Browsing by Author "Ceballos, S."
Now showing 1 - 20 of 28
Results Per Page
Sort Options
Item Amplitude control of the neutral-point voltage oscillations in the three-level converter(2008) Zaragoza, J.; Pou, J.; Arias, A.; Ceballos, S.; Robles, E.; Ibáñez, P.; Gabiola, I.; POWER ELECTRONICS AND SYSTEM EQUIPMENT; RENOVABLES OFFSHORE; SGThis paper presents a control method to regulate the amplitude of the voltage oscillations that appear in the neutral-point of the three-level diode-clamped converter for some operating conditions. The control is applied to the hybrid modulation technique, which is based on combining two modulation techniques. One of them is based on two modulation signals per phase, and can remove completely the low-frequency voltage oscillations on the neutral point. However, such a modulation strategy has an important drawback; it increases significantly switching losses on the converter. The hybrid modulation used here combines such a modulation with sinusoidal PWM. The main characteristic of this hybrid modulation is the capacity to reduce switching losses at the cost of having some low-frequency voltage oscillations on the neutral point. The amplitude of these oscillations can be regulated thanks to the proposed controller, which defines the exact degree of mixture between the two modulation strategies. Some simulation and experimental results are presented in this paper.Item Analysis of the technology currently used in Offshore Wind energy systems(2011) Madariaga, A.; De Alegría, I. Martínez; Martin, J. L.; Eguía, P.; Ceballos, S.; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis paper gives an overview to the foundations, the Offshore Wind Turbines (OWTs) and the collection and transmission systems of Offshore Wind Farms (OWFs). Although for some of the components of their Electric Systems (ESs) there are different technical possibilities under consideration, under certain conditions of sea depth and distance from shore there are already tested industrial solutions available. However, the technology is not mature yet and decisions adopted today could condition the future expansion of operating OWFs or the development of the already planned Offshore Wind Power Plants (OWPPs). This paper presents the information gathered from about 93% of the currently operating OWFs. Moreover, OWPPs under construction have also been considered to confirm the conclusions presented and to detect current technological trends.Item Comparative small-signal evaluation of advanced grid-forming control techniques(2022-10) Aragon, D. A.; Unamuno, E.; Ceballos, S.; Barrena, J. A.; Tecnalia Research & Innovation; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis paper presents the small-signal modelling and analysis of the most recent grid-forming control techniques, namely the matching control (MC) and the dispatchable virtual oscillator (dVOC). These are compared to more classical SME techniques such as synchronverters (SV) and voltage-controlled virtual synchronous machines (VCVSM) under different grid conditions. In addition to studying the time-domain response (inertial behaviour, steady-state operation point, etc.), a thorough evaluation of the dominant eigenvalues of each control is carried out by obtaining the participation factors and the sensitivity to physical and control parameter variations. Simulation results are obtained for a grid-forming converter connected to a dynamic grid model that emulates different properties of low-inertia power systems—e.g. primary reserve, inertial strength, coupling strength, etc. Besides, hardware-in-the-loop experimental results are presented to validate the analysis.Item Comparison of speed control strategies for maximum power tracking in a wind energy conversion system(2010) Zaragoza, J.; Staines, C. Spiteri; Arias, A.; Pou, J.; Robles, E.; Ceballos, S.; RENOVABLES OFFSHORE; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis paper presents two different variable-speed control strategies to obtain the maximum power from wind turbines (WT). The two control strategies are composed by three regulators, which may be based on linear or nonlinear controllers. The first control strategy is composed of three standard proportional-integral (PI) regulators. The PI controllers are tuned for a specific operation mode. However, since the system is nonlinear, for different operating conditions, the values of the PI parameters may not be optimal. The second control approach includes a nonlinear (fuzzy) controller to compensate for the nonlinearity of the WT, to achieve improved speed performance under different operating points. The proposed control strategy uses a fuzzy controller and two standard PIs. The results show that in most cases the fuzzy controller obtains superior performance to that of the standard PI-based solution.Item Current