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- Fregelius, Martin
(författare)
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An experimental approach on linear synthetic inertia
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The interest in renewable energy has significantly increased in the last decades which has led to an increased amount of renewable energy sources in the grid. In the Nordic grid, the major contribution to renewable energy is hydro power and wind power and an increase in the amount of wind power is expected in the future. The increase in wind power and decommissioning of nuclear power is expected to decrease the mechanical inertia in the system which helps to stabilise the electrical grid frequency. The inertia is expected to decrease by a factor of two within 20 years and other solutions for frequency stability must be implemented to assure a stable power system. At Uppsala University several projects are investigating how grid-connected energy storages can increase the frequency stability with a high penetration of intermittent renewable energy sources. In this thesis, a linear synthetic inertia control algorithm is implemented on a national Instruments FPGA for controlling the power flow from a supercapacitor energy storage via a two-level three-phase inverter. The control strategy is evaluated both via simulations and experimental tests in a nano grid. The results of the simulations and experimental work are presented and show that it is possible to calculate the frequency derivative in real time to reduce the frequency ROCOF and nadir. The results of the increased frequency stability are presented.
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| 3. |
- Fregelius, Martin
(författare)
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An experimental approach to energy storage based synthetic inertia and fast frequency regulation for grid balancing
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing interest in renewable energy has significantly increased in the last decades. The increasing amount of variable renewable energy resources in the grid, which are connected via power electronics, reduces the total mechanical system inertia. Frequency-regulating resources such as hydropower will become more important in balancing variable renewable energy resources, setting higher requirements on stability and performance to maintain a stable electrical grid. This thesis concerns the decreased mechanical inertia from non-directly electrically coupled generation units. The thesis starts with a description of the grid system inertia situation today and presents two methods for estimating the grid frequency derivative used to provide synthetic inertia and one method used to enhance the mechanical inertia response of a synchronous generator. The synthetic inertia and enhanced inertia methods are tested in a small-scale experimental setup and compared with results from tests in the Nordic grid. A full-scale hybrid energy storage system was designed and built using a split frequency method as a power controller. The results show that a power-frequency derivative controller-based synthetic inertia method achieved an improved grid frequency quality during regular operation in the nano-grid experimental setup. The results are evaluated both via simulations and experimental tests. The results from the hybrid energy storage solution showed the possibility of increasing frequency quality by using a slow run of the river hydroelectric power plants and a battery energy storage system for frequency containment reserve.
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| 4. |
- Fregelius, Martin, et al.
(författare)
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Enhanced Inertia using amplified power response from synchronous machines compared with frequency derivative-based inertia
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Tidskriftsartikel (refereegranskat)abstract
- Two approaches for delivery of inertia-like grid services are described and compared. Voltages and currents are measured and logged from two synchronous generators during large grid disturbances. The data is used in Matlab Simulinkfor comparison and evaluation of control strategies. A novel enhanced inertia control strategy is proposed and compared with two synthetic inertia controllers utilizing frequency derivative estimators, a frequency locked loop and a Savitzgy Golay finite impulse response filter. Both inertia delivery approaches naturally rely on that the properties of the surrounding grid are such that the frequency variations due to power imbalances are large compared to other variations. Furthermore, the synthetic inertia controllers face the usual software signal filtering problems if the signal-to-noise ratio is low. The other approach, to enhance a physical Inertialresponse from a real machine, is a way to avoid such filtering challenges. However, the physical properties of the machine, mainly rotor angle oscillations, might call for software filtering anyway, adding phase shift to the otherwise low latency shown to be achievable
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| 5. |
- Fregelius, Martin, et al.
(författare)
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Full scale hybrid hydroelectric lithium-ion energy storage for supplying frequency containment reserve
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Tidskriftsartikel (refereegranskat)abstract
- A full scale hybrid energy storage system consistingof two 14.5 MVA bulb hydro turbines and a 1.1 MWh lithium-ion battery energy storage system was designed, built andcommissioned in the North of Sweden. A hybrid power controllerwas designed and tested were grid frequency disturbances weresimulated in the programmable logic controllers and voltagesand currents were logged from each generating unit. Responsetimes and rise times were measured for each generating unit. Itwas shown that the battery energy storage has the capability ofchanging output power fast to meet new grid services require-ments such as fast frequency response. The hybrid energy storagecontroller was shown to be able to divide the frequency of thegrid frequency disturbances into slow and fast changes for eachgenerating unit and letting the battery energy storage handle fastpower responses and the bulb hydro turbines the slow and longterm power responses to fulfil frequency control requireme
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| 6. |
- Fregelius, Martin, et al.
(författare)
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Hardware Implementation of A Synthetic Inertia System for Grid Stability
- 2019
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Ingår i: 2019 8th International Conference on Renewable Energy Research and Applications (ICRERA). - 9781728135878 - 9781728135861 - 9781728135885 ; , s. 186-190
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Konferensbidrag (refereegranskat)abstract
- The frequency in the electrical grid is, on the short time-scale, stabilized by the total rotational mass given predominantly by synchronously connected devices. These devices include the generators themselves and, on slightly longer timescales, the control system acting on turbine governors. As the inverter-connected technologies increase their share of total power, the total inertia in the grid is significantly reduced. One way to stabilize the frequency and reduce low frequency oscillations is to add synthetic inertia provided by a small energy, high power, storage devices combined with a fast control system. This paper describes a possible hardware topology for linear synthetic inertia. It uses an inverter coupled to a local energy storage unit comprised of supercapacitors. The paper presents the implementation and some selected experimental results. The system response is fast enough on a small test grid to act as inertia.
