Nuestros investigadores

Luis Fontán Agorreta

Publicaciones científicas más recientes (desde 2010)

Autores: Rodriguez, F., (Autor de correspondencia); Flórez Tapia, Ane Miren; Fontán Agorreta, Luis; et al.
Revista: RENEWABLE ENERGY
ISSN 0960-1481  Vol. 145  2020  págs. 1517 - 1527
The aim of this study was to develop an artificial intelligence-based tool that is able to predict wind power density. Wind power density is volatile in nature, and this creates certain challenges, such as grid controlling problems or obstacles to guaranteeing power generation capacity. In order to ensure the proper control of the traditional network, energy generation and demand must be balanced, yet the variability of wind power density poses difficulties for fulfilling this requirement. This study addresses the complex control in systems based on wind energies by proposing a tool that is able to predict future wind power density in the near future, specifically, the next 10 min, allowing microgrid's control to be optimized. The tool is validated by examining the root mean square error value of the prediction. The deviation between the actual and forecasted wind power density was less than 6% for 81% of the examined days in the validation step, from January 2017 to August 2017. In addition, the obtained average deviation for the same period was 3.75%. After analysing the results, it was determined that the forecaster is accurate enough to be installed in systems that have wind turbines in order to improve their control strategy.
Autores: Rodriguez, F., (Autor de correspondencia); Fleetwood, A.; Galarza Rodríguez, Ainhoa; et al.
Revista: RENEWABLE ENERGY
ISSN 0960-1481  Vol. 126  2018  págs. 855 - 864
This paper proposes an artificial neural network (ANN) to predict the solar energy generation produced by photovoltaic generators. The intermittent nature of solar power creates two main issues. Firstly, power production and demand have to be balanced to ensure the control of the whole system, and the inherent variability of clean energies makes this difficult. Secondly, energy generation companies need a highly accurate day-ahead or intra-day estimation of the energy to be sold in the electricity pool. For the tool developed in this paper, we address the issue of the complexity of control in systems that are based on solar energies. The tool's ability to predict the parameters that are involved in solar energy production will allow us to estimate the future power production in order to optimise grid control. Our tool uses an ANN which we developed using MATLAB (R) software. The results were validated by analysing the root mean square error of the prediction for days outside the database used for training the ANN. The difference between the actually produced and predicted energy is about 0.5-9%, meaning that the accuracy of our tool is sufficient enough to be installed in systems which have integrated solar generators. (C) 2018 Elsevier Ltd. All rights reserved.
Autores: Urrutia, K.; Fontán Agorreta, Luis; Díez, J.; et al.
Revista: DYNA (ESPAÑA)
ISSN 1989-1490  Vol. 94  Nº 3  2018  págs. 332 - 338
Nowadays urban environments concentrate more than half the world¿s population, reaching up to 70% on 2050 according to forecasts. This concentration implies that most of future challenges will take place in cities as well as the opportunities coming from their potential solutions. Current technological innovation can provide support in facing one of main challenges society is facing: reducing carbon footprint from our cities. This ambitious transition, steered by the Smart Zero Carbon City (SZCC) concept, needs a flexible characterisation method, which can be adapted to different kinds of cities to evaluate the main features of each city, hence proposing and prioritising most suitable interventions. The aim of this study is focused on the characterisation of cities according to the SZCC concept through a set of indicators: the Smart Zero Carbon City Readiness Level (SZCC Readiness Level), able to analyse key aspects of cities according to SZCC concept (Characteristics of the city; City plans and strategies; Energy; Mobility; Infrastructures and ICT services; Citizen Engagement). This characterisation enlightens the development of SZCC concept in the city, identifying its strengths and weaknesses in order to ease the alternatives¿ selection towards decarbonisation, being handy at a time for those small and medium-sized municipalities, so common in the European context, which usually hold less resources than big capitals to implement decision-making support diagnoses. In order
Autores: Rodriguez, F.; Fleetwod,A.; Galarza Rodríguez, Ainhoa; et al.
