Articles de revista
http://hdl.handle.net/2117/3669
2016-09-28T18:55:33ZComparative study of reactive power control methods for photovoltaic inverters in low-voltage grids
http://hdl.handle.net/2117/86884
Comparative study of reactive power control methods for photovoltaic inverters in low-voltage grids
Momeneh, Arash; Castilla Fernández, Miguel; Miret Tomàs, Jaume; Martí Colom, Pau; Velasco García, Manel
The increasing installation of photovoltaic panels in low-voltage grids causes an over voltage problem, especially during high production and low consumption periods. Generally the over voltage problem is overcome by implementing reactive power control methods. The advances in networked control systems theory and practice create new scenarios where reactive power control methods can offer additional features and benefits. To explore these new capabilities, this study presents two new reactive power control methods that exploit the networked approach. These two methods are evaluated in a comparative reference framework that also includes the base-line case where no reactive control method is applied, the conventional droop method approach, and a solution based on a near-optimal location of a high power STATCOM derived from one of the new proposed networked methods. The main merit factors used to compare the control methods are the maximum voltage across the distribution grid, the power factor in the point of common coupling, and the total power losses and economic cost of the installation. With these merit factors, the advantages and limitations of the new and existing control methods are revealed and discussed. A useful discussion for selecting the best control solution is also reported.
2016-05-10T14:45:57ZMomeneh, ArashCastilla Fernández, MiguelMiret Tomàs, JaumeMartí Colom, PauVelasco García, ManelThe increasing installation of photovoltaic panels in low-voltage grids causes an over voltage problem, especially during high production and low consumption periods. Generally the over voltage problem is overcome by implementing reactive power control methods. The advances in networked control systems theory and practice create new scenarios where reactive power control methods can offer additional features and benefits. To explore these new capabilities, this study presents two new reactive power control methods that exploit the networked approach. These two methods are evaluated in a comparative reference framework that also includes the base-line case where no reactive control method is applied, the conventional droop method approach, and a solution based on a near-optimal location of a high power STATCOM derived from one of the new proposed networked methods. The main merit factors used to compare the control methods are the maximum voltage across the distribution grid, the power factor in the point of common coupling, and the total power losses and economic cost of the installation. With these merit factors, the advantages and limitations of the new and existing control methods are revealed and discussed. A useful discussion for selecting the best control solution is also reported.Model-based control for a three-phase shunt active power filter
http://hdl.handle.net/2117/84364
Model-based control for a three-phase shunt active power filter
Guzmán Solà, Ramon; García de Vicuña Muñoz de la Nava, José Luis; Morales López, Javier; Castilla Fernández, Miguel; Miret Tomàs, Jaume
This paper presents a robust model-based control
in natural frame for a three-phase shunt active power filter.
For the proposed control method a linear converter model is
deduced. Then, this model is used in a Kalman filter in order
to estimate the system state-space variables. Even though the
states estimation do not match the variables of the real system,
it has allowed to design three sliding mode controllers providing
the following features to the closed loop system: a) robustness
due to the fact that control specifications are met independently
of any variation in the system parameters; b) noise immunity,
since a Kalman filter is applied; c) a lower THD of the current
delivered by the grid compared with the standard solution using
measured variables; d) the fundamental component of the voltage
at point of common coupling is estimated even in the case of
a distorted grid; and e) a reduction in the number of sensors.
Thanks to this solution the sliding surfaces for each controller are
independent. This decoupling property of the three controllers
allows using a fixed switching frequency algorithm that ensures
a perfect current control. Finally, experimental results validate
the propos
2016-03-15T11:07:33ZGuzmán Solà, RamonGarcía de Vicuña Muñoz de la Nava, José LuisMorales López, JavierCastilla Fernández, MiguelMiret Tomàs, JaumeThis paper presents a robust model-based control
in natural frame for a three-phase shunt active power filter.
For the proposed control method a linear converter model is
deduced. Then, this model is used in a Kalman filter in order
to estimate the system state-space variables. Even though the
states estimation do not match the variables of the real system,
it has allowed to design three sliding mode controllers providing
the following features to the closed loop system: a) robustness
due to the fact that control specifications are met independently
of any variation in the system parameters; b) noise immunity,
since a Kalman filter is applied; c) a lower THD of the current
delivered by the grid compared with the standard solution using
measured variables; d) the fundamental component of the voltage
at point of common coupling is estimated even in the case of
a distorted grid; and e) a reduction in the number of sensors.
