| 1. |
- Bessegato, Luca, et al.
(författare)
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Design of a Modular Multilevel Converter Prototype for Research Purposes
- 2018
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Konferensbidrag (refereegranskat)abstract
- As modular multilevel converters gradually become the preferred topology for many high-voltage andhigh-power applications, they are widely studied among researchers, who need experimental results tovalidate their studies. This paper discusses the design of a down-scaled modular multilevel converterprototype for research purposes, equipped with 30 full-bridge submodules and 10 kW rating. The designof this prototype is aimed at safety, flexibility, orderliness, and compactness. The challenges posed by theimplementation of the converter prototype are examined, discussing the design of the prototype structure,the communication scheme, the full-bridge submodules, and the control hierarchy. The control systemis based on Xilinx Zynq system-on-chip, which integrates programmable logic and processing system,allowing for extensive computational capability as well as simple reconfiguration. Experimental resultsshowing the prototype in operation at nominal ratings are presented along with the devised graphical userinterface.
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| 2. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
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Impact of control loops on the low-frequency passivity properties of grid-forming converters
- 2020
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Ingår i: 2020 22nd European Conference on Power Electronics and Applications, EPE 2020 ECCE Europe. ; , s. P.1-P.10
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Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to evaluate the low-frequency passivity properties of grid-forming converters. Through the analysis of the frequency-dependent input admittance of the converter, the impact of various control loops is investigated. A simplified analytical model that is valid in the low-frequency range is also derived in order to identify possible control modifications to enhance the passivity of the system.
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| 3. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
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Impact of Control Loops on the Passivity Properties of Grid-Forming Converters with Fault-Ride through Capability
- 2021
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:19
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Tidskriftsartikel (refereegranskat)abstract
- Due to the increasing integration of renewable energy sources (RES) and a corresponding reduction of conventional generating units, there is nowadays a demand from the power-electronic converters to provide grid-forming properties through proper control of the converter systems. This paper aims to evaluate the impact of various control loops in a grid-forming control strategy equipped with a fault-ride through capability on the passivity properties of the converter system. Through the analysis of the frequency-dependent input admittance of the converter, the main factors affecting the passivity properties are identified. A simplified analytical model is derived in order to propose possible control modifications to enhance the system’s passivity at various frequencies of interest and the findings are validated through detailed time-domain simulations and experimental tests.
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| 4. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
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Passivity characterization of grid-forming converters with fault-ride through capability
- 2021
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Ingår i: 2021 23rd European Conference on Power Electronics and Applications, EPE 2021 ECCE Europe.
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Konferensbidrag (refereegranskat)abstract
- Due to the increase in the use of renewable energy sources (RES) and a corresponding reduction in the conventional energy generation systems, there is nowadays a demand from the power-electronic converters to provide grid-forming properties through proper control of the converter systems. This paper aims at evaluating the impact of various control loops of a grid-forming control strategy equipped with a fault-ride through capability on the passivity properties of the converter system. Through the analysis of the frequency-dependent input admittance of the converter, the main factors affecting the passivity property are identified. A simplified analytical model has been derived in order to propose possible control modifications to enhance system’s passivity at various frequencies of interest and the findings are verified through detailed time-domain simulations and experiments.
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| 5. |
- Imgart, Paul, 1990, et al.
(författare)
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A Cascaded Power Controller for Robust Frequency Ride-Through of Grid-Forming Converters
- 2022
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Ingår i: 2022 IEEE Energy Conversion Congress and Exposition, ECCE 2022.
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Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to present a grid-forming (GFM) control strategy with a novel active-power loop (APL) structure facilitating limitation of active power while providing maximum available inertial support. This is achieved by decoupling the synchronization duties of the APL from the inertial support. The latter is provided by calculating an active-power reference through a dedicated inertia-emulation loop (IEL), which is connected in cascade with the APL. The effectiveness of the proposed method is demonstrated through time-domain simulations including frequency transients of varying size and unbalanced operating conditions.
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| 6. |
- Imgart, Paul, 1990, et al.
(författare)
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External Inertia Emulation to Facilitate Active-Power Limitation in Grid-Forming Converters
- 2024
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Ingår i: IEEE Transactions on Industry Applications. - 0093-9994 .- 1939-9367. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to present a grid-forming (GFM) control strategy with a novel active-power loop (APL) structure facilitating limitation of active power while providing maximum available inertial support. This is achieved by decoupling the synchronization duties of the APL from the inertial support. The latter is provided by calculating the active-power reference through a dedicated inertia-emulation loop (IEL), which is connected in cascade with the APL. The effectiveness of the proposed method is demonstrated through laboratory experiments including frequency transients of varying size and unbalanced operating conditions.
