KSA, which has a high irradiation rate especially in the northwest area, Tabuk Region, plans to invest 41 GW maximum of solar power. In light of this decision, this research will present a comprehensive study of PV penetration up to peak output of 40 MW with battery storage to the isolated northwest grid, Tabuk Grid, as a first stage development. However, the increase of grid-connected photovoltaic (PV) in the presence of nonlinear loads, and the growth of power electronic applications produce harmonics in the power system. These harmonics may distort the current and voltage waveforms which impact the power quality and affect the operation of all electric devices. Renewable energy systems nowadays are sufficiently developed to be widely used for environmental and economic dispatch (ED) concerns. However, renewable energy that are not geographically distributed present a considerable challenge with respect to variability and availability. One of the solutions for addressing the challenge of solar variability is to use battery storage, which has been found to be effective when working in parallel with PV in peak load shaving. Time shifting renewable energy generation through the use of Battery Energy Storage Systems (BESS) can reduce the operating cost. Many studies have been focused on optimal operation with PV and battery storage. However, while achieving this optimal operation for the generators is necessary, it does not ensure secure operation of power systems. Therefore, validating secure operation with optimal generation scheduling is important. Furthermore, disregarding the battery life in optimal power scheduling creates an unrealistic scenario since replacing the battery is costly. In this research, a comprehensive study of a 40 MW PV penetration with battery storage to the Tabuk Grid is presented. The study includes complete simulation and analysis of the PV integration with storage. Moreover, a power quality study for the PV farm is conducted, one that included nonlinear loads to enhance the analysis regarding harmonics penetration. In addition, this research presents an optimal generation scheduling considering renewable energy sources, the BESS, battery life and short term outages. This will enables the system to respond and resolve outages quickly without affecting the optimal operation. The feasibility of the proposed approach is demonstrated on Tabuk system – an isolated northwest grid in Saudi Arabia

A Statistical Approach for Modeling the Aging Effects in Li-Ion Energy Storage Systems

This paper presents a novel approach for the technical and economic assessment of Li-ion battery energy storage systems (BESS) in smart grids supported by renewable energy sources. The approach is based on the definition of a statistical battery degradation cost model (SBDCM), able to estimate the expected costs related to BESS aging, according to the statistical properties of its expected cycling patterns. This new approach can improve the assessment of the economical sustainability of BESSs in this kind of applications, helping in this way the planning processes in electricity infrastructures in presence of high penetration of intermittent renewable energy sources. The SBDCM proposed in this paper is a statistical generalization of a battery degradation model presented in the literature. The proposed approach has been validated numerically comparing the results with those of the deterministic model considering for the BESS a stochastic dataset of input signals. In order to test the usefulness of the proposed model in a real world application, the proposed SBDCM has been applied to the evaluation of the economic benefit associated to the development of distributed energy storage system scenarios in the Italian power system, aimed to provide ancillary services for supporting electricity market

Green Principles, Parametric Analysis, and Optimization for Guiding Environmental and Economic Performance of Grid-scale Energy Storage Systems

The development and deployment of grid-scale energy storage technologies have increased recently and are expected to grow due to technology improvements and supporting policies. While energy storage can help increase the penetration of renewables, reduce the consumption of fossil fuels, and increase the grid sustainability, its integration into the electric grid poses unique sustainability challenges that need to be investigated through systematic sustainability assessment frameworks. The main objective of this dissertation is to develop principles and models to assess the environmental and economic impacts of grid-scale energy storage and guide its development and deployment. The first study of this dissertation is an initial case study of energy storage to examine the role of cost-effective energy storage in supporting high penetration of wind energy and achieving emissions targets in an off-grid configuration. In this study, the micro-grid system includes wind energy integrated with vanadium redox flow battery (VRFB) as energy storage, and natural gas engine. Life cycle greenhouse gas (GHG) emissions and total cost of delivered electricity are evaluated and generation mixes are optimized to meet emissions targets at the minimum cost. The results demonstrate that while incorporating energy storage consistently reduces life cycle GHG emissions in the system by integrating more wind energy, its integration is cost-effective only under very ambitious emission targets. The insights from this case study and additional literature review led to the development of a set of twelve principles for green energy storage, presented in the second study. These principles are applicable to the wide range of energy storage technologies and grid applications, and are developed to guide the design, maintenance, and operation of energy storage systems for grid applications. The robustness of principles was tested through a comprehensive literature review and also through in-depth quantitative analyses of the VRFB off-grid system. An in-depth parametric analysis is developed in the third study to evaluate the impacts of six key parameters (e.g. energy storage service-life) that influence the environmental performance of six energy storage technologies within three specific grid applications (including time-shifting, frequency regulation, and power reliability). This study reveals that round-trip efficiency and heat rate of charging and displaced generation technologies are dominant parameters in time-shifting and regulation applications, whereas energy storage service life and production burden dominate in power reliability. Finally, an optimization model is developed in the fourth study to examine the real-world application of energy storage in bulk energy time-shifting in California grid under varying renewable penetration levels. The objective was to find the optimal operation and size of energy storage in order to minimize the system total costs (including monetized GHG emissions), while meeting the electricity load and systems constraints. Simulations were run to investigate how the operation of nine distinct storage technologies impacted system cost, given each technology’s characteristics. The results show that increasing the renewable capacity and the emissions tax would make it more cost-effective for energy storage deployment. Among storage technologies, pumped-hydro and compressed-air energy storage with lower capital costs, are deployed in more scenarios. Overall, this research demonstrates how sustainability performance is influenced by storage technology characteristics and the electric grid conditions. The systematic principles, model equations, and optimizations developed in this dissertation provide specific guidance to industry stakeholders on design and deployment choices. The targeted audience ranges from energy storage designers and manufacturers to electric power utilities.PHDNatural Resources & EnvironmentUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143942/1/marbab_1.pd

