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  • Control and Operation of Multi-Terminal VSC-DC Networks

     Gavriluta, Catalin
    Universitat Politècnica de Catalunya
    Theses

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    Durante el siglo pasado, las redes de corriente alterna se han consolidado como la tecnología estándar para los sistemas de transmisión de energía eléctrica. Sin embargo, los sistemas de transmisión en continua se han seguido utilizando en algunas aplicaciones. La capacidad de estos para transmitir mayores potencias a distancias más largas, la posibilidad de interconectar redes asincrónicas, y su alta eficiencia han propiciado que se mantuviera el interés académico, de investigación e industrial en esta tecnología . Aunque históricamente se utilizaron sistemas basados en generadores de continua y válvulas de mercurio para las redes de transmisión, en la década de los 90 todas las instalaciones ya contaban con convertidores conmutados basados en tiristores (LCC). En 1999, se instaló el primer sistema basado en convertidores en fuente de tensión (VSC) en Gotland, Suecia, marcando el comienzo de una nueva era para la transmisión en corriente continua. En los últimos 15 años, la potencia de los sistemas de transmisión en continua basados en VSC ha aumentado desde los 50 hasta los 700 MN, la tensión de servicio de 120 a 500 kV y las distancias recorridas han llegado a ser, en algunos casos, de hasta 950 kilómetros (HVDC-light de ABB en Namibia en 201 O). El trabajo presentado en esta tesis se centra en el control y operación de redes de corriente continua VSC multi-terminal (MTDC). El enfoque propuesto se basa en una arquitectura de control jerárquico, inspirada en la estrategia de control de generación automática aplicada a redes de corriente alterna.En la arquitectura propuesta, el control primario del sistema MTDC está descentralizado e implementado mediante una estrategia de 'droop' generalizada. Más allá del análisis del comportamiento del control primario, esta tesis presenta una metodología para el diseño de los diferentes parámetros que influyen en el mismo. Se destaca la importancia de dimensionar correctamente condensador de salida del VSC, ya que este elemento, cuando se encuentra en el contexto de una red MTDC, se convierte en el elemento inercial de la red y tiene un impacto directo en el comportamiento transitorio de las tensiones. Asimismo, se propone unaestrategia de control de 'droop' mejorada que atenúa las oscilaciones de tensión durante los transitorios. En el marco del control jerárquico propuesto, el control secundario está centralizado y regula el punto de funcionamiento de la red de manera que se consigue un flujo de potencia óptimo (OPF). En comparación con otros trabajos, esta tesis lleva a cabo, tanto de forma analítica como a través de simulaciones, un estudio detallado sobre la coordinación entre las capas de control primario y secundario en redes MTDC.

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    Adaptive droop for control of multiterminal DC bus integrating energy storage  Open access

     Gavriluta, Catalin; Candela Garcia, Jose Ignacio; Rocabert Delgado, Joan; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE transactions on power delivery
    Vol. 30, num. 1
    DOI: 10.1109/TPWRD.2014.2352396
    Date of publication: 2015-02-01
    Journal article

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    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.

    Postprint (author’s final draft)

  • Hierarchical control of HV-MTDC systems with droop-based primary and OPF-based secondary

     Gavriluta, Catalin; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Gomez Exposito, Antonio; Rodriguez Cortes, Pedro
    IEEE Transactions on Smart Grid
    DOI: 10.1109/TSG.2014.2365854
    Date of publication: 2014-11-12
    Journal article

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    This paper proposes a hierarchical control architecture designed for an arbitrary high voltage multiterminal dc (MTDC) network. In the proposed architecture, the primary control of the MTDC system is decentralized and implemented using a generalized droop strategy. Design criteria for dimensioning the primary control parameters, including voltage limits, are offered by analyzing the transients appearing in the system. The proposed secondary control is centralized and regulates the operating point (OP) of the network so that optimal power flow (OPF) is achieved. Compared to previous works, this paper further elaborates, both analytically and through simulations, on the coordination between the primary and secondary control layers. This includes how local primary controllers have to be driven by the centralized controller in order to ensure a smooth transition to the optimal OP.

  • Decentralized primary control of MTDC networks with energy storage and distributed generation

     Gavriluta, Catalin; Candela Garcia, Jose Ignacio; Citro, Costantino; Rocabert Delgado, Joan; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE transactions on industry applications
    Vol. 50, num. 6, p. 4122-4131
    DOI: 10.1109/TIA.2014.2315715
    Date of publication: 2014-11-01
    Journal article

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    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.

  • An active power self-synchronizing controller for grid-connected converters emulating inertia

     Remón, D.; Mir Cantarellas, Antonio; Rakhshani, Elyas; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    p. 424-429
    DOI: 10.1109/ICRERA.2014.7016421
    Presentation's date: 2014-10-22
    Presentation of work at congresses

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    Renewable energy sources are increasing their penetration in power systems, making necessary new control systems that offer services usually provided only by conventional generators. In this paper, an active power controller able to achieve synchronization with the grid and to control the DC link voltage is proposed. This controller allows identifying the converter with a virtual synchronous generator whose inertia can be modified online, considering that its virtual kinetic energy is stored in the DC link. Additionally, the resulting active power loop is a second order system whose damping factor can be defined freely.

  • Proposals for flexible operation of multi-terminal DC grids: introducing flexible DC transmission system (FDCTS)

     Rouzbehi, Kumars; Miranian, Arash; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    p. 180-184
    DOI: 10.1109/ICRERA.2014.7016553
    Presentation's date: 2014-10-22
    Presentation of work at congresses

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    The current route of achieving the ultimate plan for flawless operation and control of the multi-terminal DC (MTDC) grids can be significantly accelerated by learning from the vast and valuable experiences gained from the operation of the AC power grids for more than a century. This paper introduces concept of flexible DC transmission system (FDCTS), inspired by the successful operation of flexible AC transmission systems (FACTS), to provide voltage regulation, power control and load flow control within MTDC grids. Considering the current advancements in the field of power electronics, this paper recognizes DC-DC converters as the first element of the FDTCS for providing voltage and power control in MTDC grids. By use of DC-DC converters, this paper developes two elements of the FDCTS, namely the cascaded power flow controller (CPFC) and hybrid power flow controller (HPFC). In this paper, to demonstrate the eligibility of the CPFC and HPFC to play the role of an FDCTS, they are included in the DC power flow formulation for DC voltage regulation and power flow control purposes.