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| 7. |
- Mohanty, Rabindra, 1989, et al.
(författare)
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Challenges in Protection of Converter Dominated Medium-Voltage Microgrids
- 2019
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Ingår i: Proceedings of 2019 IEEE PES Innovative Smart Grid Technologies Europe, ISGT-Europe 2019. ; 2019
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Konferensbidrag (refereegranskat)abstract
- This paper presents a comprehensive review of major challenges in protection of medium-voltage microgrids with large amount of converter interfaced distributed generations (DGs). The challenges are mainly due to the limited fault current contributed by the DGs during the fault. This paper focuses on key issues with overcurrent protection schemes with various configurations of DGs and connection points. It was found that the current magnitude based conventional overcurrent relays would fail to operate in islanded operation of microgrids, while in grid-connected mode, the relays would operate but with extended time delay or would not operate for certain fault locations with high penetration of DGs. Overrated converter interfaced DGs would cause problems such as relay blinding and sympathetic tripping. The problems are examined and discussed in cases with DGs interfaced by rated and overrated converters in islanded and grid-connected operations, as well as in cases of different connection points of DGs, energy storage system and fault locations in the microgrid. The paper also attempts to suggest and discuss a number of protection solutions to the presented issues considering cost and reliability aspects.
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| 8. |
- Narula, Anant, 1993, et al.
(författare)
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Comparison of Grid-Forming Converter Control Strategies
- 2021
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Ingår i: 2021 IEEE Energy Conversion Congress and Exposition, ECCE 2021 - Proceedings. ; , s. 361-368
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Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to compare three different categories of grid-forming converter control strategies based on their structural differences, and ability to fulfill the requirements that have been recently identified by the European Network of Transmission and System Operators for Electricity (ENTSOE). Among these requirements, the ones associated with the frequency characteristics of the converter system, such as its ability to prevent the risk for adverse control interactions, and act as a sink for harmonics are in focus. These properties are assessed through the frequency-dependent input-admittance models of the converter system. In addition, robust performance of the converter system at various grid strength is paramount, which is investigated both analytically and through detailed time-domain simulations in PSCAD.
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| 9. |
- Narula, Anant, 1993, et al.
(författare)
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Coordinated control of grid-forming converters and hydro generators to enhance frequency quality of future power system
- 2022
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Ingår i: Electric Power Systems Research. - : Elsevier BV. - 0378-7796. ; 212
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to propose a coordinated control strategy between grid-forming converters equipped with energy storage, and hydro generators to facilitate frequency support from the converters in future power systems. In this way, it is possible to take advantage of the fast dynamic properties of the converter system, and at the same time minimize the energy storage requirements associated with the converter system. The proposed tuning criterion for the frequency controller of the grid-forming converter facilitates a natural coordination between the converter system and hydro generators. The effectiveness of the proposed control strategy is compared against the conventional droop-based approach available in the literature. Finally, the analytical findings are validated using detailed time-domain simulation model in PSCAD.
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| 10. |
- Narula, Anant, 1993, et al.
(författare)
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Empowering Offshore Wind With Es-Statcom For Stability Margin Improvement and Provision of Grid-Forming Capabilities
- 2024
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Ingår i: Electric Power Systems Research. - 0378-7796. ; 234
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Tidskriftsartikel (refereegranskat)abstract
- Offshore wind power plants (WPPs) play a pivotal role in achieving a CO2-neutral electricity sector. However, their grid connection presents significant challenges and costs. High-voltage alternating current (HVAC) offers a cost-effective solution, but it may necessitate the installation of a static synchronous compensator (STATCOM) at the onshore bus to ensure stability and compliance with connection requirements. Integrating energy storage into the STATCOM (ES-STATCOM) enables the provision of ancillary services, such as inertial response and frequency support, which require active power. This paper utilizes the generalized Nyquist criterion to demonstrate that operating the ES-STATCOM with grid-forming control enhances the stability margin of the grid-connected WPP when compared to operating it with grid-following control. Furthermore, it illustrates through network frequency perturbation (NFP) plots that the overall WPP, comprising grid-following wind turbines and a grid-forming ES-STATCOM, imparts grid-forming behavior at the grid-connection point.
