Hybrid energy sources for electric and fuel cell vehicle propulsion

Given the energy (and hence range) and performance limitations of electro-chemical batteries, hybrid systems combining energy and power dense storage technologies have been proposed for electric vehicle propulsion. The paper will discuss the application of electro-chemical batteries, supercapacitors and fuel cells in single and hybrid source configurations for electric vehicle drive-train applications. Simulation models of energy sources are presented and used to investigate the design optimisation of electric vehicle on-board energy source in terms of energy efficiency and storage mass/volume. Results from a case study considering a typical small urban electric vehicle are presented, illustrating the benefits of hybrid energy sources in terms of system mass and vehicle range. The models and approach can be applied to other vehicles and driving regimes

Energy Storage Technologies for Smoothing Power Fluctuations in Marine Current Turbines

With regard to marine renewable energies, significant electrical power can be extracted from marine tidal current. However, the power harnessed by a marine current turbine varies due to the periodicity of the tidal phenomenon and could be highly fluctuant caused by swell effect. To improve the power quality and make the marine current generation system more reliable, energy storage systems will play a crucial role. In this paper, the power fluctuation phenomenon is described and the state of art of energy storage technologies is presented. Characteristics of various energy storage technologies are analyzed and compared for marine application. The omparison shows that high-energy batteries like sodiumsulphur battery and flow battery are favorable for smoothing the long-period power fluctuation due to the tide phenomenon while supercapacitors and flywheels are suitable for eliminating short-period power disturbances due to swell or turbulence phenomena. It means that hybrid storage technologies are needed for achieving optimal performance in marine current energy systems

Advanced control strategies for vehicle to grid systems with electric vehicles as distributed sources

University of Technology Sydney. Faculty of Engineering and Information Technology.This thesis focuses on the control and implementation of the vehicle to grid (V2G) system in a smart grid. Important issues like structure, principle, performance, and control of energy storage systems for electrical vehicles and power systems are discussed. In recent decades, due to rapid consumption of the earth’s oil resources, air pollution and global warming (a result of the “greenhouse effect”), the development of electrical vehicles (EVs), hybrid electrical vehicles (HEVs) and plug-in electric vehicles (PEVs) are attracting more and more attentions. In order to provide regulation services and spinning reserves (to meet sudden demands for power), V2G services have a promising prospective future for grid support. It has been proposed that in the future development, such use of V2G could buffer and support effectively the penetration of renewable sources in power systems. This PhD thesis project aims to develop novel and competitive control strategies for V2G services implementation for EVs in smart electrical car parks or Smartparks. Through a comprehensive literature review of the current EV development and energy storage systems used for EVs, several energy storage technologies are compared and a hybrid energy storage system consisting of batteries and supercapacitors is proposed. This system combines effectively the advantages of high energy density of battery banks and high power density of supercapacitor banks. Supercapacitor and battery cells are tested in the laboratory using different charging and discharging procedures. Different supercapacitor and battery models are compared, discussed, and verified using the experimental data. For the energy storage system package, a cell voltage balance circuit is developed for the supercapacitor module. The principle of this circuit is also applicable to the battery module. The proposed balancing method is simple and reliable, and presents good performance for voltage balancing to prolong the lifetime of the energy storage system. The essential technology of V2G is based on the bidirectional power flow control of the charger. Besides charging the EV batteries, it can utilize the stored energy to feed electricity back to the power grid when there is a need. Three-phase AC/DC converters have been extensively used in industrial applications and also the V2G chargers. The power converters used for the V2G services are required to operate more efficiently and effectively to maintain high power quality and dynamic stability. Then the AC/DC converter used for the bidirectional V2G charger is developed and modelled. For the control aspect of AC/DC converter, a new control approach using a model predictive control (MPC) scheme is developed for V2G applications. With the advanced control strategy, the EVs in Smartparks can exchange both active and reactive power with the grid flexibly. The MPC algorithm presents excellent steady-state and dynamic performance. When a very large number of EVs are aggregated in Smartparks, the charging and discharging power should be a significant viable contributor to the power grid. New challenges will be introduced into the power system planning and operation. While discharging, the V2G power brings more potential benefits to enhance the power quality and system reliability. Using V2G services, EVs can provide many grid services, such as regulation and spinning reserve, load levelling, serving as external storage for renewable sources. An effective approach to deal with the negligibly small impact of a single EV is to group a large number of EVs. An aggregator is a new player whose role is to collect the EVs by attracting and retaining them so as to result in a MW capacity that can beneficially impact the grid. From the aggregator’ decision, the EVs are determined by the optimal deployment. The aggregator can act as a very effective resource by helping the operator to supply both capacity and energy services to the grid. By supplying active power and reactive power from EVs, the aggregation may be used for frequency and voltage regulation to control frequency and voltage fluctuations that are caused by supply–demand imbalances. Different case studies of EVs’ support to grid are carried out; the results show that V2G services can stabilize the frequency and voltage variations and have control flexibilities to fulfil system reliability and power quality requirements. The main attractiveness of V2G to consumers is that it can produce income to the vehicle owner to maximize car use. On the other hand, the utility companies can use EVs to stabilize the frequency in the power system and improve the utility operation. It also makes the utility companies more efficient with less loss because the energy is generated locally. From this point of view, V2G is a source of revenue in both electricity and transportation system, and it can help the environment reduce pollution and global warming. Various data of V2G systems have been collected for economic analysis, such as EV battery capacities, charging time, and grid electricity price and load demands. Then for the economic issues related to V2G services, optimal charging based on different objectives is presented. Dumbing charging, maximization of the average state of charge (SOC), maximum revenue and minimum cost are compared. Economic issues are a very special aspect of the V2G technology and how a large profit from V2G services can be produced is the main point of attraction to vehicle owners. Significant conclusions based on the research findings are drawn, and possible future works for further development including commercialisation of the V2G technology are proposed

