Grid synchronization based on Virtual Flux (VF) estimation allows for control of grid-connected power converter without depending on AC-voltage measurements. This is useful in voltage-sensor-less applications for reducing cost and complexity of the control hardware, and can be utilized in case of limited reliability or availability of voltage measurements at the intended point of synchronization to the grid. However, for Voltage Source Converters (VSC) with LCL filters, the influence of the capacitor current must be taken into account to ensure accurate VF estimation at the Point of Common Coupling (PCC) with the grid. This paper presents a comparative evaluation of three VF-based methods for grid synchronization of VSCs with LCL filters, with three different ways of obtaining the capacitor current. The VF estimation in the first method is based only on the measured converter currents. The second method includes capacitor voltage measurements used for estimating the capacitor currents, while the capacitor currents are measured in the third approach. Comparative results from time-domain simulations are presented demonstrating good performance of the estimation and accurate control of the active and reactive power at the PCC with all three methods, as long as sufficiently accurate filter parameters and current measurements are available. However, the approach based on capacitor current measurements is sensitive to noise due to the high ripple current compared to the fundamental frequency current in the capacitors. The operation of a converter with VF-based grid synchronization including estimation of the capacitor current is demonstrated by experimental results, verifying the voltage sensor-less operation with LCL-filter.
Muñoz-Aguilar, R. S.; Candela, J.; Rocabert, J.; Rodriguez, P. IEEE International Conference on Renewable Energy Research and Applications p. 429-434 DOI: 10.1109/ICRERA.2017.8191098 Data de presentació: 2017-11-05 Presentació treball a congrés
In this paper the grid harmonic resonance on long lines is studied, in particular the resonance phenomena between the grid series inductance and the line parallel capacitor. Later, the resonance is attenuated by using a renewable energy generator. Experimental results are depicted and the conclusions are stated.
Abdollahi, M.; Candela, J.; Rocabert, J.; Muñoz-Aguilar, R. S.; Rodriguez, P. IEEE International Conference on Renewable Energy Research and Applications p. 1067-1072 DOI: 10.1109/ICRERA.2017.8191220 Data de presentació: 2017-11-05 Presentació treball a congrés
Control of renewables by Synchronous Power Controller (SPC) technology provides virtual damping and inertia which results to support phase stability on the grid and keep synchronism of interconnected areas tighter. Serving these benefits needs to have proper dynamic interaction between renewables and grid. In this paper, according to the dynamic modeling of Renewable Static Synchronous Generation unit based on SPC (RSSG-SPC) connected to an external grid, an index is introduced for the study of the dynamic interaction between RSSG-SPC and grid by analysis of synchronization power. Mathematical analysis for weak then stiff external grid confirms that the proposed index can be trustable for both single and two-dimensional design. Modal analysis and detailed time domain test approve that the suggested indices can clarify adjustment range for dynamic parameters aim to have optimal synchronization process between RSSG-SPC and grid, which leads to control this dynamic interaction.
Abdollahi, M.; Candela, J.; Rocabert, J.; Muñoz-Aguilar, R. S.; Rodriguez, P. IEEE International Conference on Renewable Energy Research and Applications p. 977-982 DOI: 10.1109/ICRERA.2017.8191204 Data de presentació: 2017-11-05 Presentació treball a congrés
Supporting frequency inside of each generation area as well as keeping proper synchronism condition between interconnected areas are two main challenges for grid operators. In this paper, after analysis of structure of Renewable Static Synchronous Generation unit based on Synchronous Power Controller (RSSG-SPC) for holding and control of frequency, it is shown that how a renewable unit based on SPC can contribute to frequency support inside of generation areas and in this way it will support synchronism of neighbor areas. Results of mathematical analysis and state space modelling, as well as time domain investigation then real time test of two area system in presence of RSSG-SPC confirm that by reducing Rate of Change of Frequency (ROCOF), increasing level of Frequency Nadir (FN) and providing stiffer Center Of Inertia (COI) for whole of the grid, the RSSG-SPC not only supports frequency on the generation areas, furthermore it will cover synchronism of these interconnected areas.
