Articles de revista
http://hdl.handle.net/2117/3669
20170821T21:58:07Z

Secondary switched control with no communications for islanded microgrids
http://hdl.handle.net/2117/106354
Secondary switched control with no communications for islanded microgrids
Rey, Juan M; Martí Colom, Pau; Velasco García, Manel; Miret Tomàs, Jaume; Castilla Fernández, Miguel
Flexibility and reliability of AC microgrids are enhanced by reducing the dependence on communications in multilayer hierarchical control. In this sense, this paper presents a secondary control with no communications for islanded microgrids. It is based on a control scheme that switches between two configurations according to a timedependent protocol. With this proposal, an excellent performance in terms of transient response and frequency restoration in steadystate is achieved. The paper also presents design considerations for the control parameters. In addition, the theoretical predictions are validated by experimental results from a laboratory microgrid.
20170712T10:30:02Z
Rey, Juan M
Martí Colom, Pau
Velasco García, Manel
Miret Tomàs, Jaume
Castilla Fernández, Miguel
Flexibility and reliability of AC microgrids are enhanced by reducing the dependence on communications in multilayer hierarchical control. In this sense, this paper presents a secondary control with no communications for islanded microgrids. It is based on a control scheme that switches between two configurations according to a timedependent protocol. With this proposal, an excellent performance in terms of transient response and frequency restoration in steadystate is achieved. The paper also presents design considerations for the control parameters. In addition, the theoretical predictions are validated by experimental results from a laboratory microgrid.

Frequencymodulation control of a DC/DC currentsource parallelresonant converter
http://hdl.handle.net/2117/106352
Frequencymodulation control of a DC/DC currentsource parallelresonant converter
Moradi Ghahderijani, Mohammad; Castilla Fernández, Miguel; Momeneh, Arash; Tomas Miret, Jaume; García de Vicuña Muñoz de la Nava, José Luis
This paper proposes a frequencymodulation control scheme for a dc/dc currentsource parallelresonant converter with two possible configurations. The basic configuration comprises an external voltage loop, an internal current loop, and a frequency modulator: the voltage loop is responsible for regulating the output voltage, the current loop makes the system controllable and limits the input current, and the modulator provides robustness against variations in resonant component values. The enhanced configuration introduces the output inductor current as a feedforward term and clearly improves the transient response to fast load changes. The theoretical design of these control schemes is performed systematically by first deriving their smallsignal models and second using Bode diagram analysis. The actual performance of the proposed control schemes is experimentally validated by testing on a laboratory prototype.
20170712T10:05:42Z
Moradi Ghahderijani, Mohammad
Castilla Fernández, Miguel
Momeneh, Arash
Tomas Miret, Jaume
García de Vicuña Muñoz de la Nava, José Luis
This paper proposes a frequencymodulation control scheme for a dc/dc currentsource parallelresonant converter with two possible configurations. The basic configuration comprises an external voltage loop, an internal current loop, and a frequency modulator: the voltage loop is responsible for regulating the output voltage, the current loop makes the system controllable and limits the input current, and the modulator provides robustness against variations in resonant component values. The enhanced configuration introduces the output inductor current as a feedforward term and clearly improves the transient response to fast load changes. The theoretical design of these control schemes is performed systematically by first deriving their smallsignal models and second using Bode diagram analysis. The actual performance of the proposed control schemes is experimentally validated by testing on a laboratory prototype.