Distortion Mitigation in Grid-Connected Vienna Rectifier during Nonunity Power Factor Operation(IEEE Computer Society, 2020-10-18) Molligoda, D. A.; Pou, J.; Ceballos, S.; Satpathi, K.; Sasongko, F.; Gajanayake, C. J.; Gupta, A. K.; POWER ELECTRONICS AND SYSTEM EQUIPMENTThe Vienna rectifier is an attractive converter solution due to the three-level voltage generation and its simple structure. When the Vienna rectifier operates with nonunity power factor, the reference voltage and the input current have different signs during some intervals around the current zero crossings. This creates low-frequency distortion in the current waveforms. One of the preferable methods to reduce this distortion is the zero sequence injection which, however, risks the converter entering into overmodulation. This paper analyses the above distortion and introduces the operation of the Vienna rectifier in two modes, which includes injecting a proper zero sequence and reactive power compensation. This allows the converter to operate in a wide range of power factors without constraining the modulation index. The required reactive current is obtained analytically from the instantaneous values of the converter at any operating point.Item Current facts about offshore wind farms(2012-06) Madariaga, A.; De Alegría, I. Martínez; Martín, J. L.; Eguía, P.; Ceballos, S.; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis paper reviews offshore wind projects with a wide perspective. The current situation of the offshore wind market is presented, pointing out the countries leading the process in terms of installed capacity and in terms of technological leadership. Feasibility studies of alternative offshore wind farms (OWFs) are interesting not only in relation to the business but in relation to the techno-economical analyses that engineering researchers need to do. Details about the average energy yield assessment, the costs and the price for the purchased energy are commented on, as key elements of those feasibility studies. The higher cost of renewable energy sources of electricity (RESE) when compared with conventional sources, demands appropriate policy support. The European regulatory framework and the support schemes established by European Member States are presented, as well as the role that different transmission system operators (TSOs) are playing at the moment. Finally, most of the OWFs currently operating are presented, analysing the technical characteristics of their electric subsystems: the wind energy conversion systems (WECSs) transforming the kinetic energy of the wind into electricity, the collector system (CS) gathering the power output of all the turbines to a central collection point (CCP) and the transmission system (TS) taking that power to the onshore main grid.Item Digital control of a three-phase four-leg inverter under unbalanced voltage conditions(2007) Vechiu, I.; Curea, O.; Camblong, H.; Ceballos, S.; Villate, J. L.; POWER ELECTRONICS AND SYSTEM EQUIPMENT; GENERALIn this paper, the implementation of an innovative inverter control strategy based on the symmetrical components is presented. Symmetrical components of the inverter output voltage and current are decomposed into dq DC quantities to control a three-phase four-leg inverter. This kind of inverter can be a good choice for the applications with hybrid power system based on renewable energy used to supply unbalanced loads. The addition of a fourth leg provides an extra degree of freedom, making possible to handle the neutral current caused by the unbalanced load. Simulation results are compared with experimental results for a prototype inverter to verify the validity of the proposed control strategy.Item Discontinuous modulation of modular multilevel converters without the need for extra submodules(Institute of Electrical and Electronics Engineers Inc., 2015) Picas, R.; Ceballos, S.; Pou, J.; Zaragoza, J.; Konstantinou, G.; Agelidis, V. G.; Balcells, J.; POWER ELECTRONICS AND SYSTEM EQUIPMENTIn this paper, a new approach to the discontinuous modulation technique for the operation of the modular multilevel converter (MMC) is presented. Discontinuous modulation is based on adding a zero-sequence to the original modulation signals so that each MMC arm is clamped to the upper or lower terminals of the dc-link bus during some intervals. In combination with a circulating current control, the original discontinuous modulation can reduce the capacitor voltage ripple amplitudes and the switching power losses. However, additional submodules (SMs) are required to control the circulating current. This new approach presents a clamping algorithm that eliminates the requirement of additional SMs. As a result, the conduction losses are reduced while the capacitor voltage ripples are maintained low. Simulation and experimental results on a silicon-carbide-based