Thanks to this solution the sliding surfaces for each controller are
independent. This decoupling property of the three controllers
allows using a fixed switching frequency algorithm that ensures
a perfect current control. Finally, experimental results validate
the proposVoltage security in AC microgrids: A power flow-based approach considering droopcontrolled inverters
http://hdl.handle.net/2117/84059
Voltage security in AC microgrids: A power flow-based approach considering droopcontrolled inverters
Souza, Antonio Carlos Zambroni de; Santos, Marcos; Castilla Fernández, Miguel; Miret Tomàs, Jaume; García de Vicuña Muñoz de la Nava, José Luis; Marujo, Diogo
This study deals with the problem of voltage security in microgrids. In general, voltage security is an issue for power systems, where the lack of reactive power is a concern. For microgrids a complexity is imposed, since frequency and voltage level deviations may take place by the operation of droop-controlled inverters. This study incorporates the load margin calculation into a microgrid structure. For this purpose, a special power flow program is developed in order to consider the effects of the droop-controlled inverters. Simulation results are obtained with the help of an islanded distribution system with only generators coupled by droop-controlled inverters, so the proposed methodology may be tested and discussed.
2016-03-09T13:43:14ZSouza, Antonio Carlos Zambroni deSantos, MarcosCastilla Fernández, MiguelMiret Tomàs, JaumeGarcía de Vicuña Muñoz de la Nava, José LuisMarujo, DiogoThis study deals with the problem of voltage security in microgrids. In general, voltage security is an issue for power systems, where the lack of reactive power is a concern. For microgrids a complexity is imposed, since frequency and voltage level deviations may take place by the operation of droop-controlled inverters. This study incorporates the load margin calculation into a microgrid structure. For this purpose, a special power flow program is developed in order to consider the effects of the droop-controlled inverters. Simulation results are obtained with the help of an islanded distribution system with only generators coupled by droop-controlled inverters, so the proposed methodology may be tested and discussed.Control strategy to maximize the power capability of PV three-phase inverters during voltage sags
http://hdl.handle.net/2117/81655
Control strategy to maximize the power capability of PV three-phase inverters during voltage sags
Sosa, Jorge Luis; Castilla Fernández, Miguel; Miret Tomàs, Jaume; Matas Alcalá, José; Al-Turki, Y.A.
Under voltage sags, grid-tied photovoltaic inverters should remain connected to the grid according to low-voltage ride-through requirements. During such perturbations, it is interesting to exploit completely the distributed power provisions to contribute to the stability and reliability of the grid. In this sense, this paper proposes a low-voltage ride-through control strategy that maximizes the inverter power capability by injecting the maximum-rated current during the sag. To achieve this objective, two possible active power situations have been considered, i.e., high- and low-power production scenarios. In the first case, if the source is unable to deliver the whole generated power to the grid, the controller applies active power curtailment to guarantee that the maximum rated current is not surpassed. In the second case, the maximum allowed current is not reached, thus, the control strategy determined the amount of reactive power that can be injected up to reach it. The control objective can be fulfilled by means of a flexible current injection strategy that combines a proper balance between positive- and negative-current sequences, which limits the inverter output current to the maximum rated value and avoid active power oscillations. Selected experimental and simulation results are reported in order to validate the effectiveness of the proposed control strategy.
