Super-capacitor energy storage system to recuperate regenerative braking energy in elevator operation of high buildings

In operating phases of elevators, accelerating, braking modes occur frequently, so braking energy recuperation of elevators has contributed considerably to decrease the total electric energy consumption for operating elevators in multi-floor buildings. In this paper, the supercapacitor energy storage system is used to recover regenerative braking energy of elevators when they operate down full-load and up no-load, reducing fluctuation of voltage on DC bus as well. Therefore, super-capacitor energy storage system (SCESS) will be parallel with line utility to recuperate regenerative braking energy in braking phase and support energy for acceleration phase. The surplus energy will be stored in the supercapacitors thanks to a DC-DC converter capable of exchanging energy bidirectionally in buck/boost modes, and designing control strategy including two control loops. Inner loop-current loop: controlling charge/discharge process of supercapacitors by current iL complying with operation characteristic of elevator; Outer loop-voltage loop: managing UDC-link at a fixed value. Simulation results with elevator system of the ten-floor building, Hanoi, Vietnam installed SCESS have been verified on MATLAB Simulink, SimPowerSystem with saving energy level about 30%

Elevator regenerative energy applications with ultracapacitor and battery energy storage systems in complex buildings

Due to the dramatic growth of the global population, building multi-story buildings has become a necessity, which strongly requires the installation of an elevator regardless of the type of building being built. This study focuses on households, which are the second-largest electricity consumers after the transportation sector. In residential buildings, elevators impose huge electricity costs because they are used by many consumers. The novelty of this paper is implementing a Hybrid Energy Storage System (HESS), including an ultracapacitor Energy Storage (UCES) and a Battery Energy Storage (BES) system, in order to reduce the amount of power and energy consumed by elevators in residential buildings. The control strategy of this study includes two main parts. In the first stage, an indirect field-oriented control strategy is implemented to provide new features and flexibility to the system and take benefit of the regenerative energy received from the elevator’s motor. In the second stage, a novel control strategy is proposed to control the HESS efficiently. In this context, the HESS is only fed by regenerated power so the amount of energy stored in the UC can be used to reduce peak consumption. Meanwhile, the BES supplies common electrical loads in the building, e.g., washing machines, heating services (both boiler and heat pump), and lighting, which helps to achieve a nearly zero energy building

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

Recuperation of Regenerative Braking Energy in Electric Rail Transit Systems

Electric rail transit systems are large consumers of energy. In trains with regenerative braking capability, a fraction of the energy used to power a train is regenerated during braking. This regenerated energy, if not properly captured, is typically dumped in the form of heat to avoid overvoltage. Finding a way to recuperate regenerative braking energy can result in substantial economic as well as technical benefits. Regenerative braking energy can be effectively recuperated using wayside energy storage, reversible substations, or hybrid storage/reversible substation systems. In this research study, we compare these recuperation techniques and investigate their application in New York City Transit (NYCT) systems, where most of the regenerative braking energy is currently being wasted. We have developed a detailed transient model to determine the applicability, feasibility, and pros and cons of deploying wayside energy storage, such as batteries, super capacitors or flywheels. This model has been validated using real measurement data on the 7-Line (Flushing), including:1) speed, current, voltage, power and energy train profiles; and 2) 24-hour interval metering data at substations. The validated model has been used to analyze and compare various ESS technologies, including Li-ion Battery, Supercapacitor and Flywheel. In addition, we have developed detailed transient models for reversible substations. A reversible substation, also known as bidirectional or inverting substation, provides a path through an inverter for regenerative braking energy to feedback to the upstream AC grid. This energy can be consumed by AC equipment within passenger stations (e.g., escalators) or fed back to the main grid based on legislations of the electric distribution utility. This study will provide crucial technical as well as financial guidelines for various stakeholders while making investment decisions pertaining to regenerative braking energy

Optimum Distribution System Architectures for Efficient Operation of Hybrid AC/DC Power Systems Involving Energy Storage and Pulsed Loads