Revista: RENEWABLE ENERGY
ISSN 0960-1481  Vol. 126  2018  págs. 855 - 864
This paper proposes an artificial neural network (ANN) to predict the solar energy generation produced by photovoltaic generators. The intermittent nature of solar power creates two main issues. Firstly, power production and demand have to be balanced to ensure the control of the whole system, and the inherent variability of clean energies makes this difficult. Secondly, energy generation companies need a highly accurate day-ahead or intra-day estimation of the energy to be sold in the electricity pool. For the tool developed in this paper, we address the issue of the complexity of control in systems that are based on solar energies. The tool's ability to predict the parameters that are involved in solar energy production will allow us to estimate the future power production in order to optimise grid control. Our tool uses an ANN which we developed using MATLAB® software. The results were validated by analysing the root mean square error of the prediction for days outside the database used for training the ANN. The difference between the actually produced and predicted energy is about 0.5¿9%, meaning that the accuracy of our tool is sufficient enough to be installed in systems which have integrated solar generators.
Autores: Federico, I.; Echeverria Ormaechea, José Martín; Fontán Agorreta, Luis
Revista: IET POWER ELECTRONICS
ISSN 1755-4535  Vol. 10  Nº 10  2017  págs. 1156 - 1164
This study reviews the causes of power losses in a DC/DC converter, relates those losses with efficiency profiles, and details different strategies for maximising efficiency when several converters are placed in parallel. The research is focused on electric bus applications, where several converters are usually connected in parallel in order to fulfil the power requirements of the bus models. In a bus, the low-voltage DC link (28V) resembles a microgrid that has some generators (DC/DC converters), an energy storage system (lead-acid batteries) and certain loads. To share the converters' output power, a droop control is proposed. Furthermore, traditional droop control is improved by adding a master-slave control. The proposed master-slave droop control improves efficiency by more than 3% at low power with no additional hardware. Experimental results show how two 5kW converters work in parallel using the proposed control.
Autores: Ibañez, F.; Echeverria Ormaechea, José Martín; Vadillo Landajuela, Javier; et al.
Revista: IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS
ISSN 2168-6777  Vol. 4  Nº 3  2016  págs. 1026 - 1035
This paper presents the analysis of a bidirectional series-resonant converter (SRC) for light loads working above or below resonance. In normal operation (heavy load), it is well known that the SRCs have a maximum voltage conversion ratio (m) equal to one. This occurs when the switching frequency (f(S)) equals the resonant frequency (f(0)) and power losses are neglected. This maximum can also be obtained for f(S) < f(0) when the switches are turned ON during a half-resonant period. Thus, zero-current switching can be achieved at both the turn-ON and turn-OFF processes. However, anomalous step-up behavior is found when the converter is attached to light loads. A comprehensive analysis of this phenomenon in the time-domain and in the state plane is presented. Based on the latter, an expression that estimates m and shows the influences of the parameters is obtained. With the aid of this expression, a solution that mitigates that effect is presented and implemented in a prototype, which is part of a bidirectional power chain for supercapacitors. This solution can be implemented for both f(S) > f(0) and f(S) < f(0).
Autores: Ibañez, F.; Echeverria Ormaechea, José Martín; Astigarraga, D.; et al.
Revista: IET POWER ELECTRONICS
ISSN 1755-4535  Vol. 9  Nº 4  2016  págs. 710 - 718
This study presents the analysis and results of a technique that allows the conventional series resonant DC/DC converter to work as a step-up and step-down converter. The controller can choose between several novel step-up modes and the traditional step-down mode. These modes are analysed by presenting their DC characteristics. The choice of mode is governed by the converter's main controller. The converter reduces the operation frequency range and maximises efficiency by selecting the appropriate mode for the particular load and voltage conversion ratio case. Experimental results in a 6 kW prototype validate the analysis and the proposed controller. Finally, the presented converter is compared with a step-up fixed mode converter in order to appreciate the advantages.