  • A hybrid power flow controller for flexible operation of multi-terminal DC grids

     Rouzbehi, Kumars; Miranian, Arash; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    p. 550-555
    DOI: 10.1109/ICRERA.2014.7016445
    Presentation's date: 2014-10-22
    Presentation of work at congresses

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    This paper develops a hybrid power flow controller (HPFC) to take one step forward for building future flexible DC transmission system (FDCTS). The idea for proposing HPFC is inspired by the successful operation of flexible AC transmission systems (FACTS) devices, the FDCTS includes static power electronics-based elements to provide voltage regulation, power control and load flow control in the multi-terminal DC (MTDC) grids. The HPFC, as one of the devices of the FDCTS, has a hybrid connection scheme (i.e. series-parallel) to the grid and allows power flow control through DC transmission lines by imposing a series voltage to the controlled DC line. In this work, in order to demonstrate the eligibilities of the HPFC, the performance of this device is included in the DC power flow formulation for the power flow control purposes. Finally, it will be shown through dynamic simulations that the proposed HPFC is able to control the power flow through a particular DC transmission line.

  • A protection strategy for fault detection and location for multi-terminal MVDC distribution systems with renewable energy systems

     Monadi, Mehdi; Koch-Ciobotaru, Cosmin; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    p. 496-501
    DOI: 10.1109/ICRERA.2014.7016434
    Presentation's date: 2014-10-22
    Presentation of work at congresses

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    A fault location method and a fault clearance strategy are presented in this paper for medium voltage dc (MVDC) distribution system. MVDC systems are applicable for connection between microgrids (MGs) and integration of renewable energy systems (RESs) to distribution systems. Due to the specifications of fault current in dc systems, it is difficult to coordinate the over current (O/C) relays based on the time inverse grading. Hence, in this paper, a communication link between O/C relays is used to diagnose the fault location. On the other hand, the fault clearance is done by the operation of dc circuit breakers (DCCB) and isolator switches. In this protection strategy, O/C relays detect the faulty part using communication links and after the fault extinguishing by DCCBs, the dc switches isolate the faulty part. Finally, the sound parts of the system re-energize when DCCB are re-closed. Moreover, data transmission by communication links is based on the standard messages of IEC61850 protocol.

  • Performance analysis of conventional PSS and fuzzy controller for damping power system oscillations

     Banna, Hasan UI; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro; Cabrera Tobar, Ana; Ghorbani, Hamidreza; Ying, Shaoqing
    International Conference on Renewable Energy Research and Applications
    p. 229-234
    DOI: 10.1109/ICRERA.2014.7016561
    Presentation's date: 2014-10-19
    Presentation of work at congresses

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    Electro-mechanical oscillations are produced, in the machines of an interconnected power network, followed by a disturbance or due to high power transfer through weak tie lines. These oscillations should be damped as quickly as possible to ensure the reliable and stable operation of the network. To damp these oscillations different controllers, based on local or wide area signals, have been the subject of many papers. This paper presents the analysis of the performance of Conventional Power System Stabilizer (CPSS) and Fuzzy Logic Controller. Two area 14 bus symmetrical system is considered to demonstrate the performance of these controllers using Simulink/MATLAB. Simulation results depict fuzzy logic based controller having dual inputs of rotor speed deviation and generator's accelerating power is the better cost effective solution for damping the inter area oscillations specifically, in comparison with conventional power system stabilizer.

  • Impacts of wind energy in-feed on power system small signal stability

     Banna, Hasan UI; Luna Alloza, Alvaro; Ying, Shaoqing; Ghorbani, Hamidreza; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    p. 615-622
    DOI: 10.1109/ICRERA.2014.7016459
    Presentation's date: 2014-10-19
    Presentation of work at congresses

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    Integration of large amount of wind energy in an interconnected power system creates concerns about secure, reliable and economical operation of the entire power system. So it becomes very necessary to investigate the impacts of wind power infeed on the dynamic behavior of the power system. This paper presents the impacts of large amount of wind power in feed on the rotor oscillatory stability. Wind turbine generator types currently employed in wind farms, optimal location of the wind farms in the interconnected power system, reliable optimal dispatch of the wind power and the degree of tie line congestion have been thoroughly investigated. Kundur's two area network model has been utilized to study the mentioned impacts on the overall system using MATLAB/Simulink. Some of the key results show that the damping characteristics of the wind farms critically depend on the location of interconnection in the network and the optimal wind energy dispatch. Increasing the penetration of the wind energy generally improves the damping of the inter area oscillations. Moreover, reducing stress on the weak tie lines also improves the inter area mode of oscillation. So with the investigation of these impacts this study is helpful for the planning of new wind power projects.

  • Distributed FLISR algorithm for smart grid self-reconfiguration based on IEC61850

     Koch-Ciobotaru, Cosmin; Monadi, Mehdi; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    p. 418-423
    DOI: 10.1109/ICRERA.2014.7016420
    Presentation's date: 2014-10-19
    Presentation of work at congresses

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    This paper proposes a distributed algorithm for Fault Location, Isolation, and Service Restoration (FLISR) to be implemented as part of the intelligent software for controlling the operation of each circuit breaker. The paper proposes an event driven finite-state machine design that assures the self-reconfiguration of the distribution power grid when a fault occurs on a certain section of a feeder. The benefits of such an approach are first of all the modularity, as each breaker is controlled by the same algorithm and requires data exchange only with the neighboring protection devices. Secondly, by using the event driven technique, the FLISR algorithm is perfectly suited for taking advantage of the features and benefits defined by the IEC 61850 protocol. Using GOOSE messages for transferring status information between the neighboring circuit breakers, the proposed distributed algorithms act in a collective manner for reconfiguring the distribution grid.

