| 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-
(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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| 3. |
- 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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