Rouzbehi, K.; Davarifar, M.; Martino, M.; Citro, C.; Luna, A.; Daneshifar, Z.; Rodriguez, P. International Congress on Technology, Communication and Knowledge p. 536-541 DOI: 10.1109/ICTCK.2015.7582725 Data de presentació: 2015-11 Presentació treball a congrés
Global warming is already having significant and costly effects on our communities, our health, and our
climate. Nowadays, In developing countries (G20) around the world, decisions are being considered and a shifting of
our dependence from fossil fuels to renewable energy sources (RES). Among RES solar energy, specially photovoltaic
system (PV) play a key role in this challenge, thus, this paper provides a comparative study on the performances of
three transformer-less inverters for photovoltaic applications (H-Bridge, H5, HERIC and NPC inverters) in terms of
power losses, considering the use of different kinds of switches. Silicon (Si) and Silicon Carbide (SiC) diodes have
been combined with two topologies of IGBTs in the performed tests. Simulation results have been obtained for each
of the systems in different operating conditions by using PLECS software. Power losses and European Efficiency (EE)
have been calculated for all the topologies, taking into account the real characteristics of the switches by using the
thermal models provided by the software library.
Rodriguez, P.; Citro, C.; Candela, J.; Rocabert, J.; Luna, A. IEEE Energy Conversion Congress and Exposition p. 450-459 DOI: 10.1109/ECCE.2015.7309723 Data de presentació: 2015-09-20 Presentació treball a congrés
Photovoltaic power plants (PV) are equipped with anti-islanding algorithms, embedded in the converters controller, to avoid the island operation. However, the current trends in the development of the future electrical networks evidence that it is technically feasible and economically advantageous to keep feeding islanded systems under these situations, without cutting the power supply to the loads connected to the network. Nevertheless, commercial PV power converters are programmed as grid-feeding converters, and they are unable to work in island mode if there is not an agent forming the grid. In order to overcome this problem the Synchronous Power Controller (SPC) is presented in this paper as a suitable alternative for controlling PV inverters. As it will be further discussed this controller permits PV plants to operate seamless in grid connected and island mode, with no need of changing the control structure in any case. Moreover, the participation of SPC based power converters integrating energy storage enables other grid-feeding systems to contribute to the grid operation in island conditions. The results achieved with the SPC will be shown in simulations and also with experiments considering a real PV power plant combining SPC and comercial converters.
Multi-terminal dc networks based on voltage source converters (VSC) are the latest trend in dc-systems; the interest in the area is being fueled by the increased feasibility of these systems for the large scale integration of remote offshore wind resources. Despite the active research effort in the field, at the moment, issues related to the operation and control of these networks, as well as sizing, are still uncertain. This paper intends to make a contribution in this field by analyzing the sizing of droop control for VSC together with the output capacitors. Analytical formulas are developed for estimating the voltage peaks during transients, and then it is shown how these values can be used to dimension the dc-bus capacitor of each VSC. Further on, an improved droop control strategy that attenuates the voltage oscillations during transients is proposed. The proposed methods are validated on the dc-grid benchmark proposed by the CIGRE B4 working group. Starting from the structure of the network and the power rating of the converters at each terminal, the output capacitors and the primary control layer are designed together in order to ensure acceptable voltage transients.(C) 2014 Elsevier B.V. All rights reserved.
Gavriluta, C.; Candela, J.; Citro, C.; Rocabert, J.; Luna, A.; Rodriguez, P. IEEE transactions on industry applications Vol. 50, num. 6, p. 4122-4131 DOI: 10.1109/TIA.2014.2315715 Data de publicació: 2014-11-01 Article en revista
Multiterminal dc networks are drawing a lot of interest lately in applications related to distributed generation, particularly in those that also integrate energy storage (ES). A few approaches for controlling the operation of such systems have been proposed in the literature; however, the existing structures can be significantly enhanced. This paper proposes an improved primary control layer, based on custom droop characteristics obtained by combining concepts of droop and dc-bus signaling control. This approach is designed to be generic and takes into account the various operating states of the network. Five operating bands, similar to the operating states of the ac grids, as well as various droop characteristics for different elements connected to the dc network, are defined. For the ES, the state of charge is taken into account at the primary control level and included in the droop characteristic, creating a two-variable droop surface. The proposed control strategy is validated through simulation and experimental results obtained from a case study that involves amicro dc network composed of a photovoltaic generator, a lead-acid battery, and a connection point to the ac grid.
This paper proposes a new method for designing fuzzy logic controllers for voltage-regulated DC DC power converters. Low sensitivity to input voltage variations, fast regulation during load transients and robustness against the aging process of the converter passive components are the main features achievable through the proposed approach. The multi-objective particle swarm optimization (MO-PSO) is used to find multiple Pareto-optimal solutions in a multi-objective optimization problem for the identification of the best possible membership functions and rules of the fuzzy controller. In order to evaluate the effectiveness of the proposed technique, different cases have been tested in laboratory on a buck converter prototype, considering deep input voltage deviations and big load transients, as well as variations in the nominal values of the passive components of the system. A comparison with a classical proportional-integral (PI) controller demonstrates the high performances of the proposed technique in terms of effective output voltage regulation under different operating conditions. (C) 2014 Elsevier B.V. All rights reserved.
Zhang, W.; Citro, C.; Cantarellas, A.M.; Remon, D.; Luna, A.; Rodriguez, P. IEEE/PES Transmission and Distribution Conference and Exposition DOI: 10.1109/TDC.2014.6863372 Data de presentació: 2014-04-14 Presentació treball a congrés
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.