Variable structure control for threephase LCLfiltered inverters using a reduced converter model
http://hdl.handle.net/2117/106253
Variable structure control for threephase LCLfiltered inverters using a reduced converter model
Guzmán Solà, Ramon; García de Vicuña Muñoz de la Nava, José Luis; Castilla Fernández, Miguel; Miret Tomàs, Jaume; Hoz Casas, Jordi de la
This paper presents a new concept in active damping techniques using a reduced model of a LCLfiltered grid connected inverter. The presence of the LCL filter complicates the design of the inverter control scheme, particularly when uncertainties in the system parameters, especially in the grid inductance, are considered. The proposed control algorithm is addressed to overcome such difficulties using a reduced model of the inverter in a state observer. In this proposal, two of the three state variables of the system are obviated from the physical inverter model and only the inverter side current is considered. Therefore, the inverter side current can be estimated emulating the case of an inverter with only one inductor, thus eliminating the resonance problem produced by the LCL filter. Besides, in the case of a distorted grid, the method allows to estimate the voltages at the point of common coupling free of noise and distortion without using any PLLbased synchronization. To complete the control scheme, a theoretical stability analysis is developed considering the effect of the observer, the system discretization and the system parameters deviation. Experimental and comparative evaluation results are presented to validate the effectiveness of the proposed control scheme
20170707T11:15:48Z
Guzmán Solà, Ramon
García de Vicuña Muñoz de la Nava, José Luis
Castilla Fernández, Miguel
Miret Tomàs, Jaume
Hoz Casas, Jordi de la
This paper presents a new concept in active damping techniques using a reduced model of a LCLfiltered grid connected inverter. The presence of the LCL filter complicates the design of the inverter control scheme, particularly when uncertainties in the system parameters, especially in the grid inductance, are considered. The proposed control algorithm is addressed to overcome such difficulties using a reduced model of the inverter in a state observer. In this proposal, two of the three state variables of the system are obviated from the physical inverter model and only the inverter side current is considered. Therefore, the inverter side current can be estimated emulating the case of an inverter with only one inductor, thus eliminating the resonance problem produced by the LCL filter. Besides, in the case of a distorted grid, the method allows to estimate the voltages at the point of common coupling free of noise and distortion without using any PLLbased synchronization. To complete the control scheme, a theoretical stability analysis is developed considering the effect of the observer, the system discretization and the system parameters deviation. Experimental and comparative evaluation results are presented to validate the effectiveness of the proposed control scheme

Variable structure control in natural frame for threephase gridconnected inverters with LCL filter
http://hdl.handle.net/2117/106247
Variable structure control in natural frame for threephase gridconnected inverters with LCL filter
Guzmán Solà, Ramon; García de Vicuña Muñoz de la Nava, José Luis; Castilla Fernández, Miguel; Miret Tomàs, Jaume; Martín Cañadas, María Elena
This paper presents a variable structure control in natural frame for a threephase voltage source inverter. The proposed control method is based on modifying the converter model in natural reference frame, preserving the low frequency state space variables dynamics. Using this model in a Kalman filter, the system statespace variables are estimated allowing to design three robust current slidingmode controllers in natural frame. The main closedloop features of the proposed method are: 1) robustness against grid inductance variations because the proposed model is independent of the grid inductance, 2) the power losses are reduced since physical damping resistors are avoided, and 3) the control bandwidth can be increased due to the combination of a variable hysteresis controller with a Kalman filter. To complete the control scheme, a theoretical stability analysis is developed. Finally, selected experimental results validate the proposed control strategy and permit illustrating all its appealing features.
20170707T10:48:30Z
Guzmán Solà, Ramon
García de Vicuña Muñoz de la Nava, José Luis
Castilla Fernández, Miguel
Miret Tomàs, Jaume
Martín Cañadas, María Elena
This paper presents a variable structure control in natural frame for a threephase voltage source inverter. The proposed control method is based on modifying the converter model in natural reference frame, preserving the low frequency state space variables dynamics. Using this model in a Kalman filter, the system statespace variables are estimated allowing to design three robust current slidingmode controllers in natural frame. The main closedloop features of the proposed method are: 1) robustness against grid inductance variations because the proposed model is independent of the grid inductance, 2) the power losses are reduced since physical damping resistors are avoided, and 3) the control bandwidth can be increased due to the combination of a variable hysteresis controller with a Kalman filter. To complete the control scheme, a theoretical stability analysis is developed. Finally, selected experimental results validate the proposed control strategy and permit illustrating all its appealing features.

