| 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)
-
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)
-
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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Simulation of Rapid Voltage Edge Related Voltage Surges in Highly Inductive Windings with Frequency Dependent Parameters
- 2023
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Ingår i: Progress in Electromagnetics Research B. - : The Electromagnetics Academy. - 1937-6472. ; 99, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- Many static and rotating electric energy converters make use of inductive coils as filters, reactive loads or exciters, where a sudden variation of the magnetizing current can produce severe overvoltage with potential subsequent insulation damage. In some applications the overvoltage is the result of a superposition of travelling voltage waves in a supplying line. Traditional tools for studying such phenomena are based on ordinary differential equations that can heavily handle variable parameters, especially if they change according to the rapidity of the observed overvoltage. In this paper the transient voltage distribution in the excitation winding of a salient pole synchronous generator is simulated by solving the problem entirely in the frequency domain, i.e., without any use of the traditional ordinary differential equations solvers. Thismakesit possible to tune the parameters of a simplified electric model to the frequency response of the studied winding. It is shown that for highly inductive windings a single transmission line model with frequency dependent parameters can reproduce voltage transients very accurately, in a broad interval of frequency, relevant for power electronics and electromagnetic compatibility applications. Furthermore, the paper presents the experimental setup which has been needed for generating the fast varying voltage edges.
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| 8. |
- 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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| 9. |
- Felicetti, Roberto, 1972-
(författare)
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Voltage Transients in the Field Winding of Salient Pole Wound Synchronous Machines : Implications from fast switching power electronics
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)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.
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