After more than a century of the ultimate dominance of AC in distribution systems, DC distribution is being re-considered. However, the advantages of AC systems cannot be omitted. This is mainly due to the cheap and efficient means of generation provided by the synchronous AC machines and voltage stepping up/down allowed by the AC transformers. As an intermediate solution, hybrid AC/DC distribution systems or microgrids are proposed. This hybridization of distribution systems, incorporation of heterogeneous mix of energy sources, and introducing Pulsed Power Loads (PPL) together add more complications and challenges to the design problem of distribution systems. In this dissertation, a comprehensive multi-objective optimization approach is presented to determine the optimal design of the AC/DC distribution system architecture. The mathematical formulation of a multi-objective optimal power flow problem based on the sequential power flow method and the Pareto concept is developed and discussed. The outcome of this approach is to answer the following questions: 1) the optimal size and location of energy storage (ES) in the AC/DC distribution system, 2) optimal location of the PPLs, 3) optimal point of common coupling (PCC) between the AC and DC sides of the network, and 4) optimal network connectivity. These parameters are to be optimized to design a distribution architecture that supplies the PPLs, while fulfilling the safe operation constraints and the related standard limitations. The optimization problem is NP-hard, mixed integer and combinatorial with nonlinear constraints. Four objectives are involved in the problem: minimizing the voltage deviation (ΔV), minimizing frequency deviation (Δf), minimizing the active power losses in the distribution system and minimizing the energy storage weight. The last objective is considered in the context of ship power systems, where the equipment’s weight and size are restricted. The utilization of Hybrid Energy Storage Systems (HESS) in PPL applications is investigated. The design, hardware implementation and performance evaluation of an advanced – low cost Modular Energy Storage regulator (MESR) to efficiently integrate ES to the DC bus are depicted. MESR provides a set of unique features: 1) It is capable of controlling each individual unit within a series/parallel array (i.e. each single unit can be treated, controlled and monitored separately from the others), 2) It is able to charge some units within an ES array while other units continue to serve the load, 3) Balance the SoC without the need for power electronic converters, and 4) It is able to electrically disconnect a unit and allow the operator to perform the required maintenance or replacement without affecting the performance of the whole array. A low speed flywheel Energy Storage System (FESS) is designed and implemented to be used as an energy reservoir in PPL applications. The system was based on a separately excited DC machine and a bi-directional Buck-Boost converter as the driver to control the charging/discharging of the flywheel. Stable control loops were designed to charge the FESS off the pulse and discharge on the pulse. All the developments in this dissertation were experimentally verified at the Smart Grid Testbed

A super-capacitor based energy storage for quick variation in stand-alone PV systems

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonPHOTOVOLTAIC (PV) system is one of the most prominent energy sources, producing electricity directly from sunlight. In additionally, it is easy to install and is supported financially by many governments as part of their strategy to reduce CO2 gas emissions, and to achieve their agreed set of reduction targets by 2020. In the meantime, researchers have been working on the PV system to make it more efficient, easy to maintain, reliable to use and cost effective. In the stand-alone PV system, a battery is required. This is due to the fluctuating nature of the output energy delivered by the PV arrays owing to the weather conditions and the unpredictable behaviour of uses with regard to the consumption of energy. During the hours of sunshine, the PV system is directly feeding the load and any surplus electrical energy is stored in the battery at a constant current. During the night, or during a period of low solar irradiation, the energy is supplied to the load from the battery. However, the stand-alone PV system is designed to provide an acceptable balance between reliability and cost, which is a major challenge to the designer owing to the approaches used to size the PV arrays and the battery bank. As a result, the unpredictable, quick daily changes on the PV output is not dependable. Moreover, battery performance, length of life and energy efficiency depends on the rate at which it is discharged. Therefore, it is essential to use other methods to deal with any quick variation in energy. In this thesis, a super capacitor is used to solve this problem, as it can deal with the fast-changing weather, or a rapid variation in the energy requirements of the customer. A critical evaluation with in-depth analysis of the placement and the implementation for the super-capacitor in the PV standalone system has been carried out. The results show, super-capacitor capacitance and the converter efficiency affect the delivered load energy. However, the bi-directional topology performs better than uni-directional under the same conditions. Finally, a further improvement of the system at component level, has been developed through an energy recovery snubber for the switching transition and achieved a recovery of energy for the resistive load, 94.44% for the turn on transition and 92.86% for the turn off transition. Moreover, for the inductive load, 78.33% and 97.33% of energy has been recovered for the turn on and for the turn off transition respectively.Engineering and Physical Sciences Research Council (EPSRC

Effective strategies to enhance electrochemical performance of carbon materials for non-aqueous potassium- and sodium-ion capacitors