Energy dissipation in the presence of subharmonic excitation in dynamic atomic force microscopy
http://hdl.handle.net/2117/103298
Energy dissipation in the presence of subharmonic excitation in dynamic atomic force microscopy
Chiesa, Matteo; Gadelrab, Karim Raafat; Verdaguer, Albert; Segura, Juan José; Barcons Xixons, Víctor; Thomson, Neil H.; Phillips, M.A.; Stefancich, M.; Santos Hernández, Sergio
Amplitude modulation atomic force microscopy allows quantifying energy dissipation in the nanoscale with great accuracy with the use of analytical expressions that account for the fundamental frequency and higher harmonics. Here, we focus on the effects of subharmonic excitation on energy dissipation and its quantification. While there might be several mechanisms inducing subharmonics, a general analytical expression to quantify energy dissipation whenever subharmonics are excited is provided. The expression is a generalization of previous findings. We validate the expression via numerical integration by considering capillary forces and provide experimental evidence of subharmonic excitation for a range of operational parameters.
20170404T14:10:15Z
Chiesa, Matteo
Gadelrab, Karim Raafat
Verdaguer, Albert
Segura, Juan José
Barcons Xixons, Víctor
Thomson, Neil H.
Phillips, M.A.
Stefancich, M.
Santos Hernández, Sergio
Amplitude modulation atomic force microscopy allows quantifying energy dissipation in the nanoscale with great accuracy with the use of analytical expressions that account for the fundamental frequency and higher harmonics. Here, we focus on the effects of subharmonic excitation on energy dissipation and its quantification. While there might be several mechanisms inducing subharmonics, a general analytical expression to quantify energy dissipation whenever subharmonics are excited is provided. The expression is a generalization of previous findings. We validate the expression via numerical integration by considering capillary forces and provide experimental evidence of subharmonic excitation for a range of operational parameters.

Cantilever dynamics in amplitude modulation AFM: continuous and discontinuous transitions
http://hdl.handle.net/2117/102923
Cantilever dynamics in amplitude modulation AFM: continuous and discontinuous transitions
Santos Hernandez, Sergio; Barcons Xixons, Víctor; Font Teixidó, Josep; Thomson, Neil H.
Transitions between the attractive and the repulsive force regimes for amplitude modulation atomic force microscopy (AFM) can be either discontinuous, with a corresponding jump in amplitude and phase, or continuous and smooth. During the transitions, peak repulsive and average forces can be up to an order of magnitude higher when these are discrete. Under certain circumstances, for example, when the tip radius is relatively large (e.g. R > 20–30 nm) and for high cantilever free amplitudes (e.g. A0 > 40–50 nm), the L state can be reached with relatively low setpoints only (e.g. Asp/A0 < 0.30). We find that these cases do not generally lead to higher resolution but increase the background noise instead. This is despite the fact that the imaging can be noncontact under these conditions. The appearance of background noise is linked to increasing cantilever mean deflection and tip–surface proximity with increasing free amplitude in the L state.
Cantilever dynamics in amplitude modulation AFM: Continuous and discontinuous transitions (PDF Download Available). Available from: https://www.researchgate.net/publication/231025693_Cantilever_dynamics_in_amplitude_modulation_AFM_Continuous_and_discontinuous_transitions [accessed Mar 27, 2017].
20170327T15:56:43Z
Santos Hernandez, Sergio
Barcons Xixons, Víctor
Font Teixidó, Josep
Thomson, Neil H.
Transitions between the attractive and the repulsive force regimes for amplitude modulation atomic force microscopy (AFM) can be either discontinuous, with a corresponding jump in amplitude and phase, or continuous and smooth. During the transitions, peak repulsive and average forces can be up to an order of magnitude higher when these are discrete. Under certain circumstances, for example, when the tip radius is relatively large (e.g. R > 20–30 nm) and for high cantilever free amplitudes (e.g. A0 > 40–50 nm), the L state can be reached with relatively low setpoints only (e.g. Asp/A0 < 0.30). We find that these cases do not generally lead to higher resolution but increase the background noise instead. This is despite the fact that the imaging can be noncontact under these conditions. The appearance of background noise is linked to increasing cantilever mean deflection and tip–surface proximity with increasing free amplitude in the L state.
Cantilever dynamics in amplitude modulation AFM: Continuous and discontinuous transitions (PDF Download Available). Available from: https://www.researchgate.net/publication/231025693_Cantilever_dynamics_in_amplitude_modulation_AFM_Continuous_and_discontinuous_transitions [accessed Mar 27, 2017].

