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Določevanje izgub 6-faznega sinhronskega stroja z metodo sintetične obremenitve
ID Darovic, Anton (Author), ID Drobnič, Klemen (Mentor) More about this mentor... This link opens in a new window

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Abstract
Magistrsko delo obravnava novo merilno metodo, ki z uporabo sintetične (fantomske, lastne) obremenitve omogoča določitev izgub, izkoristka in temperaturnega porasta večfaznega električnega stroja za različne delovne točke. Običajni pristop, ki izhaja in je uveljavljen v klasični 3-fazni tehnologiji električnih strojev, namreč zahteva mehansko sklopitev merjenca z dovolj veliko aktivno zavoro (ang. back-to-back), kar merilni proces zaplete in podraži ter je posebej pri strojih večjih moči lahko celo neizvedljiv. V 1. poglavju sta na kratko predstavljeni tako klasična metoda naravne obremenitve (MNO) kot njej alternativna metoda sintetične obremenitve (MSO). MSO je omejena na večfazne stroje s sodim številom faznih navitij in je zmožna oceniti izgubno moč sinhronskega stroja s trajnimi magneti v širokem obratovalnem območju. Posebej primerna je aplikacija MSO v večfaznih strojih, katerih statorsko navitje sestavlja sodo število 3-faznih skupin navitij. MSO smo zato aplicirali na 6-faznem sinhronskem stroju z notranje nameščenimi trajnimi magneti z dvema 3-faznima skupinama navitij. Tekom merilnega preizkusa ena izmed 3-faznih skupin deluje v motorskem režimu, medtem ko druga skupina v generatorskemu režimu. Glavnina moči teče iz motorske v generatorsko skupino, medtem ko iz enosmernega tokokroga doteka zgolj moč, ki je potrebna za pokrivanje izgub pogona. Zaradi različnega obratovalnega režima posameznih skupin navitij se lahko med izvajanjem MSO pojavi izrazitejša radialna komponenta magnetne sile, kar povzroči magnetno neuravnoteženost (ang. unbalanced magnetic pull). Pojavi se dodatna radialna obremenitev ležajev, ki lahko tudi skrajša njihovo življenjsko dobo. Za ovrednotenje magnetne neuravnoteženosti je bilo razvito računalniško orodje, ki je podrobneje opisano v 2. poglavju. Na podlagi vhodnih podatkov geometrije stroja in razporeditve navitij se s pomočjo programskega paketa Matlab v programu za analizo s končnimi elementi FEMM samodejno izgradi simulacijski model. FEMM nato na podlagi želenega toka in zasuka rotorja izvede magnetostatično analizo, ki vrne tudi informacijo o rezultančni radialni komponenti magnetne sile. Simulacija je bila izvedena za omenjeni 6-fazni stroj in na podlagi rezultatov je bila sprejeta odločitev, da je vrednost radialne komponente magnetne sile tekom MSO v dopustnih mejah (3. poglavje). ii MSO kot alternativni pristop za izvajanje preizkusa obremenjevanja stroja je podrobneje predstavljena v 4. poglavju. Opisano je fizikalno ozadje delovanja MSO ter navedene njene prednosti in slabosti. Za 6-fazni sinhronski stroj, ki deluje v režimu sintetične obremenitve, je bilo na podlagi matematičnega modela 3-faznega stroja razvito nadomestno vezje, ki vključuje tudi modeliranje izgub v železu. Z nadomestnim vezjem enostavneje pojasnimo koncept kroženja moči med skupinama navitij, delujočima v motorskem in generatorskem režimu. Merilni sistem, praktična implementacija MSO ter način izvajanja meritev so opisani v 5. poglavju. Meritve izgubnih moči so bile izvedene s 3-faznim analizatorjem moči, vezanim v konfiguraciji Aronove vezave. Za meritev moči 3-faznega sistema sta bila tako potrebna zgolj 2 vatmetra, tretji pa je bil uporabljen za istočasno meritev moči enosmernega tokokroga, ki pokriva izgube celotnega pogona. Ker je bil na voljo zgolj en analizator moči, sta bili meritvi moči v generatorski in motorski skupini navitij izvedeni ločeno. Pri tem je bilo treba zagotoviti isto obratovalno točko, kar smo storili z identično nastavitvijo obratovalnih točk preko uporabniškega vmesnika. Sočasno smo izvajali meritev moči enosmernega tokokroga, temperature pretvornika in stroja. Te informacije so služile kot dodatna potrditev, da se nahajamo v istih obratovalnih točkah. Za termično stabilizacijo komponent pogona med meritvijo sta bila stroj in pretvornik priključena na kapljevinski hladilni sistem. Merilni rezultati za MSO so predstavljeni v 6. poglavju. Na podlagi časovnih potekov faznih tokov motorske in generatorske skupine navitij smo potrdili predvidevanja, da je iznos tokov motorske skupine navitij višji od generatorske skupine. Zaradi načina implementacije regulacijske zanke sintetične obremenitve to velja le, dokler se ne nahajamo v področju slabljenja polja. Tok motorske skupine navitij postane tedaj nižji kot je tok generatorske skupine navitij. Iz meritve moči obeh skupin 3-faznih navitij ter enosmernega tokokroga so bile določene izgube tako stroja kot pretvornika. Iz rezultatov je mogoče sklepati, da se izgubne moči stroja povečujejo tako z vrtilno hitrostjo kot s povečevanjem obremenitve. Izgube pretvornika se s povečevanjem vrtilne hitrosti do področja slabljenja polja ne spreminjajo in se spreminjajo zgolj s spreminjanjem obremenitve. Za dokončno potrditev ustreznosti MSO bi bilo treba rezultate neposredno primerjati z rezultati dobljenimi z MNO, kar v okviru magistrske naloge ni bilo mogoče realizirati. Kljub temu pa lahko na podlagi smiselnih merilnih rezultatov sklepamo, da je MSO dober ekvivalent MNO. Na izgube stroja vplivajo predvsem izgube v statorskem navitju, ki so odvisne od iii statorskega toka, izgube v železu, ki so pogojene z gostoto magnetnega polja ter vrtilno hitrostjo in izgube zaradi trenja v ležajih. Zaradi načina napajanja stroja v primeru MSO sklepamo, da je gostota magnetnega polja v železu nižja kot v primeru MNO, zato so izgube v železu v primeru MSO nekoliko podcenjene. Zaradi povečane radialne komponente magnetne sile, ki dodatno pritiska na ležaje pa predvidevamo, da so izgube zaradi trenja v primeru MSO višje kot za primer MNO.