  • A proportional resonant controller tuning method for grid connected power converters with LCL+trap filter

     Zhang, Weiyi; Mir Cantarellas, Antonio; Remón, D.; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    p. 445-450
    DOI: 10.1109/ICRERA.2014.7016425
    Presentation's date: 2014-10-19
    Presentation of work at congresses

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    Three-phase power converters are largely employed in power generation facilities based on renewable energy sources, and these converters commonly working in grid connection mode are frequently connected to the grid through passive filters. Nowadays the need for larger power converter-based generation plants increases continuously, and LCL+trap filter arises as a solution when switching frequency is reduced due to the power increase. However, the tuning of current controllers becomes more complex as the LCL+trap filter lead to a considerably high order system. In this work a method for tuning the gains of proportional resonant current controllers for three-phase high power converters linked to the grid through a LCL+trap filter is proposed and analyzed. Simulation and experimental results taken in different cases are shown to validate the proposed method.

  • A control strategy for DC-link voltage control containing PV generation and energy storage — An intelligent approach

     Rouzbehi, Kumars; Miranian, Arash; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    p. 268-271
    DOI: 10.1109/ICRERA.2014.7016568
    Presentation's date: 2014-10-19
    Presentation of work at congresses

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    In this paper, DC-link voltage control in DC microgrids with photovoltaic (PV) generation and battery, is addressed based on an intelligent approach. The proposed strategy is based on the modeling of the power interface, i.e. power electronic converter, located between the PV array, battery and DC bus, by use of measurement data. For this purpose, a local model network (LMN) is developed to model the converter and then a local linear control (LLC) strategy is designed based on the LMN. Simulation results on a DC microgrid demonstrates efficacy of the proposed approach.

  • Storage system requirements for grid supporting PV-power plants

     Gavriluta, Catalin; Candela Garcia, Jose Ignacio; Rocabert Delgado, Joan; Etxeberria Otadui, Ion; Rodriguez Cortes, Pedro
    IEEE Energy Conversion Congress and Exposition
    p. 5323-5330
    DOI: 10.1109/ECCE.2014.6954131
    Presentation's date: 2014-09-18
    Presentation of work at congresses

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    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.

  • Evaluation and control design of virtual-synchronous-machine-based STATCOM for grids with high penetration of renewable energy

     Chi, Li; Burgos, R.; Cvetkovic, I.; Boroyevich, D.; Mili, L.; Rodriguez Cortes, Pedro
    IEEE Energy Conversion Congress and Exposition
    p. 5652-5658
    DOI: 10.1109/ECCE.2014.6954176
    Presentation's date: 2014-09-14
    Presentation of work at congresses

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    Because renewable energy sources are environment-friendly and inexhaustible, more and more said renewable energy power plants have been integrated into power grids worldwide. To compensate for their inherent variability, STATCOMs are typically installed at the point of common coupling (PCC) to help their operation by regulating the PCC voltage. However under different contingencies, PCC voltage fluctuations in magnitude and frequency may impede the STATCOM from tracking the grid frequency correctly, hence worsening its overall compensation performance, and putting at risk the operation of the power plant. Further, the virtual synchronous machine (VSM) concept has recently been introduced to control grid-connected inverters emulating the behavior of rotating synchronous machines, in an effort to eliminate the shortcomings of conventional d-q frame phase-locked loops (PLL). In this paper, the VSM concept is extended by developing a STATCOM controller with it, which then behaves like a fully-adjustable synchronous condenser, including the adjustment of its “virtual” inertia and impedance. The proposed controller is compared against existent d-q frame STATCOM control strategies, evincing how the VSM-based approach guarantees not just better synchronization, but an improved voltage regulation performance at the PCC, attained through its virtual impedance, as well as a lower sensitivity to system disturbances, attained through its virtual inertia. The paper will include the complete design procedure for the VSM-STATCOM, and the verification of key results through detailed simulation studies.

  • Towards fully controllable multi-terminal DC grids using flexible DC transmission systems

     Rouzbehi, Kumars; Miranian, Arash; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE Energy Conversion Congress and Exposition
    p. 5312-5316
    DOI: 10.1109/ECCE.2014.6954129
    Presentation's date: 2014-09-14
    Presentation of work at congresses

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    This paper develops a flexible DC transmission system (FDCTS) to power control and load flow control within the multi-terminal (MTDC) grids. The FDCTS include static power electronics-based elements for electric energy transmission inside a DC grid. Considering the current advancements in the field of power electronics, this paper proposes a cascaded power flow controller (CPFC) as the first element of the FDTCS for providing power control in MTDC grids. It is shown through dynamic simulations that the CPFC is able to control power flowing through a particular DC transmission line, and thus enhancing controllability in the MTDC grids.

  • Enhanced control strategy for MMC-based STATCOM for unbalanced load compensation

     Nieves, M.; Maza, J.M.; Mauricio, J.M.; Teodorescu, Remus; Bongiorno, M.; Rodriguez Cortes, Pedro
    European Conference on Power Electronics and Applications
    DOI: 10.1109/EPE.2014.6911014
    Presentation's date: 2014-08-26
    Presentation of work at congresses

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    Modular Multilevel Converters (MMC) technology is today one of the preferred technology in HVDC and large STATCOM applications due to modularity, fault tolerance and high efficiency, but the voltage balancing becomes very challenging, especially during negative sequence current injection as required for load unbalance compensation. This paper proposes an improved balancing strategy for the delta configuration to overcome this situation based on the injection of a third harmonic zero sequence current. Simulation results have proved the effectiveness of the proposal even where different switching losses and capacitor tolerance are taken in consideration.

  • Posicast control: a novel approach to mitigate multi-machine power system oscillations in presence of wind farm

     Ghorbani, Hamidreza; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE Power & Energy Society General Meeting
    DOI: 10.1109/PESGM.2014.6939414
    Presentation's date: 2014-07-31
    Presentation of work at congresses

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    In this paper, application of Posicast control method to generator excitation system is presented. The method is one of the simplest possible control design methods that can be applied to damp the oscillations caused by changing the excitation reference signal. Stability and robustness of the designed controller are shown using extensive time domain simulations. All the detailed simulations are carried out in MATLAB/Simulink environment.

