DIE - GCP - Artículos en revistas internacionales / Articles in international journals

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Active power filtering embedded in the frequency control of an offshore wind farm connected to a diode-rectifier-based HVDC link
(MDPI, 2018-10-11) Nami, Ashkan; Rodríguez Amenedo, José Luis; Arnaltes Gómez, Santiago; Cardiel Álvarez, Miguel Ángel
This paper presents a novel active power filtering (APF) scheme embedded in a centralised frequency control of an offshore wind farm (OWF) connected to a high voltage direct current link through a diode rectifier station. The APF is carried out by a voltage source converter (VSC), which is connected to the rectifier station to provide frequency control for the offshore ac-grid. The proposed APF scheme eliminates harmonic currents at a capacitor bank placed at the rectifier station. This leads to a significant reduction in the total harmonic distortion of the offshore ac-grid voltage, and thus, to an improvement in the OWF power. Hence, the rectifier passive ac-filter bank is not needed anymore. A new selective harmonic compensation method based on the dynamic phasor (DP) theory is used in the proposed APF scheme which allows the extraction of the phasor form of harmonics in dc-signals. Therefore, the well-known proportional-integral regulators are used for the harmonic current compensation. Moreover, the offshore ac-grid is modelled for the system harmonic analysis using a grid solution based on the DP theory. Finally, a VSC power rating analysis is studied. The performance of the proposal is validated by simulations in both steady-state and transient conditions.
A Voltage and Frequency Control Strategy for Stand-Alone Full Converter Wind Energy Conversion Systems
(MDPI, 2018-02-25) Peña Asensio, Andrés; Arnaltes Gómez, Santiago; Rodríguez Amenedo, José Luis; García Plaza, Manuel; Eloy-García Carrasco, Joaquín; Alonso-Martínez de las Morenas, Jaime Manuel; Comunidad de Madrid
This paper addresses the design and analysis of a voltage and frequency control (VFC) strategy for full converter (FC)-based wind energy conversion systems (WECSs) and its applicability for the supply of an isolated load. When supplying an isolated load, the role of the back-to-back converters in the FC must change with respect to a grid-connected application. Voltage and frequency are established by the FC line side converter (LSC), while the generator side converter (GSC) is responsible for maintaining constant voltage in the DC link. Thus, the roles of the converters in the WECS are inverted. Under such control strategies, the LSC will automatically supply the load power and hence, in order to maintain a stable operation of the WECS, the wind turbine (WT) power must also be controlled in a load-following strategy. The proposed VFC is fully modelled and a stability analysis is performed. Then, the operation of the WECS under the proposed VFC is simulated and tested on a real-time test bench, demonstrating the performance of the VFC for the isolated operation of the WECS.
Sequence Control Strategy for Grid-Forming Voltage Source Converters Based on the Virtual-Flux Orientation under Balanced and Unbalanced Faults
(MDPI, 2023-04-01) Dolado Fernández, Juan José; Eloy-García Carrasco, Joaquín; Arnaltes Gómez, Santiago; Rodríguez Amenedo, José Luis; Agencia Estatal de Investigación (España)
Renewable power generation has increased in recent years, which has led to a decrease in the use of synchronous generators (SGs). These power plants are mainly connected to the power system through electronic converters. One of the main differences between electronic converters connected to power systems and SGs connected to the grid is the current contribution during faults, which can have an impact on protection systems. New grid codes set requirements for fast current injection, but the converters' maximum current limitation during faults make it challenging to develop control strategies for such current contribution. This paper presents a positive and negative sequence current injection strategy according to the new Spanish grid code requirements for the novel grid-forming converter control algorithm based on virtual-flux orientation. The behavior of the proposed strategy is tested in a hardware in the loop (HiL) experimental set-up under balanced faults, meaning that the fault is symmetrically distributed among the three phases, and unbalanced faults, where the fault current is distributed asymmetrically between the phases.
