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Hydrokinetic river (HKT) and photovoltaic (PV) panels systems are of the promising technologies to be used for remote rural electrification. In rural areas with access to water and solar resources, renewable generation is a promising option for electrification. This paper presents a study by two sizing methods for a stand-alone hybrid generation system integrating renewable energies (PV panels and hydrokinetic) and storage system based on battery and backup generator diesel. In the first case, optimal technical sizing is achieved by using basic equations and Simulink Design Optimization (SDO). The other method perform an optimal techno-economical sizing by using the hybrid system optimization software HOMER. These methods have been applied to design a stand-alone hybrid system that supplies the load energy demand for one year, minimizing the use of the diesel generator. The results are reported and discussed in the paper.

This paper presents a comparative study of four sizing methods for a stand-alone hybrid generation system integrating renewable energies (photovoltaic panels and wind turbine) and backup and storage system based on battery and hydrogen (fuel cell, electrolyzer and hydrogen storage tank). Two of them perform a technical sizing. In one case, the sizing is based on basic equations, and in the other case, an optimal technical sizing is achieved by using Simulink Design Optimization. The other two methods perform an optimal techno-economical sizing by using the hybrid system optimization software HOMER and HOGA, respectively. These methods have been applied to design a stand-alone hybrid system which supplies the load energy demand during a year. A MATLAB-Simulink model of the hybrid system has been used to simulate the performance of hybrid system designed by each method for the stand-alone application under study in this work. The results are reported and discussed in the paper.

This paper presents two novel hourly energy supervisory controls (ESC) for improving long-term operation of off-grid hybrid systems (HS) integrating renewable energy sources (wind turbine and photovoltaic solar panels), hydrogen system (fuel cell, hydrogen tank and electrolyzer) and battery. The first ESC tries to improve the power supplied by the HS and the power stored in the battery and/or in the hydrogen tank, whereas the second one tries to minimize the number of needed elements (batteries, fuel cells and electrolyzers) throughout the expected life of the HS (25 years). Moreover, in both ESC, the battery state-of-charge (SOC) and the hydrogen tank level are controlled and maintained between optimum operating margins. Finally, a comparative study between the controls is carried out by models of the commercially available components used in the HS under study in this work. These ESC are also compared with a third ESC, already published by the authors, and based on reducing the utilization costs of the energy storage devices. The comparative study proves the right performance of the ESC and their differences.

Improving grid connection of wind farms is a relevant issue to be addressed, especially for fixed-speed wind turbines. Certain elements, such as FACTS (Flexible AC Transmission Systems), are able to perform voltage and reactive power regulation in order to support voltage stability of wind farms, and compensate reactive power consumption from the grid. Several devices are grouped under the name of FACTS, which embrace different technologies and operating principles. Here, three of them are evaluated and compared, namely STATCOM (Static Synchronous Compensator), SVC (Static Var Compensator) and SSSC (Static Synchronous Series Compensator). They have been modeled in MATLAB / Simulink, and simulated under various scenarios, regarding both normal operation and grid fault conditions. Their response is studied together with the case when no FACTS are implemented. Results show that SSSC improves the voltage stability of the wind farm, whereas STATCOM and SVC provide additional reactive power.

This paper presents and evaluates three energy management systems (EMSs) based on Particle Swarm Optimization (PSO) for long-term operation optimization of a grid-connected hybrid system. It is composed of wind turbine (WT) and photovoltaic (PV) panels as primary energy sources, and hydrogen system (fuel cell –FC–, electrolyzer and hydrogen storage tank) and battery as energy storage system (ESS). The EMSs are responsible for making the hybrid system produce the demanded power, deciding on the energy dispatch among the ESS devices. The first PSO-based EMS tries to minimize the ESS utilization costs, the second one to maximize the ESS efficiency, and the third one to optimize the lifetime of the ESS devices. Long-term simulations of 25 years (expected lifetime of the hybrid system) are shown in order to demonstrate the right performance of the three EMSs and their differences. The simulations show that: 1) each EMS outperforms the others in the designed target; and 2) the third EMS is considered the best EMS, because it needs the least ESS devices, and presents the lowest total acquisition cost of hybrid system, whereas the rest of parameters are similar to the best values obtained by the other EMSs.

Hybrid systems comprising battery energy storage systems (BESSs) and wind power generation entail considerable advances on the grid integration of renewable energy. Doubly fed induction generators (DFIGs) stand out among different wind turbine (WT) technologies. On the other hand, electrochemical batteries have proved to be valid for these purposes. In this paper, a comparative analysis is carried out between two alternative configurations for hybrid WT-BESS systems, where the BESS is connected either outside or inside the DFIG. The modeling of these two configurations and the control systems applied for achieving the coordinate operation of the energy sources (DFIG and batteries) are illustrated. The hybrid systems under study are evaluated by simulation under normal operation (wind speed fluctuations and grid demand changes) and grid faults. Simulation results show that both configurations improve the grid integration capability of the WT, although the configuration with external BESS presents better results since it can provide additional active/reactive power injection. Copyright © 2014 John Wiley & Sons, Ltd.

