Hybrid Energy Storage System for Hybrid Generation / SISTEMA HÍBRIDO DE ALMACENAMIENTO DE ENERGÍA PARA SISTEMAS HÍBRIDOS DE GENERACIÓN (SH2)
Industrial interest towards energy storage systems for grid applications is increasing year after year. Microgrids and renewable energies are becoming the catalysts for a whole family of energy storage technologies such as batteries, supercapacitors and flywheels. These technologies are ready from the technical point of view, but they still lack some maturity from the industrial and economical point of view.
One clear way to improve these storage technologies consists in hybridizing them, combining two or more systems whose technical characteristics are suitable to complement each other. This results in better performance and less oversizing, and therefore in a more optimized system. This improvement could make energy storage systems feasible and competitive for certain grid applications.
In this context, Gamesa Electric, CIEMAT and the University of Alcalá are collaborating in a project called “Hybrid Energy Storage Systems for Hybrid Generation Systems” (SH2) with the goal of developing a hybrid energy storage system (batteries + supercapacitors) which will be used to improve the quality of an isolated grid with hybrid generation (diesel + renewables). The resulting energy storage system will help achieve voltage and frequency control of the isolated grid with minimum diesel consumption.
In this project, CIEMAT is responsible for the design, dimensioning, assembly, testing and commissioning of the supercapacitors and their corresponding power electronics converter. CIEMAT’s R&D tasks include the design of an equalization hardware and software to prevent cell imbalances, the development of a supervisory system to monitor the supercaps state of health in real time (conceptually similar to the BMS used with batteries), the optimization of the cooling system to achieve maximum energy efficiency, and the development of the high-level control strategy which decides who to split the power between the two energy storage systems.
4 prototypes will be built during the project. The first 2 are scaled prototypes of up to 80V and 200A (30 cells in series). These prototypes have been used to perform extensive testing on the supercaps, including capacitance, ESR (equivalent series resistance), self-discharge, thermal behavior and cell unbalancing, both in healthy conditions and after suffering some electrical damage. The main differences between the two prototypes are the spatial distribution of the cells and the equalization hardware.
The 3rd prototype will increase the voltage level up to 650V (240 cells in series), reaching a maximum power of 125 kW. This prototype will also be extensively tested in the laboratory. Finally, the 4th prototype will double the number of cells by using 2 branches (2x240 cells), yielding up to 250kW. This last prototype will be tested in an operational environment (a microgrid with both conventional and renewable generation) under real working conditions, reaching a TRL of 7.
In 2003, a first project related to flywheels named ACE2 was launched by ADIF (Spanish Railway Infrastructure Manager) for developing a Kinetic Energy Storage System (KESS) for power management in high speed lines substations with the aims of power consumption leveling and braking energy recovery. The CIEMAT participated in the development of the power electronics, control and tests of the flywheel.
A second project started in 2006. The main objective of this second project (named SA2VE, ref PSE-370000-2008-7, and financed by the Education and Science Ministry of Spain) was the application of the KESS to both smoothing the consumption of a DC substation (3kV for urban trains) and storing the energy back from the train braking. Many National research institutions, Universities as well as private companies were involved, such as Tekniker, GreenPower, University of Sevilla, CEDEX, CIEMAT, ZIGOR, ACCIONA and Inabensa.
The flywheel developed for the railway application (SA2VE) is made of high-resistance forged steel, weights 6 tons, is capable of spinning at a speed of 6500 rpm, and it has an energy storage capacity of 200 MJ (55 kWh). The mechanical part is also formed by conventional ceramic bearings although, given the load on the axle and the highly elevated rotation speed, a magnetic levitation system has been put in place using permanent magnets and an electromagnet to give regulation capacity, reducing in this way the stress on the axle and therefore the sizing of the bearings. The electrical machine which serves for acceleration and braking (depending on whether one wishes to store or release energy) is a switched reluctance machine operating at 350 kW and which turns at the same speed as the wheel. The KESS is connected to the DC railway power line by means of a DC/DC converter plus a flywheel converter. Additionally, there is a DC/AC converter to drain power to the power consumptions at the substation. The control hardware has been developed specifically by CIEMAT for this application, as well as the control strategy, and it is based on a distributed network of microcontrollers which manage all the electronic devices and inform the system operator command center, from where they can be controlled.