Wavelet Analysis to Detect Ground Faults in Electrical Power Systems with Full Penetration of Converter Interface Generation
(MDPI, 2023-03-01) Azuara Grande, Luis; Granizo, Ricardo; Arnaltes Gómez, Santiago; Comunidad de Madrid
The requirements for the increased penetration of renewable energy sources in electrical power systems have led to a dominance of power electronic interfaces. As a result, short-circuit currents have been reduced by the thermal limitations of power electronics, leading to problems associated with the sensitivity, selectivity, and reliability of protective relays. Although many solutions can be found in the literature, these depend on communications and are not reliable in all grid topologies or under different types of electrical fault. Hence, in this paper, the analysis of ground fault currents and voltages using a wavelet transform in combination with a new algorithm not only detects such ground faults but also allows them to be cleared quickly and selectively in scenarios with low fault current contribution due to a full penetration converter-interface-based generation. To verify and validate the proposed protection system, different ground faults are simulated using an arc ground fault model in a grid scheme based on the IEEE nine-bus standard test system, with only grid-forming power converters as generation sources. The test system is modelled in the MATLAB/Simulink environment. Therefore, the protection relays that verify all the steps established in the new algorithm can detect and clear any ground defect. Simulations are also presented involving different fault locations to demonstrate the effectiveness of the proposed ground fault protection method.
Black-start capability of PV power plants through a grid-forming control based on reactive power synchronization
(Elsevier, 2023-03) Peña Asensio, Andrés; Arnaltes Gómez, Santiago; Rodríguez Amenedo, José Luis; Agencia Estatal de Investigación (España)
Power system restoration is a critical process for any power system. As synchronous generators are being replaced by power electronic converters used in renewable energy generation, the contribution of renewable energy power plants to power system restoration (PSR) after a black-out is becoming more relevant, the so-called black start capability. Existing solutions for providing black start capability to photovoltaic (PV) power plants rely on the use of energy storage systems (ESS) in a hybrid PV plant. In contrast, this paper proposes a solution for the contribution of PV power plants to the PSR that allows a completely autonomous black start process. Reactive power synchronization is used for controlling the PV inverters as virtual synchronous generators (VSG), providing grid-forming control and ensuring synchronism. During the black start process, the PV power is regulated to match the demand using a decentralized solution to share the load between multiple PV inverters. The solution has been validated to handle the most critical situations during the black start process such as the variation on the power source, i.e. irradiance, or on the supplied load and the connection to the main grid.
Analysis of the converter synchronizing method for the contribution of battery energy storage systems to inertia emulation
(MDPI, 2020-03-02) Peña Asensio, Andrés; González-Longatt, Francisco; Arnaltes Gómez, Santiago; Rodríguez Amenedo, José Luis; Comunidad de Madrid
This paper presents a comprehensive analysis of the effect of the converter synchronizing methods on the contribution that Battery Energy Storage Systems (BESSs) can provide for the support of the inertial response of a power system. Solutions based on phase-locked loop (PLL) synchronization and virtual synchronous machine (VSM) synchronization without PLL are described and then compared by using time-domain simulations for an isolated microgrid (MG) case study. The simulation results showed that inertial response can be provided both with and without the use of a PLL. However, the behavior in the first moments of the inertia response differed. For the PLL-based solutions, the transient response was dominated by the low-level current controllers, which imposed fast under-damped oscillations, while the VSM systems presented a slower response resulting in a higher amount of energy exchanged and therefore a greater contribution to the support of the system inertial response. Moreover, it was demonstrated that PLL-based solutions with and without derivative components presented similar behavior, which significantly simplified the implementation of the PLL-based inertia emulation solutions. Finally, results showed that the contribution of the BESS using VSM solutions was limited by the effect of the VSM-emulated inertia parameters on the system stability, which reduced the emulated inertia margin compared to the PLL-based solutions.