Gavriluta, C.; Candela, J.; Citro, C.; Luna, A.; Rodriguez, P. IEEE Annual International Energy Conversion Congress and Exhibition for the Asia/Pacific p. 2657-2663 DOI: 10.1109/ECCE.2013.6647044 Data de presentació: 2013-09-15 Presentació treball a congrés
Rodriguez, P.; Candela, J.; Citro, C.; Rocabert, J.; Luna, A. European Conference on Power Electronics and Applications DOI: 10.1109/EPE.2013.6634621 Data de presentació: 2013-09-06 Presentació treball a congrés
The connection of electronic power converters to the electrical network is increasing mainly due to massive integration of renewable energy systems. However, the electrical dynamic performance of these converters does not match the behavior of the network, which is mainly formed by generation facilities based on big synchronous generation systems. Depending on the desired electrical operation mode different control structures can be implemented in the converters in order to get adapted with the grid conditions. However, changing between different control structures and operation is not an optimal solution, as the resulting system results complex and is not highly robust. As an alternative, this paper presents a new control technique for grid connected power converters based on the concept of virtual admittance. The proposed control permits to emulate the electrical performance of generation facilities based on classical synchronous generators with a power converter, with no need of implementing different control structures, giving rise to a system that provides a friendly and robust operation with the network.
The connection of electronic power converters to the electrical network is increasing mainly due to
massive integration of renewable energy systems. However, the electrical dynamic performance of
these converters does not match the behavior of the network, which is mainly formed by generation
facilities based on big synchronous generation systems. Depending on the desired electrical operation
mode different control structures can be implemented in the converters in order to get adapted with the
grid conditions. However, changing between different control structures and operation is not an
optimal solution, as the resulting system results complex and is not highly robust. As an alternative,
this paper presents a new control technique for grid connected power converters based on the concept
of virtual admittance. The proposed control permits to emulate the electrical performance of
generation facilities based on classical synchronous generators with a power converter, with no need
of implementing different control structures, giving rise to a system that provides a friendly and robust
operation with the network.
Rouzbehi, K.; Miranian, A.; Citro, C.; Luna, A.; Rodriguez, P. Annual Conference of the IEEE Industrial Electronics Society p. 382-387 DOI: 10.1109/IECON.2012.6388790 Data de presentació: 2012-10-25 Presentació treball a congrés
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
A detailed harmonic resonance analysis of power systems is more and more important due to the increasing number of power electronic devices. The topic is especially wellgrounded
in wind power plants that besides having several possible sources of harmonics have many inductive and capacitive elements. This combination forms a severe concern
over harmonic resonance that composes a threat to the power quality and the function of wind power plants. This paper presents and applies the harmonic resonance mode analysis (HRMA) in a model of an off shore wind power plant with and without a passive filtering. The results of the harmonic
resonance mode analysis are verified and compared with the results calculated with the frequency scan.
Citro, C.; Gavriluta, C.; Nizak Md , H.; Beltran, H. IEEE International Symposium on Industrial Electronics p. 2032-2035 DOI: 10.1109/ISIE.2012.6237406 Data de presentació: 2012 Presentació treball a congrés
This paper presents a design procedure for linear current controllers of three-phase grid-connected inverters. The proposed method consists in deriving a numerical model of the converter by using software simulations and applying the pole
placement technique to design the controller with the desired performances. A clear example on how to apply the technique is
provided. The effectiveness of the proposed design procedure has been verified through the experimental results obtained with
a 10kW grid-connected three-phase inverter prototype.
Gavriluta, C.; Citro, C.; Nisak, K.; Beltrán, H. IEEE International Symposium on Industrial Electronics p. 2015-2019 DOI: 10.1109/ISIE.2012.6237403 Data de presentació: 2012 Presentació treball a congrés
Initial control prototyping in power electronics is often a matter of trial and error because of the complicated mathematics involved in modeling systems based on their
internal structure. Moreover, in practice, small changes as the introduction of a measurement filter or the change of the sensing system appear all the time. If the controller design method was based on the internal structure of the system, then these small changes would mean a re-iteration through all the cumbersome equations. This paper presents a simple methodology for fast
control prototyping based on the approximation of the Bode plots. As prerequisites, a power electronics simulation software as PSIM is needed. The method is presented by taking as a study
case the design of a current control loop of a 30kW three phase interleaved DC-DC converter. Simulations are presented for the
different considered controllers, and finally the method is validated by experimental results.
Citro, C.; Luna, A.; Rocabert, J.; Muñoz-Aguilar, R. S.; Candela, J.; Rodriguez, P. Annual Conference of the IEEE Industrial Electronics Society p. 2417-2423 DOI: 10.1109/IECON.2011.6119701 Data de presentació: 2011-11-07 Presentació treball a congrés
The level of penetration of grid-connected photovoltaic (PV) systems has grown very quickly in recent years. Nonetheless, network stresses related to the recurrent voltage and frequency oscillations caused by their irregular power production could be a limiting factor on the future expansion of these applications. With the capability of storing and releasing electrical energy on demand, Energy Storage Devices (ESDs) may play a key role in finding an effective solution to overcome these kinds of problems. The aim of this paper is to provide a description of the state-of-the-art power conversion systems used to combine ESDs and grid-connected PV plants. The work has been edited after an accurate analysis of the current scientific literature, focusing particular attention on medium-high-power PV applications utilizing batteries and/or supercapacitors. A detailed analysis on advantages, disadvantages and range of application is provided for each of the reported conversion systems.