Abdollahi, M.; Candela, J.; Rocabert, J.; Muñoz-Aguilar, R. S.; Rodriguez, P. IEEE International Conference on Renewable Energy Research and Applications p. 728-733 DOI: 10.1109/ICRERA.2017.8191156 Data de presentació: 2017-11-05 Presentació treball a congrés
Management of Renewable Static Synchronous Generation units based on Synchronous Power Controller (RSSG-SPC), not only provides grid synchronization without using PLL and gives proper dynamic to output active power, moreover yields simple solution to overcome technical constraints on these units. Control of active power level injected to the grid is one of these key constraints which can overcome by an Active Power Limiter (APL). In this work, an APL designed based on the classic power equation is proposed for this kind of modern RSSG-SPCs. Primary Simulink analysis and real time test results confirm that suggested APL can control and limit both maximum and minimum level of output active power for several grid connection cases.
Tarrasó, A.; Candela, J.; Rocabert, J.; Rodriguez, P. Annual Conference of the IEEE Industrial Electronics Society p. 2712-2717 DOI: 10.1109/IECON.2017.8216456 Data de presentació: 2017-10-29 Presentació treball a congrés
The increasing penetration of renewable energy systems force the grid-connected power converters to use advanced active power controls, which needs to add more functionalities to their control strategies. A power reserve control is being required for grid support capabilities on Renewable Energy Sources (RES). Classical algorithms as the Maximum Power Point Tracking (MPPT) cannot withstand power reserve on its control, due to this, different control strategies have to be formulated to gain the power reserve capability. On this paper a cost-effective solution to perform the power reserve is presented, which provide a good solution for frequency regulation as well as for general grid fault conditions. Simulation test have been performed to verify the control capacity of this cost-effective solution.
Tarrasó, A.; Candela, J.; Rocabert, J.; Rodriguez, P. Annual Conference of the IEEE Industrial Electronics Society p. 1453-1458 DOI: 10.1109/IECON.2017.8216247 Data de presentació: 2017-10-29 Presentació treball a congrés
The increasing penetration of grid-connected RES systems, advanced control algorithms have been developed to operate under grid faults and fulfill strict requirements of the grid codes. In order to overcome this, the current controller performance is critical considering it as the inner control loop of any grid-connected RES system. Based on the resonant control concept, this paper presents a modified structure for this controller which results advantageous when implemented on RES systems, as it permits better performance during the dynamic state of the controller. This paper also deals with the analysis of the decoupling terms in the aß reference frame, as well as the capability to generate a decoupled control of the positive and the negative sequence. The proposed controller will be analyzed, discussed and finally validated by means of simulation analysis.
Tarrasó, A.; Candela, J.; Rocabert, J.; Rodriguez, P. IEEE Energy Conversion Congress and Exposition p. 64-68 DOI: 10.1109/ECCE.2017.8095762 Data de presentació: 2017-10-01 Presentació treball a congrés
The appearance of harmonics in the grid voltage is an issue for the generation systems and grid connected consumers. This paper presents the basic control strategy to be implemented in Synchronous Power Control (SPC) based power converters, which contributes to reduce the harmonic content in the voltage by means of injecting different harmonic current to the grid using a separated virtual admittance algorithm. This control strategy is capable of generating such a current reference that attenuates the harmonic values at the point of connection of the converter.
Abdollahi, M.; Candela, J.; Rocabert, J.; Muñoz-Aguilar, R. S.; Hermoso, J.R. IEEE Energy Conversion Congress and Exposition p. 3266-3273 DOI: 10.1109/ECCE.2017.8096591 Data de presentació: 2017-10-01 Presentació treball a congrés
High penetration of Renewable Generation Units (RGU), has led to that the interaction of this newfound participators in power network with conventional units be more critical challenges for network operators. Effect on the phase stability in emplacement as well as on neighbor generation units is one of this essential challenges. In this paper, a RGU controlled by Synchronous Power Controller (SPC) which behaves as a big Static Synchronous Generation (SSG-SPC) units, are presented as solution to cope with this challenge. Small signal modelling of a power network in presence of SSG-SPC unit is used to analysis this solution. After illustrating SPC dynamic capabilities, study on IEEE-14B test system based on modal analysis, time domain investigation and real time test confirms that a SSG-SPC not only has not damaging impact on phase stability and dynamic of network, but on the contrary can improve it. Moreover, by having at least two dynamic freedom degrees in SPC, the SSG-SPC can adapt itself for keeping this improvement effect.
Marín , L.; Rodriguez, P.; Candela, J.; Rocabert, J. IEEE Energy Conversion Congress and Exposition p. 4983-4988 DOI: 10.1109/ECCE.2017.8096843 Data de presentació: 2017-10-01 Presentació treball a congrés
VSCs connected to the grid through LCL filters are common in the integration of renewable energies into electrical systems. Therefore, in this paper small signal stability of the current loop of this configuration is performed.