The system developed for this application offers a series of advantages in comparison with other commercial devices, such as simplicity and robustness, and it has been designed with the aim of providing competitive technology with adequate power and energy levels, and number of cycles, as opposed to other types of technology such as chemical batteries and supercapacitors.
The complete system was first installed and tested in the CEDEX Laboratory in Madrid (Spain) in similar conditions than at the substation in terms of voltage and power levels. Different operation modes, thermal behavior, response capacity and reliability of the communication and controls were checked during this stage.
Finally, the system was moved to the Cerro Negro railway substation in Madrid, owned by ADIF, were it would be commissioned.
A more extended concept of energy management can be considered for railways, since their power lines are high capacity transportation lines, by integrating the train traffic and the grid stability with renewable energy generation, presence of electric vehicles recharge, and energy storage of different types so as to increase the reliability of the whole system. Some projects are being carried out currently in Spain based on this idea.
UNDIGEN project: Functionality Tests of Ocean-Wave Energy Conversion System (IPT-2011-1770-920000).
In the last years, CIEMAT has been working on the conversion of ocean-wave energy into electric power. Electrical Engineering Division of the Technology Department has collaborated, through its Power Systems Unit, in R&D projects from 2011. It has collaborated in the project UNDIGEN of the 2011 INNPACTO National Funding Call, and in the project UNDIGEN MAS of the 2014 Collaboration RETOS National Funding Call, both of the Ministry of Economy and Competitiveness. The first project – UNDIGEN – has been based on testing the functionality of a new wave energy electric power generation system based on a linear generator and its electric drive, for which a 1:1 scale prototype has been tested on the coast of the island of Gran Canaria. The budget has been 2.5 M€, and CIEMAT has collaborated with the industry (WEDGE GLOBAL S.L. and FCC S.A.) and the Canary Island Oceanic Platform (PLOCAN). The second project – UNDIGEN MAS – which is currently active, is aimed at operating the generation system developed in UNDIGEN for use as a power supply for isolated loads by means of the integration of energy storage systems –. The budget is €430 K and again industry and PLOCAN have taken part.
The Power Systems Unit has carried out collaborations directly with the industry from 2007, mainly consisted on analysis and characterization of an electric linear generator design for ocean-wave energy applications (designed by the industry), and including a preliminary design and development of the power electronics and DSP-based control platform for the linear electric generator.
In addition, under the R&D projects UNDIGEN and UNIDGEN MAS it has carried out a wave energy converter (WEC) design and modelling methodology, followed by an analysis to validate the hydrodynamic model. Most of the electric, electronic and control systems involved in the operation of the device have been designed, developed and tested. Finally, it has participated in the WEC tests at sea and in the subsequent analysis of the power data collected by the system.
The main objectives of these projects have been to:
- Develop a wave energy converter (WEC) that includes a new concept of power extraction system (power take-off– PTO) to demonstrate its functionality and robustness. This PTO is based on the use of a new concept of switched reluctance electric machine and its corresponding power converter, developments in which the group has extensive prior experience –.
- Validate the developed hydrodynamic model with the collected data for subsequent studies of the device at other sites.
- Obtain experimental power results, optimizing the system operation strategy in order to maximize the wave-energy extraction.
These projects have developed energy generation and storage technologies and methodologies associated with ocean energy (in particular with the devices called point absorbers), thereby significantly improving CIEMAT’s capabilities in this area of renewable energies (one of the key issues of the research centre). Participation of CIEMAT in these projects demonstrates the Power Systems Unit capabilities and it significantly broadened its experience in this field of renewable energies. The tasks undertaken include:
- Study of the WEC dynamics in order to collaborate with the WEC point absorber geometry definition –.