A Review on the Degradation Implementation for the Operation of Battery Energy Storage Systems
(MDPI, 2022-09-03) Camuñas García-Miguel, Pedro Luis; Alonso-Martínez de las Morenas, Jaime Manuel; Arnaltes Gómez, Santiago; García Plaza, Manuel; Peña Asensio, Andrés
A naive battery operation optimization attempts to maximize short-term profits. However, it has been shown that this approach does not optimize long-term profitability, as it neglects battery degradation. Since a battery can perform a limited number of cycles during its lifetime, it may be better to operate the battery only when profits are on the high side. Researchers have dealt with this issue using various strategies to restrain battery usage, reducing short-term benefits in exchange for an increase in long-term profits. Determining this operation restraint is a topic scarcely developed in the literature. It is common to arbitrarily quantify degradation impact into short-term operation, which has proven to have an extensive impact on long-term results. This paper carries out a critical review of different methods of degradation control for short-time operation. A classification of different practices found in the literature is presented. Strengths and weaknesses of each approach are pointed out, and future possible contributions to this topic are remarked upon. The most common methodology is implemented in a simulation for demonstration purposes.
Damping low-frequency oscillations in power systems using grid-forming converters
(IEEE, 2021-11-23) Rodríguez Amenedo, José Luis; Arnaltes Gómez, Santiago; Ministerio de Ciencia e Innovación (España)
The increasing incorporation of renewable energy in power systems is causing growing concern about system stability. Renewable energy sources are connected to the grid through power electronic converters, reducing system inertia as they displace synchronous generators. New grid-forming converters can emulate the behavior of synchronous generators in terms of inertia provision and other grid services, like power-frequency and voltage-reactive regulation. Nevertheless, as a consequence of synchronous generator emulation, grid-forming converters also present angle oscillations following a grid disturbance. This paper proposes two novel power stabilizers for damping low-frequency oscillations (LFOs) in the power system. The first power stabilizer provides power oscillation damping through active power (POD-P), and it is implemented in a grid-forming converter, using the active power synchronization loop to damp system oscillations by acting on the converter angle. The second one provides power oscillation damping through reactive power (POD-Q), and it is implemented in a STATCOM, using the voltage control loop to damp system oscillations. Both proposals are first assessed in a small-signal stability study and then in a comprehensive simulation. Moreover, two cases are considered: damping the oscillations of a single machine connected to an infinite bus through a tie-line, and damping the inter-area oscillations in a two-area system. Simulation results, as well as the stability study, demonstrate the ability of both stabilizers to damp power system oscillations, being the POD-P more effective than the POD-Q, but at the cost of requiring some kind of energy provision at the DC bus.
Improving the inertial response of a Grid-Forming voltage source converter
(MDPI, 2022-08-01) Dolado, Juan José; Rodríguez Amenedo, José Luis; Arnaltes Gómez, Santiago; Eloy-García Carrasco, Joaquín; Ministerio de Ciencia e Innovación (España)
In recent years, the use of synchronous generators (SGs) has been displaced due to the increased use of renewable energy sources. These types of plants mostly use power electronic converters to connect to power grids, which, due to their mode of operation, cannot provide the same services. This paper analyzes the synchronization of Grid-Forming converters (GFM) without phase-locked loop (PLL) through the active power control loop. Stability analysis shows that when increasing the emulated moment of inertia in a voltage source converter (VSC) using grid-forming control, the system becomes oscillatory. The paper proposes a novel compensation mechanism in order to damp the system oscillation, allowing the implementation of inertia emulation. Finally, the real-time implementation is executed using a Hardware in the Loop experimental set-up. The response of VSC under grid disturbances is simulated in a real time simulator, while the proposed control system is implemented in a real-time controller platform.