A hybrid energy storage solution based on supercapacitors and batteries for the grid integration of utility scale photovoltaic plants

This paper presents a 2-level controller managing a hybrid energy storage solution (HESS) for the grid integration of photovoltaic (PV) plants in distribution grids. The HESS is based on the interconnection of a lead-acid battery pack and a supercapacitor pack through a modular power electronics cabinet. The inclusion of the HESS into the PV plant –and not an state-of-the-art energy storage system based on a single technology–, is motivated by the diversity of technical requirements for the provision of the services of grid peak power shaving and PV output power ramp limitation. The 2-level controller ensures a synergistic exploitation of the two storage technologies aiming for an optimal service level of the HESS and minimum battery degradation. The higher level of the controller is based on a mathematical optimization problem that solves with the optimal schedule of the storage technologies for peak power shaving purposes. The power setpoints of this optimization are then complemented by a real time controller managing PV plant output ramp limitation. The HESS performance and associated controller has been proved effective through two case studies. The first one adopts a 6.6 MW PV plant including a HESS solution combining a 5.5 MWh and 2.64 MW lead-acid battery pack with a 0.25 MWh and 1.32 MW supercapacitor pack. The second one reports experimental data from an analogous scenario scaled down to kW level and using a laboratory scale prototype for the HESS. All in all, the hardware and software solutions proposed in this paper contribute to a feasible exploitation of multi-purpose energy storages targeting the needs of renewables' and distribution system operators.Peer ReviewedPostprint (published version