2016-01-19T09:24:18ZSosa, Jorge LuisCastilla Fernández, MiguelMiret Tomàs, JaumeMatas Alcalá, JoséAl-Turki, Y.A.Under voltage sags, grid-tied photovoltaic inverters should remain connected to the grid according to low-voltage ride-through requirements. During such perturbations, it is interesting to exploit completely the distributed power provisions to contribute to the stability and reliability of the grid. In this sense, this paper proposes a low-voltage ride-through control strategy that maximizes the inverter power capability by injecting the maximum-rated current during the sag. To achieve this objective, two possible active power situations have been considered, i.e., high- and low-power production scenarios. In the first case, if the source is unable to deliver the whole generated power to the grid, the controller applies active power curtailment to guarantee that the maximum rated current is not surpassed. In the second case, the maximum allowed current is not reached, thus, the control strategy determined the amount of reactive power that can be injected up to reach it. The control objective can be fulfilled by means of a flexible current injection strategy that combines a proper balance between positive- and negative-current sequences, which limits the inverter output current to the maximum rated value and avoid active power oscillations. Selected experimental and simulation results are reported in order to validate the effectiveness of the proposed control strategy.Contribution to the PV-to-inverter sizing ratio determination using a custom flexible experimental setup
http://hdl.handle.net/2117/78227
Contribution to the PV-to-inverter sizing ratio determination using a custom flexible experimental setup
Camps, Xavier; Velasco Quesada, Guillermo; Hoz Casas, Jordi de la; Martín Cañadas, María Elena
This work presents a novel approach to the experimental validation of the optimal PV-to-inverter sizing ratio value for the energy yield maximization of a GCPVS by means the implementation of a custom workbench using a solar array simulator which has allowed to replicate a wide variety of technical configurations and environmental data. The compliance between the experimental setup and the mathematical model developed to simulate the optimal PV-to-inverter sizing ratio value was demonstrated by the specific tests carried out on its two main subsystems (the PV generator and the inverter), thus the subsequent simulations were made on a firm basis. Likewise, the evaluation of the overall system also showed a good agreement between the experimental and the simulated energy yield and optimal PV-to-inverter sizing ratio results, rendering relative errors below 3% for both magnitudes. (C) 2015 Elsevier Ltd. All rights reserved.
2015-10-26T12:10:10ZCamps, XavierVelasco Quesada, GuillermoHoz Casas, Jordi de laMartín Cañadas, María ElenaThis work presents a novel approach to the experimental validation of the optimal PV-to-inverter sizing ratio value for the energy yield maximization of a GCPVS by means the implementation of a custom workbench using a solar array simulator which has allowed to replicate a wide variety of technical configurations and environmental data. The compliance between the experimental setup and the mathematical model developed to simulate the optimal PV-to-inverter sizing ratio value was demonstrated by the specific tests carried out on its two main subsystems (the PV generator and the inverter), thus the subsequent simulations were made on a firm basis. Likewise, the evaluation of the overall system also showed a good agreement between the experimental and the simulated energy yield and optimal PV-to-inverter sizing ratio results, rendering relative errors below 3% for both magnitudes. (C) 2015 Elsevier Ltd. All rights reserved.Promotion of concentrating solar thermal power (CSP) in Spain: Performance analysis of the period 1998–2013
http://hdl.handle.net/2117/77310
Promotion of concentrating solar thermal power (CSP) in Spain: Performance analysis of the period 1998–2013
Martín Cañadas, María Elena; Hoz Casas, Jordi de la; Velasco Quesada, Guillermo; Castilla Fernández, Miguel; García de Vicuña Muñoz de la Nava, José Luis
A thorough analysis of the Concentrating Solar Thermal Power (CSP) development in Spain in the period 1998–2013 has been carried out in order to identify the main drivers behind the bubble-like behaviour exhibited by this renewable technology. Tending a parallelism with the basic principles of the control systems theory has facilitated the identification of the main shortcomings in the design of the various control frameworks governing the CSP deployment in the studied period. The CSP disorderly proliferation propitiated by inefficient control mechanisms has resulted in an overrun cost to the electricity system that has tried to be mitigated with the application of retroactive measures seriously harmful for the investors. It is expected that the conclusions drawn from this comprehensive review of the Spanish case have a general relevance for other countries undertaking the development path of renewable technologies.