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| 11. |
- Narula, Anant, 1993
(författare)
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Grid-forming wind power plants
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With growing concerns over climate change, the power system is witnessing an unprecedented growth in electricity generation from intermittent renewable energy sources (RES) such as wind and solar, which are commonly interfaced to the grid by power-electronic converters. However, increasing the penetration level of converter-interfaced generation units reduces the number of synchronous generators (SGs) in the grid that provide system services to support voltage and frequency, either inherently or through mandatory requirements and market products. This brings several challenges for the grid operators, which include increasing risk of harmonic interactions, decreasing system inertia and reduction in the short-circuit power of the grid, which all together might jeopardize the security and availability of the power systems. As a countermeasure, it is necessary that the power-electronic-based generation units not only provide grid support services that are originally provided by the SGs, but also operate in harmony with other generation units in all kinds of grid conditions. As a result, the concept of grid-forming (GFM) control, which mimics the beneficial properties of the SGs in converter systems, has emerged as a viable solution to allow effective and secured operation of power systems with increased penetration of converter-based resources. This thesis investigates the application of GFM control strategies in wind power plants (WPPs). In particular, the focus of the work will be on developing an effective GFM control strategy for the energy storage systems (ESS) in WPPs that not only supports the operation of the WPP in various grid conditions, but also offers a certain degree of GFM properties to the overall WPP. To start with, the selection of the most suitable GFM control strategy for wind power applications is made by evaluating and comparing various control strategies available in the literature. The comparison is based on their influence on the frequency characteristics of the converter and robustness of the controller in varying grid strength. To address the transient stability problem of GFM converters during current limitation, a novel strategy based on the limitation of converter's internal voltage vector is developed, which effectively limits the converter current to a desired value and retains the GFM properties of the converter at all times. An experimental setup is used to validate the effectiveness of the proposed limitation strategy in case of various grid disturbances. By implementing the proposed GFM control strategy for the ESS in a test WPP model, it is shown using detailed time-domain simulation results that the GFM behaviour can be offered to the overall WPP. The Network Frequency Perturbation (NFP) plots are used to verify the GFM behaviour of the considered WPP. Furthermore, an overview of various energy storage technologies (ESTs) suitable for providing ancillary services from WPPs is presented. With a focus on the two most suitable ESTs, i.e., batteries and supercapacitors, recommendations are given for design and sizing of the ESS for a given application. Finally, a coordinated control strategy between the WPP and SGs is developed, which facilitates the provision of frequency support from the WPP and at the same time reduces the energy storage requirements for the converter system.
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| 12. |
- Narula, Anant, 1993, et al.
(författare)
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Impact of steady-state grid-frequency deviations on the performance of grid-forming converter control strategies
- 2020
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Ingår i: 2020 22nd European Conference on Power Electronics and Applications, EPE 2020 ECCE Europe. ; 22
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Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to investigate the impact of steady-state deviations in the grid-frequency on the performance of grid-forming converter control strategies. In particular, the virtual synchronous machine (VSM) control structure has been the focus of study in this paper. Two alternative solutions to address the issue with the conventional VSM structure are suggested, and their impact on the active power response and the power dissipation properties of the converter are compared. For the latter, the ac-side input admittance of the grid-connected converter is derived for the different control structures under consideration. Finally, the dynamic performance of the different control structures is verified through the time-domain simulations.
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| 13. |
- Narula, Anant, 1993, et al.
(författare)
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Tuning and evaluation of grid-forming converters for grid-support
- 2021
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Ingår i: 2021 23rd European Conference on Power Electronics and Applications, EPE 2021 ECCE Europe.
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Konferensbidrag (refereegranskat)abstract
- Grid-forming converters interfacing renewable energy sources to the power system have emerged in recent years to account for the reduction of the conventional synchronous generators in the power system. This paper proposes a new structure and tuning approach for the active power controller of grid-forming converters. This is aimed at reducing the overshoot in the step-response of the active power controller, which is typically observed with other structures found in the literature. In order to ensure robustness of the proposed controller, the dynamic response of the active power injected by the converter is evaluated at various short-circuit ratio (SCR) of the grid. In addition, the performance of the converter system is investigated during parallel operation of converters in both grid-connected as well as islanded modes. Finally, the analytical findings are verified using detailed time-domain simulations in PSCAD.
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| 14. |
- Narula, Anant, 1993, et al.
(författare)
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Voltage-based Current Limitation Strategy to Preserve Grid-forming Properties Under Severe Grid Disturbances
- 2023
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Ingår i: IEEE Open Journal of Power Electronics. - 2644-1314. ; 4, s. 176-188
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Tidskriftsartikel (refereegranskat)abstract
- Grid-forming (GFM) converters are a promising solution to enable large scale integration of renewable energy sources into the power system. However, due to the intrinsic voltage-source behaviour of GFM converters, current limitation during large grid disturbances is challenging. This paper presents a novel limitation strategy that preserves the GFM properties of the converter and at the same time effectively limits the converter current to the desired value. Through the limitation of the converter's internal voltage, stable operation even during faults and in case of large frequency disturbances in the grid is achieved. Experimental results show the effectiveness of the proposed current limitation strategy in case of various grid disturbances.
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