  • An active power synchronization control loop for grid-connected converters

     Remón, D.; Mir Cantarellas, Antonio; Rakhshani, Elyas; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    IEEE Power & Energy Society General Meeting
    DOI: 10.1109/PESGM.2014.6939250
    Presentation's date: 2014-07-31
    Presentation of work at congresses

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    The increasing penetration of renewable energy sources in power systems requires new control systems that provide services similar to those of conventional generators. This paper proposes an active power controller that is able to automatically achieve synchronization with the grid and to control the DC link voltage. Through this controller, the converter can be identified with a virtual synchronous generator whose kinetic energy is stored in the DC link. Moreover, the active power loop becomes a second order system whose damping can be programmed freely.

  • Integration of renewable generation for frequency support of HVDC/AC interconnected systems under power market scenario

     Rakhshani, Elyas; Remón, D.; Mir Cantarellas, Antonio; Rouzbehi, Kumars; Rodriguez Cortes, Pedro
    IEEE General Meeting | Conference & Exposition
    p. 1-5
    DOI: 10.1109/PESGM.2014.6938795
    Presentation's date: 2014-07-27
    Presentation of work at congresses

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    This paper proposes a modified model for active power/ frequency support of multi-area power system analysis that takes into account the effects of AC/DC systems under deregulated environment of the power market. The AC part of studied system is comprised of conventional generators and HVAC lines, while DC systems are related to the parts with converter station models and HVDC interconnection. Simulations performed by Matlab software demonstrate how renewable power plants can serve as conventional generators in AGC control loops under constraints determined by the market rules. This scenery is considered one of the most promising evolutions of the future electrical power systems.

  • DC voltage control and power sharing in multiterminal DC grids based on optimal DC power flow and voltage-droop strategy

     Rouzbehi, Kumars; Miranian, Arash; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE Journal of emerging and selected topics in power electronics
    Vol. 2, num. 4, p. 1171-1180
    DOI: 10.1109/JESTPE.2014.2338738
    Date of publication: 2014-07-11
    Journal article

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    This paper proposes an effective dc voltage and power-sharing control structure for multiterminal dc (MTDC) grids based on an optimal power flow (OPF) procedure and voltage-droop control implemented in the different hierarchical layers. In the proposed approach, an OPF algorithm is executed at the secondary control level of the MTDC grid to find the optimal reference values for the dc voltages and active power of the voltage-regulating converters. Then, at the primary control level, the voltage-droop characteristics of the voltage-regulating converters are tuned based upon the OPF results. In this control structure, the optimally-tuned voltage-droop controllers lead to the optimal operation of the MTDC grid. In case of variation in load or generation of the grid, a new stable operating point is achieved based on the voltage-droop characteristics. Then by executing a new OPF, the voltage-droop characteristics are returned for optimal operation of the MTDC grid after the load or generation variations. This paper also considers the integration of frequency support loop in the proposed control framework in case of connection of weak ac grids. The simulations performed on a study case inspired by the CIGRE B4 dc grid test system demonstrate the efficient grid performance under the proposed control strategy.

  • A generalized voltage droop strategy for control of multiterminal DC grids

     Rouzbehi, Kumars; Miranian, Arash; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro; Luna Alloza, Alvaro
    IEEE transactions on industry applications
    Vol. 51, num. 1, p. 607-618
    DOI: 10.1109/TIA.2014.2332814
    Date of publication: 2014-06-24
    Journal article

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    This paper proposes a generalized voltage droop (GVD) control strategy for dc voltage control and power sharing in voltage source converter (VSC)-based multiterminal dc (MTDC) grids. The proposed GVD control is implemented at the primary level of a two-layer hierarchical control structure of the MTDC grid, and constitutes an alternative to the conventional voltage droop characteristics of voltage-regulating VSC stations, providing higher flexibility and, thus, controllability to these networks. As a difference with other methods, the proposed GVD control strategy can be operated in three different control modes, including conventional voltage droop control, fixed active power control, and fixed dc voltage control, by adjusting the GVD characteristics of the voltage-regulating converters. Such adjustment is carried out in the secondary layer of the hierarchical control structure. The proposed strategy improves the control and power-sharing capabilities of the conventional voltage droop, and enhances its maneuverability. The simulation results, obtained by employing a CIGRE B4 dc grid test system, demonstrate the efficiency of the proposed approach and its flexibility in active power sharing and power control as well as voltage control. In these analysis, it will be also shown how the transitions between the operating modes of the GVD control does not give rise to active power oscillations in the MTDC grids.

  • Analysis and design of virtual synchronous machine based STATCOM controller

     Chi, Li; Burgos, R.; Cvetkovic, I.; Boroyevich, D.; Mili, L.; Rodriguez Cortes, Pedro
    IEEE Workshop on Control and Modeling for Power Electronics
    DOI: 10.1109/COMPEL.2014.6877134
    Presentation's date: 2014-06-22
    Presentation of work at congresses

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    this paper extends the virtual synchronous machine (VSM) concept, recently proposed as alternative means to synchronize grid-connected inverters, by developing a VSM-based STATCOM controller operating as synchronous condenser. To this end, a mathematical model is derived and used to analyze the inherent dynamics of the VSM-based STATCOM controller, which are then used to formulate design guidelines that further detach the proposed method from the perceived physical constraints introduced by the VSM concept.

  • Application of Posicast control method to generator excitation system

     Ghorbani, Hamidreza; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE International Symposium on Industrial Electronics
    p. 58-63
    DOI: 10.1109/ISIE.2014.6864586
    Presentation's date: 2014-06-01
    Presentation of work at congresses

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    Application of Posicast control method to generator excitation system is presented in this paper. Presented control method is one of the simplest control design methods which can be installed in generators excitation to damp the oscillations caused by changing the excitation reference signal. Stability of the designed controller is shown using extensive time domain simulations. Performance of Posicast controller in IEEE power system standard models with presence of PV power plant is evaluated in MATLAB/Simulink environment.