Energy storage systems (ESSs) appear as a viable solution to some of the stability and intermittency problems of wind power generation. As a consequence, it is crucial to develop adequate control strategies that allow the coordinate operation of both energy sources. Moreover, in order to minimize the impact of large wind farms on the power system, many countries have set strict grid codes that wind power generators must accomplish. Hence, it is also necessary to pay due attention to the fault ride through capabilities of these hybrid systems. In this paper two different hybrid configurations are modeled in MATLAB/Simulink, consisting on a doubly fed induction generator driven wind turbine and electrochemical batteries as ESS. They are simulated and compared under various operating conditions (i.e. real fluctuating wind speed input with variable active and reactive power grid demand, voltage sags, three-phase and single-phase fault to ground, and overvoltage). A conventional wind turbine without ESS is also considered as a base-case in order to highlight the main benefits of the hybrid schemes. The results show that by implementing one of the presented control strategies, it is possible to enhance the response to faults of the hybrid systems, achieving higher active power injection and helping the recovery to steady-state, thus improving the grid connection capabilities of hybrid wind farms.

Integrating energy storage systems (ESS) with wind turbines results to be an interesting option for improving the grid integration capability of wind energy. This paper presents and evaluates a wind hybrid system consisting of a 1.5 MW doubly-fed induction generator (DFIG) wind turbine and double battery-ultracapacitor ESS. Commercially available components are used in this wind hybrid system. A novel supervisory control system (SCS) is designed and implemented, which is responsible for setting the active and reactive power references for each component of the hybrid system. A fuzzy logic controller, taking into account the grid demand, power generation prediction, actual DFIG power generation and state-of-charge (SOC) of the ESSs, sets the active power references. The reactive power references are proportionally delivered to each element regarding their current limitations in the SCS. The appropriate control of the power converters allows each power source to achieve the operation defined by the SCS. The wind hybrid system and SCS are assessed by simulation under wind fluctuations, grid demand changes, and grid disturbances. Results show an improved performance in the overall response of the system with the implementation of the SCS.

Fuel cell (FC) is an efficient energy conversion technology that is growing rapidly and will have a significant role to play in a number of energy end-use sectors, from small-scale applications to large-scale power plants. In this paper, two new methods for voltage harmonic compensation of a stand-alone single phase inverted-based FC are presented and evaluated. The stand-alone power system under study consists of: 1) Proton-Exchange-Membrane (PEM) FC with unidirectional DC/DC converter, which converts the DC voltage delivered by the FC to the DC bus voltage; 2) single-phase pulse width modulated (PWM) inverter; 3) transformer; 4) passive filter; and 5) linear and non-linear loads. The dynamic model of this system and the non-sinusoidal output-based controls applied to the PWM inverter for voltage regulation and harmonic compensation are detailed in this paper, and evaluated by simulation under different linear and non-linear loads. Simulation results show the effectiveness of the two purposed methods for voltage harmonic compensation to acceptable levels defined in grid codes.

This paper evaluates a hybrid powertrain based on fuel cell (FC), battery, and supercapacitor (SC) for the “Urbos 3” tramway, which currently operates powered by SC in the city of Zaragoza, Spain. Due to the dynamic limitations of the main energy source, a proton-exchange-membrane (PEM) FC, other energy secondary sources (ESSs), battery and SC, are needed to supply the vehicle power demand. Moreover, these energy sources allow the energy recovery during regenerative braking. The different sources are connected to a dc bus through dc-dc converters which adapt their variable voltages to the bus voltage and allow the control of energy flow between the sources and the load. The components of the hybrid tramway have been modeled in Matlab/Simulink and are based on commercially available devices. The energy management system used in this work to achieve a proper operation of the energy sources of the hybrid powertrain is based on predictive control. Simulations for the real cycle of the tramway show the suitability of the proposed powertrain and control strategy.