The analysis includes the getting of a state-space representation of the system, the calculation of their eigenvalues and the sensitivity analysis to the variation of some relevant parameters. Real-time simulations have also been carried out in order to validate the theoretical analysis.
Control of grid-connected power converters is continuously developing to meet the grid codes, according to which the generation units should keep connected to the grid and further provide ancillary services, such as voltage and frequency support, negative sequence current injection, inertia emulation, etc. A virtual admittance controller is proposed in this paper for the objective of voltage support under asymmetrical grid faults. By using independent and selective admittances for positive and negative sequence current injection, the unbalanced voltage can be significantly compensated during asymmetrical faults. The controller is based on the generic control framework of the synchronous power controller (SPC), which is able to control a power converter with emulated and improved synchronous generator characteristics. Simulation and experimental results based on two paralleled 100 kW grid-connected power converters demonstrate the controller to be effective in supporting unbalanced voltage sags.
Abdollahi, M.; Candela, J.; Rocabert, J.; Muñoz-Aguilar, R. S.; Hermoso, J.R. IEEE International Conference on Renewable Energy Research and Applications p. 1-6 Data de presentació: 2016-11-20 Presentació treball a congrés
Abdollahi, M.; Candela, J.; Rocabert, J.; Muñoz-Aguilar, R. S.; Hermoso, J.R. IEEE International Conference on Renewable Energy Research and Applications p. 1-6 Data de presentació: 2016-11-20 Presentació treball a congrés
Zhang, W.; Cantarellas, A.M.; Rocabert, J.; Luna, A.; Rodriguez, P. IEEE Transactions on Sustainable Energy Vol. 7, num. 4, p. 1572-1582 DOI: 10.1109/TSTE.2016.2565059 Data de publicació: 2016-10-01 Article en revista
The increasing amount of renewable power generation systems is a challenging issue for the control and operation of the electrical networks. One of the main issues is their lack of inertia, which is becoming a greater problem as much as the share of the power plants based on traditional synchronous generators gets reduced. In this regard, the new grid codes ask these plants to provide new functionalities such as the frequency support and inertia emulation. In this paper, a synchronous power controller for grid-connected converters is proposed as a good solution for the renewable generation systems with energy storage. It provides inertia, damping, and flexible droop characteristics. Different from the faithful replication of the swing equation of synchronous machines, an alternative control structure is proposed, by which the damping and inherent droop slope can be configured independently to meet the requirements in both dynamics and frequency regulations. Analysis and experimental results are both shown to validate the proposed controller.
Capo, R.; Muñoz-Aguilar, R. S.; Rocabert, J.; Candela, J.; Rodriguez, P. IEEE Energy Conversion Congress and Exposition p. 1-6 DOI: 10.1109/ECCE.2016.7854966 Data de presentació: 2016-09-18 Presentació treball a congrés
Roslan, N.; Suul, J.; Luna, A.; Rocabert, J.; Candela, J.; Rodriguez, P. IEEE Energy Conversion Congress and Exposition p. 1-6 DOI: 10.1109/ECCE.2016.7854660 Data de presentació: 2016-09-18 Presentació treball a congrés
Grid connected Voltage Source Converters (VSCs) with LCL filters usually have voltage measurements at the filter capacitors, while it can be important to control the active or reactive power injection at the grid-side of the LCL filter, for instance at a Point of Common Coupling (PCC). Synchronization to the PCC voltage can be obtained by Virtual Flux (VF) estimation, which can also allow for voltage sensor-less operation of VSCs. This paper is presenting a comparative evaluation of methods for estimating the VF at the PCC, considering a VSC connected to the grid through an LCL filter with a Proportional Resonant (PR) controller as the inner current control loop. The VF estimation is achieved by using frequency adaptive dual SOGI-QSGs (DSOGI-VF). The Frequency Locked Loop (FLL) is used in order to keep the positive and negative sequence (PNS) VF estimation inherently frequency adaptive. Three different methods are considered for obtaining the capacitor current needed for estimating the VF at the grid side of the LCL filter which are based on fully estimation by using the voltage sensor-less method, by estimating the capacitor current from the measured voltage or by using additional capacitor current sensors. The results have been compared and validated by simulation studies.