  • Harmonic compensation analysis in offshore wind power plants using hybrid filters

     Hasan, Khurshid N Md; Kalle, Rauma; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    IEEE transactions on industry applications
    Vol. 50, num. 3, p. 2050-2060
    DOI: 10.1109/TIA.2013.2286216
    Date of publication: 2014-05-16
    Journal article

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    The harmful effects of harmonics are an important issue in wind power plants (WPPs), especially in offshore applications. In offshore WPPs, the wind turbines are linked to the network through high-power converters that produce harmonics at relative low frequencies. Moreover, in the network of a WPP, the propagation of noncharacteristic harmonics and the effect of resonance contribute as well in boosting the harmonic distortion. In this paper, a solution for compensating the harmonics in a WPP by means of using hybrid filters is proposed. In this paper, not only the filtering solution is tested, but also a method for finding the best place where to connect the filter, based on a modal analysis or a harmonic modal resonance analysis, is implemented. The proposed solution has been tested by considering the model of a real 400-MW offshore WPP as the study case. As it will be shown, the hybrid filter is capable of damping the resonances in the plant, while the analysis conducted permits us to optimize its location in the plant

  • Tuning of proportional resonant controllers for three phase PV power converters with LCL+trap filter

     Zhang, Weiyi; Citro, Costantino; Mir Cantarellas, Antonio; Remón, D.; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE PES Transmission & Distribution Conference and Exposition
    DOI: 10.1109/TDC.2014.6863372
    Presentation's date: 2014-04-14
    Presentation of work at congresses

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    Power generation facilities based on renewable energy sources, such as PV or wind, are frequently connected to the grid through three-phase power converters. As the power of the plant increases, the design of the grid connection filters becomes critical, as a fast dynamic performance is needed while the injection of current harmonics to the network should be prevented. LCL filters, together with trap filters tuned at the switching frequency, provide a good trade-off between both needs. However, the tuning of the controllers becomes more complex as the LCL+trap filter lead to a considerably higher order system. In this paper a tuning method for determining the parameters of proportional resonant current controllers for three-phase high power converters linked to the grid through a LCL+trap filter is proposed and analyzed. In order to validate the proposed solution, different results taken in different scenarios are shown.

  • A sensor-less sliding mode control scheme for a stand-alone wound rotor synchronous generator under unbalanced load conditions

     Muñoz Aguilar, Raul Santiago; Rodriguez Cortes, Pedro; Doria Cerezo, Arnau; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro
    International journal of electrical power and energy systems
    Vol. 60, p. 275-282
    DOI: 10.1016/j.ijepes.2014.03.003
    Date of publication: 2014-04-01
    Journal article

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    This paper presents a sliding mode control for a wound rotor synchronous machine acting as an isolated generator connected to an unbalanced load. In order to simplify the control methodology, the standard dq-model of the machine is connected to a balanced resistive load. A switching function is defined in order to fulfill the control objective. From the desired surface, the standard sliding methodology is applied to obtain a robust and very simple controller. Then, the actual measured voltage of the machines is acquired and treated trough a frequency locked loop algorithm in order to extract the positive sequence and control it to guarantee a good definition of the park transformation. A phase locked loop algorithm is also used to avoid speed sensors. Numerical simulations and experimental results validate the control law and show good performance and a fast response to load and reference changes

  • Intelligent voltage control in a DC micro-grid containing PV generation and energy storage

     Rouzbehi, Kumars; Miranian, Arash; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE/PES Transmission and Distribution Conference and Exposition: Latin America
    p. 6863334-1-6863334-5
    Presentation's date: 2014-04
    Presentation of work at congresses

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    This paper proposes an intelligent control scheme for DC voltage regulationin a DC micro-grid integrating photovoltaic (PV) generation, energy storage and electric loads. The maximum power generation of the PV panel is followed using the incremental conductance (IC) maximum power point tracking (MPPT) algorithm while a high-performance local linear controller (LLC)is developed for the DC voltage control in the micro-grid.The LLC, as a data-driven control strategy, controls the bidirectional converter located between the battery and the DC micro-grid to regulate the micro-grid's voltage at the specified reference value.In order to validate the controller different simulations including variations in the load and in the solar irradiance are performed. Finally a comparison with PI based controller demonstrates the advantages of the proposed control technique for regulating theDC micro-grid's voltage.

  • Connection and disconnection transients for micro-grids under unbalance load condition

     Rocabert Delgado, Joan; Azevedo, Gustavo M.S.; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Blaabjerg, Frede; Rodriguez Cortes, Pedro
    EPE journal
    Vol. 24, num. 1, p. 1-9
    Date of publication: 2014-03
    Journal article

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    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.

  • Thermal and efficiency analysis of five-level multilevel-clamped multilevel converter considering grid codes

     Ke, Ma; Muñoz Aguilar, Raul Santiago; Rodriguez Cortes, Pedro; Blaabjerg, Frede
    IEEE transactions on industry applications
    Vol. 50, num. 1, p. 415-423
    DOI: 10.1109/TIA.2013.2266391
    Date of publication: 2014-02
    Journal article

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    In this paper, a five-level multilevel-clamped multilevel converter (5L-MLC2) topology is analyzed based on a typical grid integration application for renewable energy system. The loss and thermal distributions of the power devices in different switching legs are investigated and illustrated under rated condition. Afterward, a loss and efficiency evaluation method is proposed and applied which takes into account various injected reactive power ranges regulated by the grid codes. It is concluded that the loss and thermal distributions of the 5L-MLC2 multilevel topology are unequal between the clamping switching legs and the main switching legs; it also shows a good and consistent efficiency characteristic under different output power ranges when complying with the grid codes.

  • Analysis of ferroresonance effects in distribution networks with distributed source units

     Monadi, Mehdi; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Rocabert Delgado, Joan; Fayezizadeh, Mostafa; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    p. 1974-1979
    DOI: 10.1109/IECON.2013.6699434
    Presentation's date: 2013-11-13
    Presentation of work at congresses

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    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.

  • Design of AC-DC power converters with LCL + tuned trap line filter using Si IGBT and SiC MOSFET modules

     Piasecki, S.; Mir Cantarellas, Antonio; Rabkowski, J.; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    p. 5957-5962
    DOI: 10.1109/IECON.2013.6700112
    Presentation's date: 2013-11-13
    Presentation of work at congresses

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    This paper presents a method for improving the design procedure of AC-DC power converters for power generation applications. The proposed methodology is based on selection of the most convenient configuration, in terms of switching frequency and design of the line filter, in order to minimize the overall losses in the system. In this work two types of semiconductor devices are considered: silicon IGBT and silicon carbide MOSFET for the design of a 100 kVA system, and they performance is compared. The AC-DC converter parameters, the design methodology and preliminary simulation results for representatives of Si IGBT and SiC MOSFET modules are presented.