This paper presents a “full green” version of a rubber tyre gantry (RTG) crane with a fuel cell (FC) unit and supercapacitors (SCs) as energy storage system (ESS), instead of using the conventional RTG powered by a diesel engine. The SCs provide the required high current peaks and power demands when accelerating the load in the hoisting-up movement. Once the power demand reaches a steady level (hoist up constant speed), the FC provides the energy needed for the rest of the movements. The SCs are also charged when the hoist down movement is taking place. In this case, the regenerative energy can be stored in the SCs instead of being burnt in the braking resistors as in the conventional RTG crane. The new hybrid powertrain based on FC and SCs is designed and evaluated from the real driving cycle of the RTG crane. Simulation results, which include a comparative study with the current configuration of the RTG crane (powered only by diesel engine), demonstrate the technical viability of the RTG crane powered by FC and SCs. This hybrid powertrain is more expensive than the diesel powertrain, but more energy-efficient, and a better solution from the environmental point of view.

The entry into force of Royal Decree-Law 1/2012 has led to the elimination of the support schemes to promote the use of the energy from renewable energy sources existing to date in Spain, and thus, certain standstill of this sector activity. In this context, some renewable technologies, mainly photovoltaic solar, can find in self-consumption an alternative for promoting their development and use. The self-consumption in the form of net-metering is mainly characterized by the possibility that the consumer can generate in situ part of the consumed electricity and use the network as storage or supply system. This option is still under study by the Government, so that there is a draft of Royal Decree that has not yet been approved. The aim of this paper is to analyze the economic viability of the net-metering mode in dwellings with small power photovoltaic facilities, considering those options that can contribute to make them viable.

This paper presents a novel hourly energy management system (EMS) for a stand-alone hybrid renewable energy system (HRES). The HRES is composed of a wind turbine (WT) and photovoltaic (PV) solar panels as primary energy sources, and two energy storage systems (ESS), which are a hydrogen subsystem and a battery. The WT and PV panels are made to work at maximum power point, whereas the battery and the hydrogen subsystem, which is composed of fuel cell (FC), electrolyzer and hydrogen storage tank, act as support and storage system. The EMS uses a fuzzy logic control to satisfy the energy demanded by the load and maintain the state-of-charge (SOC) of the battery and the hydrogen tank level between certain target margins, while trying to optimize the utilization cost and lifetime of the ESS. Commercial available components and an expected life of the HRES of 25 years were considered in this study. Simulation results show that the proposed control meets the objectives established for the EMS of the HRES, and achieves a total cost saving of 13% over other simpler EMS based on control states presented in this paper.

This paper presents a sizing method and different control strategies for the suitable energy management of a stand-alone hybrid system based on photovoltaic (PV) solar panels, hydrogen subsystem and battery. The battery and hydrogen subsystem, which is composed of fuel cell (FC), electrolyzer and hydrogen storage tank, act as energy storage and support system. In order to efficiently utilize the energy sources integrated in the hybrid system, an appropriate sizing is necessary. In this paper, a new sizing method based on Simulink Design Optimization (SDO) of MATLAB was used to perform a technical optimization of the hybrid system components. An analysis cost has been also performed, in that the configuration under study has been compared with those integrating only batteries and only hydrogen system. The dynamic model of the designed hybrid system is detailed in this paper. The models, implemented in MATLAB-Simulink environment, have been designed from commercially available components. Three control strategies based on operating modes and combining technical-economic aspects are considered for the energy management of the hybrid system. They have been designed, primarily, to satisfy the load power demand and, secondarily, to maintain a certain level at the hydrogen tank (hydrogen energy reserve), and at the state of charge (SOC) of the battery bank to extend its life, taking into account also technical-economic analysis. Dynamic simulations were performed to evaluate the configuration, sizing and control strategies for the energy management of the hybrid system under study in this work. Simulation results show that the proposed hybrid system with the presented controls is able to provide the energy demanded by the loads, while maintaining a certain energy reserve in the storage sources.

Large mammal communities, integral components of Neotropical ecosystems, are increasingly threatened by habitat fragmentation and degradation due to anthropogenic pressures and climate change. Lowland Neotropical palm forests harbor diverse mammal communities, including threatened and endangered species. We monitored three transects in the Barra del Colorado Wildlife Refuge in Northeast Costa Rica from February 2014 until April 2015 documenting large terrestrial mammal and primate detections. Following established large mammal survey methodology, each transect was walked weekly alternating between early morning and late afternoon to maximize detection. The three transects represent three levels of anthropogenic disturbance with highest disturbance at the Cerro, followed by Cano Palma Biological Station (CPBS), and lowest levels in Tortuguero National Park (TNP). Overall we found higher diversity and increased presence of endangered species in TNP and the lowest diversity and lower presence of those species in the Cerro. Overall we detected 25 species; 19 at the Cerro, 22 in TNP and 23 at CPBS. TNP had the highest diversity as calculated by Simpson index (28.3) followed by CBPS (27.9), and the Cerro had the lowest diversity of mammals (2.27). The most influential species driving the differences of communities between the three transects included the white-lipped and collared peccaries, which were both present in higher densities in transects with lower disturbance and higher levels of protection, and domestic dogs which were present in higher densities at the Cerro. This study has documented baseline densities of large mammal communities in the wildlife refuge which can be used as preliminary data for future comparisons. As development is continuing in the region, including construction of a tourist trail at the Cerro, a continued monitoring is recommended to understand the effect of development on mammal communities.