Autores: Ibañez, F.; Echeverria Ormaechea, José Martín; Astigarraga, D.; et al.
Revista: IET POWER ELECTRONICS
ISSN 1755-4535  Vol. 8  Nº 10  2015  págs. 1978 - 1986
This study presents the analysis and design of a novel technique that improves the efficiency of the conventional forward DC-DC converter by reducing switching losses, along with a comprehensive analysis of the circuit and detailed information for designers. The converter uses the current control mode to trigger the switches. To use this control mode, an equalising circuit is presented in the input port to guarantee that the voltage in each half-switching period will be equal; otherwise, the current control mode cannot be applied. A 5 kW step-down (from 350-500 to 28.8 V) prototype is presented and compared with the traditional hard-switching forward converter for fully electric vehicle applications. In addition, the small-signal characteristics and the dynamic response for load variation are presented. Efficiency improvements of over 2% are obtained.
Autores: Prieto, B.; Martínez-Iturralde Maiza, Miguel; Fontán Agorreta, Luis; et al.
Revista: IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS
ISSN 0278-0046  Vol. 62  Nº 5  2015  págs. 2742 - 2752
This paper obtains analytical expressions for the calculation of the slot leakage inductance for fractional-slot concentrated-winding (FCSW) machines with one-, two-, or four-layer windings. The formulas are derived from solving the 2-D Poisson problem associated with the slot region, making them more accurate than classically used expressions that assume a leakage flux path parallel to the placement of the conductors in the slot. Explicit formulas are given in the case of one-and two-layer FSCWs with a number of phases ranging from 3 to 7. The obtained analytical expressions are validated by a finite-element analysis, showing excellent agreement between both calculation methods, even for large slot-opening-to-slot-pitch ratios. A brief comment with regard to the fault-tolerant capability of permanent-magnet FSCW machines with respect to the number of layers is also given.
Autores: Fossati Pintos, Juan Pablo; Galarza Rodríguez, Ainhoa; Martín Villate, Ander; et al.
Revista: RENEWABLE ENERGY
ISSN 0960-1481  Vol. 77  2015  págs. 539 - 549
This paper proposes a genetic algorithm-based method for sizing the energy storage system (ESS) in microgrids. The main goal of the proposed method is to find the energy and power capacities of the storage system that minimizes the operating cost of the microgrid. The energy management strategy (EMS) used in this paper is based on a fuzzy expert system which is responsible for setting the power output of the ESS. The design of the EMS is carried out by means of a genetic algorithm that is used to set the fuzzy rules and membership functions of the expert system. Given that the size of the storage system has a major influence on the energy management strategy, in this paper the EMS and ESS capacities are jointly optimized. In addition, the proposed method uses an aging model to predict the lifetime of the ESS. In this way it is possible to determine the cost associated with energy storage in a more precise manner. The unit commitment problem, which is crucial for the proper operation of the microgrid, has been also considered in the present work. The suggested sizing methodology has been validated in two case studies. (c) 2014 Elsevier Ltd. All rights reserved.
Autores: Ibanez, F.M.; Echeverria Ormaechea, José Martín; Vadillo Landajuela, Javier; et al.
Revista: IEEE TRANSACTIONS ON POWER ELECTRONICS
ISSN 0885-8993  Vol. 30  Nº 3  2015  págs. 1393 - 1402
This paper presents the analysis and design of a novel technique that allows the conventional series resonant dc/dc converter (SRC) to work as a step-up and step-down converter. This is useful in bidirectional dc/dc converters where one port is attached to a fixed voltage dc line, e. g., a 360-V dc line, and the other port is attached to an energy storage device such as a bank of supercapacitors or batteries. Every converter that works in this scenario requires step-up and step-down modes to transfer energy from one port to the other. The paper presents the SRC as an alternative to the well-known dual active bridge (DAB). The dc analysis is detailed to demonstrate the step-up capability. In addition, the ac analysis is presented. Experimental results from a 6-kW prototype validate the theoretical analysis. The results indicate that this technique achieves better efficiency compared to the phase-shift DAB in a wide power range, from heavy to light loads. The main reason for this is that the converter works with smaller currents than the DAB at light loads.