2015-10-05T08:35:23ZMartín Cañadas, María ElenaHoz Casas, Jordi de laVelasco Quesada, GuillermoCastilla Fernández, MiguelGarcía de Vicuña Muñoz de la Nava, José LuisA thorough analysis of the Concentrating Solar Thermal Power (CSP) development in Spain in the period 1998–2013 has been carried out in order to identify the main drivers behind the bubble-like behaviour exhibited by this renewable technology. Tending a parallelism with the basic principles of the control systems theory has facilitated the identification of the main shortcomings in the design of the various control frameworks governing the CSP deployment in the studied period. The CSP disorderly proliferation propitiated by inefficient control mechanisms has resulted in an overrun cost to the electricity system that has tried to be mitigated with the application of retroactive measures seriously harmful for the investors. It is expected that the conclusions drawn from this comprehensive review of the Spanish case have a general relevance for other countries undertaking the development path of renewable technologies.Reactive current injection protocol for low-power rating distributed generation sources under voltage sags
http://hdl.handle.net/2117/28430
Reactive current injection protocol for low-power rating distributed generation sources under voltage sags
Miret Tomàs, Jaume; Camacho Santiago, Antonio; Castilla Fernández, Miguel; García de Vicuña Muñoz de la Nava, José Luis; Hoz Casas, Jordi de la
Voltage sags are one of the main problems in transmission and distribution networks. This study proposes a voltage support control scheme for grid-connected low-power rating inverters under voltage sags. Voltage support capability is provided thanks to reactive current injection. The main objective is to inject the maximum rated reactive current during the voltage sag. Second, to raise the higher phase voltage to a predefined maximum boundary, thus preventing over-voltage. Moreover, with this strategy the phase voltages can be equalised. The first objective can be always accomplished during voltage sags. Achieving the second objective depends on the grid characteristics, the sag profile and the power rating of the inverter. Selected experimental results are reported to validate the effectiveness of the proposed control.
2015-06-26T10:41:39ZMiret Tomàs, JaumeCamacho Santiago, AntonioCastilla Fernández, MiguelGarcía de Vicuña Muñoz de la Nava, José LuisHoz Casas, Jordi de laVoltage sags are one of the main problems in transmission and distribution networks. This study proposes a voltage support control scheme for grid-connected low-power rating inverters under voltage sags. Voltage support capability is provided thanks to reactive current injection. The main objective is to inject the maximum rated reactive current during the voltage sag. Second, to raise the higher phase voltage to a predefined maximum boundary, thus preventing over-voltage. Moreover, with this strategy the phase voltages can be equalised. The first objective can be always accomplished during voltage sags. Achieving the second objective depends on the grid characteristics, the sag profile and the power rating of the inverter. Selected experimental results are reported to validate the effectiveness of the proposed control.Subharmonic excitation in amplitude modulation atomic force microscopy in the presence of adsorbed water layers
http://hdl.handle.net/2117/27854
Subharmonic excitation in amplitude modulation atomic force microscopy in the presence of adsorbed water layers
Santos Hernández, Sergio; Barcons Xixons, Víctor; Verdaguer, Albert; Chiesa, Matteo
In ambient conditions, nanometric water layers form on hydrophilicsurfaces covering them and significantly changing their properties and characteristics. Here we report the excitation of subharmonics in amplitude modulation atomic force microscopy induced by intermittent water contacts. Our simulations show that there are several regimes of operation depending on whether there is perturbation of water layers. Single period orbitals, where subharmonics are never induced, follow only when the tip is either in permanent contact with the water layers or in pure noncontact where the water layers are never perturbed. When the water layers are perturbed subharmonic excitation increases with decreasing oscillation amplitude. We derive an analytical expression which establishes whether water perturbations compromise harmonic motion and show that the predictions are in agreement with numerical simulations. Empirical validation of our interpretation is provided by the observation of a range of values for apparent height of water layers when subharmonic excitation is predicted.
