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  • A novel approach for voltage control of multi-terminal DC grids with offshore wind farms

     Rouzbehi, Kumars; Miranian, Arash; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE Annual International Energy Conversion Congress and Exhibition for the Asia/Pacific
    Presentation of work at congresses

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    This paper proposes a novel control strategy in multi-terminal DC (MTDC) grids with offshore wind generation based on the idea of generalized voltage droop (GVD). In the proposed strategy, the GVD characteristics are assigned to the voltage-regulating converter station, enhancing their control maneuverability and enabling them to perform necessary DC voltage control and power sharing tasks. By adjusting the coefficients of the corresponding GVD characteristic, a converter station can be operated in three operating modes, namely (1) fixed active power control mode, (2) conventional voltage droop control mode or (3) fixed DC voltage control mode. Results of simulations on a test four-terminal DC grid including two offshore wind farm and two AC grids show the capabilities of the proposed control strategy. Moreover, simulation results confirmed stable operation of the GVD control in transition from one operating mode to another.

  • PSO-based LQR controller for multi modular converters

     Rakhshani, Elyas; Mir Cantarellas, Antonio; Remón, D.; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE Annual International Energy Conversion Congress and Exhibition for the Asia/Pacific
    Presentation's date: 2013-06
    Presentation of work at congresses

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    In this paper a new application of PSO technique for optimizing the controller parameters of multi modular converters is presented. PSO based LQR controller is designed for averaged model of modular converter and to obtain better control parameters though the minimizing a quadratic-performance index. In this method in order to have more accuracy and better design for controller parameters, PSO algorithm is added to find the gain matrix of the controller. Simulation results show that with using this method better dynamic responses are accessible.

    In this paper a new application of PSO technique for optimizing the controller parameters of multi modular converters is presented. PSO based LQR controller is designed for averaged model of modular converter and to obtain better control parameters though the minimizing a quadraticperformance index. In this method in order to have more accuracy and better design for controller parameters, PSO algorithm is added to find the gain matrix of the controller. Simulation results show that with using this method better dynamic responses are accessible.

  • Grid connection design and control of LCL+Trap filter based two-level VSC for wave power plant applications

     Mir Cantarellas, Antonio; Rakhshani, Elyas; Remón, D.; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE Annual International Energy Conversion Congress and Exhibition for the Asia/Pacific
    Presentation of work at congresses

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    This paper presents a filter design methodology and control design strategy for LCL+Trap filters deployed in large scale wave power plants. This filter topology appears as an alternative for the widely used LCL filters, since effective harmonic mitigation can be achieved while reducing the overall passive filter components size. As a result, the use of LCL+Trap filters for two-level power converters arise as a suitable power processing solution to match the requirements of large scale wave energy applications, since such well-known power converter technology is very robust, reliable and very cost effective. The designed LCL+Trap filter is validated through simulation by performing a comparative analysis between LCL and LCL+Trap filters, and finally, the control of the converter is introduced with the purpose of validating the grid connection compliance of the entire power processing system.

    This paper presents a filter design methodology and control design strategy for LCL+Trap filters deployed in large scale wave power plants. This filter topology appears as an alternative for the widely used LCL filters, since effective harmonic mitigation can be achieved while reducing the overall passive filter components size. As a result, the use of LCL+Trap filters for two-level power converters arise as a suitable power processing solution to match the requirements of large scale wave energy applications, since such well-known power converter technology is very robust, reliable and very cost effective. The designed LCL+Trap filter is validated through simulation by performing a comparative analysis between LCL and LCL+Trap filters, and finally, the control of the converter is introduced with the purpose of validating the grid connection compliance of the entire power processing system.

  • 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
    Presentation's date: 2013-11-13
    Presentation of work at congresses

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  • 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
    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.

  • 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
    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.

  • 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
    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.

  • 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
    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.

  • 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
    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.

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

     Nisak, Khairul; Mir Cantarellas, Antonio; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    Presentation's date: 2013-11-13
    Presentation of work at congresses

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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
    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.

