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An experimental approach to energy storage based synthetic inertia and fast frequency regulation for grid balancing
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. (Hydropower)ORCID iD: 0000-0003-0466-4392
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2022. , p. 77
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2202
Keywords [en]
Renewable energy, Synthetic inertia, Enhanced inertia, Energy storage system, Hybrid energy storage system
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-486779ISBN: 978-91-513-1631-4 (print)OAI: oai:DiVA.org:uu-486779DiVA, id: diva2:1704057
Public defence
2022-12-06, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2022-11-14 Created: 2022-10-17 Last updated: 2022-11-14
List of papers
1. Hardware Implementation of A Synthetic Inertia System for Grid Stability
Open this publication in new window or tab >>Hardware Implementation of A Synthetic Inertia System for Grid Stability
2019 (English)In: 2019 8th International Conference on Renewable Energy Research and Applications (ICRERA), 2019, p. 186-190Conference paper, Published paper (Refereed)
Abstract [en]

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.

Series
International Conference on Renewable Energy Research and Applications (ICRERA), ISSN 2377-6897, E-ISSN 2572-6013
Keywords
energy storage, invertors, power generation control, power grids, power system stability, supercapacitors, hardware implementation, synthetic inertia system, grid stability, electrical grid, synchronously connected devices, slightly longer timescales, turbine governors, inverter-connected technologies, low frequency oscillations, storage devices, fast control system, hardware topology, linear synthetic inertia, local energy storage unit, test grid, supercapacitors, Frequency control, Inverters, Energy storage, Damping, Hardware, Renewable energy sources, Frequency synchronization, Synthetic inertia, Three phase inverter, Super capacitors, Field programmable gate array, distributed generation, Grid tied energy storage
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Energy Systems
Identifiers
urn:nbn:se:uu:diva-430746 (URN)10.1109/ICRERA47325.2019.8997097 (DOI)000761668400023 ()978-1-7281-3587-8 (ISBN)978-1-7281-3586-1 (ISBN)978-1-7281-3588-5 (ISBN)
Conference
8th International Conference on Renewable Energy Research and Applications, 3-6 Nov, 2019, Brasov, Romania
Funder
Swedish Energy Agency, 44346-1
Available from: 2021-01-12 Created: 2021-01-12 Last updated: 2022-10-17Bibliographically approved
2. Magnetic thrust bearing for a 10 MW hydropower generator with a Kaplan turbine
Open this publication in new window or tab >>Magnetic thrust bearing for a 10 MW hydropower generator with a Kaplan turbine
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2018 (English)Conference paper, Published paper (Refereed)
National Category
Energy Systems
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-363975 (URN)
Conference
Hydro 2018, Oct 15 - Oct 17, Gdansk, Poland 2018,
Available from: 2018-10-22 Created: 2018-10-22 Last updated: 2022-10-17Bibliographically approved
3. Enhanced Inertia using amplified power response from synchronous machines compared with frequency derivative-based inertia
Open this publication in new window or tab >>Enhanced Inertia using amplified power response from synchronous machines compared with frequency derivative-based inertia
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

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

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-486778 (URN)
Available from: 2022-10-17 Created: 2022-10-17 Last updated: 2022-10-17
4. Performance Evaluation of a Supercapacitor Based Synthetic Inertia System Using Frequency Locked Loop and Real-Time Frequency Derivative Estimation
Open this publication in new window or tab >>Performance Evaluation of a Supercapacitor Based Synthetic Inertia System Using Frequency Locked Loop and Real-Time Frequency Derivative Estimation
2023 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 144, article id 108554Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2023
National Category
Signal Processing Control Engineering
Identifiers
urn:nbn:se:uu:diva-437901 (URN)10.1016/j.ijepes.2022.108554 (DOI)000860635900003 ()
Available from: 2021-03-17 Created: 2021-03-17 Last updated: 2022-10-17Bibliographically approved
5. Full scale hybrid hydroelectric lithium-ion energy storage for supplying frequency containment reserve
Open this publication in new window or tab >>Full scale hybrid hydroelectric lithium-ion energy storage for supplying frequency containment reserve
(English)In: ISSN 1687-5257Article in journal (Refereed) Submitted
Abstract [en]