A smart power electronic multiconverter for the residential sector

El futuro de la red incluye la generación distribuida y las tecnologías de red inteligente. Los sistemas de gestión del lado de la demanda (DSM) también serán esenciales para lograr un alto nivel de confiabilidad y robustez en los sistemas de energía. Para hacer eso, es necesario expandir la Infraestructura de medición avanzada (AMI) y los Sistemas de gestión de energía (EMS). La dirección de la tendencia es hacia la creación de centros de recursos energéticos, como el concepto de comunidad inteligente. Este documento presenta un sistema multiconvertidor inteligente para el sector residencial / vivienda con un Sistema de Almacenamiento de Energía Híbrido (HESS) que consta de supercapacitador y batería, y con integración de fuente de energía fotovoltaica (PV) local. El dispositivo funciona como una unidad de energía distribuida ubicada en cada casa de la comunidad, recibiendo puntos de ajuste de energía activos proporcionados por una comunidad inteligente EMS. Este SGA central es responsable de administrar los flujos de energía activa entre la red eléctrica, las fuentes de energía renovables, los equipos de almacenamiento y las cargas existentes en la comunidad. El multiconvertidor propuesto es responsable de cumplir con los puntos de referencia de potencia activa de referencia con la calidad de potencia adecuada; garantizando que los módulos fotovoltaicos locales funcionen con un algoritmo de seguimiento del punto de máxima potencia (MPPT); y prolongando la vida útil de la batería gracias a un funcionamiento cooperativo del HESS. Se ha desarrollado un modelo de simulación para mostrar el funcionamiento detallado del sistema. Finalmente, se implementó un prototipo de la plataforma de multiconversores y se realizaron algunas pruebas experimentales para validarlo.The future of the grid includes distributed generation and smart grid technologies. Demand Side Management (DSM) systems will also be essential to achieve a high level of reliability and robustness in power systems. To do that, expanding the Advanced Metering Infrastructure (AMI) and Energy Management Systems (EMS) are necessary. The trend direction is towards the creation of energy resource hubs, such as the smart community concept. This paper presents a smart multiconverter system for residential/housing sector with a Hybrid Energy Storage System (HESS) consisting of supercapacitor and battery, and with local photovoltaic (PV) energy source integration. The device works as a distributed energy unit located in each house of the community, receiving active power set-points provided by a smart community EMS. This central EMS is responsible for managing the active energy flows between the electricity grid, renewable energy sources, storage equipment and loads existing in the community. The proposed multiconverter is responsible for complying with the reference active power set-points with proper power quality; guaranteeing that the local PV modules operate with a Maximum Power Point Tracking (MPPT) algorithm; and extending the lifetime of the battery thanks to a cooperative operation of the HESS. A simulation model has been developed in order to show the detailed operation of the system. Finally, a prototype of the multiconverter platform has been implemented and some experimental tests have been carried out to validate it.Ministerio de Economía y Competitividad (España) y Fondos FEDER: Proyecto TEC2013-47316-C3-3-PpeerReviewe

Control of AC/DC microgrids with renewables in the context of smart grids including ancillary services and electric mobility