  • 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
    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.

  • 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
    ICRERA-IEEE International Conference on Renewable Energy Research and Applications
    Presentation's date: 2013-10-20
    Presentation of work at congresses

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  • 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
    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.

  • Advanced structures for grid synchronization of power converters in distributed generation applications

     Luna Alloza, Alvaro; Rocabert Delgado, Joan; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro; Teodorescu, Remus; Blaabjerg, Frede
    IEEE Energy Conversion Congress and Exposition
    Presentation's date: 2012-09-15
    Presentation of work at congresses

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    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

  • Application of imperialist competitive algorithm to design an optimal controller for LFC problem

     Rakhshani, Elyas; Luna Alloza, Alvaro; Rouzbehi, Kumars; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    Presentation's date: 2012-10-25
    Presentation of work at congresses

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    A novel optimization algorithm is presented to improve the design of optimal controllers for load frequency control problem. This algorithm is applied for two area LFC system with using an output feedback controller. In the practical power system, access to some of the state variables in LFC system is limited and measuring is also impossible. So an optimal output feedback controller with a practical viewpoint is proposed. The optimal control law is determined by minimizing a performance index under the output feedback conditions leading to a coupled matrix equation. In order to solve these equations traditional methods may be used. But for more accuracy and better design for this controller, ICA algorithm is applied to find the global optimal gain matrix of the controller. Simulation results of ICA are compared with the conventional design. Comparison shows the success of ICA for design of optimal controller

  • Effect of VSC-HVDC on load frequency control in multi-area power system

     Rakhshani, Elyas; Luna Alloza, Alvaro; Rouzbehi, Kumars; Rodriguez Cortes, Pedro; Etxeberria Otadui, Ion
    IEEE Energy Conversion Congress and Exposition
    Presentation's date: 2012-09-15
    Presentation of work at congresses

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    This study presents a solution for reducing the frequency oscillations in multi-area interconnected power system by means of using an VSC-HVDC interconnection transmission line. The upcoming power-electronics based HVDC transmission system offers new features that can be advantageous for improving the frequency control and thus for enhancing the stability in transmission networks. This paper is structured in two main parts; the first one is be devoted to introduce the basic elements of HVDC links and the second part will be focused on the effects of the HVDC links in the frequency control of interconnected power systems. In order to show the positive effects of HVDC links under random load disturbance, a model with parallel AC-DC interconnected power system, including a new power modulation controller of bi-directional VSC-HVDC link, is proposed and simulated. Comparisons between HVAC and HVDC transmissions are presented and its performance is evaluated using Matlab/Simulink

  • Enhanced average current-mode control for DC-DC converters based on an optimized fuzzy logic controller

     Rouzbehi, Kumars; Miranian, Arash; Citro, Costantino; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    Presentation's date: 2012-10-25
    Presentation of work at congresses

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    This paper proposes a novel optimized fuzzy logic controller (OFLC) for current-mode control (CMC)-based voltage regulation in DC-DC converters. The implementation of the proposed fuzzy logic controller (FLC) does not depend on the mathematical model of the converter and only requires knowledge about its operation modes. The fast and efficient algorithm of particle swarm optimization (PSO) has been employed to enhance the performance of the FLC by fine tuning its membership functions. The reference current for the current control loop has been obtained in the outer voltage loop by measuring load current and output voltage and calculating the load resistive impedance. The proposed OFLC has been used in four different case studies for evaluating its performance under different conditions of input voltage and load variations as well as variations in the system parameters, e.g. inductance and capacitance of the converter circuit. The results of simulations and comparison to a proportional-integral (PI) controller demonstrates the fast and robust performance of the proposed controller, able to effectively regulate the output voltage in presence of high perturbations in the input voltage and high variation of the converter components nominal values

  • Harmonic resonances damping using hybrid filter for WPP

     Nisak, Khairul; Rauma, Kalle; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    Presentation's date: 2012-10-25
    Presentation of work at congresses