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

Keywords
Hybrid energy storage, Primary frequency con- trol, Kaplan turbine, BESS, HESS
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering with specialization in Signal Processing; Electrical Engineering with specialization in Automatic Control
Identifiers
urn:nbn:se:uu:diva-486776 (URN)
Available from: 2022-10-17 Created: 2022-10-17 Last updated: 2022-10-17
6. Start of a synchronous motor using rotor field polarity inversion and rotor back-emf sensing
Open this publication in new window or tab >>Start of a synchronous motor using rotor field polarity inversion and rotor back-emf sensing
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2020 (English)In: 2020 International Conference on Electrical Machines (ICEM), 2020, Vol. 1, p. 338-344Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

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.

Keywords
Rotors;Windings;Torque;Stator windings;Reluctance motors;Shock absorbers;Permanent magnet motors;Synchronous machines;Finite element analysis;Torque control;Field current control;Motor start
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-430759 (URN)10.1109/ICEM49940.2020.9270780 (DOI)000635705300051 ()
Conference
International Conference on Electrical Machines, ICEM 2020, Online, Aug 23-26, 2020
Available from: 2021-01-12 Created: 2021-01-12 Last updated: 2022-10-17Bibliographically approved
7. A Comparative Analysis of Linear and Nonlinear Control of Wave Energy Converter for a Force Control Application
Open this publication in new window or tab >>A Comparative Analysis of Linear and Nonlinear Control of Wave Energy Converter for a Force Control Application
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(English)In: International Marine Energy Journal, ISSN 2631-5548Article in journal (Refereed) Submitted
Abstract [en]

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.

Place, publisher, year, edition, pages
Southampton, UK: International Marine Energy Journal
Keywords
current control, force control, neural NARMAX, permanent magnet linear generator (PMLG), wave energy converter
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering with specialization in Automatic Control
Identifiers
urn:nbn:se:uu:diva-390099 (URN)
Funder
Swedish Research Council, 2015-03126StandUp
Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2022-10-17
8. Virtual Synchronous Generator Based Current Synchronous Detection Scheme for a Virtual Inertia Emulation in SmartGrids
Open this publication in new window or tab >>Virtual Synchronous Generator Based Current Synchronous Detection Scheme for a Virtual Inertia Emulation in SmartGrids
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2019 (English)In: Energy and Power Engineering, ISSN 1949-243X, E-ISSN 1947-3818, Vol. 11, no 3, p. 99-131Article in journal (Refereed) Published
Abstract [en]

Renewable energy sources, such as photovoltaicwind turbines, and wave power converters, use power converters to connect to the grid which causes a loss in rotational inertia. The attempt to meet the increasing energy demand means that the interest for the integration of renewable energy sources in the existing power system is growing, but such integration poses challenges to the operating stability. Power converters play a major role in the evolution of power system towards SmartGrids, by regulating as virtual synchronous ge-nerators. The concept of virtual synchronous generators requires an energy storage system with power converters to emulate virtual inertia similar to the dynamics of traditional synchronous generators. In this paper, a dynamic droop control for the estimation of fundamental reference sources is imple-mented in the control loop of the converter, including active and reactive power components acting as a mechanical input to the virtual synchronous generator and the virtual excitation controller. An inertia coefficient and a droop coefficient are implemented in the control loop. The proposed con-troller uses a current synchronous detection scheme to emulate a virtual iner-tia from the virtual synchronous generators. In this study, a wave energy converter as the power source is used and a power management of virtual synchronous generators to control the frequency deviation and the terminal voltage is implemented. The dynamic control scheme based on a current synchronous detection scheme is presented in detail with a power manage-ment control. Finally, we carried out numerical simulations and verified the scheme through the experimental results in a microgrid structure.