Electric vehicles are the most promising sustainable transport technology for solving the environmental, economic and social problems associated to the internal combustion engine vehicles. The research and development of new charging methods is necessary for a further integration of electric vehicles in transport sector. Inductive power transfer is the most promising technology for dynamic wireless charging of electric vehicles, which can be used to supply the motors and/or charge the battery of the electric vehicle while it is moving. This charging system can help to reduce the size and cost of the battery, increase the driving range and expand the use of electric vehicles. This paper presents an analysis methodology of a Dynamic Wireless Charging system applied to evaluate the power and energy requirements for charging electric vehicles moving along a stretch of the A-381 Highway in Cadiz (Spain). The study shows the great dependency of the energy transferred to the electric vehicles with the speed and the great variability of power and energy requirements related to the daily traffic.

Currently, electric vehicles (EV) are going through an important emergence, nevertheless, the technology associated to them is still under development. This paper presents a fast charging station (FCS) for EVs supplied by renewable energy with a novel decentralized control of the system. The fast CS is composed of a photovoltaic (PV) system, an energy storage system (ESS), and a connection with the local grid. Thanks to this configuration, the FCS is able to work as a stand-alone system most of the time, with occasional grid support. The proposed control is based on the voltage control of the common medium voltage DC (MVDC) bus, to which all the energy sources are connected. Thus, depending on its voltage, the PV system, the ESS or the grid are used to supply the energy demanded by the EVs. To show the viability of this control, the charging of two EVs is simulated under different operating conditions. Simulation results show the proper operation of the FCS.

Electric power systems will need to accommodate large amounts of renewables and a growing number of DC loads with reduced costs and losses. Medium-voltage DC distribution lines can play a key role. Moreover, a higher availability and reliability of the power supply can be achieved with energy storage systems (ESSs). In this paper, a hybrid configuration merging both concepts is evaluated. A medium-voltage DC distribution system with an integrated ESS has been proposed, modelled, and simulated. Voltage source converters have been used for the AC/DC conversions. The ESS is connected to the DC bus through a dual active bridge enabling bidirectional power flow while covering a large voltage gap. The controllers for all converters and a supervisory control scheme have been implemented. Simulations show the capability of the hybrid configuration to fulfill variable grid demand regardless of the wind power generation, thus transforming a fluctuating source into a dispatchable supply.

We define a new association between graphs and orthonormal bases of even-dimensional Euclidean vector spaces endowed with an special isomorphism motivated by the recently introduced theory of submanifolds associated with graphs. We provide several interesting examples and we analyze the shape of such graphs by proving some general results.

This paper evaluates the option of using a new powertrain based on fuel cell (FC), battery and supercapacitor (SC) for the Urbos 3 tramway in Zaragoza, Spain. In the proposed powertrain configuration, a hydrogen Proton-Exchange-Membrane (PEM) FC acts as main energy source, and a Li-ion battery and a SC as energy support and storage systems. The battery supports the FC during the starting and accelerations, and furthermore, it absorbs the power generated during the regenerative braking. Otherwise, the SC, which presents the fastest dynamic response, acts mainly during power peaks, which are beyond the operating range of the FC and battery. The FC, battery and SC use a DC/DC converter to connect each energy source to the DC bus and to control the energy exchange. This configuration would allow the tramway to operate in an autonomous way without grid connection. The components of the hybrid tramway, selected from commercially available devices have been modeled in MATLAB-Simulink. The energy management system used for controlling the components of the new hybrid system allows optimizing the fuel consumption (hydrogen) by applying an equivalent consumption minimization strategy. This control system is evaluated by simulations for the real driving cycle of the tramway. The results show that the proposed control system is valid for its application to this hybrid system.

SUMMARY This article presents a comparative study among four control strategies for the energy management of a fuel cell (FC) battery–powered hybrid system applied to a surface tramway of 400 kW, which, at present, operates as catenary-powered tramway in the center of Seville, Spain. The proposed hybrid system is composed of a polymer electrolyte membrane FC with a unidirectional dc/dc boost converter and a rechargeable nickel–metal hydride battery with a bidirectional dc/dc converter, both of which are coupled to a traction dc bus. This configuration allows a suitable control of the energy of the hybrid tramway and the traction dc bus voltage. The polymer electrolyte membrane FC and nickel–metal hydride battery models are designed from commercially available components. The control strategies presented in this work are as follows: (i) control strategy based on operating states of the tramway (state machine control), (ii) control strategy based on cascade control loops (cascade control), (iii) control strategy based on fuzzy logic (fuzzy logic control), and (iv) control strategy based on the fuel consumption minimization (equivalent consumption minimization strategy. The control strategies are tested and compared for the real driving cycle of the tramway. The simulation results reflect the optimal performance of the presented control systems. Copyright © 2012 John Wiley & Sons, Ltd.