Performance evaluation of secondary control policies with respect to digital communications properties in inverterbased islanded microgrids
http://hdl.handle.net/2117/102634
Performance evaluation of secondary control policies with respect to digital communications properties in inverterbased islanded microgrids
Martí Colom, Pau; Velasco García, Manel; Martín Rull, Enric Xavier; García de Vicuña Muñoz de la Nava, José Luis; Miret Tomàs, Jaume; Castilla Fernández, Miguel
A key challenge for invertedbased microgrids working in islanded mode is to maintain their own frequency and voltage to a certain reference values while regulating the active and reactive power among distributed generators and loads. The implementation of frequency and voltage restoration control policies often requires the use of a digital communication network for realtime data exchange (tertiary control covers the coordi nated operation of the microgrid and the host grid). Whenever a digital network is placed within the loop, the operation of the secondary control may be affected by the inherent properties of the communication technology. This paper analyses the effect that properties like transmission intervals and message dropouts have for four existing representative approaches to secondary control in a scalable islanded microgrid. The simulated results reveals pros and cons for each approach, and identifies threats that properly avoided or handled in advance can prevent failures that otherwise would occur. Selected experimental results on a low scale laboratory microgrid corroborate the conclusions extracted from the simulation study.
20170320T08:14:59Z
Martí Colom, Pau
Velasco García, Manel
Martín Rull, Enric Xavier
García de Vicuña Muñoz de la Nava, José Luis
Miret Tomàs, Jaume
Castilla Fernández, Miguel
A key challenge for invertedbased microgrids working in islanded mode is to maintain their own frequency and voltage to a certain reference values while regulating the active and reactive power among distributed generators and loads. The implementation of frequency and voltage restoration control policies often requires the use of a digital communication network for realtime data exchange (tertiary control covers the coordi nated operation of the microgrid and the host grid). Whenever a digital network is placed within the loop, the operation of the secondary control may be affected by the inherent properties of the communication technology. This paper analyses the effect that properties like transmission intervals and message dropouts have for four existing representative approaches to secondary control in a scalable islanded microgrid. The simulated results reveals pros and cons for each approach, and identifies threats that properly avoided or handled in advance can prevent failures that otherwise would occur. Selected experimental results on a low scale laboratory microgrid corroborate the conclusions extracted from the simulation study.

Modelbased active damping control for threephase voltage source inverters with LCL filter
http://hdl.handle.net/2117/91268
Modelbased active damping control for threephase voltage source inverters with LCL 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 modelbased active
damping control in natural frame for a threephase voltage
source inverter with LCL filter. The presence of the LCL
filter complicates the design of the control scheme, particularly
when system parameters deviations are considered. The proposed
control method is addressed to overcome such difficulties and
uses a modified converter model in an state observer. In this
proposal, the converter model is modified by introducing a virtual
damping resistor. Then, a Kalman filter makes use of this model
to estimate the system statespace variables. Although the state
estimates do not obviously match the real world system variables,
they permit designing three current slidingmode controllers that
provide the following features to the closed loop system: a) robust
ande active damping capability like in the case of using a physical
damping resistor, b) robustness because the control specifications
are met independently of variation in the system parameters, c)
noise immunity due to the application of the Kalman filter, and
d) power loss minimization because the system losses caused
by the physical damping resistor are avoided. An interesting
side effect of the proposed control scheme is that the sliding
surfaces for each controller are independent. This decoupling
property for the three controllers allows using a fixed switching
frequency algorithm that ensures perfect current control. To
complete the control scheme, a theoretical stability analysis is
developed. Finally, selected experimental results validate the
proposed control strategy and permit illustrating all its appealing
features.
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20161031T10:50:17Z
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 modelbased active
damping control in natural frame for a threephase voltage
source inverter with LCL filter. The presence of the LCL
filter complicates the design of the control scheme, particularly
when system parameters deviations are considered. The proposed
control method is addressed to overcome such difficulties and
uses a modified converter model in an state observer. In this
proposal, the converter model is modified by introducing a virtual
damping resistor. Then, a Kalman filter makes use of this model
to estimate the system statespace variables. Although the state
estimates do not obviously match the real world system variables,
they permit designing three current slidingmode controllers that
provide the following features to the closed loop system: a) robust
ande active damping capability like in the case of using a physical
damping resistor, b) robustness because the control specifications
are met independently of variation in the system parameters, c)
noise immunity due to the application of the Kalman filter, and
d) power loss minimization because the system losses caused
by the physical damping resistor are avoided. An interesting
side effect of the proposed control scheme is that the sliding
surfaces for each controller are independent. This decoupling
property for the three controllers allows using a fixed switching
frequency algorithm that ensures perfect current control. To
complete the control scheme, a theoretical stability analysis is
developed. Finally, selected experimental results validate the
proposed control strategy and permit illustrating all its appealing
features.