  • Grid harmonic detection and system resonances indentification in wave power plant applications

     Nisak Md Hasan, Khairul; Mir Cantarellas, Antonio; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    p. 1644-1649
    DOI: 10.1109/IECON.2013.6699379
    Presentation's date: 2013-11-13
    Presentation of work at congresses

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    There is a growing interest in electrical grid connection of single unit Wave Energy Converters (WECs), as well as the multiple units based Wave Power Plant (WPP) applications. Due to the increasing integration of high power converters in WPP, additional concerns on the harmonic current mitigation of WEC device arise which requires the grid filter installation. Furthermore, the identification and appropriate mitigation of additional harmonics at the WPP level is needed, as any inductances and capacitors of the WPP can interact with the resonant frequency of the entire system and lead to detrimental effects on equipment. The present paper focuses on the potential harmonic studies of a realistic proposed WPP layout, in which the system resonances are identified by performing the frequency scan and modal analysis (HRMA) methods. The later technique has the ability of determining the participation factor of each bus, finding in this way the nodes in the system that have more influence on the obtained results. In this way, the most suitable nodes in which additional filtering solutions should be implemented can be identified.

  • Comprehensive analogy between conventional AC grids and DC grids characteristics

     Rouzbehi, Kumars; Gavriluta, Catalin; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    p. 2004-2010
    DOI: 10.1109/IECON.2013.6699439
    Presentation's date: 2013-11-13
    Presentation of work at congresses

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    The high penetration of renewable energy resources, such as wind and photovoltaic, as well as the development of power electronics devices play an important role in the development of DC grids. However, the evolution of DC-systems from point-to-point connections to ‘Multi-terminal’ DC (MTDC) networks is not so straight forward. At the current moment there is a large gap in the literature concerning the dynamics, control and operation of MTDC networks. On the other hand, conventional AC networks have been studied exhaustively in the past decades providing for a rich inspiration source. In this paper we are going to establish a comprehensive analogy between the characteristics of conventional AC grids and the emerging DC grids. The key similarities and differences between the two types of grids are identified in an attempt to better understand the characteristics and behavior of DC grids. In the end, the extent to which concepts like planning for operation and control of AC grids can be conveniently extrapolated to DC grids is evaluated.

    The high penetration of renewable energy resources, such as wind and photovoltaic, as well as the development of power electronics devices play an important role in the development of DC grids. However, the evolution of DC-systems from point-to-point connections to ‘Multi-terminal’ DC (MTDC) networks is not so straight forward. At the current moment there is a large gap in the literature concerning the dynamics, control and operation of MTDC networks. On the other hand, conventional AC networks have been studied exhaustively in the past decades providing for a rich inspiration source. In this paper we are going to establish a comprehensive analogy between the characteristics of conventional AC grids and the emerging DC grids. The key similarities and differences between the two types of grids are identified in an attempt to better understand the characteristics and behavior of DC grids. In the end, the extent to which concepts like planning for operation and control of AC grids can be conveniently extrapolated to DC grids is evaluated.

  • Grid connection control of VSC-based high power converters for wave energy applications

     Mir Cantarellas, Antonio; Rakhshani, Elyas; Remón, D.; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    p. 5092-5097
    DOI: 10.1109/IECON.2013.6699961
    Presentation's date: 2013-11-13
    Presentation of work at congresses

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    In the wave energy sector, an increasing concern regarding the grid connection of wave energy converters is recently being experienced, as well as in the main challenges resulting from the grid integration of large scale wave power plants. This increasing interest arise due to the near-commercial developments of several wave energy converter devices, which have already proved its hydrodynamic and power take-off performance. Therefore, this paper proposes a suitable power processing system configuration and its suitable control design used for interfacing the grid connection of such high power wave energy converters while ensuring acceptable grid connection standards compliance. An advanced filter topology will be introduced based on the superposition of LCL+Trap filters as an alternative solution to the conventional LCL filters, as it allows for smaller filter size, while ensuring a reliable and cost-effective power processing solution. Finally, the evaluation of the filter design as well as the power converter control will be introduced in simulation with the purpose of validating the grid connection of wave energy converters.

  • A hierarchical control structure for multi-terminal VSC-based HVDC grids with GVD characteristics

     Rouzbehi, Kumars; Miranian, Arash; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    Presentation's date: 2013-10-20
    Presentation of work at congresses

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    This paper presents a hierarchical control structure for Multi terminal HVDC grids. The hierarchical control structure is inspired by the three-layer control structure of largescale AC power systems and it is divided into primary, secondary and tertiary control. This structure permits to create an easy interaction between power dispatch and the lower controllers. Moreover, a generalized voltage droop (GVD) characteristic is also proposed which facilitates control issues inside the Multi terminal HVDC grids. In the proposed control structure, the coefficients of the GVD characteristics are set based on the solution of a DC power flow algorithm, executed in the secondary control level.

  • Identification and local linear control of a DC-DC buck converter using local model networks

     Rouzbehi, Kumars; Miranian, Arash; Rakhshani, Elyas; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    International Conference on Renewable Energy Research and Applications
    Presentation's date: 2013-10-20
    Presentation of work at congresses

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  • IEEE Power Electronics Society Paper Award

     Rodriguez Cortes, Pedro; Luna Alloza, Alvaro; Muñoz Aguilar, Raul Santiago; Etxeberria Otadui, Ion; Teodorescu, Remus; Blaabjerg, Frede
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  • IEEE Power Electronics Society Prize Letter Award

     Rodriguez Cortes, Pedro; Dias Bellar, Maria; Muñoz Aguilar, Raul Santiago; Busquets Monge, Sergio
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  • Decentralized control of MTDC networks with energy storage and distributed generation

     Gavriluta, Catalin; Candela Garcia, Jose Ignacio; Citro, Costantino; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE Annual International Energy Conversion Congress and Exhibition for the Asia/Pacific
    p. 2657-2663
    DOI: 10.1109/ECCE.2013.6647044
    Presentation's date: 2013-09-15
    Presentation of work at congresses

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    Multi-terminal dc (MTDC) networks are drawing a lot of interest lately in applications related to distributed generation, especially in those that integrate energy storage. Several 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 droop and dc-bus signaling to serve as a base framework for implementing a hierarchical control structure in a MTDC system. As it will be further discussed in this work, five operating bands as well as various droop characteristics for different elements connected to the dc-bus were defined. For the energy storage the state of charge (SoC) was taken into account at the primary control level and it was included in the droop characteristic, creating a two variables droop surface. The proposed control strategy was validated through simulation and experimental results obtained from a case study that involves a micro dc network composed of a PV generator, a lead-acid battery and one connection point to the ac grid. © 2013 IEEE.