- Design and development of its associated power electronics, electrical and control equipment. The power electronics manages the generated electric power injected to the grid or to an isolated load.
- Preliminary tests of all the equipment in the laboratory and WEC startup at sea, as well as assistance during the testing at sea. The preliminary lab test allows to check the interaction between the equipment and how they operate together , –. These tests are indispensable due to the limited accessibility of their offshore location on the high seas, what reduces the startup period, the total project cost and the risks during the early stages of system operation.
The WEC developed in these projects is of the type known as point absorber , . It consists of a buoy with two sections (a floating body called float and submerged body which consist on two bodies called spar and plate) that move vertically with respect to each other due to the effect of the forces resulting from the kinetic and potential energy variation of the ocean-waves.
The motion of the float with respect to the plate is transformed into electric power via the PTO, which is housed inside the spar. Part of this generated electric power (by the linear generator and its associated power electronics) passes through an auxiliary power electronic converter to supply power to the electric consumptions included in the WEC (control, operation, measurement sensors, pneumatic system compressor, electro-valves and instrumentation system). There is also a battery set connected in this stage that will be used to ensure system operation. On the other hand, the rest of the power obtained from the generator, not required to supply power to auxiliaries or to recharge batteries, would be injected into the grid via an electronic grid converter and an underwater cable. In the above mentioned projects there has been no grid connection point or underwater cable, but rather the excess generated power is dissipated in an electrical resistance via a direct current converter. All the electronic converters, sensors and instrumentation and the operation of the entire system are managed by a control system based on microcontrollers and digital signal processors (DSP) that receive the system measurements, decide on the actuation of the different subsystems, control the power electronics and determine for the device all the defined operating modes.
- M. Lafoz, L. Beloqui, M. Blanco, P. Moreno-Torres, G. Navarro, and L. García-Tabarés, “Dimensioning Methodology for Energy Storage Devices Applied to Wave Energy Converters,” in OSES 2015: Offshore Energy & Storage Symposium, 2015.
- P. Moreno-Torres, M. Blanco, G. Navarro, and M. Lafoz, “Power Smoothing System for Wave Energy Converters by means of a Supercapacitor-based Energy Storage System,” in 17th European Conference on Power Electronics and Applications (EPE’15-ECCE Europe), 2015.
- M. Lafoz, P. Moreno-Torres, L. Beloqui, G. Navarro, and M. Blanco, “Dimensioning Methodology for Energy Storage Devices and Wave Energy Converters supplying isolated loads,” IET Renew. Power Gener., May 2016.
- M. Blanco, G. Navarro, and M. Lafoz, “Control of Power Electronics driving a Switched Reluctance Linear Generator in Wave Energy Applications,” in Proceedings of the Power Electronics and Applications, 2009. EPE ’09. 13th European Conference on, 2009, pp. 1–9.
- M. Blanco, M. Lafoz, G. Pinilla, L. Gavela, L. Garcia -Tabares, and A. Echeandia, “Laboratory Testing Schema for Linear Generators used in Ocean Wave Energy Conversion,” in Proceedings it the 11thWorld Renewable Energy Conference, 2010.
- M. Blanco, M. Lafoz, G. Pinilla, L. Gavela, and A. Echeandia, “Electric Linear Generator to Optimize a Point Absorber Wave Energy Converter,” in Proceedings of the 3rd International Conference on Ocean Energy (ICOE 2010), 2010, pp. 1–5.
- M. Santos, L. García-Tabarés, M. Blanco, M. Lafoz, and L. Gavela, “Testing of a full-scale PTO based on a Switched Reluctance Linear Generator for Wave Energy Conversion,” in 4th International Conference on Ocean Energy (ICOE), 2012.