This paper deals with the modeling and control of a hybrid system integrating a doubly-fed induction generator (DFIG) wind turbine and batteries as energy storage system (ESS). The modeling of the mechanical and electrical main components of a 1.5 MW wind turbine is described. Specific focus is to be taken on the power converter of the DFIG, since it allows the interconnection of the ESS to the generator and a proper energy management. A lead-acid battery is used as energy storage device, which is connected through a bidirectional DC/DC converter to the DC bus of the DFIG power converter. A new supervisory control system, responsible for the coordinate operation of power sources (DFIG wind turbine and ESS), is described and evaluated by simulation under wind speed fluctuations and grid demand changes. It is based on using the wind turbine as primary power source and the ESS as auxiliary power source, providing or storing the power mismatching between the actual wind power and grid demand, whenever the battery state-of-charge (SOC) remains within the recommended limits. This configuration increases the generation capability and smooths the output power fluctuations caused by the wind speed variability, and therefore, improves the grid integration of wind turbines.

[ES] El presente artículo se centra en la descripción de un nuevo sistema de gestión de energía para un nuevo tranvía, en la ciudad de Zaragoza (España), propulsado mediante pila de combustible de hidrógeno, como fuente principal de energía, y batería de ión-litio y supercondensador, como fuentes secundarias y de almacenamiento de energía. En la nueva configuración para este tranvía, la batería apoya a la pila de combustible durante los arranques y absorbe la potencia disponible durante las desaceleraciones y frenadas. Por su parte, el supercondensador, al ser el elemento de respuesta dinámica más rápida, actúa principalmente durante los picos de potencia, en los que ni la pila ni la batería son capaces de trabajar. El nuevo sistema de control y de gestión de la energía está basado en lógica difusa, siendo éste el encargado de generar la potencia de referencia en la pila y la variación de la potencia a intercambiar por parte de la batería. En el caso del supercondensador, un control en cascada formado por dos lazos de control ha sido utilizado para poder mantener constante la tensión del bus de continua. Las simulaciones, realizadas todas ellas bajo la plataforma MATLAB-Simulink® y utilizando el ciclo de trabajo real del actual tranvía, muestran como el nuevo sistema de control y gestión de la energía es perfectamente válido para su aplicación en este sistema híbrido., Este trabajo ha sido financiado por Hynergreen Technologies S.A. y por el Programa Cenit del CDTI del Ministerio de Ciencia e Innovación de España, bajo el proyecto de investigación Ecotrans.

This paper describes the confi guration, modelling and control of a new hybrid propulsion system for the Zaragoza tramway.The new tramway confi guration is composed by a Proton-Exchange- Membrane Fuel-Cell (PEM FC) as main energy source and a Li-ion battery and an Ultra-Capacitor (UC) as energy storage systems. Thus, the battery supports to the FC during the starting and absorbs the power generated by the regenerative braking. Otherwise, the UC, which is the element with the fastest dynamic response, acts mainly during power peaks which are beyond the operation range of the FC and battery. The FC, battery and UC provide with DC/DC converters which allow their connection to the DC bus and control the energy exchange. The new energy management system described is composed by three control loops in cascade for the FC converter and two control loops for the battery and UC. This control system has been evaluated for the real driving cycle of the tramway. The results show how the control system is valid for its application in this hybrid system.

This paper focuses on describing a control strategy for a real surface tramway powered by a hybrid system based on fuel cell and battery. This tramway, called Metro Centro , serves the centre of Seville, a city in Spain. Currently, it operates as catenary-powered tramway. The configuration and modeling of all principal components of the hybrid system are briefly described. The models, implemented in MATLAB-Simulink environment, have been designed from commercially available components. The implemented control is based on an equivalent consumption minimization strategy. It allows a suitable energy management of the hybrid system, minimizing the hydrogen consumption.

This paper presents a comparative study of Proton Exchange Membrane (PEM) Fuel Cell (FC) models for integration in hybrid propulsion systems, based on a commercial FC from Nuvera, which is especially manufactured for this application. An existing model is used as a reference in order to build dynamical mathematical models which describe its dynamical behavior in the time domain. These mathematical models are obtained by applying system identification techniques to the reference model. The proposed FC models have been tested through simulations for the real drive cycle of the existing Metro Centro tramway in Seville.