MMC are reported and compared against the original discontinuous modulation and a conventional carrier-based pulse-width modulation.Item Electrical generators in ocean energy converters(Institution of Engineering and Technology, 2013-01-01) O’Sullivan, D.; Bard, J.; Kracht, P.; Ceballos, S.; Robles, E.; POWER ELECTRONICS AND SYSTEM EQUIPMENT; RENOVABLES OFFSHOREThis chapter provides an outline of the issues confronting the designer of an ocean energy converter (OEC) when selecting or designing the electrical generator and its associated control system. It is clear that, especially for wave energy converters (WECs), this is a complex problem due to the high variance in device power take-off (PTO) type, and indeed the functionality of the generator itself within the power chain. Specification and design of the generator system in tidal energy converters (TECs) have been reviewed and shown to be highly dependent on the device, turbine and current characteristics. Both squirrel cage induction generators (SCIGs) and permanent magnet synchronous generators (PMSGs) are promising generator technologies for application in TECs, showing individual advantages and disadvantages. As important as the choice of the generator technology are the concepts to deal with the special requirements of TEC devices like marine environment, submerged operation and extended maintenance intervals. A consistent requirement in both WEC and TEC system generators is the need for variable speed control and operation. In this context, the power converter technology and controller algorithms related to this need have been introduced.Item Electrical losses in multi-MW wind energy conversion systems(2012-04) Madariaga, A.; Martínez de Ilarduya, C. J.; Ceballos, S.; Martínez de Alegría, I.; Martín, J. L.; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis paper proposes a procedure to assess the electrical losses in Wind Energy Conversion Systems (WECSs) with different electrical topologies. Those losses are evaluated in an annual basis considering the randomness of the wind with a Rayleigh probability distribution function. Due to the lack of specific standards, the analysis is based on standards applicable to low voltage (LV) and medium voltage (MV) installations. After reviewing the WECSs offered in main manufacturers’ portfolio, three electric topologies have been studied with the proposed calculation procedure. The main difference among alternatives is the position of the power transformer and, therefore, the characteristics of the voltage in the wiring going down the tower. Another two alternative topologies with direct current (DC) output have also been studied. The parameters of the base case study are commented in detailed and the results of several sensitivity analyses are also presented.Item Evaluation methodologies and input data for offshore wind power plant electric topology assessment(Nova Science Publishers, Inc., 2013) Madariaga, A.; Zamora, I.; Martín, J. L.; Martínez De Alegría, I.; Ceballos, S.; POWER ELECTRONICS AND SYSTEM EQUIPMENTOffshore wind power is attracting the interest of experts in a range of disciplines such as electricity, electronics, mechanics, materials, control, project management and financing. The objectives are bold. On the one hand, with the fossil era showing slight signs of decay, renewable sources of electricity are seen as a realistic supply of energy for societies of the XXI century. Marine renewable energies in general, and offshore wind energy in particular, are one of the most promising alternatives in this slow but global shift to renewable sources of electricity. On the other hand, during the last decade onshore wind has proven itself as a powerful economic drive for the countries leading its development. And that drive continues worldwide in areas with vast land and wind resources. In contrast, appropriate onshore sites are dwindling in some countries and governments, companies and academia are focusing on offshore wind.Item High power high voltage DC/DC converter for MVDC distribution applications(2012) De Alegría, I. Martínez; Santamaria, V.; Madariaga, A.; Martín, J. L.; Ceballos, S.; POWER ELECTRONICS AND SYSTEM EQUIPMENTSmart grids and distributed power will play a big role in the future power grid. In the future many DC grids will coexist with the traditional AC grids. This paper presents an efficient and low cost alternative for unidirectional or asymmetric interconnection of DC grids using MVDC transmission lines using High Frequency Transformers.Item Innovative permanent magnet generator for an easy integration into direct drive wind turbines(2007) Robles, E.; Zaragoza, J.; Merino, J. M.; Ceballos, S.; Vechiu, I.; Curea, O.; RENOVABLES OFFSHORE; Tecnalia Research & Innovation; POWER ELECTRONICS AND SYSTEM EQUIPMENTPermanent Magnet (PM) direct driven