| 1. |
- Felicetti, Roberto, 1972-, et al.
(författare)
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A Synchronous Machine Transient Model Based upon an Algebraic Loop Accounting for Nonlinearity and Cross-Magnetization
- 2023
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Ingår i: International Journal of Rotating Machinery. - : Hindawi Publishing Corporation. - 1023-621X .- 1542-3034. ; 2023
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to carry out an alternative to the present transient models for field wound synchronous machines, which is able to take into account the nonlinearity of the magnetic materials as well as the cross-magnetization. After presenting the principal model structures according to the state variables, a model based on two lookup tables for the magnetizing flux linkages is introduced and built step by step. The resulting signal flowchart shows an algebraic loop within the model, where the main flux linkage rapidly converges to its instantaneous value by simple iteration. The proof of this convergence is given for both saturated and unsaturated machine. Even though the proposed model uses the total linkage flux as state variable, as many alternative models do, it does not require the inversion of the current to flux linkage function (i.e., of lookup tables). This can spare a heavy computational task, especially with very large lookup tables. In the proposed model, the computational effort in the worst case scenario is reduced to few iterations (<10). Finally, the nonlinear behavior of the model is verified in four different transient scenarios by comparing its outcomes with those of a linear model for the same test machine.
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| 2. |
- Felicetti, Roberto, 1972-, et al.
(författare)
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An alternative Run-Up Strategy for Salient Pole Wound Field Synchronous Machines
- 2024
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Ingår i: IEEE Open Journal of Industrial Applications. - : Institute of Electrical and Electronics Engineers (IEEE). - 2644-1241. ; 5, s. 15-28
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Tidskriftsartikel (refereegranskat)abstract
- Salient pole wound field synchronous motors find many industrial applications thanks to their favorable characteristics: reactive power regulation, stiff mechanical characteristic and overall outstanding efficiency. Nevertheless, their competitiveness towards the induction motors, especially for medium and small power sizes, depends crucially on their capability to be asynchronously started as well. Regrettably, the asynchronous run-up of a synchronous motor can be sometimes very problematic because of thermal issues, torsional vibrations and grid voltage disturbances. This paper presents an alternative method of starting salient pole wound field synchronous machines by activating the field winding in a special manner, which makes it possible to mitigate the three problems at once. The suggested method is validated through a 2D finite elements simulation and by starting a 60 kVA prototype generator. The requirements for the application of the proposed run-up strategy are critically discussed together with related pros and cons.
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| 3. |
- Felicetti, Roberto, 1972-, et al.
(författare)
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An experimentally determined field winding model with frequency-dependent parameters
- 2021
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Ingår i: IET Electric Power Applications. - : Institution of Engineering and Technology. - 1751-8660 .- 1751-8679. ; 15:6, s. 696-716
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Tidskriftsartikel (refereegranskat)abstract
- Herein, a set of experimental procedures is presented for determining the main electrical distributed parameters of the field winding in salient pole synchronous machines. It applies to the electrical characterisation of iron-core power inductors and transformer windings as well, in a range of frequency useful for power electronics applications. A first estimation of the parameters is obtained by forcing the winding into resonance with capacitors of known capacitance. The obtained estimates are then refined through an iterative process, which makes use of the winding natural frequencies. The presented procedures are applied step-by-step to the field winding of a 60-kVA salient pole synchronous generator with solid poles. The distributed parameters model, featured using the outlined procedures, accurately reproduces the winding voltage distribution in a large range of frequency. Finally, it is explored how the interaction between armature and rotor influences the field winding parameters, pointing to the differences of measuring them with the rotor inside or outside the machine bore.
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| 4. |
- Felicetti, Roberto, 1972-, et al.
(författare)
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Experimentally validated model of a fast switched salient pole rotor winding
- 2019
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Ingår i: 2019 IEEE Workshop on Electrical Machines Design, Control and Diagnosis (WEMDCD). - : IEEE. - 9781538681077 ; , s. 150-156
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Konferensbidrag (refereegranskat)abstract
- The article proposes a model of a salient pole synchronous machine field winding based on a single transmission line model. An experimental method to derive the parameters is also presented and validated. Finally, the measured voltage distribution in the winding is compared to the model voltage distribution and the results match, demonstrating the model capabilities. The model describes the intrinsic resonance phenomena and accurately determines the voltage amplification factor.
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| 5. |
- Felicetti, Roberto, 1972-
(författare)
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Run-Up Transient Analysis for Salient Pole Wound Field Synchronous Motors : Field winding and power electronics implications for a smoother and cooler asynchronous start
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Salient Pole Wound Field Synchronous Machines have better efficiency at full load than asynchronous machines of the same capability. Moreover, where asynchronous machines need inherently to draw a magnetizing current from the grid, Salient Pole Wound Field Synchronous Machines can work efficiently at unity power factor. When needed, their power factor can even turn leading in order to provide reactive power to the grid. It is well known, that the asynchronous machines performances deteriorate very quickly in presence of voltage drops, while the Wound Field Synchronous Machines prove to be capable of riding through voltage sags without stalling of falling out of step. Besides, for short-time overload, machines with a field winding can provide a pull-out torque even three times larger than the nominal one. Finally, when working as generators, Wound Field Synchronous Machines can perform a black starting where asynchronous machines cannot. Why are then asynchronous machines so successful in comparison to synchronous ones when used as motors? Robustness, low-maintenance, simplicity are the key-features that translate immediately in low fixed costs for asynchronous motors. But, even though lower variable costs for a synchronous motor should envisage a break-even starting form a given power rate on, there are still some technical issues to be overcome. A synchronous motor must be first sped-up to the synchronism for it to deliver mechanical power. And when it is directly on-line started like an asynchronous motor, it draws large reactive currents due to its large airgap. Therefore, additional means are needed for avoiding the motor overheating and voltage disturbances on the grid, such as autotransformers, transformers and reactors. Besides, in Salient Pole Wound Field Synchronous Machines. due to the inherent magnetic and electric rotor asymmetry, the starting asynchronous torque presents a nasty large pseudo-periodic ripple. In this work, a novel starting technique is presented, which mitigates all problems related to the run-up by means of a special rotor winding and excitation-system arrangement. The suggested start strategy is validated by an experimental test carried out on a build prototype and through a field-to-circuit coupled transient simulation. Since AC currents are essentially injected into the rotor winding during the machine start, in its first part the thesis explores what does happen in a winding traditionally designed for the direct current supply when an alternated current is injected into it by a power electronics device. To that end, changes in the main field winding parameters are firstly investigated, which take place under AC-supply. The obtained results make it possible to build a wide-band frequency electromagnetic model for the field winding. The model is useful for studying the potentially harmful voltage surges and voltage gradients triggered by fast rising/falling voltage-edges. Finally, within the specific application of the field current control and with the aim to prevent large voltage surges, the research provides some hints for the design of the field winding and for the coordination of the power electronics and the field winding properties.