Zhang, W.; Remon, D.; Rocabert, J.; Luna, A.; Candela, J.; Rodriguez, P. IEEE Energy Conversion Congress and Exposition p. 1-8 DOI: 10.1109/ECCE.2016.7855127 Data de presentació: 2016-09-18 Presentació treball a congrés
Grid-connected converters with primary frequency control and inertia emulation have emerged and are promising for future renewable generation plants because of the contribution in power system stabilization. This paper gives a synchronous active power control solution for grid-connected converters. As design considerations, the virtual angle stability and transient response are both analyzed, and the detailed implementation structure is also given without entailing any difficulty in practice. The analysis and validation of frequency support characteristics are particularly addressed. The 10 kW simulation and experimental frequency sweep tests on a regenerative source test bed present good performance of the proposed control in terms of showing inertia and droop characteristics, and the controllable transient response is also demonstrated.
Rodriguez, P.; Citro, C.; Candela, J.; Rocabert, J.; Luna, A. IEEE Energy Conversion Congress and Exposition p. 450-459 DOI: 10.1109/ECCE.2015.7309723 Data de presentació: 2015-09-20 Presentació treball a congrés
Photovoltaic power plants (PV) are equipped with anti-islanding algorithms, embedded in the converters controller, to avoid the island operation. However, the current trends in the development of the future electrical networks evidence that it is technically feasible and economically advantageous to keep feeding islanded systems under these situations, without cutting the power supply to the loads connected to the network. Nevertheless, commercial PV power converters are programmed as grid-feeding converters, and they are unable to work in island mode if there is not an agent forming the grid. In order to overcome this problem the Synchronous Power Controller (SPC) is presented in this paper as a suitable alternative for controlling PV inverters. As it will be further discussed this controller permits PV plants to operate seamless in grid connected and island mode, with no need of changing the control structure in any case. Moreover, the participation of SPC based power converters integrating energy storage enables other grid-feeding systems to contribute to the grid operation in island conditions. The results achieved with the SPC will be shown in simulations and also with experiments considering a real PV power plant combining SPC and comercial converters.
Zhang, W.; Remon, D.; Cantarellas, A.M.; Luna, A.; Rocabert, J.; Candela, J.; Rodriguez, P. IEEE Energy Conversion Congress and Exposition p. 3780-3787 DOI: 10.1109/ECCE.2015.7310194 Data de presentació: 2015-09-20 Presentació treball a congrés
The impact caused by the large scale penetration of renewable energy sources into electrical grid has been given an increasing concern in the past decade. Multiple challenges will occur in the future when the share of the traditional synchronous generators is reduced. One of the main issues is the lack of rotational inertia in the grid, which may cause stability issues. Therefore, the renewable energy generation plants have been asked for new control objectives and services.
In this paper, three types of active power synchronizing controllers are analyzed and compared with each other. All the three types of controllers are able to provide inertia, damping and droop characteristics, which are the favored features for the future renewable energy generation plants. The comparisons are hence conducted in these three aspects. Theoretical and experimental comparisons are both given, with the comments and conclusions.
Luna, A.; Rocabert, J.; Candela, J.; Hermoso, J.R.; Teodorescu, R.; Blaabjerg, F.; Rodriguez, P. IEEE transactions on industry applications Vol. 51, num. 4, p. 3414-3425 DOI: 10.1109/TIA.2015.2391436 Data de publicació: 2015-07-01 Article en revista
The actual grid code requirements for the grid connection of distributed generation systems, mainly wind and photovoltaic (PV) systems, are becoming very demanding. The transmission system operators (TSOs) are especially concerned about the low-voltage-ride-through requirements. Solutions based on the installation of STATCOMs and dynamic voltage regulators (DVRs), as well as on advanced control functionalities for the existing power converters of distributed generation plants, have contributed to enhance their response under faulty and distorted scenarios and, hence, to fulfill these requirements. In order to achieve satisfactory results with such systems, it is necessary to count on accurate and fast grid voltage synchronization algorithms, which are able to work under unbalanced and distorted conditions. This paper analyzes the synchronization capability of three advanced synchronization systems: the decoupled double synchronous reference frame phase-locked loop (PLL), the dual second order generalized integrator PLL, and the three-phase enhanced PLL, designed to work under such conditions. Although other systems based on frequency-locked loops have also been developed, PLLs have been chosen due to their link with dq0 controllers. In the following, the different algorithms will be presented and discretized, and their performance will be tested in an experimental setup controlled in order to evaluate their accuracy and implementation features.