- M. Blanco, P. Moreno-Torres, M. Lafoz, and D. Ramírez, “Design Parameter Analysis of Point Absorber WEC via an Evolutionary-Algorithm-Based Dimensioning Tool,” Energies, vol. 8, no. 10, pp. 11203–11233, Oct. 2015.
- M. Blanco, M. Lafoz, A. Álvarez, and M. I. Herreros, “Multi-objective Differential Evolutionary Algorithm for Preliminary Design of a Direct-Drive Power Take-Off,” in Proceedings of the Ninth European Wave and Tidal Energy Conference (EWTEC), 2011.
- M. Lafoz, M. Blanco, S. Ligüerzana, and G. Navarro, “Study of a Linear Generator Control Integrated in an Inertial Point Absorber,” in Proceedings of the Ninth European Wave and Tidal Energy Conference (EWTEC), 2011.
- M. Blanco, M. Lafoz, C. Platero, and F. Blázquez, “Design Procedure For A Wave Energy Converter Based On Electric Linear Generator Parameters,” in Proceedings of the RENEWABLE ENERGY (RE) INTERNATIONAL CONFERENCE, 2010.
- M. Blanco, M. Lafoz, and G. Navarro, “Wave energy converter dimensioning constrained by location, power take-off and control strategy,” in Proceedings of the IEEE International Symposium on Industrial Electronics 2012, 2012, pp. 1462–1467.
- M. Lafoz, M. Blanco, G. Navarro, P. Moreno-Torres, C. Vazquez, and A. Lazaro, “Laboratory tests before sea trials of a wave energy converter,” in 2015 IEEE International Conference on Industrial Technology (ICIT), 2015, pp. 2493–2498.
- M. Blanco, P. Moreno-Torres, M. Lafoz, M. Beloqui, and A. Castiella, “Development of a laboratory test bench for the emulation of wave energy converters,” in 2015 IEEE International Conference on Industrial Technology (ICIT), 2015, pp. 2487–2492.
- M. Blanco, M. Lafoz, and L. Garcia -Tabares, “Laboratory tests of linear electric machines for wave energy applications with emulation of wave energy converters and sea waves,” in Proceedings of the Power Electronics and Applications, 2009. EPE ’11. 14th European Conference on, 2011, pp. 1–10.
- A. F. de O. Falcão, “Wave energy utilization: A review of the technologies,” Renew. Sustain. Energy Rev., vol. 14, no. 3, pp. 899–918, Apr. 2010.
- J. Falnes, Ocean waves and oscillating systems?: linear interactions including wave-energy extraction. Cambridge: Cambridge University Press, 2002.
UNDIGEN Project links:
Electric vehicles are moving towards technological maturity, and many car companies have already developed their own models. Sales are finally starting to take off, reaching market shares of around 1% in most developed countries. In this sense, one of the key aspects for the massive penetration of electric vehicles in the market is the fast charge capability of their batteries. In the next decade, a fast-charging infrastructure will potentially be needed in large cities to properly support these vehicles.
Fast charging is a very demanding service, since the power level required for each vehicle is 50 kW during a time around 15 minutes. Therefore, its requirements over the urban electric distribution system will predictably be quite high. In this sense, it would be desirable to re-use preexisting installations to avoid oversizing and/or overloading the electric system.
A good alternative to the conventional urban distribution system is the utilization of the local subway power lines as a secondary distribution system for electric vehicle charging. The advantages of using railway power lines to support the fast-charging service within a city are cost reduction; system redundancy; and, in the case of subway power lines, reduced magnetic field exposure of pedestrians (given that all the power equipment would be underground).
Obviously, the re-utilization of the railway power lines requires some adaptation of the infrastructure. There are at least a few potential solutions, with different devices and topologies, which would allow fast charging from the railway line. In any case, such a system requires some power electronics to adapt the voltage level of the line to that of the charger. Besides, some energy storage is very convenient, for it is the only way to optimize energy efficiency in the system as a whole.