synchronous generators are becoming an interesting solution to implement in large wind turbines. They are simpler, have less maintenance costs, and offer increased efficiencies. The objective of this project is to analyse this alternative with different power electronics and improved control algorithms. The standard PM machines have a very poor characterisation in terms of electrical parameters for modelisation. In this work, a new PM generator has been built and characterisation test realized. This new generator has been introduced in a test bench, and will be connected to grid through a back-to-back multilevel converter.Item Innovative solutions in power electronics for variable speed wind turbines(2006) Villate, J. L.; Robles, E.; Ibáñez, P.; Gabiola, I.; Ceballos, S.; GENERAL; RENOVABLES OFFSHORE; SG; POWER ELECTRONICS AND SYSTEM EQUIPMENTWind energy has experienced a dramatic development over the last decade. Offshore wind farms with multimegawatt machines and variable speed solutions are gaining ground. The power converter is a key component in modern wind turbines with higher power, higher efficiency and lower costs. In addition, the utilities demand increasingly exacting power quality requirements, which can only be met if research on power converters is done. This paper presents a survey of existing power electronics solutions for wind turbines, covering trends and new studies in this field.Item Market forecasts, feasibility studies and regulatory framework for offshore wind energy integration(2011) Madariaga, A.; Martínez De Alegría, I.; Martín, J. L.; Eguía, P.; Ceballos, S.; POWER ELECTRONICS AND SYSTEM EQUIPMENTThis paper gives an overview of several aspects of Offshore Wind Power (OWP) integration. During last year the wind market has exceed forecasts despite of the global crisis, with the offshore market offering very good numbers. Moreover, some projections presented in the paper show that OWP installed during the next five years will probably overcome European Wind Energy Association (EWEA)'s forecasts. Logically, investors of OWP projects demand accurate viability plans, which in turn ask for rigorous cost analysis and revenue forecasts considering the whole life cycle of the installation. However, the electricity price in an open market is expected to show certain volatility in the presence of large amount of Renewable Energy Supplies for Electricity (RESE), which makes governmental supporting schemes essential. The European Commission (EC) has established a new regulatory framework called to play a key role in promoting and sustaining RESE and Member States have specified those support schemes in their National Renewable Energy Action Plans (NREAPs).Item Matrix converter Double Sided Space Vector Modulation: A fast way to synthesize via S-Function(2006) Andreu, J.; De Alegría, Martínez; Martín, J. L.; Ceballos, S.; Gabiola, I.; POWER ELECTRONICS AND SYSTEM EQUIPMENTMatrix Converters present several advantages in some power electronic applications, but their control is a complicated task. Matlab-Simulink is a very useful tool for the developing of control algorithms for power converters. In this paper, an exhaustive analysis of Double Sided Space Vector Modulation for a Matrix Converter is presented. The synthesis of the complex Space Vector Modulator is done using a single SFunction, thus simplifying and accelerating the implementation and debugging of the controller of a Matrix Converter. The implementation procedure of the modulation strategy presents several important advantages, mainly, an acceleration of the time dedicated to the implementation of the modulator, a more reliable design, because the debugging is straightforward, and faster simulation times of the entire platform. The simulation method allows an easy way to synthesize the modulation algorithm in a FPGA, in this way, this paper contributes to the development of the IPMs. Finally, the results of applying the present Space Vector Modulator for the control of a Doubly Fed Induction Generator (DFIG) are presented, showing that complex control of Matrix Converter is minimized.Item Minimization of the capacitor voltage fluctuations of a modular multilevel converter by circulating current control(2012) Picas, R.; Pou, J.; Ceballos, S.; Agelidis, V. G.; Saeedifard, M.; POWER ELECTRONICS AND SYSTEM EQUIPMENTThe modular multilevel converter (MMC) is one of the most potential converter topologies for medium/high power/voltage applications. One of the main technical challenges of an MMC is to eliminate/minimize the circulating currents within the legs. Circulating currents, if not properly controlled, increase the amplitude of capacitor voltage variations, rating values of the converter components and converter losses. This paper proposes a closed-loop circulating current control strategy for an MMC to