| 11. |
|
|
| 12. |
|
|
| 13. |
- Ehya, Hossein, et al.
(author)
-
Time Domain Signature Analysis of Synchronous Generator under Broken Damper Bar Fault
- 2019
-
In: 45Th Annual Conference Of The Ieee Industrial Electronics Society (IECON 2019). - : IEEE. - 9781728148786 ; , s. 1423-1428
-
Conference paper (peer-reviewed)abstract
- Fault detection of electrical machines can avoid unplanned outage of the electricity generation at a power plant. Research related to a different type of faults in the synchronous generator, the broken damper bar (BDB) fault attracts less attention due to the low statistical population. However, a comprehensive condition monitoring system requires a method to diagnose this few in number faults also. Detection of BDB fault is difficult since damper bars are active only during a transient period, which could be start-up intervals or as a reaction to power system dynamics. In this paper, the BDB fault is detected during the machine start-up. The Radius of Gyration (RG) was introduced using a time series data mining (TSDM) approach that was applied to induced electromotive force of the rotor field winding due to BDB fault. Location and number of BDBs effect on the nominated feature are also studied.
|
|
| 14. |
- Evestedt, Fredrik, et al.
(author)
-
Controlling airgap magnetic flux density harmonics in synchronous machines using field current injection
- 2021
-
In: Electrical engineering (Berlin. Print). - : Springer. - 0948-7921 .- 1432-0487. ; 103, s. 195-203
-
Journal article (peer-reviewed)abstract
- In this paper, a method to control the harmonic content of the magnetic flux density in the airgap of a synchronous machine is presented. Voltage harmonics in one phase as well as the exciting magnetic forces can be affected. Switched power electronics were used to provide the field current to a synchronous machine, the control added specific current harmonics to the DC field current in order to minimize either voltage harmonics or magnetic forces. The method is verified and compared with simulations and experiments on an existing electrical machine.
|
|
| 15. |
- Evestedt, Fredrik, et al.
(author)
-
Mitigation of Unbalanced Magnetic Pull in Synchronous Machines With Rotating Exciters
- 2021
-
In: IEEE transactions on energy conversion. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8969 .- 1558-0059. ; 36:2, s. 812-819
-
Journal article (peer-reviewed)abstract
- A magnetization system with active compensation of unbalanced magnetic pull for synchronous machines with rotating exciters is demonstrated. The system used switched power electronics and a digital control system to control the currents in four rotor pole groups, each consisting of 3 poles. It was mounted on the shaft of a synchronous machine, providing an interface between a permanent magnet outer-pole brushless exciter and the segmented field winding. Measurements of magnetic flux density on each pole face and current control made it possible to control the airgap magnetic flux density to balance the machine magnetically, thus removing flux density space harmonics in the airgap and also the unbalanced magnetic pull. The construction of the system is presented along with results from experiments and simulations. Tests were performed with the stator winding both in series and with two parallel circuits. Approximately 80% reduction of static forces and 60% reduction of dynamic forces between the stator and rotor were observed when the system was running.
|
|
| 16. |
- Felicetti, Roberto, 1972-
(author)
-
Voltage Transients in the Field Winding of Salient Pole Wound Synchronous Machines : Implications from fast switching power electronics
- 2021
-
Licentiate thesis (other academic/artistic)abstract
- Wound Field Synchronous Generators provide more than 95% of the electricity need worldwide. Their primacy in electricity production is due to ease of voltage regulation, performed by simply adjusting the direct current intensity in their rotor winding. Nevertheless, the rapid progress of power electronics devices enables new possibilities for alternating current add-ins in a more than a century long DC dominated technology. Damping the rotor oscillations with less energy loss than before, reducing the wear of the bearings by actively compensating for the mechanic unbalance of the rotating parts, speeding up the generator with no need for additional means, these are just few of the new applications which imply partial or total alternated current supplying of the rotor winding.This thesis explores what happens in a winding traditionally designed for the direct current supply when an alternated current is injected into it by an inverter. The research focuses on wound field salient pole synchronous machines and investigates the changes in the field winding parameters under AC conditions. Particular attention is dedicated to the potentially harmful voltage surges and voltage gradients triggered by voltage-edges with large slew rate. For this study a wide frequency band simplified electromagnetic model of the field winding has been carried out, experimentally determined and validated. Within the specific application of the fast field current control, the research provides some references for the design of the rotor magnetic circuit and of the field winding. Finally the coordination between the power electronics and the field winding properties is addressed, when the current control is done by means of a long cable or busbars, in order to prevent or reduce the ringing.
|
|
| 17. |
- Fregelius, Martin
(author)
-
An experimental approach to energy storage based synthetic inertia and fast frequency regulation for grid balancing
- 2022
-
Doctoral thesis (other academic/artistic)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.
|
|
| 18. |
- Fregelius, Martin, et al.
(author)
-
Enhanced Inertia using amplified power response from synchronous machines compared with frequency derivative-based inertia
-
Journal article (peer-reviewed)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
|
|
| 19. |
- Fregelius, Martin, et al.
(author)
-
Full scale hybrid hydroelectric lithium-ion energy storage for supplying frequency containment reserve
-
Journal article (peer-reviewed)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
|
|
| 20. |
- Fregelius, Martin, et al.
(author)
-
Hardware Implementation of A Synthetic Inertia System for Grid Stability
- 2019
-
In: 2019 8th International Conference on Renewable Energy Research and Applications (ICRERA). - 9781728135878 - 9781728135861 - 9781728135885 ; , s. 186-190
-
Conference paper (peer-reviewed)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.
|
|