Zhang, W.; Luna, A.; Candela, J.; Rocabert, J.; Rodriguez, P. IEEE International Symposium on Power Electronics for Distributed Generation Systems DOI: 10.1109/PEDG.2015.7223055 Data de presentació: 2015-06-22 Presentació treball a congrés
Improving the dynamics of the widely applied gridconnected power converters has been drawing a lot of interests in recent years. Since the currently installed grid-connected converters doesn’t shown inertia effect in power processing, the lack of inertia in the electrical networks will become increasingly significant and less admissible when more and more renewable energy sources penetrate into the grid through grid-connected converters.
An active power synchronizing controller for grid-connected power converters with configurable natural droop characteristics is proposed in this paper. The proposed controller is able to incorporate inertia, damping and configurable natural droop effect in the dynamics of the controlled converter. And in addition to the inertia characteristics, the droop and damping behaviors are discussed in detail. By a modified form of the swing equation of the synchronous generators, the droop behavior can be properly configured without undermining the damping characteristics. Experimental results are shown to validate the proposed controller
Multiterminal dc (MTDC) systems are drawing a lot of interest lately in applications related to distributed generation, especially in those that integrate wind or photovoltaic (PV) generation with energy storage (ES). Several approaches for controlling the operation of such systems have been proposed in the literature; however, the existing structures are mainly application specific and, thus, can be still improved in order to provide a more generic approach. This paper proposes an improved primary control layer for an MTDC system. The concept is based on the combination of a droop control method and dc bus signaling in order to provide a more generic and flexible solution. In this paper, different droop characteristics are proposed for the various elements connected to the dc bus. All of them are specifically tailored around five operation bands, which depend on the dc bus voltage level. Special attention is paid to the integration of ES: the state of charge (SoC) is considered at the primary control level, yielding a surface characteristic that depends on the SoC and the dc bus voltage. The scaling of the system has been analyzed together with the proposed control strategy and the overall operation has been validated through simulations by considering a 100 kW PV system with energy storage. Experimental results were obtained on a scaled laboratory prototype rated at 10 kW.
Gavriluta, C.; Candela, J.; Citro, C.; Rocabert, J.; Luna, A.; Rodriguez, P. IEEE transactions on industry applications Vol. 50, num. 6, p. 4122-4131 DOI: 10.1109/TIA.2014.2315715 Data de publicació: 2014-11-01 Article en revista
Multiterminal dc networks are drawing a lot of interest lately in applications related to distributed generation, particularly in those that also integrate energy storage (ES). A few approaches for controlling the operation of such systems have been proposed in the literature; however, the existing structures can be significantly enhanced. This paper proposes an improved primary control layer, based on custom droop characteristics obtained by combining concepts of droop and dc-bus signaling control. This approach is designed to be generic and takes into account the various operating states of the network. Five operating bands, similar to the operating states of the ac grids, as well as various droop characteristics for different elements connected to the dc network, are defined. For the ES, the state of charge is taken into account at the primary control level and included in the droop characteristic, creating a two-variable droop surface. The proposed control strategy is validated through simulation and experimental results obtained from a case study that involves amicro dc network composed of a photovoltaic generator, a lead-acid battery, and a connection point to the ac grid.
Gavriluta, C.; Candela, J.; Rocabert, J.; Etxeberria, I.; Rodriguez, P. IEEE Energy Conversion Congress and Exposition p. 5323-5330 DOI: 10.1109/ECCE.2014.6954131 Data de presentació: 2014-09-18 Presentació treball a congrés
Large penetration of renewable energy is currently attenuated by concerns regarding their impact on the controllability and reliability of the electrical system. As the inclusion of energy storage is to a great extent the solution to these issues, this paper proposes a methodology for approaching the calculation of the size of the energy storage to be connected to a PV power plant for providing inertia emulation, primary control, and the reduction of power fluctuation. A complete control strategy, developed for the inclusion of these services in the operation of a dc-ac grid connected converter has been implemented and validated through simulation results. The obtained results are validated by experimental tests performed on a scaled 10 kW prototype.
In this paper the design and the implementation of a method oriented to carry out a safe and a stable intentional disconnection, and re-connection, of local micro-grids from the main distribution network under generic grid conditions, avoiding the appearance of undesired transients, will be presented. In this work a seamless transfer between grid-connected and isolated mode is achieved by means of using an adapted frequency based synchronization control loop, which works in the ab stationary reference frame, whose response can be dynamically adapted in function of the micro-grid operating conditions. In addition to this feature, the inner loops of the control algorithm proposed in this application have been implemented in order to provide a proper operation of the system under generic conditions, even in the presence of unbalanced loads. In order to prove the reliability and good performance of the proposed method simulation and experimental results will be provided and discussed in the last sections of the paper.