We present a characterization theorem for the Maslov form in certain non-invariant slant submanifolds of S-space-forms to be closed and, from it, we deduce a topological obstruction for these types of non-invariant slant immersions. Moreover, we also give conditions for an anti-invariant submanifolds of an S-manifold, tangent to the structure vector fields, to have closed and conformal Maslov form.

This paper presents a hybrid electric power system for a real surface tramway. The hybrid system consists of two electrical energy sources integrating a single dc/dc converter to provide the power demanded by the tramway loads (four electric traction motors and auxiliary services): (1) a Polymer Electrolyte Membrane (PEM) fuel cell (FC) as the primary and (2) a rechargeable Ni–MH battery as electrical energy storage to supplement the FC over the driving cycle. According to the requirements of the real driving cycle of the tramway, it was considered a 200 kW PEM FC system with two FCs connected in parallel and a 34 Ah Ni–MH battery. The PEM FC and Ni–MH battery models were designed from commercially available components. The power conditioning system provides the appropriate power for the tramway. It is composed of: (1) a unique dc/dc boot converter which adapts the FC output voltage to the 750 V traction standard dc bus; (2) three phase inverters to drive properly each electric motors; and (3) a braking chopper to dissipate excess of regenerative braking energy. Suitable state machine control architecture is presented for the hybrid system, its objective being to provide demanded power by the driving cycle, optimizing the energy generated. Following this objective, a new state machine control strategy based on eight states decides the operating point of each component of the system and a cascade control structure allows achieving the operating points determined by the strategy. Simulation results of the real driving cycle of the tramway check the adequacy of the hybrid electric power system.

Steady state and dynamic simulations are performed in order to compare the models. Considering the external response of FC system integrated in the tramway hybrid system, both reduced models show similar results with an important reduction of computation time with respect to the complete model. However, the reduced model 1 shows better results than the reduced model 2 when representing the internal behaviour of FC system, so that this model is considered the most appropriate for propulsion system applications.

This paper describes the configuration, modeling, and control of a fuel cell (FC)-battery-powered hybrid system for the Metro Centro tramway in Seville, Spain. The proposed hybrid system presents a polymer electrolyte membrane FC as the primary energy source and a nickel-metal hydride cell battery as the secondary energy source, which supplements the output of the FC during tramway acceleration or whenever else needed and cruise and for energy recovery during braking. The tramway presents a traction system which is composed of four traction induction motor drives. The hybrid system also supplies the power for the auxiliary services. The power conditioning system is composed of two converters: 1) a boost-type unidirectional dc/dc converter for the FC and 2) a boost-type bidirectional dc/dc converter for the battery. The energy management system (EMS) of the hybrid tramway determines the reference signals for the electric motor drives, FC, and power converters in order to regulate accurately the power from the two electrical sources. EMS also determines the reference signal for energy dissipation in braking chopper when required during regenerative braking. In this paper, the proposed hybrid system is evaluated for the real driving cycle of the tramway. The results demonstrate the hybrid system capability to meet appropriate driving cycle.

In this study, the energy management and switching control of plug-in hybrid electric vehicles (PHEVs) in a hybrid smart micro-grid system was designed. The charging station in this research consists of real market PHEVs of different companies with different sizes. The rate of charging of PHEVs is managed via switching control to receive maximum benefits from renewable energy sources and reduce the consumption of electricity from the grid. To support the optimum utilization of sustainable power, charging time and network stability, seven scenarios were developed for different interaction among the proposed micro-grid system and PHEVs. The proposed hybrid smart micro-grid system consists of three renewable energy sources: photovoltaic (PV) array controlled via an intelligent fuzzy control maximum power point subsystem, a fuel cell stack and a microturbine set controlled by proportional integral differential/proportional integral subsystems. A hybrid energy storage system (super-capacitor, battery storage bank and hydrogen) and residential load are also included in the proposed architecture. The hybrid smart micro-grid system is checked in terms of voltage regulation, frequency deviation and total harmonic distortion (THD). It was found that these are in limits according to the international standards. The simulations verify the feasibility of the proposed system and fulfill the requirement of vehicle-to-grid and grid-to-vehicle operations in a smart grid environment.