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    Harmonic distortion is one of important factor to consider in power system network. In a big network such as wind power plant (WPP), careful analysis and mitigation steps is essential. Many aspects including resonances created from interactions between inductive and capacitive elements must be considered. Passive filter or tuned filters are common solution for mitigating harmonics by creating path for specific harmonic but many times it created a resonance issue. By implementing hybrid filter, an active filter connected in series with shunt passive filter, it enhances the ability of damping the resonant. The concept is adapted from previous research works and in this paper it is implemented on a WPP network. This paper presents a study on harmonic resonances in a WPP, particularly on parallel resonance. The damping of resonance by using common passive filter and an alternative hybrid filter is proved through simulation in PSCAD-EMTDC software. An aggregated WPP model of 400 MW with 40 wind turbines of 10 MW each are used as a study case

  • Decoupled double synchronous reference frame current controller for unbalanced grid voltage conditions

     Reyes Díaz, Manuel; Rodriguez Cortes, Pedro; Vázquez Pérez, Sergio; Luna Alloza, Alvaro; Carrasco Solís, Juan Manuel; Teodorescu, Remus
    IEEE Energy Conversion Congress and Exposition
    Presentation's date: 2012-09-15
    Presentation of work at congresses

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  • Study on harmonic resonances and damping in wind power plant

     Md. Hasan, Khairul Nisak; Rauma, Kalle; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    International Conference on Intelligent & Advanced Systems
    Presentation's date: 2012-06-12
    Presentation of work at congresses

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    Harmonic resonance is among imperative aspect need to be analyzed in a wind power plant (WPP). It becomes complex since it involves a large network with high operating power. This paper presents a study on harmonic resonances in a WPP, particularly on parallel resonance. Important factors including length of cable, number of operating wind turbine and usage of output grid-side filter are analyzed. The damping of resonance by using common passive filter and an alternative hybrid filter is also explored. An aggregated WPP model of 400 MW with 40 wind turbines of 10 MW each are used as a study case

  • Harmonic resonance damping in Wind Power Plant

     Nisak, Khairul; Rauma, Kalle; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    IEEE Energy Conversion Congress and Exposition
    Presentation's date: 2012-09-15
    Presentation of work at congresses

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    Harmonic is one of main concern in Wind Power Plant (WPP) as growing usage of power electronic converter is observed. Besides the injection of harmonic by individual wind turbine (WT) as source of harmonic, its propagation in network and problem of resonance is also an issue. By implementing passive filter for harmonic mitigation, additional resonance peak is observed due to its interaction with system side impedance. This paper explores the solution for harmonic mitigation with capability of damping resonance in WPP. An aggregated model of 400-MW WPP network is analyzed in correlating resonance and amplification. A passive filter and hybrid filter is designed to mitigate harmonic accordingly. It is shown that hybrid filter able to provide damping capability and improve the performance

  • PSO based optimal output feedback controller for two-area LFC system

     Rakhshani, Elyas; Luna Alloza, Alvaro; Sadeh, J.; Rodriguez Cortes, Pedro
    Mediterranean Conference on Control and Automation
    Presentation's date: 2012
    Presentation of work at congresses

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    A new combined method based on optimal control is proposed to enhance load frequency control dynamics. This method include of PSO and optimal output feedback controller. In the output feedback method only the measurable state variables within each control area is required to use for feedback. The optimal control law is determined by minimizing a performance index under the output feedback conditions leading to a coupled matrix equation. But for more accuracy and better design for this controller, PSO algorithm is applied to find the gain matrix of the controller. The results of the simulation are shown that with using this method, the load frequency control requirements in a practical environment are satisfied and also better dynamic responses are accessible

  • Power control of VSC HVDC converters for limiting the influence of ac unbalanced faults on multi-terminal DC grids

     Suul, Jon Are; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    International Conference on AC and DC Power Transmission
    Presentation's date: 2012-12-04
    Presentation of work at congresses

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    It will be important for the operation of future multi-terminal HVDC systems that each converter unit is capable of limiting the influence of nearby AC faults on the DC grid. Thus, the local control systems at each terminal should be able to prevent double frequency active power oscillations caused by unbalanced AC faults from propagating to the DC-side of the converter. A simple approach for achieving this objective, while ensuring that the converter currents are limited to safe values, is therefore presented in this paper. The proposed method is based on estimation of Positive and Negative Sequence Virtual Flux components at the terminals of the converter. Double frequency oscillations in the active power flow through the converter can...