Monadi, M.; Luna, A.; Candela, J.; Rocabert, J.; Fayezizadeh, M.; Rodriguez, P. Annual Conference of the IEEE Industrial Electronics Society p. 1974-1979 DOI: 10.1109/IECON.2013.6699434 Data de presentació: 2013-11-13 Presentació treball a congrés
The connection of Distributed Generation (DG) units
to existing networks may give rise to harmful effects on the
network and the DG units itself. Therefore, due to increasing
penetration of DG units, it is important to consider these effects
in order to avoid some of harmful events. Ferroresonance is one
of these destructive phenomena. Over voltages due to this
phenomena can damage devices which are connected to the
network. In DG systems, due to the use of capacitor banks which
are used for VAR compensation, grid connection filters, etc.
ferroresonance may appear. Also, special operations like
islanding, may lead these systems to ferroresonance. In
traditional systems ferroresonance normally appear after there is
an unbalance in the system. Nevertheless, for networks with
significant penetration of DG units, the situation that gives rise to
ferroresonance may be different from traditional systems and
they can happen without any unbalancing occurrence. In this
paper a distribution system integrating wind (WT) and
photovoltaic (PV) power systems has been evaluated in order to
analyze the performance of ferroresonance in such systems.
Finally, the most appropriate techniques to prevent its
appearance, and the associated over voltages, have been studied
and implemented using PSCAD/EMTDC.
Rodriguez, P.; Candela, J.; Citro, C.; Rocabert, J.; Luna, A. European Conference on Power Electronics and Applications DOI: 10.1109/EPE.2013.6634621 Data de presentació: 2013-09-06 Presentació treball a congrés
The connection of electronic power converters to the electrical network is increasing mainly due to massive integration of renewable energy systems. However, the electrical dynamic performance of these converters does not match the behavior of the network, which is mainly formed by generation facilities based on big synchronous generation systems. Depending on the desired electrical operation mode different control structures can be implemented in the converters in order to get adapted with the grid conditions. However, changing between different control structures and operation is not an optimal solution, as the resulting system results complex and is not highly robust. As an alternative, this paper presents a new control technique for grid connected power converters based on the concept of virtual admittance. The proposed control permits to emulate the electrical performance of generation facilities based on classical synchronous generators with a power converter, with no need of implementing different control structures, giving rise to a system that provides a friendly and robust operation with the network.
The connection of electronic power converters to the electrical network is increasing mainly due to
massive integration of renewable energy systems. However, the electrical dynamic performance of
these converters does not match the behavior of the network, which is mainly formed by generation
facilities based on big synchronous generation systems. Depending on the desired electrical operation
mode different control structures can be implemented in the converters in order to get adapted with the
grid conditions. However, changing between different control structures and operation is not an
optimal solution, as the resulting system results complex and is not highly robust. As an alternative,
this paper presents a new control technique for grid connected power converters based on the concept
of virtual admittance. The proposed control permits to emulate the electrical performance of
generation facilities based on classical synchronous generators with a power converter, with no need
of implementing different control structures, giving rise to a system that provides a friendly and robust
operation with the network.
Gavriluta, C.; Candela, J.; Luna, A.; Rocabert, J.; Rodriguez, P. European Conference on Power Electronics and Applications p. 1-9 DOI: 10.1109/EPE.2013.6631976 Data de presentació: 2013-09-06 Presentació treball a congrés
Multi-terminal DC (MTDC) systems are drawing a lot of interest lately in applications related to distributed generation, especially in those that integrate wind or PV systems together with energy storage. This paper proposes an improved strategy for the primary control of MTDC integrating energy storage (ES) units. The concept is based on the combination of a droop control method and dc-bus signaling in order to provide a generic approach to be used as basis for a hierarchical control structure in a multi-point DC-bus system.
The proposed method considers the State of Charge (SoC) of the energy storage system at the primary control level, yielding a surface characteristic for a droop control that depends both on the SoC and the dc bus voltage.
Finally, a method for designing and tuning the system is proposed and analyzed theoretically and through simulations and experiments on a 10kVA system with energy storage.