Grid-forming control of doubly-fed induction generators based on the rotor flux orientation
(Elsevier, 2023-05) Castro Martínez, Jesús; Rodríguez Amenedo, José Luis; Arnaltes Gómez, Santiago; Alonso-Martínez de las Morenas, Jaime Manuel; Ministerio de Ciencia e Innovación (España)
The increasing penetration of renewable energies in power systems demands new services from renewable generation plants. System operators are concerned about system stability since renewable generators behave as constant power sources. Therefore, new requirements have been imposed to grid-following generators to improve their contribution to system stability acting as grid-supporting generators. Nevertheless, grid-supporting control can still compromise system stability for high penetration of renewables, and grid-forming control has arised to ensure proper operation. This paper proposes a novel grid-forming control scheme for doubly-fed induction generators, so they behave as real voltage sources. The proposed grid-forming control is based on the rotor flux orientation to a reference axis obtained from the emulation of the synchronous generator swing equation. The rotor flux is oriented to the reference axis by means of a flux controller that also controls the flux magnitude. The flux orientation in turn allows to control the doubly-fed induction generator torque, while the flux magnitude control allows to regulate the generator reactive power or terminal voltage. The proposed control system has been validated through a comprehensive real-time simulation with hardware in the loop, assessing its grid-forming capability. Moreover, small signal analysis has also been performed to assess system stability.
Comparison of Two Energy Management System Strategies for Real-Time Operation of Isolated Hybrid Microgrids
(MDPI, 2021-10-17) Azuara Grande, Luis; Arnaltes Gómez, Santiago; Alonso-Martínez de las Morenas, Jaime Manuel; Rodríguez Amenedo, José Luis; Comunidad de Madrid
The propagation of hybrid power systems (solar–diesel–battery) has led to the development of new energy management system (EMS) strategies for the effective management of all power generation technologies related to hybrid microgrids. This paper proposes two novel EMS strategies for isolated hybrid microgrids, highlighting their strengths and weaknesses using simulations. The proposed strategies are different from the EMS strategies reported thus far in the literature because the former enable the real-time operation of the hybrid microgrid, which always guarantees the correct operation of a microgrid. The priority EMS strategy works by assigning a priority order, while the optimal EMS strategy is based on an optimization criterion, which is set as the minimum marginal cost in this case. The results have been obtained using MATLAB/Simulink to verify and compare the effectiveness of the proposed strategies, through a dynamic microgrid model to simulate the conditions of a real-time operation. The differences in the EMS strategies as well as their individual strengths and weaknesses, are presented and discussed. The results show that the proposed EMS strategies can manage the system operation under different scenarios and help power system operator obtain the optimal operation schemes of the microgrid.
Optimal Power Transmission of Offshore Wind Power Using a VSC-HVdc Interconnection
(MDPI, 2017-07) Montilla D'Jesús, Miguel Eduardo; Arnaltes Gómez, Santiago; Castronuovo, Edgardo Daniel; Santos Martín, David; Comunidad de Madrid
High-voltage dc transmission based on voltage-source converter (VSC-HVdc) is quickly increasing its power rating, and it can be the most appropriate link for the connection of offshore wind farms (OWFs) to the grid in many locations. This paper presents a steady-state operation model to calculate the optimal power transmission of an OWF connected to the grid through a VSC-HVdc link. The wind turbines are based on doubly fed induction generators (DFIGs), and a detailed model of the internal OWF grid is considered in the model. The objective of the optimization problem is to maximize the active power output of the OWF, i.e., the reduction of losses, by considering the optimal reactive power allocation while taking into account the restrictions imposed by the available wind power, the reactive power capability of the DFIG, the DC link model, and the operating conditions. Realistic simulations are performed to evaluate the proposed model and to execute optimal operation analyses. The results show the effectiveness of the proposed method and demonstrate the advantages of using the reactive control performed by DFIG to achieve the optimal operation of the VSC-HVdc.