    It will be important for the operation of future multi-terminal HVDC systems that each converter unit is capable of limiting the influence of nearby AC faults on the DC grid. Thus, the local control systems at each terminal should be able to prevent double frequency active power oscillations caused by unbalanced AC faults from propagating to the DC-side of the converter. A simple approach for achieving this objective, while ensuring that the converter currents are limited to safe values, is therefore presented in this paper. The proposed method is based on estimation of Positive and Negative Sequence Virtual Flux components at the terminals of the converter. Double frequency oscillations in the active power flow through the converter can...

  • A stationary reference frame grid synchronization system for three-phase grid-connected power converters under adverse grid conditions

     Rodriguez Cortes, Pedro; Luna Alloza, Alvaro; Muñoz Aguilar, Raul Santiago; Etxebarría, Ion; Teodorescu, Remus; Blaabjerg, Frede
    IEEE transactions on power electronics
    Date of publication: 2012-01
    Journal article

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    Grid synchronization algorithms are of great importance in the control of grid-connected power converters, as fast and accurate detection of the grid voltage parameters is crucial in order to implement stable control strategies under generic grid conditions. This paper presents a new grid synchronization method for three-phase three-wire networks, namely dual second-order generalized integrator (SOGI) frequency-locked loop. The method is based on two adaptive filters, implemented by using a SOGI on the stationary αβ reference frame, and it is able to perform an excellent estimation of the instantaneous symmetrical components of the grid voltage under unbalanced and distorted grid conditions. This paper analyzes the performance of the proposed synchronization method including different design issues. Moreover, the behavior of the method for synchronizing with highly unbalanced grid is proven by means of simulation and experimental results, demonstrating its excellent performance.

  • Voltage-sensor-less synchronization to unbalanced grids by frequency-adaptive virtual flux estimation

     Suul, Jon Are; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro; Undeland, Tore
    IEEE transactions on industrial electronics
    Date of publication: 2012-07
    Journal article

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    This paper proposes a simple method for inherently frequency-adaptive virtual flux (VF) estimation intended for voltage-sensor-less grid synchronization and control of voltage source converters. The frequency-adaptive characteristics are obtained by using a second-order generalized integrator configured as a quadrature signal generator (SOGI-QSG) with the grid frequency as an explicit input variable. It is also shown how the properties of VF estimation based on SOGI-QSGs can be utilized to achieve a simple and effective synchronization technique that integrates frequency-adaptive bandpass filtering, VF estimation, and symmetrical component sequence separation into one operation. This new method avoids cascaded delays of VF estimation and sequence separation and is labeled as dual SOGI-based VF (DSOGI-VF) estimation since it is based on two parallel SOGI-QSGs. The properties and performance of the DSOGI-VF estimation are analyzed in comparison to conventional configurations of VF estimation and sequence separation, demonstrating that it is a simpler structure with improved dynamic response. In fact, similar response time as for grid synchronization based on voltage measurements is achieved. The operation and performance of the proposed DSOGI-VF estimation method have been verified by laboratory experiments in a small-scale converter setup.