Luna, A.; Rocabert, J.; Candela, J.; Rodriguez, P.; Teodorescu, R.; Blaabjerg, F. IEEE Energy Conversion Congress and Exposition p. 2769-2776 DOI: 10.1109/ECCE.2012.6342381 Data de presentació: 2012-09-15 Presentació treball a congrés
The Transmission System Operators are specially concerned about the Low Voltage Ride Through requirements of distributed generation power plants. Solutions based on the installation of STATCOMs and DVRs, as well as on advanced control functionalities for the existing power converters have contributed to enhance their response under faulty and distorted scenarios, and hence to fulfill these requirements. In order to achieve satisfactory results it is necessary to count on accurate and fast grid voltage synchronization algorithms, which are able to work under unbalanced and distorted conditions. This paper analyzes and compares the synchronization capability of three advanced synchronization systems: the Decoupled Double Synchronous Reference Frame-Phase-Locked Loop, the Dual Second Order Generalized Integgrator- Phase-Locked Loop and the Three-Phase Enhanced Phase-Locked Loop, designed to work under such conditions. Its response will be analyzed with respect the synchronization needs that can be extracted from the standards
Citro, C.; Luna, A.; Rocabert, J.; Muñoz-Aguilar, R. S.; Candela, J.; Rodriguez, P. Annual Conference of the IEEE Industrial Electronics Society p. 2417-2423 DOI: 10.1109/IECON.2011.6119701 Data de presentació: 2011-11-07 Presentació treball a congrés
The level of penetration of grid-connected photovoltaic (PV) systems has grown very quickly in recent years. Nonetheless, network stresses related to the recurrent voltage and frequency oscillations caused by their irregular power production could be a limiting factor on the future expansion of these applications. With the capability of storing and releasing electrical energy on demand, Energy Storage Devices (ESDs) may play a key role in finding an effective solution to overcome these kinds of problems. The aim of this paper is to provide a description of the state-of-the-art power conversion systems used to combine ESDs and grid-connected PV plants. The work has been edited after an accurate analysis of the current scientific literature, focusing particular attention on medium-high-power PV applications utilizing batteries and/or supercapacitors. A detailed analysis on advantages, disadvantages and range of application is provided for each of the reported conversion systems.
Rodriguez, P.; D. Bellar, M.; Muñoz-Aguilar, R. S.; Rocabert, J.; Luna, A. Annual Conference of the IEEE Industrial Electronics Society p. 4280-4285 Data de presentació: 2011-11-07 Presentació treball a congrés
In this paper a new multilevel power conversion
concept is proposed, whereby an additional auxiliary circuit
composed of multilevel clamping cells is applied to a main DCAC
converter. The resultant structure, the multilevel-clamped
multilevel converter, or simply multilevel-clamped converter
(MLC2), has the number of levels increased, while keeping
circuitry simple, wherein the number of parts count can be
reduced, when compared with classical NPC counterparts.
Hence, the well established three-level neutral-point-clamped
(NPC) technology can be applied, which has been the preferred
choice in medium-voltage (MV) high power industry for several
industrial products. A description of the proposed concept is
provided, on which different topologies are derived. Moreover, a
cost comparison analysis is shown to illustrate their
attractiveness. Simulation and experimental results based on the
space vector pulse width modulation (SVPWM) are shown, in
order to illustrate the operation and effectiveness of the new
Azevedo, G.; Bradaschia, F.; Calvancanti, M.; Neves, F.; Rodriguez, P.; Rocabert, J. IEEE Energy Conversion Congress and Exposition p. 2191-2195 DOI: 10.1109/ECCE.2011.6064058 Data de presentació: 2011-11-01 Presentació treball a congrés
Master-Slave configuration is a suitable alternative
to droop control method used in microgrids. In this configuration,
only one inverter is the master, while the others are slaves. The
slave inverters are always current controlled whereas the master
inverter should have two selectable operation modes: current
controlled, when the microgrid is connected to the grid; and
voltage controlled, when it is operating in island mode. In gridconnected
mode, the master needs a synchronization system to
perform the accurate control of its delivered power, and, in
island mode, it needs a voltage reference oscillator that serves
as a reference to the slave inverters. Based on the master-slave
concept, this paper proposes a single system that perform both
functions, i.e., it can act as a synchronization system or as
a voltage reference oscillator depending on an input selector.
Moreover, the system ensures a smoothly transition between
the two operation modes, guaranteeing the safety operation of
the microgrid. Experimental results are provided to confirm the
effectiveness of the proposed system.