This paper describes a comparative study of two control schemes for the energy management system of a hybrid tramway powered by a Polymer Electrolyte Membrane (PEM) Fuel Cell (FC) and an Ni-MH battery. The hybrid system was designed for a real surface tramway of 400 kW. It is composed of a PEM FC system with a unidirectional dc/dc boost converter (FC converter) and a rechargeable Ni-MH battery with a bidirectional dc/dc converter (battery converter), both of which are coupled to a traction dc bus. The PEM FC and Ni-MH battery models were designed from commercially available components. The function of the two control architectures was to effectively distribute the power of the electrical sources. One of these control architectures was a state machine control strategy, based on eight states. The other was a cascade control strategy which was used to validate the results obtained. The simulation results for the real driving cycle of the tramway reflected the optimal performance of the control systems compared in this study.

This paper describes the modelling and control system of a direct-drive PMSG wind turbine for effective active and reactive power generation control and voltage control at the grid connection point. This study focuses on the maximum power capability of the wind turbine, which is limited by its generator and power converter. The ability of this model and control strategy are assessed by means of simulations and discussed at length. The results of our study show that a PMSG wind turbine is able to actively participate in grid operation because it can independently control active and reactive power production (operating as a PQ node) or the active power and voltage at the connection node (operating as a PV node).

Since energy consumption and pollution levels are increasing worldwide, the traditional fossil fuel-based generation methods are open to debate. A considerable number of countries are promoting the use of renewable resources in order to set a new energetic scenario. Wind power generation needs to improve some specific aspects that hinder its development. Several devices have been designed and are currently in use to solve the problem of energy volatility, since they are able to store energy in different forms for a given period of time. All these devices have different characteristics; therefore, they behave dissimilarly under certain operating conditions. Lead-acid batteries are being used either for energy or power applications. However, there exist other devices that may provide better performance. These devices are here described and compared, coming to the conclusion that some of them will substitute current technology in the near future if they are able to improve several indicated aspects.

We introduce and study generalized S-space-forms with two structure vector fields. We also present several examples of these manifolds such as certain hypersurfaces of Sasakianspace-forms, principal toroidal bundles and warped products. Moreover, we investigate generalized S-space-forms endowed with an additional structure and we obtain some obstructions for them to be S-manifolds.

We study non-anti-invariant slant submanifolds of generalized S-space-forms with two structure vector felds in order to know if they inherit the ambient structure. In this context, we focus on totally geodesic, totally umbilical, totally ƒ-geodesic and totally ƒ-umbilical non-anti-invariant slant submanifolds and obtain some obstructions. Moreover, we present some new interesting examples of generalized S-space-forms.

We get a characterization theorem for equivalent discrete Morse functions defined on simplicial complexes in terms of their gradient vector field. As a consequence, we also characterize them in the 1-dimensional case by using critical elements.

We establish an interesting link between differential geometry and graph theory by defining submanifolds weakly associated with graphs. We prove that, in a local sense, every submanifold satisfies such an association, and other general results. Finally, we study submanifolds associated with graphs either in low dimensions or belonging to some special families. Junta de Andalucía Ministerio de Educación y Ciencia Fondo Europeo de Desarrollo Regional

As a result of the increasing wind farms penetration on power systems, the wind farms begin to influence power system, and therefore the modeling of wind farms has become an interesting research topic. In this paper, new equivalent models of wind farms equipped with wind turbines based on squirrel-cage induction generators and doubly-fed induction generators are proposed to represent the collective behavior on large power systems simulations, instead of using a complete model of wind farms where all the wind turbines are modeled. The models proposed here are based on aggregating wind turbines into an equivalent wind turbine which receives an equivalent wind of the ones incident on the aggregated wind turbines. The equivalent wind turbine presents re-scaled power capacity and the same complete model as the individual wind turbines, which supposes the main feature of the present equivalent models. Two equivalent winds are evaluated in this work: (1) the average wind from the ones incident on the aggregated wind turbines with similar winds, and (2) an equivalent incoming wind derived from the power curve and the wind incident on each wind turbine. The effectiveness of the equivalent models to represent the collective response of the wind farm at the point of common coupling to grid is demonstrated by comparison with the wind farm response obtained from the detailed model during power system dynamic simulations, such as wind fluctuations and a grid disturbance. The present models can be used for grid integration studies of large power system with an important reduction of the model order and the computation time.

As a result of the increasing wind power penetration on power systems, the wind farms are today required to participate actively in grid operation by an appropriate generation control. This paper presents a comparative study on the performance of three control strategies for DFIG wind turbines. The study focuses on the regulation of the active and reactive power to a set point ordered by the wind farm control system. Two of them (control systems 1 and 2) are based on existing strategies, whereas the third control system (control system 3) presents a novel control strategy, which is actually a variation of the control system 2. The control strategies are evaluated through simulations of DFIG wind turbines, under normal operating conditions, integrated in a wind farm with centralized control system controlling the wind farm generation at the connection point and computing the power reference for each wind turbine according to a proportional distribution of the available power. The three control systems present similar performance when they operate with power optimization and power limitation strategies. However, the control system 3 with down power regulation presents a better response with respect to the reactive power production, achieving a higher available reactive power as compared with the other two. This is a very important aspect to maintain an appropriate voltage control at the wind farm bus.