  • Enhanced decoupled double synchronous reference frame current controller for unbalanced grid-voltage conditions

     Reyes, M.; Rodriguez Cortes, Pedro; Vazquez, S.; Luna Alloza, Alvaro; Teodorescu, Remus; Carrasco, J.M.
    IEEE transactions on power electronics
    Date of publication: 2012
    Journal article

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    In the last few years, restrictive grid codes have arisen to ensure the performance and stability of electrical networks, which experience amassive integration of renewable energy sources and distributed generation systems that are normally connected to the grid through electronic power converters. In these codes, the injection of positive- and negative-sequence current components becomes necessary for fulfilling, among others, the low-voltage ride-through requirements during balanced and unbalanced grid faults. However, the performance of classical dq current controllers, applied to power converters, under unbalanced grid-voltage conditions is highly deficient, due to the unavoidable appearance of current oscillations. This paper analyzes the performance of the double synchronous reference frame controller and improves its structure by adding a decoupling network for estimating and compensating the undesirable current oscillations. Experimental results will demonstrate the validity of the proposed decoupled DSRF controller

  • Virtual-Flux-Based Voltage-Sensor-Less Power Control for Unbalanced Grid Conditions

     Suul, Jon Are; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro; Undeland, Tore
    IEEE transactions on power electronics
    Date of publication: 2012-09
    Journal article

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  • Control of power converters in AC microgrids

     Rocabert Delgado, Joan; Luna Alloza, Alvaro; Blaabjerg, Frede; Rodriguez Cortes, Pedro
    IEEE transactions on power electronics
    Date of publication: 2012
    Journal article

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  • CONTROL INTERACTIVO CON RED ELECTRICA DE PLANTA FV DE GENERACION CON ALMACENAMIENTO DE ENERGIA

     Luna Alloza, Alvaro; Jornet Alvarez, Atanasi; Rodriguez Cortes, Pedro; Aldabas Rubira, Emiliano
    Participation in a competitive project

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  • Identification and maximum power point tracking of photovoltaic generation by a local neuro-fuzzy model

     Rouzbehi, Kumars; Miranian, Arash; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    Annual Conference of the IEEE Industrial Electronics Society
    Presentation's date: 2012-10-25
    Presentation of work at congresses

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    With the rapid proliferation of the DC distribution systems, special attentions are paid to the photovoltaic (PV) generations. This paper addresses the problem of maximum power point tracking (MPPT) for PV systems using a local neuro fuzzy (LNF) network and steepest descent (SD) optimization algorithm. The proposed approach, termed LNF + SD, first identifies a valid an accurate model for the PV system using the LNF network and through measurement data. Then the identified PV model is used for MPPT by SD optimization algorithm. The salient modeling abilities of the proposed LNF network results in a reliable and dependable PV model which takes voltage, temperature and insolation variations into account. The proposed approach is evaluated using several identification and MPPT simulations. The simulation results showed the accuracy of the LNF network in modeling of PV systems. Furthermore, simulations carried out for assessment of the MPPT performance during insolation transients demonstrated the high efficiency of the proposed LNF + SD approach for MPPT applications. Performance of the proposed method MPPT, while the PV array was supplying loads through DC-DC converters was also analyzed. Comparisons to the perturb-and-observe (P&O) and fuzzy logic methods revealed the superiority of the proposed approach

  • Photovoltaic plants generation improvement using Li-ion batteries as energy buffer

     Beltran, H.; Swierczynski, M.; Luna Alloza, Alvaro; Vazquez, G.; Belenguer, E.
    IEEE International Symposium on Industrial Electronics
    Presentation's date: 2011-06-27
    Presentation of work at congresses

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    This paper analyzes the PV power plants operability improvement obtained when introducing energy storage (ES) systems which allow decoupling the power received from the sun on the photovoltaic (PV) panels from the power injected by the power plant into the grid. Two energy management strategies are presented and analyzed, using Li-ion batteries as the energy storage buffer. The generated power redistribution and its variability reduction are All the results obtained in this paper are based on one year long simulations which used real irradiance data sampled every two minutes.