Contribution of wind farms to the stability of power systems with high penetration of renewables
(MDPI, 2021-04-02) Castro Martínez, Jesús; Arnaltes Gómez, Santiago; Alonso-Martínez de las Morenas, Jaime Manuel; Rodríguez Amenedo, José Luis; Ministerio de Ciencia, Innovación y Universidades (España)
Power system inertia is being reduced because of the increasing penetration of renewable energies, most of which use power electronic interfaces with the grid. This paper analyses the contribution of inertia emulation and droop control to the power system stability. Although inertia emulation may appear the best option to mitigate frequency disturbances, a thorough analysis of the shortcomings that face real-time implementations shows the opposite. Measurement noise and response delay for inertia emulation hinder controller performance, while the inherently fast droop response of electronic converters provides better frequency support. System stability, expressed in terms of rate of change of frequency (ROCOF) and frequency nadir, is therefore improved with droop control, compared to inertia emulation.
Frequency Control of Offshore Wind Farm with Diode-Rectifier-based HVdc Connection
(IEEE, 2020-03) Nami, Ashkan; Rodríguez Amenedo, José Luis; Arnaltes Gómez, Santiago; Cardiel Álvarez, Miguel Ángel; Alves Baraciarte, Roberto
This paper presents a direct frequency control for offshore wind farms (OWFs) connected to the diode-rectifier-based (DR-based) high voltage direct current (HVDC) link. The frequency control is guaranteed through reactive power balance at the DR station without a capacitor bank placed at the DR station; while AC-voltage magnitude is clamped by the DR, provided that the HVDC link voltage is imposed by the onshore inverter. The control system is implemented by a voltage source converter (VSC) connected to the DR station. The VSC is also used to compensate harmonic currents, leading to passive AC-filters being also removed from the DR station. The proposed control system provides comparative advantages in terms of DR station volume and OWF installation cost with other centralized controls where besides a VSC, a high-voltage large capacitor bank is needed to be placed at the DR station. A new average-value model (AVM) of the DR system is derived to test the proposed frequency control, while the stability of the system is evaluated through a small-signal analysis. The proposed control system performance and the accuracy of the proposed AVM are verified through a detailed switching model of the system using operation of a cascaded H-bridge VSC.
Reactive power synchronization method for voltage-sourced converters
(IEEE, 2019-07) Peña Asensio, Andrés; Arnaltes Gómez, Santiago; Cardiel Álvarez, Miguel Ángel; Rodríguez Amenedo, José Luis; Comunidad de Madrid
There is a growing interest in the parallel operation of voltage source converters (VSCs) both in an isolated microgrid or connected to the utility grid. The most common solution in the literature for the paralellization of VSCs is the so-called droop control, which brings about a relationship between active power and frequency. In this paper, a different approach is proposed where reactive power is used instead of active power to ensure synchronous operation. Active and reactive power are independently controlled using a dq-frame representation based on the vector oriented control, which inherently provides current limitation capability. A detailed dynamic model of the system is used to demonstrate the relation between reactive power and frequency. Due to the intrinsic synchronizing mechanism, the proposed scheme can operate in both isolated and grid-connected modes. As opposed to droop control schemes, active power is not used for synchronization and thus synchronization is possible even if active power is not controllable. Simulation and experimental results, for a case study where a VSC is connected to a host grid, are presented to validate the proposal.
Control of the Parallel Operation of VSC-HVDC Links Connected to an Offshore Wind Farm
(IEEE, 2019-02) Rodríguez Amenedo, José Luis; Arnaltes Gómez, Santiago; Aragüés Peñalba, Mònica; Gomis Bellmunt, Oriol; Ministerio de Economía y Competitividad (España)
This paper introduces the control of the parallel operation of two voltage source converter (VSC)-HVdc links interconnecting an offshore wind farm. The aim of the study is to propose and validate a control system that allows the parallel operation of two VSC-HVdc links by controlling the currents injected by the VSC converters. The currents set points are established by a voltage controller in order to maintain constant voltage and frequency in the capacitor of the output filter and therefore within the offshore wind farm (OWF). It is demonstrated that the decoupled control of the d-q component of the voltage at the capacitor allows achieving the direct control of voltage and frequency, respectively. The voltage and frequency control is implemented by orienting the capacitor voltage toward a synchronous axis that is generated within the controller and therefore is not subjected to any grid disturbance. Both converters collaborate therefore in maintaining constant voltage and frequency, achieving in this way the parallel operation of the converters. The validation of this approach is demonstrated by simulation where the OWF and the VSC-HVdc rectifier have been modeled. Simulation results demonstrate that the proposed control system allows the parallelization of the converters while maintaining constant voltage and frequency within the OWF, even during transient faults.