Autores: Prieto, B.; Martínez-Iturralde Maiza, Miguel; Fontán Agorreta, Luis; et al.
Revista: IET ELECTRIC POWER APPLICATIONS
ISSN 1751-8660  Vol. 9  Nº 2  2015  págs. 138 - 149
Interest in permanent magnet synchronous machines for safety-critical applications has been increasing over the years. One of the most common methods for providing fault tolerance to a permanent magnet machine is the active control from the drive side. This method requires designing machines with the lowest possible mutual coupling between phases and a self-inductance that is high enough to limit the fault currents. Fractional-slot concentrated windings have been proposed as the most advantageous solution to meet these requirements. When comparing the numerous combinations of phases, poles and slots that give rise to a fractional-slot concentrated winding, the usual criteria only focus on obtaining a single-layer winding and do not actually consider the relationship between the self-inductance and the mutual inductance between phases. Moreover, they give no recommendations regarding the optimal number of phases from a magnetic point of view. The present work aims to cover this gap by obtaining analytical expressions for the calculation of the inductances in a permanent magnet machine. The derived expressions are investigated regardless of the geometry of the machine, and the criteria for selecting the most promising combinations in terms of the machine's fault tolerance are extracted.
Autores: Fossati Pintos, Juan Pablo; Galarza Rodríguez, Ainhoa; Martín Villate, Ander; et al.
Revista: INTERNATIONAL JOURNAL OF ELECTRICAL POWER AND ENERGY SYSTEMS
ISSN 0142-0615  Vol. 68  2015  págs. 61 - 70
This paper presents an algorithm for reducing the operating cost of microgrids. The proposed algorithm determines the day-ahead microgrid scheduling and builds a fuzzy expert system to control the power output of the storage system. To perform such tasks, two genetic algorithms were employed. One of them generates the microgrid scheduling and determines the fuzzy rules of the expert system, whereas the other is used to tune the membership functions. In this way it is possible to optimize the expert system according to load demand, wind power availability and electricity prices. Simulations were carried out in a microgrid comprising a diesel generator, a microturbine, a fuel cell, a wind turbine and a battery. Both interconnected and island operation modes were considered. Simulation results verify the effectiveness of the proposed algorithm. (C) 2014 Elsevier Ltd. All rights reserved.
Autores: Ibañez, F.; Echeverria Ormaechea, José Martín; Vadillo Landajuela, Javier; et al.
Revista: IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS
ISSN 0093-9994  Vol. 50  Nº 1  2014  págs. 68 - 77
This paper analyzes the benefits and drawbacks of using a modified center-tab rectifier in a high current bidirectional DC-DC converter. This topology is also optimized in order to reduce diode/switch reverse voltage stress. One side of the converter has to transfer currents up to 100A, so the main reason for choosing this topology is the lower conduction losses that it presents. Simulation and experimental data from a prototype are studied. The converter is designed to be attached to a supercapacitor stack in order to make a regulated output power supply.
Autores: Ibañez, F.; Echeverria Ormaechea, José Martín; Vadillo Landajuela, Javier; et al.
Revista: IET POWER ELECTRONICS
ISSN 1755-4535  Vol. 7  Nº 9  2014  págs. 2374 - 2386
This study analyses the frequency response of a bidirectional series-resonant DC/DC converter (SRC) working in a discontinuous mode (DCM). The converter can reach a voltage conversion ratio higher or lower than one, depending on whether the operation mode is step-up or step-down. The analysis is based on a novel mixed technique using both the state-space average method and the Fourier method to obtain a state-space averaged model of the converter. The study presents the model for the two operation modes. It also presents the frequency response of the output voltage as a function of the input voltage and as a function of the off-time, which is the control parameter of the converter. The results of those transfer functions are compared with measurements in a 2000 W prototype. The model provides enough information to properly control the SRC in DCM.