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| 6. |
- Felicetti, Roberto, 1972-, et al.
(författare)
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Salient pole electrical machine
- 2022
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Patent (populärvet., debatt m.m.)abstract
- An electrical machine (1) comprises a stator (20) having armature windings (24), a rotor (10) having salient poles (12) and being rotably arranged with respect to the stator (20), and a rotor excitation system (30). The rotor excitation system (30) has a rotor winding arrangement (14), a rotor power supply (34) for exciting the salient poles (12), and a rotor driving unit (32) configured to control currents provided to the rotor winding arrangement (14). In a first operation mode, the rotor excitation system (30) is sconfigured for providing a rotating magnetic field by supplying alternating currents to the rotor winding arrangement (14), while the armature windings (24) being short-circuited or closed on external resistors. A method for operating an electrical machine is also disclosed.
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| 7. |
- Felicetti, Roberto, 1972-, et al.
(författare)
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The influence of eddy currents on the excitation winding impedance of solid and laminated salient pole synchronous machines
- 2020
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Ingår i: Electrical engineering (Berlin. Print). - : Springer Science and Business Media LLC. - 0948-7921 .- 1432-0487. ; 102:4, s. 2553-2566
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates the establishment of steady-state eddy currents in solid and laminated salient poles and rotor rim of synchronous machines due to a periodic excitation voltage. It shows that the presence of eddy currents in the rotor magnetic circuit has the double effect of increasing the excitation winding AC-resistance and decreasing its magnetizing AC-inductance. According to that a simple analytical model is presented in here which allows a rapid rough estimation of the excitation winding AC-resistance when little information is available about the machine geometry and its electric/magnetic materials properties. The model is then verified by reproducing in frequency the excitation winding AC-resistance and the related power loss measured in two synchronous generators. Finally, the limits of reliability and applicability of the model are discussed. The model has implications for periodic field winding current control and voltage regulation in synchronous machines.
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| 8. |
- Larsson, Bengt, et al.
(författare)
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Molecular oxygen in the rho Ophiuchi cloud
- 2007
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 466:3, s. 5-
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Tidskriftsartikel (refereegranskat)abstract
- Context: Molecular oxygen, O2, has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission.Aims: The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. Methods: The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core ρ Oph A was observed with Odin for 34 days during several observing runs.Results: We detect a spectral line at v_LSR =+3.5 km s-1 with Δ v_FWHM=1.5 km s-1, parameters which are also common to other species associated with ρ Oph A. This feature is identified as the O2 (NJ = 11 - 1_0) transition at 118 750.343 MHz.Conclusions: The abundance of molecular oxygen, relative to H{2} , is 5 × 10-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Étude Spatiale (CNES). The Swedish Space Corporation has been the industrial prime contractor and also is operating the satellite. Appendix A is only available in electronic form at http://www.aanda.org
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| 9. |
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| 10. |
- Dahlborg, Elin, 1990-
(författare)
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Grid frequency stability from a hydropower perspective
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many AC grids suffer from decreased frequency stability due to less system inertia. This has increased the risk of large-scale blackouts. This thesis and its papers address the frequency stability problem from a hydropower perspective.Grid frequency stability assessments often require accurate system inertia estimates. One approach is to estimate the inertia of all individual power plants and sum up the results. We implemented three inertia estimation methods on a Kaplan unit and compared their results. The generator contributed with 92-96% of the unit inertia, which verified the results from previous studies. However, the three methods estimated slightly different values for the unit inertia, which raises the question of when to use which method.Hydropower often deliver frequency control, yet we found no studies which validate Kaplan turbine models for large grid frequency disturbances on strong grids. Therefore, we performed frequency control tests on a Kaplan unit, implemented three hydropower models, and compared the simulation results to the measurement data. The models overestimated the change in output power and energy delivered within the first few seconds after a large change in frequency. Thus, it is important to have sufficient stability margin when using these types of hydropower models to assess the grid frequency stability.The Nordic transmission system operators are updating their frequency control requirements. We used measurement data and simulation models to assess whether improved runner blade angle control could help a Kaplan unit fulfill the coming requirements. The results showed that improved runner control does not improve the performance sufficiently for requirements fulfillment. The requirements are based on an assumption on minimum system inertia and became easier to fulfill if they were implemented with more system inertia. Thus, more inertia could allow more participants to deliver frequency control in the Nordic grid.
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