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    Control proposals for the operation of power converters in wind power systems  Open access

     Luna Alloza, Alvaro; Aguilar, Daniel; Muñoz Aguilar, Raul Santiago; Corcoles Lopez, Felipe; Rodriguez Cortes, Pedro
    International Conference on Power Engineering, Energy and Electrical Drives
    Presentation's date: 2011-05-11
    Presentation of work at congresses

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    The wind turbines based on Doubly Fed Induction Generators (DFIG) represent almost the 60% of the installed windpower worldwide. Nowadays most of the existing algorithms, used for regulating the production of active and reactive power in such systems, are based on control techniques that use rotational reference frames theories, where the dq0 is maybe the most popular. Despite of its good operation under balanced conditions its behaviour depends on a good phase synchronization, otherwise the different transformations cannot be performed with enough guarantees. Of course this kind of response is becomming insuficient, as far as the windpower penetration is increasing. This paper will present a new control topology for DFIG, that are connected using back to back inverters, that is able to behave better in case of faulty grids. Besides some proposals for improving the operation of the DFIG will be presented as well. The aim of that part is to extend the possibilities that the back to back inverters are able to offer to the generator system by means of including new functionalities, as the active filtering capability or the reduction of the flicker emission that will be later discussed.

  • Control of power converters in distributed generation applications under grid fault conditions

     Rodriguez Cortes, Pedro; Luna Alloza, Alvaro; Muñoz Aguilar, Raul Santiago; Corcoles Lopez, Felipe; Teodorescu, Remus; Blaabjerg, Frede
    IEEE Energy Conversion Congress and Exposition
    Presentation's date: 2011-09-17
    Presentation of work at congresses

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    The operation of distributed power generation systems under grid fault conditions is a key issue for the massive integration of renewable energy systems. Several studies have been conducted to improve the response of such distributed generation systems under voltage dips. In spite of being less severe, unbalanced fault cause a great number of disconnections, as it may produce the injection of unbalanced currents that can easily conduct to the tripping of the converter. In this paper a current control strategy for power converters able to deal with these grid conditions, without exceeding the current ratings of the converter is introduced. Moreover, a novel flexible algorithm has been proposed in order to regulate easily the injection of positive and negative currents for general purpose applications.

  • Sensorless control of PMSG¿based wind energy conversion systems using a FLL¿based synchronization technique

     Aguilar, Daniel; Candela Garcia, Jose Ignacio; Muñoz Aguilar, Raul Santiago; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro
    IEEE International Conference on Industrial Electronics
    Presentation's date: 2011-11-07
    Presentation of work at congresses

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  • Multilevel-clamped multilevel converters (MLC2) ¿ an alternative approach for multilevel power conversion

     Rodriguez Cortes, Pedro; D. Bellar, maria; Muñoz Aguilar, Raul Santiago; Rocabert Delgado, Joan; Luna Alloza, Alvaro
    IEEE International Conference on Industrial Electronics
    Presentation's date: 2011-11-07
    Presentation of work at congresses

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    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 multilevel method.

  • Current control method for distributed generation power generation plants under grid fault conditions

     Rodriguez Cortes, Pedro; Luna Alloza, Alvaro; Hermoso Costa, Juan Ramon; Etxeberria Otadui, Ion; Teodorescu, Remus; Blaabjerg, Frede
    Annual Conference of the IEEE Industrial Electronics Society
    Presentation's date: 2011-11-07
    Presentation of work at congresses

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    The operation of distributed power generation systems under grid fault conditions is a key issue for the massive integration of renewable energy systems. Several studies have been conducted to improve the response of such distributed generation systems under voltage dips. In spite of being less severe, unbalanced fault cause a great number of disconnections, as it may produce the injection of unbalanced currents that can easily conduct to the tripping of the converter. In this paper a current control strategy for power converters able to deal with these grid conditions, without exceeding the current ratings of the converter is introduced. Moreover, a novel flexible algorithm has been proposed in order to regulate easily the injection of positive and negative currents for general purpose applications.

  • Overview of power processing structures for embedding energy storage in PV power converters

     Citro, Costantino; Luna Alloza, Alvaro; Rocabert Delgado, Joan; Muñoz Aguilar, Raul Santiago; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    IEEE International Conference on Industrial Electronics
    Presentation's date: 2011-11-07
    Presentation of work at congresses

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    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.