  • Control of grid-connected power converters based on a virtual admittance control loop

     Rodriguez Cortes, Pedro; Candela Garcia, Jose Ignacio; Citro, Costantino; Rocabert Delgado, Joan; Luna Alloza, Alvaro
    European Conference on Power Electronics and Applications
    DOI: 10.1109/EPE.2013.6634621
    Presentation's date: 2013-09-06
    Presentation of work at congresses

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    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.

  • Optimized control of multi-terminal DC GridsUsing particle swarm optimization

     Rouzbehi, Kumars; Miranian, Arash; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    European Conference on Power Electronics and Applications
    p. 1-9
    DOI: 10.1109/EPE.2013.6634326
    Presentation's date: 2013-09-06
    Presentation of work at congresses

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    This paper addresses the important issue of Multi-Terminal DC (MTDC) grid control strategy based on the particle swarm optimization (PSO) technique. The MTDC grid is controlled by the concept of vector control, in which the AC currents and voltages are transformed into the rotating directquadrature (d-q) reference quantities which are subsequently used for decoupled control of the active and reactive powers as well as the DC and AC voltages. The paper employs an efficient PSO algorithm for optimal tuning of the controllers’ parameters in an MTDC grid. In addition, voltage droop control scheme is utilized to ensure the balance of active power within the MTDC grid. Simulation results that has obtained through detailed modeling of a four-terminal DC grid, demonstrate the efficiency of the proposed approach. Comparison to controllers optimized by genetic algorithm (GA) also confirmed the favorable performance of the proposed PSO-tuned controllers.

  • Adaptive droop for primary control in MTDC networks with energy storage

     Gavriluta, Catalin; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Rocabert Delgado, Joan; Rodriguez Cortes, Pedro
    European Conference on Power Electronics and Applications
    p. 1-9
    DOI: 10.1109/EPE.2013.6631976
    Presentation's date: 2013-09-06
    Presentation of work at congresses

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    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.

  • Analysis on capability of harmonic damping using active filter acting as resistive harmonic impedance

     Hasan, Khurshid N Md; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    IEEE Annual International Energy Conversion Congress and Exhibition for the Asia/Pacific
    p. 2928-2933
    DOI: 10.1109/ECCE.2013.6647082
    Presentation's date: 2013-09
    Presentation of work at congresses

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    This paper presents the analysis of shunt active filter (SAF) in harmonic damping. SAF with voltage-based detection control act as an active damping and able to attenuate harmonic propagation throughout the power distribution network. The active filter is implemented on two different power line networks to assess its practicality in different network configuration. The first network is 220-V distribution power line and the second network is the reduced equivalent WPP network of 150-kV, 444.4-MVA. Assessment on the best place for active filter implementation is supported by using harmonic resonance mode analysis method.

    This paper presents the analysis of shunt active filter (SAF) in harmonic damping. SAF with voltage-based detection control act as an active damping and able to attenuate harmonic propagation throughout the power distribution network. The active filter is implemented on two different power line networks to assess its practicality in different network configuration. The first network is 220-V distribution power line and the second network is the reduced equivalent WPP network of 150-kV, 444.4-MVA. Assessment on the best place for active filter implementation is supported by using harmonic resonance mode analysis method.

  • Modeling and control of multi modular converters using optimal LQR controller with integral action

     Rakhshani, Elyas; Mir Cantarellas, Antonio; Remón, D.; Rodriguez Cortes, Pedro; Candela Garcia, Jose Ignacio
    IEEE Energy Conversion Congress and Exposition
    p. 3965-3970
    DOI: 10.1109/ECCE.2013.6647226
    Presentation's date: 2013-09
    Presentation of work at congresses

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    A new application of LQR controller with the ability of reference tracking for a multi modular converter with several cells is proposed. First, the mathematical model for the grid connected MMC is presented and then, the small signal state space model is obtained. MMC is a very complex MIMO system with several state variables and global control for this system is very important issue. Optimal advanced controller based on linear quadratic regulator with integral action is a very good candidate for controlling the AC signals and energy balancing in multi cells MMC system. The performance and validity of obtained model and designed linear controller are evaluated with non-linear model of MMC in SimPower System toolbox/Matlab. Simulation results are verified the excellent performance of the proposed approach in the transient and steady state operational conditions.

    A new application of LQR controller with the ability of reference tracking for a multi modular converter with several cells is proposed. First, the mathematical model for the grid connected MMC is presented and then, the small signal state space model is obtained. MMC is a very complex MIMO system with several state variables and global control for this system is very important issue. Optimal advanced controller based on linear quadratic regulator with integral action is a very good candidate for controlling the AC signals and energy balancing in multi cells MMC system. The performance and validity of obtained model and designed linear controller are evaluated with non-linear model of MMC in SimPower System toolbox/Matlab. Simulation results are verified the excellent performance of the proposed approach in the transient and steady state operational conditions.

  • Design of the LCL+trap filter for the two-level VSC installed in a large-scale wave power plant

     Mir Cantarellas, Antonio; Rakhshani, Elyas; Remón, D.; Rodriguez Cortes, Pedro
    IEEE Annual International Energy Conversion Congress and Exhibition for the Asia/Pacific
    p. 707-712
    DOI: 10.1109/ECCE.2013.6646771
    Presentation's date: 2013-09
    Presentation of work at congresses

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    This paper presents a methodology for designing the link passive filter of the power converters installed in a multi-megawatt wave power plant. Such filter is based on the superposition of both LCL and trap filter configurations with the purpose of achieving enhanced grid interaction of a two-level voltage source converter. The LCLTrap filter design is highly dependent on the electrical network characteristics; hence the distribution system of the plant is introduced in the paper to take into account its effects on the tuning parameters. The proposed LCLtrap filter topology arises as a successful alternative solution for the conventional LCL filter topology, thanks to its improved filtering capability while ensuring a reduced filter size. The validation of the proposed filter performance is evaluated in simulation by performing a comparative analysis between the LCLtrap and the LCL filters when operate in a wave farm application.