Microgrids are a very good solution for current problems raised by the constant growth of load demand and high penetration of renewable energy sources, that results in grid modernization through “Smart-Grids” concept. The impact of distributed energy sources based on power electronics is an important concern for power systems, where natural frequency regulation for the system is hindered because of inertia reduction. In this context, Direct Current (DC) grids are considered a relevant solution, since the DC nature of power electronic devices bring technological and economical advantages compared to Alternative Current (AC). The thesis proposes the design and control of a hybrid AC/DC Microgrid to integrate different renewable sources, including solar power and braking energy recovery from trains, to energy storage systems as batteries and supercapacitors and to loads like electric vehicles or another grids (either AC or DC), for reliable operation and stability. The stabilization of the Microgrid buses’ voltages and the provision of ancillary services is assured by the proposed control strategy, where a rigorous stability study is made. A low-level distributed nonlinear controller, based on “System-of-Systems” approach is developed for proper operation of the whole Microgrid. A supercapacitor is applied to deal with transients, balancing the DC bus of the Microgrid and absorbing the energy injected by intermittent and possibly strong energy sources as energy recovery from the braking of trains and subways, while the battery realizes the power flow in long term. Dynamical feedback control based on singular perturbation analysis is developed for supercapacitor and train. A Lyapunov function is built considering the interconnected devices of the Microgrid to ensure the stability of the whole system. Simulations highlight the performance of the proposed control with parametric robustness tests and a comparison with traditional linear controller. The Virtual Synchronous Machine (VSM) approach is implemented in the Microgrid for power sharing and frequency stability improvement. An adaptive virtual inertia is proposed, then the inertia constant becomes a system’s state variable that can be designed to improve frequency stability and inertial support, where stability analysis is carried out. Therefore, the VSM is the link between DC and AC side of the Microgrid, regarding the available power in DC grid, applied for ancillary services in the AC Microgrid. Simulation results show the effectiveness of the proposed adaptive inertia, where a comparison with droop and standard control techniques is conducted.As Microrredes são uma ótima solução para os problemas atuais gerados pelo constante crescimento da demanda de carga e alta penetração de fontes de energia renováveis, que resulta na modernização da rede através do conceito “Smart-Grids”. O impacto das fontes de energia distribuídas baseados em eletrônica de potência é uma preocupação importante para o sistemas de potência, onde a regulação natural da frequência do sistema é prejudicada devido à redução da inércia. Nesse contexto, as redes de corrente contínua (CC) são consideradas um progresso, já que a natureza CC dos dispositivos eletrônicos traz vantagens tecnológicas e econômicas em comparação com a corrente alternada (CA). A tese propõe o controle de uma Microrrede híbrida CA/CC para integrar diferentes fontes renováveis, incluindo geração solar e frenagem regenerativa de trens, sistemas de armazenamento de energia como baterias e supercapacitores e cargas como veículos elétricos ou outras (CA ou CC) para confiabilidade da operação e estabilidade. A regulação das tensões dos barramentos da Microrrede e a prestação de serviços anciliares são garantidas pela estratégia de controle proposta, onde é realizado um rigoroso estudo de estabilidade. Um controlador não linear distribuído de baixo nível, baseado na abordagem “System-of-Systems”, é desenvolvido para a operação adequada de toda a rede elétrica. Um supercapacitor é aplicado para lidar com os transitórios, equilibrando o barramento CC da Microrrede, absorvendo a energia injetada por fontes de energia intermitentes e possivelmente fortes como recuperação de energia da frenagem de trens e metrôs, enquanto a bateria realiza o fluxo de potência a longo prazo. O controle por dynamical feedback baseado numa análise de singular perturbation é desenvolvido para o supercapacitor e o trem. Funções de Lyapunov são construídas considerando os dispositivos interconectados da Microrrede para garantir a estabilidade de todo o sistema. As simulações destacam o desempenho do controle proposto com testes de robustez paramétricos e uma comparação com o controlador linear tradicional. O esquema de máquina síncrona virtual (VSM) é implementado na Microrrede para compartilhamento de potência e melhoria da estabilidade de frequência. Então é proposto o uso de inércia virtual adaptativa, no qual a constante de inércia se torna variável de estado do sistema, projetada para melhorar a estabilidade da frequência e prover suporte inercial. Portanto, o VSM realiza a conexão entre lado CC e CA da Microrrede, onde a energia disponível na rede CC é usada para prestar serviços anciliares no lado CA da Microrrede. Os resultados da simulação mostram a eficácia da inércia adaptativa proposta, sendo realizada uma comparação entre o controle droop e outras técnicas de controle convencionais

Firm technological responses to regulatory changes: A longitudinal study in the Le Mans Prototype racing

Despite the critical role of regulations on competition and innovation, little is known about firm responses and related effects on performance under regulatory contingencies that are permissive or restrictive. By longitudinally investigating hybrid cars competing in the Le Mans Prototype racing (LMP1), we counter-intuitively suggest that permissive regulations increase technological uncertainty and thus decrease the firms’ likelihood of shifting their technological trajectory, while restrictive regulations lead to the opposite outcome. Further, we suggest that permissive regulations favour firms that innovate their products by sequentially upgrading core and peripheral subsystems, while restrictive regulations—in the long term— favour firms upgrading them simultaneously. Implications for theory and practice are discussed