Evaluating the 2014 retroactive regulatory framework applied to the grid connected PV systems in Spain
http://hdl.handle.net/2117/90837
Evaluating the 2014 retroactive regulatory framework applied to the grid connected PV systems in Spain
Hoz Casas, Jordi de la; Martín Cañadas, María Elena; Miret Tomàs, Jaume; Castilla Fernández, Miguel; Guzmán Solà, Ramon
© 2016 Elsevier Ltd. The RD 413/2014 new economic and regulatory framework for producers of electricity from renewable energy sources in Spain has been here analysed, putting the focus on its impact on the economic results of the existing grid connected PV systems. A complete formulation of the new remuneration scheme is first presented, making evident its high complexity and the great number of regulatory parameters involved. Then, in order to facilitate the discernment of its operating mechanism a simplified model is proposed. This approach has proven to be a useful tool to identify the most influential regulatory parameters and also which could be the plausible future regulatory actions in order to contain the cost to the Spanish Electricity System. Finally, the NPV and the IRR among other indicators are calculated for a representative case study facility, evidencing a substantial profitability reduction in the transition from the former economic and regulatory framework to the RD 413/2014 new remuneration scheme.
20161018T10:31:08Z
Hoz Casas, Jordi de la
Martín Cañadas, María Elena
Miret Tomàs, Jaume
Castilla Fernández, Miguel
Guzmán Solà, Ramon
© 2016 Elsevier Ltd. The RD 413/2014 new economic and regulatory framework for producers of electricity from renewable energy sources in Spain has been here analysed, putting the focus on its impact on the economic results of the existing grid connected PV systems. A complete formulation of the new remuneration scheme is first presented, making evident its high complexity and the great number of regulatory parameters involved. Then, in order to facilitate the discernment of its operating mechanism a simplified model is proposed. This approach has proven to be a useful tool to identify the most influential regulatory parameters and also which could be the plausible future regulatory actions in order to contain the cost to the Spanish Electricity System. Finally, the NPV and the IRR among other indicators are calculated for a representative case study facility, evidencing a substantial profitability reduction in the transition from the former economic and regulatory framework to the RD 413/2014 new remuneration scheme.

Comparative study of reactive power control methods for photovoltaic inverters in lowvoltage grids
http://hdl.handle.net/2117/86884
Comparative study of reactive power control methods for photovoltaic inverters in lowvoltage grids
Momeneh, Arash; Castilla Fernández, Miguel; Miret Tomàs, Jaume; Martí Colom, Pau; Velasco García, Manel
The increasing installation of photovoltaic panels in lowvoltage 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 baseline case where no reactive control method is applied, the conventional droop method approach, and a solution based on a nearoptimal 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.
20160510T14:45:57Z
Momeneh, Arash
Castilla Fernández, Miguel
Miret Tomàs, Jaume
Martí Colom, Pau
Velasco García, Manel
The increasing installation of photovoltaic panels in lowvoltage 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 baseline case where no reactive control method is applied, the conventional droop method approach, and a solution based on a nearoptimal 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.