  • Sensor-less sliding mode control of a stand-alone wound rotor synchronous generator with unbalanced load

     Muñoz Aguilar, Raul Santiago; Rodriguez Cortes, Pedro; Doria Cerezo, Arnau; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro
    IEEE International Conference on Industrial Electronics
    Presentation's date: 2011-11-07
    Presentation of work at congresses

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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 a validate the control law and show good performance and a fast response to load and reference changes.

  • Voltage feed-forward performance in stationary reference frame controllers for wind power applications

     Ma, Lin; Luna Alloza, Alvaro; Rocabert Delgado, Joan; Muñoz Aguilar, Raul Santiago; Corcoles Lopez, Felipe; Rodriguez Cortes, Pedro
    International Conference on Power Engineering, Energy and Electrical Drives
    Presentation's date: 2011-05-11
    Presentation of work at congresses

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  • A simplified model for wind turbine based on doubly fed induction generator

     Lima, F. K. A.; Watanabe, Edson H.; Rodriguez Cortes, Pedro; Luna Alloza, Alvaro
    International Conference on Electrical Machines and Systems
    Presentation's date: 2011-08-21
    Presentation of work at congresses

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    Improving the Fault Ride Through capability (FRT) of Doubly Fed Induction Generators (DFIG) in wind power applications is a very important challenge for wind power industry. The mathematical models of such generators permit to analyze their response under generic conditions. However, their mathematical complexity does not contribute to simplify the analysis of the system under transient conditions, and hence do not help to find straight-forward solutions to enhance their FRT. This paper presents a simplified model of the DFIG, that has been extracted from the classical fifth order model, which is able to estimate accurately the behavior of the system while reduces significantly its complexity. In this work, the mathematical deduction of this model will be presented and simulations and experimental results will be shown, in order to demonstrate the accuracy and reliability of the proposed algorithm.

  • An overview of harmonic analysis and resonances of large wind power plant

     Rauma, Kalle; Rodriguez Cortes, Pedro; Candela Garcia, Jose Ignacio; Muñoz Aguilar, Raul Santiago; Luna Alloza, Alvaro; Nisak, Khairul
    IEEE International Conference on Industrial Electronics
    Presentation's date: 2011-11-07
    Presentation of work at congresses

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    This paper presented an overview of harmonic analysis and resonance in large wind power plant. The harmonic related problem becomes a concern as the growing numbers of nonlinear load and the increased possibility of harmonic resonances occurrence. In WPP, several conditions may contribute to the resonance phenomenon that will amplify the effect of the harmonic frequency. General overview of international standards and grid codes and basic modeling of WPP for harmonic analysis is also presented. Furthermore, an overview of the harmonic analysis methods are reviewed with emphasize given on the harmonic resonance analysis. A simple three-bus system example is evaluated applying three resonance analysis methods.

  • Discrete fault-clearing instant influence on the simulation of voltage-source-inverter-fed adjustable-speed drives subjected to voltage sags

     Corcoles Lopez, Felipe; Bogarra Rodriguez, Santiago; Pedra Duran, Joaquin; Luna Alloza, Alvaro
    IET electric power applications
    Date of publication: 2011-05
    Journal article

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    This study analyses the influence of modelling sags with discrete fault-clearing instants on the behaviour of adjustablespeed drives (ASDs) subjected to sags caused by faults. The effects are compared with those of sags modelled with simultaneous fault clearance in all faulted phases (i.e. abrupt fault clearance; the most common approach to voltage sag modelling). In many cases, abrupt fault clearance is far more severe than discrete fault clearance. Thus, if an ASD rides through a more severe case of an abrupt fault clearance test, it will likely ride through a discrete fault clearance sag. As current protocols for testing the immunity of ASDs to voltage sags only consider abrupt fault clearance, it is not necessary to consider the more complicated discrete fault clearance in equipment sag-testing methodology if more severe abrupt clearance sags are properly chosen and tested.