Autores: Ibañez, F.; Echeverria Ormaechea, José Martín; Vadillo Landajuela, Javier; et al.
Revista: IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS
ISSN 0093-9994  Vol. 50  Nº 1  2014  págs. 68 - 77
This paper analyzes the benefits and drawbacks of using amodified center-tab rectifier in a high-current bidirectional dc-dc converter. In order to do this, an analytical model of the rectifier is proposed, and a design procedure based on this model is presented. Simulations and experimental data from a prototype validate this model. This topology is also optimized to reduce diode/switch reverse voltage stress. The prototype is designed to be attached to a supercapacitor stack in order to generate a regulated output power supply. Because one side of the converter (the supercapacitor side) has to transfer currents of up to 100 A at a low voltage (less than 50 V), the main reason for choosing this topology is the low conduction losses that it presents.
Autores: Caballero González, Damián; Zeberio, I.; Fontán Agorreta, Luis; et al.
Revista: INTERNATIONAL REVIEW OF ELECTRICAL ENGINEERING-IREE
ISSN 1827-6660  Vol. 8  Nº 4  2013  págs. 1181 - 1188
In this paper, an analytical method to obtain the magnetic flux in the air gap and the flux densities in surface mounted permanent magnet synchronous machines is described. The particularity of the method, which is based on the magnetic lumped parameter circuit approach, is that it is capable of predicting the magnetic decrease in the air gap due to the cross coupling between the d-axis and the q-axis (cross-magnetizing effect), shifting the angle of the magnetic axis. Moreover, the presented method can also evaluate the local flux density level at the sides of the pole magnets, which is very useful for preventing local magnet demagnetization at load conditions. The methodology is compared with Finite Element Method based simulations, with very good results.
Autores: Ibañez, F.; Echeverria Ormaechea, José Martín; Fontán Agorreta, Luis
Revista: IET POWER ELECTRONICS
ISSN 1755-4535  Vol. 6  Nº 5  2013  págs. 1019 - 1028
This study analyses a novel technique for obtaining a voltage conversion ratio greater than one in a bidirectional series-resonant DC/DC converter (SRC). The converter works in a discontinuous mode: it transfers energy in packets, but it also accumulates some packets in order to raise the output voltage. This study presents a comprehensive theoretical analysis for the two modes: the step-down mode (common mode) and the novel step-up mode. The converter transfers energy during fixed time intervals (called states), and it is also able to accumulate energy in a novel state called the accumulation state. With this, the circuit can achieve a voltage conversion ratio of up to two. In addition, a design methodology is presented, and it is validated in the design of a high-current bidirectional DC/DC converter for battery applications. The results of the voltage conversion ratio and efficiency measurement are presented along with a comparison with an resonant LLC converter. The converter reaches an efficiency rate of 91% and the voltage conversion ratio varies from 0.8 to 1.22 at maximum power. Using this novel technique, the SRC can now be used in a bidirectional DC/DC converter applied to energy storage devices, such as batteries or supercapacitors.
Autores: Gutierrez, S.; Sancho Seuma, Juan Ignacio; Fontán Agorreta, Luis; et al.
Revista: IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION
ISSN 1070-9878  Vol. 19  Nº 5  2012  págs. 1774 - 1781
This paper presents an analysis to determine the effect of the stress enhancement factor due to the presence of protrusions in the semiconductor shields of HVDC cables. The theoretical analysis of the electric field containing protrusions is based on a harmonic solution for the electric field for spherical and spheroidal protrusions. HVDC analysis takes into account the additional space charge accumulation due to the presence of protrusions.