Place, publisher, year, edition, pages
Scientific Research Publishing, 2019
Keywords
Dynamic Droop Control, Energy Storage, Virtual Inertia, Virtual Synchronous Generator
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-379215 (URN)10.4236/epe.2019.113007 (DOI)
Funder
Swedish Research Council, 2015-03126StandUp
Available from: 2019-03-13 Created: 2019-03-13 Last updated: 2023-10-02Bibliographically approved
9. Grid Integration and a Power Quality Assessment of a Wave Energy Park
Open this publication in new window or tab >>Grid Integration and a Power Quality Assessment of a Wave Energy Park
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2019 (English)In: IET Smart Grid, ISSN 2515-2947, p. 1-14Article in journal (Refereed) Published
Abstract [en]

This study presents a step toward the grid connection of a wave-energy park through an electric power conversion system (EPCS) developed and installed for the wave-energy harvesting in Lysekil, Sweden. The EPCS comprises a rectifier, a DC bus, and an inverter followed by a harmonic filter (HF). The higher- and lower-order harmonics injected by the inverter in a power quality context are investigated. The lower-order voltage harmonics partially distort the voltage-source inverter output grid current. A phase-locked loop-based (PLL) grid-phase tracking is used to attenuate the lower-order harmonics by reflecting the grid harmonics in the inverter output. An expression for the grid-current harmonics as a function of the grid-voltage harmonics has been derived and implemented. A mathematical model is derived to obtain a transfer function for the PLL, and finally, proportional–integral gains are tuned for stable system operation. An HF for mitigating the higher-order harmonics has been implemented. The total harmonic distortion is evaluated experimentally, and the results fulfil the grid-code requirements at various frequencies and harmonic orders.

Place, publisher, year, edition, pages
UK: , 2019
Keywords
WAVE ENERGY SMART GRID HARMONIC DISTORTION
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-389779 (URN)10.1049/iet-stg.2019.0009 (DOI)
Funder
Swedish Research Council, 2015-03126
Available from: 2019-07-25 Created: 2019-07-25 Last updated: 2023-02-23Bibliographically approved
10. Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System
Open this publication in new window or tab >>Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System
Show others...
2018 (English)In: 2018 5th International Conference on Electric Power and Energy Conversion Systems (EPECS), 2018Conference paper, Published paper (Refereed)
Abstract [en]

This paper provides an overview of electric power conversion system installed at the Lysekil research site, located at the west coast of Sweden. The electric power conversion system consists of rectifiers, rectifying the power from the wave energy converters, a DC-link and a grid-tied inverter. The paper focuses on the performance of the inverter and the filter and presents experimental results obtained during the grid integration.

Series
International Conference on Electric Power and Energy Conversion Systems, ISSN 2325-2677
Keywords
wave energy converter (WEC), wave energy havesting, grid integration, LCL filter response
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-373349 (URN)10.1109/EPECS.2018.8443488 (DOI)000450072100010 ()978-1-5386-6457-5 (ISBN)
Conference
5th International Conference on Electric Power and Energy Conversion Systems (EPECS), Kitakyushu, April 23-25, 2018
Funder
Swedish Research Council, 2015-03126Swedish Energy AgencyStandUpÅForsk (Ångpanneföreningen's Foundation for Research and Development)
Available from: 2019-01-15 Created: 2019-01-15 Last updated: 2022-10-17Bibliographically approved
11. Energy management for a grid-connected wave energy park through a hybrid energy storage system
Open this publication in new window or tab >>Energy management for a grid-connected wave energy park through a hybrid energy storage system
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2018 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 231, p. 399-411Article in journal (Refereed) Published
Abstract [en]

The concern for climate change and energy consumption has increased the demand for renewable energy production considerably. Marine energy sources attract attention because of their high energy density. Wave energy is an attractive renewable energy source with large potential. Due to the nature of the ocean waves, a linear wave energy converter generates intermittent power. It is therefore crucial to regularize the power before connecting to the grid. Energy storage systems present effective ways to minimize the power fluctuations and deliver a steady power to the grid. In this paper, we present an energy management control system with a dynamic rate limiter. The method is applied to control a hybrid energy storage system, combining battery and supercapacitor, with a fully active topology controlled by the power converters. The results show that the method is able to control the charging and discharging states of the battery and the supercapacitor, and minimize the power fluctuation to the grid. The algorithm ensures low losses by shifting the required power and the stored power smoothly over the energy storage system.

Keywords
Wave energy converter, Hybrid energy storage system, Energy management control system, Dynamic rate limiter, State of charge
National Category
Energy Systems
Identifiers
urn:nbn:se:uu:diva-361207 (URN)10.1016/j.apenergy.2018.09.146 (DOI)000452345400030 ()
Funder
StandUpSwedish Research Council, 2015-03126Carl Tryggers foundation
Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2022-10-17Bibliographically approved

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