Modeling and Control of LCC Rectifiers for Offshore Wind Farms Connected by HVDC Links
(IEEE, 2017-12) Cardiel Álvarez, Miguel Ángel; Rodríguez Amenedo, José Luis; Arnaltes Gómez, Santiago; Montilla D'Jesús, Miguel Eduardo; Ministerio de Economía y Competitividad (España)
This paper presents a voltage and frequency control (VFC) and an average-value model (AVM) of a line-commutated converter for a rectifier station in an offshore wind farm (OWF) connected by a high-voltage direct current link. A capacitor bank is placed at the AC terminals of the rectifier station to perform VFC within the OWF. The proposed model uses the active and reactive power generated by the OWF as inputs, while the state variables are the voltage magnitude and phase angle at the capacitor bank bus. The proposed VFC is based on the orientation of the voltage vector at the capacitor bank bus toward a synchronous reference axis. It is then demonstrated that frequency control is achieved by regulating the reactive power balance at the capacitor bank bus, while voltage control is carried out by regulating the active power balance. Moreover, it is demonstrated that in a diode rectifier, although voltage cannot be controlled as in a thyristor rectifier, it is bounded within acceptable limits. In addition, small-signal study is performed to facilitate controller design and system stability analysis. VFC and the accuracy of the proposed AVM are validated by simulation, using both the proposed AVM and a detailed switching model.
Decentralized Control of Offshore Wind Farms Connected to Diode-Based HVdc Links
(IEEE, 2018-09) Cardiel Álvarez, Miguel Ángel; Arnaltes Gómez, Santiago; Rodríguez Amenedo, José Luis; Nami, Ashkan
This paper presents a novel decentralized control for offshore wind farms connected to the onshore grid through a high-voltage dc link by means of a diode rectifier. The proposed control system is implemented in each wind turbine generator system (WTGS). The capacitor placed at the filter of the wind turbine front-end converter is used for the proposed control implementation. Frequency control is achieved by aligning the capacitor voltage vector along a reference axis rotating at the reference frequency. Then, a frequency-reactive power droop control allows the synchronization of all the WTGSs. On the other hand, this droop strategy also leads to total reactive power sharing among WTGSs without relying on communications. An additional secondary frequency control is also implemented to compensate the frequency deviation caused by the droop control. The proposed control system has been validated by simulation and results demonstrate the appropriate performance even during start-up and faults.
Energetic, economic and environmental viability of off-grid PV-BESS for charging electric vehicles: Case study of Spain
(Elsevier, 2018-02) Azuara Grande, Luis; Yahyaoui, Imene; Arnaltes Gómez, Santiago
Nowadays, the optimum technical design of Photovoltaic and Battery Energy Storage System (PV-BESS) is crucial for ensuring their economic feasibility, which implies the minimum cost sizing of the system components. In fact, a good design of the off-grid PV-BESS system allows the outages to be avoided, ensures the quality and the security of the power supply, from the one hand, and guarantees the economic and environmental benefits, from the other one. In this context, this paper analyses the technical and economic viability of an off-grid PVBESS for Charging Electric Vehicles (EVs). The study is performed using HOMER software and meteorological data of Madrid, Spain, and by applying the load shifting principle. In order to verify the effectiveness and rentability of the studied system, its efficiency has been compared to grid-connected charging points, considering the environmental aspects. The obtained results demonstrate that the off-grid PV-BESS are technically and economically viable and reliable. Moreover, they are profitable while allowing a significant reduction of the air pollution.

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