Hybrid-Ionen-Kondensatoren werden seit Jahrzehnten als eine aufstrebende Klasse von Energiespeichersystemen betrachtet, die die Leistung kommerzieller elektrischer Doppelschichtkondensatoren mit hoher Leistung und konventioneller Sekundär-Ionen-Batterien mit ausgezeichnet energischem Output überbrücken können. In der letzten Zeit wurden Kalium- und Natrium-Ionen-Kondensatoren aufgrund der Abundanz und der Kosten-Günstigkeit des Kalium- und -Natriumressourcen als aussichtsreiche Energiespeicher für kommerzielle Anwendungen angesehen. Aber drei wesentliche Herausforderungen sollen zuerst diskutiert werden. Die limitierte Elektrodenkapazität aufgrund der Komplexität der hybriden Ionenspeicherung, die Diffusionskinematik der Ionen beschränkt durch den großen Radius der K- und Na-Ionen und die fehlende Elektrolytforschung. Um die obengenannten Herausforderungen zu bewältigen, werden drei neuartige und effektive Strategien entwickelt, sodass die drei wichtigen Komponenten bzw. die Kathode, der Elektrolyt und die Anode der Hybrid-Ionen-Kondensatoren optimiert werden können. Zuerst wird eine mit dem Sauerstoff funktionalisierter Kohlenstoff-Elektrode als höher Kapazität-Kathode der Kalium-Ionen-Kondensatoren hergestellt. Dabei wird die Rationalität der Auswahl der Kohlenstoff-Precursoren und die Sauerstofffunktionalisierungstechnik diskutiert. Demnächst wird eine systematische Korrelationsuntersuchung zwischen den Elektrolyten und der Dual-Ionenspeicherung der Sauerstoffkatode der Kalium-Ionen Kondensatoren durchgeführt. Die Interaktion zwischen Kationen und Anionen spielt eine wichtige Rolle bei der Dual-Ionen-Speicherung der Kohlenstoff-Kathode. Darüber hinaus wird gezeigt, dass der Ether-Elektrolyt bei der Kationen- und Anionen-Speicherung mit hohen Raten besser als der Ester-Elektrolyt wirkt. Drittens wird eine Kombination aus Adsorptions- und Co-Interkalationsmechanismus als neue Ionenspeicherungsmechanismus vorgeschlagen, um eine effiziente schnelle Na-Ionen-Speicherung auf der Kohlenstoff-Anode der Nalium-Ionen Kondensatoren zu realisieren. Alle drei Arbeiten werden sowohl in Halb- als auch in Vollzellen demonstriert, sodass eine verbesserte elektrochemische Leistung in Bezug auf große Kapazität, lange Lebensdauer und das High-Rate Vermögens erreichen werden kann. Die obengenannten effektiven Strategien haben ausführlich gezeigt, wie die Gestaltung der Materialsynthese, die Optimierung des Elektrolyten und die Modifizierung des Mechanismus für die leistungsstarken Hybrid-Ionen-Kondensatoren sind.Hybrid ion capacitors have attracted much attention for decades as an emerging class of energy storage system that may bridge the performance of commercial electric double-layer capacitors with high-power output and conventional secondary ion batteries with high-energy output. Recently, potassium- and sodium-ion capacitors have been considered as promising energy storage devices to realize commercial applications owing to the abundant and low-cost sodium and potassium resources. However, there are still three key challenges to promote their development. First, electrode capacity suffers from the complexity of hybrid ion storage. Second, ionic diffusion kinetics suffers from the large radius of Na and K ions. Third, the lack of electrolyte research. In order to tackle these challenges, three novel and effective strategies are developed to optimize three important components of hybrid ion capacitors: cathode, electrolyte, and anode. First, an oxygen-functionalized carbon electrode is fabricated as the high-capacity cathode for potassium-ion capacitor. The rationality of the carbon precursor selection and oxygen functionalization engineering are discussed. Second, a systematic investigation between the electrolytes and dual-ion storage is carried out. This work first reveals that the interaction of the cations and anions plays a key role in the dual-ion storage of the carbon cathode. It further demonstrates that the ether electrolyte outperforms the ester electrolytes in high-rate cation and anion storage. Third, a combination of adsorption mechanism and co-intercalation mechanism is proposed to realize fast Na-ion storage on the carbon anode. All three works are demonstrated in both half cells and full cells, they achieve improved electrochemical performance in terms of large capacity, long cycle life, and high rate capability. These effective strategies can provide valuable guidance regarding materials synthesis design, electrolyte optimization, and mechanism modification for approaching high-performance hybrid ion capacitors