    This paper presents a methodology for designing the link passive filter of the power converters installed in a multi-megawatt wave power plant. Such filter is based on the superposition of both LCL and trap filter configurations with the purpose of achieving enhanced grid interaction of a twolevel voltage source converter. The LCL+Trap filter design is highly dependent on the electrical network characteristics; hence the distribution system of the plant is introduced in the paper to take into account its effects on the tuning parameters. The proposed LCL+trap filter topology arises as a successful alternative solution for the conventional LCL filter topology, thanks to its improved filtering capability while ensuring a reduced filter size. The validation of the proposed filter performance is evaluated in simulation by performing a comparative analysis between the LCL+trap and the LCL filters when operate in a wave farm application.

  • A generalized voltage droop strategy for control of multi-terminal DC grids

     Rouzbehi, Kumars; Miranian, Arash; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE Energy Conversion Congress and Exposition
    p. 59-64
    DOI: 10.1109/ECCE.2013.6646681
    Presentation's date: 2013-09
    Presentation of work at congresses

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    This paper proposes a generalized voltage droop (GVD) control strategy for control and power sharing in voltage source converter (VSC)-based multi-terminal DC (MTDC) grids. In the proposed approach, the conventional voltage droop characteristics of voltage-regulating VSC stations are replaced by the GVD characteristics. The proposed GVD control strategy can be operated in three different control modes including conventional voltage droop control, fixed active power control and fixed DC voltage control by proper adjustment of the GVD characteristics of the voltage-regulating converters. The proposed strategy improves the control and power-sharing capabilities of the conventional voltage droop, and enhances its maneuverability. Simulation results, obtained by detailed modeling in a four-terminal high voltage DC grid demonstrated the efficacy of the proposed approach and its flexibility in active power sharing. Moreover, based on the obtained results, switching between operating mode of the GVD control approach does not results in oscillations of the active powers flowing inside the MTDC grids.

  • Control of PV generation systems using the synchronous power controller

     Rodriguez Cortes, Pedro; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro
    IEEE Energy Conversion Congress and Exposition
    p. 993-998
    DOI: 10.1109/ECCE.2013.6646811
    Presentation's date: 2013-09
    Presentation of work at congresses

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    The high penetration of distributed generation, as PV or wind power, has forced the Transmission System Operators (TSOs) to set restrictive requirements for the operation of such systems. As it can be extracted from the forthcoming grid codes drafts, the future distributed generation systems will be requested to have the equivalent performance of a synchronous generator, which is seen from the TSOs as the only solution if a massive integration of renewable in the electrical network should be achieved. In this paper a method for controlling PV grid connected power converters as a synchronous generator, namely Synchronous Power Controller (SPC), is presented. As a difference with previous works this method permits to take advantage of emulating the synchronous behavior meanwhile it is able to get rid of its drawbacks. The main concept of the SPC, as well as some simulation and experimental results will be shown in this paper considering a PV power plant as a study case.

    The high penetration of distributed generation, as PV or wind power, has forced the Transmission System Operators (TSOs) to set restrictive requirements for the operation of such systems. As it can be extracted from the forthcoming grid codes drafts, the future distributed generation systems will be requested to have the equivalent performance of a synchronous generator, which is seen from the TSOs as the only solution if a massive integration of renewable in the electrical network should be achieved. In this paper a method for controlling PV grid connected power converters as a synchronous generator, namely Synchronous Power Controller (SPC), is presented. As a difference with previous works this method permits to take advantage of emulating the synchronous behavior meanwhile it is able to get rid of its drawbacks. The main concept of the SPC, as well as some simulation and experimental results will be shown in this paper considering a PV power plant as a study case.

  • Analysis and comparison of battery energy storage technologies for grid applications

     Saez-de Ibarra, Andoni; Milo, Aitor; Gaztañaga, Haizea; Etxeberria Otadui, Ion; Rodriguez Cortes, Pedro; Bacha, Seddik; Debusschere, V.
    IEEE PowerTech Conference
    DOI: 10.1109/PTC.2013.6652509
    Presentation's date: 2013-06-20
    Presentation of work at congresses

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    Battery Energy Storage Systems (BESSs) could contribute to the generation/consumption balance of the grid and could provide advanced functionalities at different grid levels (generation, T&D, end-user and RES integration). In this paper an analysis and comparison of Battery Energy Storage (BES) technologies for grid applications is carried out. The comparison is focused on the most installed technologies in the recent experimental BESS installations. Furthermore, the paper presents a new methodology aimed at selecting the most suitable BES technology for a specific grid application. This methodology defines a priority level for each technical and economical characteristic of the BES technologies. Finally, the proposed methodology is applied for a specific grid application confirming its contribution in the selection of the best-suited technology.

  • Access to the full text
    Thermal and efficiency analysis of five-level multi-level clamped multilevel converter considering grid codes  Open access

     Ma, Ke; Muñoz Aguilar, Raul Santiago; Rodriguez Cortes, Pedro; Blaabjerg, Frede
    IEEE transactions on industry applications
    DOI: 10.1109/TIA.2013.2266391
    Date of publication: 2013-06-05
    Journal article

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    In this paper a five-level Multi-Clamped Multilevel Converter (5L-MLC2) topology is analyzed based on a typical grid integration application for renewable energy system. The loss and thermal distribution of the power devices in different switching legs are investigated and illustrated under rated condition. Afterwards, a loss and efficiency evaluation method is proposed and applied which take into account various injected reactive power ranges regulated by the grid codes. It is concluded that the loss and thermal distribution of 5L-MLC2 multilevel topology is unequal between the clamping switching legs and the main switching legs, it also shows a good and consistent efficiency characteristic under different output power ranges when complying with the grid codes.