  • Intelligent connection agent for three-phase grid-connected microgrids

     Rocabert Delgado, Joan; Azevedo, Gustavo M.S.; Luna Alloza, Alvaro; Guerrero Zapata, Josep Maria; Candela Garcia, Jose Ignacio; Rodriguez Cortes, Pedro
    IEEE transactions on power electronics
    Date of publication: 2011
    Journal article

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    Multi-resonant frequency-locked loop for grid synchronization of power converters under distorted grid conditions  Open access

     Rodriguez Cortes, Pedro; Luna Alloza, Alvaro; Candela Garcia, Jose Ignacio; Mujal Rosas, Ramon Maria; Teodorescu, Remus; Blaabjerg, Frede
    IEEE transactions on industrial electronics
    Date of publication: 2011-01
    Journal article

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    This paper presents a new multiresonant frequencyadaptive synchronization method for grid-connected power converters that allows estimating not only the positive- and negative-sequence components of the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies. The proposed system is calledMSOGI-FLL since it is based on both a harmonic decoupling network consisting of multiple second-order generalized integrators (MSOGIs) and a frequency-locked loop (FLL), which makes the system frequency adaptive. In this paper, the MSOGI-FLL is analyzed for singleand three-phase applications, deducing some key expressions regarding its stability and tuning. Moreover, the performance of the MSOGI-FLL is evaluated by both simulations and experiments to show its capability for detecting different harmonic components in a highly polluted grid scenario.

  • Control of STATCOM in wind power plants based on induction generators during asymmetrical grid faults

     Rodriguez Cortes, Pedro; Luna Alloza, Alvaro; Medeiros, G.; Teodorescu, Remus; Blaabjerg, Frede
    International Power Electronics Conference
    Presentation's date: 2010-06-21
    Presentation of work at congresses

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    An approach to the performance-oriented model of variable-speed wind turbines  Open access

     Rolan Blanco, Alejandro; Luna Alloza, Alvaro; Rocabert Delgado, Joan; Aguilar Galván, Daniel; Vázquez Guzmán, Gerardo
    IEEE International Symposium on Industrial Electronics
    Presentation's date: 2010-07-05
    Presentation of work at congresses

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    The aim of this work is to give an approach to the Performance-Oriented Model of Variable-Speed Wind turbines (VSWTs) equipped with permanent magnet synchronous generator (PMSG), and compare it to the component-oriented model. In the present work it will be analyzed how a change in the wind speed affects the power delivered from the generator by means of two approaches: firstly, the component-oriented model of the VSWT-based PMSG is given, i.e. the dynamic equations of the system are shown, and then, it is discussed how to obtain an equivalent transfer function of the whole system. A comparison between both approaches is discussed in this work.

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    Frequency-adaptive virtual flux estimation for grid synchronization under unbalanced conditions  Open access

     Suul, Jon Are; Luna Alloza, Alvaro; Rodriguez Cortes, Pedro; Undeland, Tore
    Annual Conference of the IEEE Industrial Electronics Society
    Presentation's date: 2010-11-08
    Presentation of work at congresses

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    This paper proposes a new and explicitly frequencyadaptive method for Virtual Flux estimation and voltage sensorless grid synchronization under unbalanced conditions. The proposed system is based on using Second Order Generalized Integrators, arranged to simultaneously fulfill the purposes of frequency-adaptive band-pass filtering, integration and quadrature signal generation. This results in a simple and efficient structure for combined Virtual Flux estimation and separation into positive and negative sequence components. The properties of the proposed Virtual Flux model is analyzed theoretically, first as an integrator for implementing generic Virtual Flux estimation, and then with respect to sequence separation. The dynamic performance of the proposed estimation method is tested by simulations for the case of an unbalanced voltage drop in the grid and for a step in grid frequency. The simulations verify the performance to be as expected, with similar dynamics as synchronization based on voltage measurements.

  • Four-branch star neutral current hybrid power filter and var compensator

     Rodriguez Cortes, Pedro; Candela Garcia, Jose Ignacio; Luna Alloza, Alvaro; Teodorescu, Remus; Blaabjerg, Frede; Rocabert Delgado, Joan
    IEEE Energy Conversion Congress and Exposition
    Presentation's date: 2010-09-12
    Presentation of work at congresses

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