Following this concept, a four-year research project named Train2Car was undertaken in Metro de Madrid (Madrid’s subway company) between 2011 and 2014. The purpose of this project was to develop an innovative system for the smart energy management of the railway power grid by introducing power feed points for electric vehicles to maximize the overall efficiency of the system. One of the specific targets of the project, undertaken by CIEMAT; was to develop a laboratory-scale test bench in which the real system could be emulated. The laboratory platform could therefore be used to prove the feasibility of the proposed system, to operate as a reduced-scale prototype and to test different control strategies for the optimization of the Energy Management System.
The project was a complete success and the real installation started operating in 2014.
SRM for Aircraft Generators
This project is related to the concept in aeronautical engineering of ‘the More Electric Aircraft’ (MEA). This trend towards new designs of aircrafts has the objective of substituting conventional equipment (pneumatic, mechanic and hydraulic power) by those which depends on electrical power. Besides, these changes provide a better system performance (high reliability, less maintenance, higher efficiency on energy conversion) and a reduction on the fuel consumption and operational costs.
Related to this concept, the objective is the design of a new electric power generation system inspired by Clean Sky architecture and equipment e.g. with 270 VDC network in order to reduce the weight of power buses and reduce power off-takes allowing engines to operate at the best efficiency.
An innovative approach for the High Voltage Direct Current Generator (HVDC generator) based on switched reluctance machine technology is proposed. This type of systems will open a new approach to HVDC generators.
The first sub-objective was to do a preliminary design of a Switched Reluctance Generator (SRG) using a simple model from basic electromagnetic and geometrical relationships. The input parameters and restrictions were extracted from the Call (topic JTI-CS2-2015-CFP02-FRC-02-13 HVDC Generator) and from other Challenges within the guidelines set by the main European programs that set the strategic roadmaps for transport and aviation research, development and innovation as Flightpath 2025 and Horizon 2020.
Based on the preliminary parameters obtained from the study, a FEM study will be carried out to determine the variables of the preliminary design and to validate the model.
The following figure shows the results obtained from the analysis from the model with the preliminary parameters. The figure a) shows the flux lines from a 2D FEM analysis, figure b) shows the flux density, figure c) the mesh used for the 3D FEM analysis and finally figure d) the flux density in 3D. All the analysis are provided at rated power (20kW) and rated speed (12,000rpm).
Figura que no está preparada todavía.
After that, a refinement of the design had been done in order to achieve the torque and power electronics requirements. The results will provide the exact current waveform, and subsequently the mechanical behavior will be calculated considering additional vibration effects due to the torque ripple due to the current commutation. Finally the HVGEN losses are calculated based these results, in order to analyze the thermal behavior of the system.
Once the previous analysis has been done, the next step was the thermal model. In order to achieve an advance thermal model, a transient electromagnetic simulation is accomplished for a specific operation point (power, DC current and angular velocity) to obtain the electromagnetic losses (core and copper losses, in particular). After achieving the thermal model results, a new analysis is required considering the influence of the coolant fluid. A Fluid-Structure Interaction (FSI) model can be carried out using FEM as well. An iterative study using two models (mechanical model and the fluids model) will be accomplished. When the analysis converges to a steady state, temperatures, pressures and air velocities would be obtained to validate thermally the design.
The next objective was to define the Power Electronics topology, the type of semiconductor topology based on the electrical restrictions. Finally a thermal dimensioning and analysis for semiconductor modules has been done in order to accomplish the specifications (weight, power and heat losses).
Finally, a 3D preliminary design of the Rotary Machine shall be modeled using 3D CAD. The Rotary Machine envelope and parts fitting shall be checked: dimensions of the shaft, bearings calculation, interference for the assembly of the rotor lamination around the shaft. The end windings of the generator are important both for fitting the generator in the available room and for the thermal analysis to be developed in the following subtask. A preliminary design of the cooling system (fan) shall be included in the general arrangement too.