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| 7. |
- Fregelius, Martin, et al.
(författare)
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Performance Evaluation of a Supercapacitor Based Synthetic Inertia System Using Frequency Locked Loop and Real-Time Frequency Derivative Estimation
- 2023
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Ingår i: International Journal of Electrical Power & Energy Systems. - : Elsevier. - 0142-0615 .- 1879-3517. ; 144
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Tidskriftsartikel (refereegranskat)abstract
- The installation of intermittent renewable energy sources (RESs) are now fast increasing, reducing fossil fuel use. Due to the fact that RESs are typically grid-connected to the power-system via grid following fast-response voltage source converters, the amount of mechanical inertia synchronised in the power system is decreasing. As a result, the power system will be more sensitive to load and generation variations, causing larger frequency fluctuations which, in turn, could result in undesirable load-shedding, or large-scale blackouts. This paper presents a performance evaluation of a concept of emulating virtual inertia via power-electronics and a energy storage unit in terms of a supercapacitor connected to the DC-bus. Simulation and experimental results are presented to validate the proposed combination of frequency estimation and frequency derivative estimation. The paper shows the feasibility of using virtual inertia and how it could be implemented.
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| 8. |
- Lundin, Urban, 1972-, et al.
(författare)
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Start of a synchronous motor using rotor field polarity inversion and rotor back-emf sensing
- 2020
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Ingår i: 2020 International Conference on Electrical Machines (ICEM). ; , s. 338-344
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Konferensbidrag (refereegranskat)abstract
- Synchronous motors are hard to line start due to torque pulsations at zero rotor speed and low starting torque when started using induced current in a damper squirrel cage. By inverting the rotor pole polarity at appropriate times it is possible to, in principle, achieve uniform torque, albeit pulsating with twice the line frequency at zero initial rotor speed. This has been demonstrated in an earlier work. In this paper we demonstrate that high torque starting using the back-emf in the field winding as triggering signal for the rotor polarity inversion is possible. We further discuss the origin of the rotational energy and active and reactive power pulsations. Finally, we show that it is possible to operate a synchronous motors at continuous asynchronous speed by inverting the polarity of the rotor current and adjusting the field current accordingly, although down rated.
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| 9. |
- Parwal, Arvind, et al.
(författare)
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A Comparative Analysis of Linear and Nonlinear Control of Wave Energy Converter for a Force Control Application
- 2024
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Ingår i: International Marine Energy Journal. - Southampton, UK : International Marine Energy Journal. - 2631-5548.
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Tidskriftsartikel (refereegranskat)abstract
- The aim of wave energy converters (WECs) is to harvest the energy from the ocean waves and convert into electricity. Optimizing the generator output is a vital point of research. A WEC behaves as a nonlinear system in real ocean waves and a control that approximates the behaviour of the system is required. In order to predict the behaviour of WEC, a controller is implemented with an aim to track the referenced trajectory for a force control application of the WEC. A neural model is implemented for the system identification and control of the nonlinear process with a neural nonlinear autoregressive moving average exogenous (NARMAX) model. The neural model updates the weights to reduce the error by using the Levenberg-Marquardt back-propagation algorithm for a single-input-single-output (SISO) nonlinear system. The performance of the system under the proposed scheme is compared to the same system under a PI-controller scheme, where the PI gains have been tuned accordingly, to verify the control capacity of the proposed controller. The results show a good tracking of dq (direct-quadrature) axes currents by regulating the stator currents, and hence a force control is achieved at different positions of the translator. The dynamic performance of the control is verified in a time domain analysis for the displacement of the translator.
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| 10. |
- Parwal, Arvind, et al.
(författare)
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A comparative analysis of linear and nonlinear control of wave energy converter for a force control application
- 2019
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Ingår i: International Marine Energy Journal. - : European Wave and Tidal Energy Conference. - 2631-5548. ; 2:1, s. 39-50
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Tidskriftsartikel (refereegranskat)abstract
- The aim of wave energy converters (WECs) is to harvest the energy from the ocean waves and convert into electricity. Optimizing the generator output is a vital point of research. A WEC behaves as a nonlinear system in real ocean waves and a control that approximates the behaviour of the system is required. In order to predict the behaviour of WEC, a controller is implemented with an aim to track the referenced trajectory for a force control application of the WEC. A neural model is implemented for the system identification and control of the nonlinear process with a neural nonlinear autoregressive moving average exogenous (NARMAX) model. The neural model updates the weights to reduce the error by using the Levenberg-Marquardt back-propagation algorithm for a single-input-single-output (SISO) nonlinear system. The performance of the system under the proposed scheme is compared to the same system under a PI-controller scheme, where the PI gains have been tuned accordingly, to verify the control capacity of the proposed controller. The results show a good tracking of dq (direct-quadrature) axes currents by regulating the stator currents, and hence a force control is achieved at different positions of the translator. The dynamic performance of the control is verified in a time domain analysis for the displacement of the translator.
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