specifically minimize the amplitude of capacitor voltage variations. The proposed strategy is based on adding an offset signal to the modulating signal of each arm. To minimize the amplitude of the capacitor voltage oscillations, an optimal circulating current component is determined and used as a reference signal for the current control of each MMC leg. Performance of the proposed control strategy is evaluated based on simulation studies in the MATLAB/Simulink environment. The reported study results demonstrate effectiveness of the proposed strategy to reduce the amplitude of the capacitor voltage oscillations.Item Open access simulation toolbox for the grid connection of offshore wind farms using multi-terminal HVDC networks(Institution of Engineering and Technology, 2017) Ugalde-Loo, C. E.; Adeuyi, O. D.; Wang, S.; Liang, J.; Jenkins, N.; Ceballos, S.; Santos, M.; Vidaurrazaga, I.; D'Arco, S.; Bergna, G.; Barenys, M.; Parker, M.; Finney, S.; Gatti, A.; Pitto, A.; Rapizza, M.; Cirio, D.; Lund, P.; Castro, A.; Azpiri, I.; POWER ELECTRONICS AND SYSTEM EQUIPMENT; POWER SYSTEMS; SISTEMAS FOTOVOLTAICOSDecarbonisation of the European electricity system can become dauntingly costly due to transmission and distribution network issues arising from the integration of intermittent renewable generation sources. It is expected that wind energy will be the principal renewable source by 2050 and, as such, a number of initiatives in the academia and in the industry are being carried out to propose solutions to best accommodate the wind resource. This paper presents work carried out by DEMO 1 partners within the EU FP7 project BEST PATHS. A MATLAB/Simulink toolbox consisting of the necessary building blocks for the simulation and integration of offshore wind farms using enabling technologies such as multiterminal high-voltage direct-current grids is presented. To illustrate the toolbox capabilities, a number of system topologies is studied. System performance is assessed and measured against a set of key performance indicators. To ensure knowledge dissemination, the toolbox has been made available as open access in the BEST PATHS project website.Item Parallel-connected legs in a grid-tied inverter system for distributed generation(2011-05) Capellá, G. J.; Pou, J.; Zaragoza, J.; Ceballos, S.; Gabiola, I.; Robles, E.; POWER ELECTRONICS AND SYSTEM EQUIPMENT; RENOVABLES OFFSHOREGrid-connected high-power inverters are often used in distributed generation and power quality systems. Those inverters have to handle high currents in order to achieve high power values without resorting to higher voltages. Connecting inverter legs in parallel is a proper way to achieve such high currents. Such parallel connection is made by means of inductors and achieving balanced currents among the legs becomes a critical issue. Circulating currents may produce additional losses and stress to the converter’s power devices. Therefore, they should be controlled and minimized. An efficient technique to achieve such balance is presented in this paper. The proposed strategy has been developed on a grid-connected three-phase system. Each phase of the inverter is made up of three legs in parallel. Besides, the control implemented in this work allows full regulation of the power factor. This way, any desired power factor value can be achieved in order to meet grid-connection requirements. Simulation and experimental results are shown in this paper.Item Power electronics solutions for grid connection of wind farms(2007) Robles, E.; Villate, J. L.; Ceballos, S.; Gabiola, I.; Zubia, L.; RENOVABLES OFFSHORE; GENERAL; POWER ELECTRONICS AND SYSTEM EQUIPMENTIn the last years grid integration is a concern of growing interest. In most countries, transmission system operators are redefining the grid codes that establish grid connection requirements of wind turbines. These grid codes are getting more and more demanding, especially regarding to fault ride through capability and reactive power control. This work studies the current solutions to overcome these new rules. It analyses differences between the three main wind turbine topologies and their difficulties to meet grid codes. Most solutions are based on additional equipment like crowbars for fault ride through voltage sags or STATCOM for injecting reactive power. But they do not manage to fulfil completely the new rules and result quite expensive. Moreover, for the moment, there is no solution for fixed speed wind turbines to overcome a grid fault. This work proposes a new alternative for these old wind farms that although expensive, allows their operation within the most demanding rules. Anyway, we consider that in the near future, the most suitable topologies will be the ones based on full power converters that as explained in the paper, have fewer difficulties to overcome the new grid codes.