As a result of increasing wind farms penetration in power systems, the wind farms begin to influence power system, and thus the modelling of wind farms has become an interesting research topic. Nowadays, doubly fed induction generator based on wind turbine is the most widely used technology for wind farms due to its main advantages such as high-energy efficiency and controllability, and improved power quality. When the impact of a wind farm on power systems is studied, the behavior of the wind farm at the point common coupling to grid can be represented by an equivalent model derived from the aggregation of wind turbines into an equivalent wind turbine, instead of the complete model including the modelling of all the wind turbines. In this paper, a new equivalent model of wind farms with doubly fed induction generator wind turbines is proposed to represent the collective response of the wind farm by one single equivalent wind turbine, even although the aggregated wind turbines operate receiving different incoming winds. The effectiveness of the equivalent model to represent the collective response of the wind farm is demonstrated by comparing the simulation results of equivalent and complete models both during normal operation and grid disturbances.

In the present work, we briefly summarize our contributions to the study of CR submanifolds of (locally conformal almost) Kaehler manifolds and normal CR submanifolds of S-manifolds.

This paper presents a new Energy Management System (EMS) for a microgrid based on four energy sources: a wind turbine (WT), photovoltaic (PV) solar panels, a battery, and a hydrogen system, which is composed of a fuel cell (FC) and an electrolyzer. This novel control strategy optimizes the total cost of the hybrid system (generation and reposition costs) through lifetime estimations calculated hourly for each energy storage device (the battery and hydrogen system). This control strategy links the expected lifespans of the energy sources to their generation costs, i.e., when the lifespan is low, the generation cost increases and, consequently, this energy source will start to be used less. The performance of the novel EMS, including these estimations, was tested for an isolated load located in Alora (Spain) and compared with two simpler EMSs: EMS-1, which considered fixed generation costs and lifetimes, and EMS-2, which prioritized the use of the battery. Simulation results show the appropriate behavior for the novel EMS to optimize the generation costs and the number of required elements throughout the expected lifetime of the hybrid system (25 years).

Relationships between the Ricci curvature and the squared mean curvature and between the shape operator associated with the mean curvature vector and the sectional curvature function for slant submanifolds of an S-space-form are proved, particularizing them to invariant and anti-invariant submanifolds tangent to the structure vector fields.

Using the notion of discrete Morse function introduced by R. Forman for finite cw-complexes, we generalize it to the infinite 2-dimensional case in order to get the corresponding version of the well-known discrete Morse inequalities on a non-compact triangulated 2-manifold without boundary and with finite homology. We also extend them for the more general case of a non-compact triangulated 2-pseudo-manifold with a finite number of critical simplices and finite homology.

This paper is about Astrodata, a Supervisory, Control and Data Adquisition system (SCADA). It was designed and implemented employing two important concepts: the effective cost and the sustainable automation. The SCADA is working at the Radio Astronomical Station of Havana. This solution has demonstrated to be more economical than the former solution implemented.

The increasing wind power penetration on power systems requires the development of adequate wind farms models for representing the dynamic behaviour of wind farms on power systems. The behaviour of a wind farm can be represented by a detailed model including the modelling of all wind turbines and the wind farm electrical network. But this detailed model presents a high order model if a wind farm with high number of wind turbines is modelled and therefore the simulation time is long. The development of equivalent wind farm models enables the model order and the computation time to be reduced when the impact of wind farms on power systems is studied. In this paper, equivalent models of wind farms with fixed speed wind turbines are proposed by aggregating wind turbines into an equivalent wind turbine that operates on an equivalent wind farm electrical network. Two equivalent wind turbines have been developed: one for aggregated wind turbines with similar winds, and another for aggregated wind turbines under any incoming wind, even with different incoming winds. The proposed equivalent models provide high accuracy for representing the dynamic response of wind farm on power system simulations with an important reduction of model order and simulation time compare to that of the complete wind farm modelled by the detailed model.

A new class of Lie algebras of finite dimension, those which are associated with a certain combinatorial configuration made up by triangles of weighted and non-directed edges, is introduced and a characterization theorem for them is proved. Moreover, some subclasses of such Lie algebras are classified.

We study some special types of slant submanifolds of S-manifolds related to the second fundamental form of the immersion: totally f-geodesic and f-umbilical, pseudo-umbilical and austere submanifolds. We also give several ex- amples of such submanifolds.