Azevedo, G.; Calvancanti, M.; Bradaschia, F.; Neves, F.; Rocabert, J.; Rodriguez, P. IEEE Energy Conversion Congress and Exposition p. 391-396 DOI: 10.1109/ECCE.2011.6063796 Data de presentació: 2011-11-01 Presentació treball a congrés
Droop control is a common method to parallel
operation of inverters. This method uses the average values of
power components which are usually obtained through low-pass
filters. However, in single-phase systems the power components
are oscillating at twice fundamental frequency and the filters
cut-off frequency must be very low. Thus, there is a tradeoff
between dynamic response and oscillation attenuation. In this
paper, a method that uses a fictitious quadrature reference frame
to calculate the average power components is presented. This
method improves the dynamic response of the power sharing
control and eliminates the double-frequency oscillation over the
voltage and frequency synthesized by the inverter. Moreover, it is
able to deal with nonlinear loads since the harmonic components
that appear in the instantaneous power are filtered. This paper
also presents a comparison between this method and the classical
one through simulation carried out in Matlab/Simulink and
The recent grid integration of Distributed Energy Resources (DER) possibility the formation of
intentional islands in the case of a grid fault conditions. For such island formation is required an active
agent capable of governing the micro-grid connection state in a safe mode, especially in connection
and disconnection transients. This paper focuses on the design of a method oriented to carry out a
stable intentional disconnection, and later re-connection, of local grids from the main distribution grid
in an intentional way; also under unbalance load condition. Seamless transfer between grid-connected
and isolated mode has been achieved in an alpha-beta stationary reference frame with a frequency
based synchronization control loop. Simulation and experimental results are provided to verify the
proper performance of the proposed solution.
Azevedo, G.; Calvancanti, M.; Neves, F.; Rodriguez, P.; Rocabert, J. IEEE International Symposium on Industrial Electronics p. 1465-1470 DOI: 10.1109/ISIE.2011.5984376 Data de presentació: 2011-06-27 Presentació treball a congrés
The droop control uses the local average values
of the active and reactive power components for sharing the
load power demand among inverters in parallel. In this paper,
a method that uses a virtual quadrature reference frame to
calculate the average power components injected by singlephase
inverters is presented. This method improves the dynamic
response of the power sharing control, as well as, completely
eliminates the double frequency oscillation over the voltage and
frequency synthesized by the inverter in steady state. Moreover,
it is able to deal with nonlinear loads since the harmonic
components that appears in the instantaneous power are filtered.
The method is compared with the classical method, which is
based on low pass filters, through simulation carried out in
Matlab/Simulink and experimental results.
Ma, L.; Luna, A.; Rocabert, J.; Muñoz-Aguilar, R. S.; Corcoles, F.; Rodriguez, P. International Conference on Power Engineering, Energy and Electrical Drives Data de presentació: 2011-05-11 Presentació treball a congrés
In order to improve the connected current and the
response speed of the controller, stationary reference frame
control strategy with proportional resonant (P-R) controller due
to its high dynamic and good harmonic compensation
performance characteristics was already used in many different
DG applications. This paper introduced an additional stationary
reference frame control strategies with voltage feed-forward
method. By using this method, both the quality of grid connected
current and the dynamic performance are improved, which also
validated by experiments.
La presente invención se refiere a un controlador de admitancia virtual basado en convertidores estáticos de potencia, que comprende un lazo de control en cuya entrada se inyecta la diferencia de tensión existente entre una tensión interna virtual (e) y la tensión existente en el punto de la red al que está conectado (v) y esa diferencia de tensiones alimenta a un procesador de admitancia virtual (13) que es el encargado de determinar el valor de una corriente de referencia (i*) que comunica a una fuente de corriente (14) la cual se encarga de inyectar físicamente dicha corriente a la red (15).
Controlador de la característica electromecánica virtual para un convertidor estático de potencia que comprende un PLC (23) ("power loop controller" o "controlador del lazo de potencia") el cual recibe a la entrada la diferencia de potencia (ΔP) existentes entre la potencia de entrada (Pin) (potencia entregada al convertidor por la fuente primaria) y la potencia entregada a la red (Pelec), y es capaz de modificar en línea los parámetros del coeficiente de inercia virtual y factor de amortiguamiento en función de la respuesta deseada y de las condiciones de la red para diferentes rangos de frecuencia.
Rocabert, J.; Azevedo, G.; Luna, A.; Guerrero, J.M.; Candela, J.; Rodriguez, P. IEEE transactions on power electronics Vol. 26, num. 10, p. 2993-3005 DOI: 10.1109/TPEL.2011.2116126 Data de publicació: 2011 Article en revista