A Review of Flywheel Energy Storage System Technologies and Their Applications

Energy storage systems (ESS) provide a means for improving the efficiency of electrical systems when there are imbalances between supply and demand. Additionally, they are a key element for improving the stability and quality of electrical networks. They add flexibility into the electrical system by mitigating the supply intermittency, recently made worse by an increased penetration of renewable generation. One energy storage technology now arousing great interest is the flywheel energy storage systems (FESS), since this technology can offer many advantages as an energy storage solution over the alternatives. Flywheels have attributes of a high cycle life, long operational life, high round-trip efficiency, high power density, low environmental impact, and can store megajoule (MJ) levels of energy with no upper limit when configured in banks. This paper presents a critical review of FESS in regards to its main components and applications, an approach not captured in earlier reviews. Additionally, earlier reviews do not include the most recent literature in this fast-moving field. A description of the flywheel structure and its main components is provided, and different types of electric machines, power electronics converter topologies, and bearing systems for use in flywheel storage systems are discussed. The main applications of FESS are explained and commercially available flywheel prototypes for each application are described. The paper concludes with recommendations for future research

Optimization of active power curtailment in grids with high renewable energy source penetration

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáThe high penetration of renewable energy in the distribution network can cause issues related to the imbalance between load and generation at certain moments, primarily due to the intermittent nature of these sources. This phenomenon has led to an increase in the curtailment of renewable energy and consequently in the regulation of this activity in order to limit these values. In this scenario, the application of optimal power flow becomes relevant to ensure that energy dispatch is carried out efficiently and respecting the regulated and security limits mof the electrical grid. This study presents the application of a multi-objective optimization method to solve the optimal power flow problem in a transmission network with high penetration of renewable energy and the incorporation of a hydrogen-based energy storage system. The algorithm used aims to optimize the dispatch of renewable energy considering two objectives: reducing active system losses and reducing energy curtailment in wind and solar parks. The results highlight the impact of the storage system in the curtailment of renewable energy and in the system losses, reducing both factors, and reinforcing the capability of these systems to improve network flexibility. Furthermore, the results demonstrate the efficiency of the multi-objective optimization method in representing and addressing both objective functions during the resolution of the proposed case study.A alta penetração de energia renovável na rede de distribuição pode causar problemas de desequilíbrio entre carga e geração de energia em certos momentos, principalmente devido à característica intermitente dessas fontes. Esse fenômeno resultou no aumento do corte da energia despachada por esses geradores e, consequentemente, na regulamentação dessa atividade para limitar esses valores. Nesse cenário, a aplicação do fluxo ótimo de potência torna-se relevante para garantir que o despacho de energia seja realizado de maneira eficiente e respeitando as restrições regulamentadas e de segurança da rede elétrica. Esse estudo apresenta a aplicação de um método de otimização multiobjectivo para solucionar o problema de fluxo potência ótimo em uma rede de transmissão com alta penetração de energia renovável e inclusão de um sistema de armazenamento de energia baseado em hidrogênio. O algoritimo utilizado tem como objetivo o despacho ótimo da energia renovavel considerando dois objetivos, a redução de perdas ativas do sistema e redução dos cortes de energia nos parques eólicos e solares. Os resultados encontrados destacam o impacto do sistema de armazenamento no corte de energia renovável e nas perdas do sistema, reduzindo ambos fatores, reforçando a capacidade desses sistemas em aumentar a flexibilidade da rede. Além disso, os resultados demostraram a eficiência do método de otimização multiobjetivo em representar e lidar ambas funções objetivas durante a solução do caso de estudo proposto

An assessment of flywheel storage for efficient provision of reliable power for residential premises in islanded operation

Energy storage systems (ESS) are key devices for improving power quality, electrical system stability and system efficiency by contributing to the balance of supply and demand. They can enhance the flexibility of electrical systems by mitigating supply intermittency, which has recently become problematic due to the increased penetration of renewable generation. The subject of this thesis is flywheel energy storage system (FESS), a technology that is gathering great interest due to benefits offered over alternative energy storage solutions, including high cycle life, long calendar life, high round‐trip efficiency, high power density, operation at high ambient temperatures and low negative environmental impact. This thesis describes the modelling and assessment of small scale energy system incorporating FESS with solar photovoltaic (PV) and a diesel generator for use in islanded residential premises with highly intermittent or non‐existent grid infrastructure. In this application, incorporation of FESS is shown to be beneficial in comparison to a system without storage or one with the alternative storage technology, Li‐Ion batteries. The thesis begins with a description of flywheel storage systems configured for electrical storage which comprises of a mechanical part; flywheel rotor, bearings and containment, and an electric drive part; motor‐generator and associated power electronics. Each of these components is described in the thesis along with the equations and modelling, itself carried out in the MATLAB/Simulink environment. Finally, the flywheel model is combined with a model of an islanded residential power system incorporating a solar PV system with a diesel generator. Such a system would be particularly useful for offgrid applications or those with weak grids as occurs in developing countries