2015-05-08T16:01:38ZSantos Hernández, SergioBarcons Xixons, VíctorVerdaguer, AlbertChiesa, MatteoIn ambient conditions, nanometric water layers form on hydrophilicsurfaces covering them and significantly changing their properties and characteristics. Here we report the excitation of subharmonics in amplitude modulation atomic force microscopy induced by intermittent water contacts. Our simulations show that there are several regimes of operation depending on whether there is perturbation of water layers. Single period orbitals, where subharmonics are never induced, follow only when the tip is either in permanent contact with the water layers or in pure noncontact where the water layers are never perturbed. When the water layers are perturbed subharmonic excitation increases with decreasing oscillation amplitude. We derive an analytical expression which establishes whether water perturbations compromise harmonic motion and show that the predictions are in agreement with numerical simulations. Empirical validation of our interpretation is provided by the observation of a range of values for apparent height of water layers when subharmonic excitation is predicted.Sliding-mode control for a three-phase unity power factor rectifier operating at fixed switching frequency
http://hdl.handle.net/2117/27273
Sliding-mode control for a three-phase unity power factor rectifier operating at fixed switching frequency
Guzmán Solà, Ramon; García de Vicuña Muñoz de la Nava, José Luis; Morales López, Javier; Castilla Fernández, Miguel; Matas Alcalá, José
This paper presents an improved variable hysteresisband current-control in natural frame for a three-phase unity power rectifier. The proposed control algorithm is based on three decoupled sliding-mode controllers combined with three independent Kalman filters. The use of Kalman filters instead of a non-adaptive state observer improves the quality of the estimated signals in presence of noise, increasing the immunity of the control loop in noisy environments. To reduce drastically the computational load in the Kalman algorithm, a reduced bilinear model is derived which allows to use a Kalman filter algorithm instead of an extended Kalman filter. A fast output-voltage control is also presented which avoids output-voltage variations when a sudden change in the load or a voltage sag appears. Moreover, a fixed switching frequency algorithm is proposed which uses a variable hysteresis-band in combination with a switching decision algorithm, ensuring a switching spectrum concentrated around the desired switching frequency. The overall control proposal has been fully integrated into a digital signal processor. Selected experimental results are introduced to validate the theoretical contributions of this paper.
2015-04-13T10:44:17ZGuzmán Solà, RamonGarcía de Vicuña Muñoz de la Nava, José LuisMorales López, JavierCastilla Fernández, MiguelMatas Alcalá, JoséThis paper presents an improved variable hysteresisband current-control in natural frame for a three-phase unity power rectifier. The proposed control algorithm is based on three decoupled sliding-mode controllers combined with three independent Kalman filters. The use of Kalman filters instead of a non-adaptive state observer improves the quality of the estimated signals in presence of noise, increasing the immunity of the control loop in noisy environments. To reduce drastically the computational load in the Kalman algorithm, a reduced bilinear model is derived which allows to use a Kalman filter algorithm instead of an extended Kalman filter. A fast output-voltage control is also presented which avoids output-voltage variations when a sudden change in the load or a voltage sag appears. Moreover, a fixed switching frequency algorithm is proposed which uses a variable hysteresis-band in combination with a switching decision algorithm, ensuring a switching spectrum concentrated around the desired switching frequency. The overall control proposal has been fully integrated into a digital signal processor. Selected experimental results are introduced to validate the theoretical contributions of this paper.Active and reactive power strategies with peak current limitation for distributed generation inverters during unbalanced grid faults
http://hdl.handle.net/2117/27022
Active and reactive power strategies with peak current limitation for distributed generation inverters during unbalanced grid faults
Camacho Santiago, Antonio; Castilla Fernández, Miguel; Miret Tomàs, Jaume; Borrell Sanz, Angel; García de Vicuña Muñoz de la Nava, José Luis
Distributed generation inverters have become a key element to improve grid efficiency and reliability, particularly during grid faults. Under these severe perturbations, inverter-based power sources should accomplish low-voltage ride-through requirements in order to keep feeding the grid and support the grid voltage. Also, rated current can be required to better utilize reactive power provisions. This paper presents a reference generator capable to accomplish these two objectives: to keep the injected currents within safety values and to compute the power references for a better utilization of the inverter power capacity. The reference generator is fully flexible since positive and negative active and reactive powers can be simultaneously injected to improve ride-through services. Selected experimental results are reported to evaluate the performance of the proposed reference generator under different control strategies.
2015-03-25T07:56:11ZCamacho Santiago, AntonioCastilla Fernández, MiguelMiret Tomàs, JaumeBorrell Sanz, AngelGarcía de Vicuña Muñoz de la Nava, José LuisDistributed generation inverters have become a key element to improve grid efficiency and reliability, particularly during grid faults. Under these severe perturbations, inverter-based power sources should accomplish low-voltage ride-through requirements in order to keep feeding the grid and support the grid voltage. Also, rated current can be required to better utilize reactive power provisions. This paper presents a reference generator capable to accomplish these two objectives: to keep the injected currents within safety values and to compute the power references for a better utilization of the inverter power capacity. The reference generator is fully flexible since positive and negative active and reactive powers can be simultaneously injected to improve ride-through services. Selected experimental results are reported to evaluate the performance of the proposed reference generator under different control strategies.