Language:Slovenian
Keywords:sintetična obremenitev, magnetna neuravnoteženost, magnetostatična analiza, meritev izkoristka, sinhronski stroj s trajnimi magneti, večfazni stroj, 6-fazni stro
Work type:Master's thesis/paper
Organization:FE - Faculty of Electrical Engineering
Year:2023
PID:20.500.12556/RUL-149564 This link opens in a new window
COBISS.SI-ID:165408515 This link opens in a new window
Publication date in RUL:07.09.2023
Views:295
Downloads:90
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Secondary language

Language:English
Title:Determination of losses in 6-phase synchronous machine using synthetic loading method
Abstract:
The master's thesis deals with a new measurement method which allows the determination of losses, efficiency as well as heating of a multiphase electrical machine for different operating points using synthetic loading. The usual approach, originating from and established in classical 3-phase electrical machine technology, requires a mechanical coupling of the test machine with a sufficiently large brake in back-to-back configuration. That complicates and makes the measurement process more expensive and, especially for higher power machines, may even be infeasible. In Chapter 1, both the classical natural loading method (NLM) and its alternative the synthetic loading method (SLM) are briefly introduced. SLM is limited to multiphase machines with an even number of phase windings. It is able to estimate the losses of a permanent magnet synchronous machine over a wide operating range. The SLM is particularly suitable for multiphase machines whose stator winding consists of an even number of 3-phase winding sets. SLM was therefore applied to a 6-phase permanent magnet synchronous machine (PMSM), which has two 3-phase winding sets. During the measurement test, one of the 3-phase sets operates in motor mode while the other set operates in generator mode. Most of the power flows from the motor to the generator set through electromagnetic field, while only the power needed to cover the drive losses flows from the DC circuit. Due to the different operation mode of each set a substantial radial component of the magnetic force can occur in SLM, causing an unbalanced magnetic pull (UMP). Moreover, there is an additional radial load on the bearings, which can also shorten their service life. A computer tool has been developed to evaluate the UMP, which is described in more detail in Chapter 2. Starting with machine geometry and winding scheme a simulation model is created using the MATLAB and FEMM. FEMM then performs a magnetostatic analysis based on the desired current and rotor angle and provides information on the resulting UMP. The simulation was performed for the aforementioned 6-phase PMSM, and based on the results, it was decided that the UMP during the SLM is within acceptable limits (Chapter 3). SLM as an alternative approach for machine loading test is presented in more detail in Chapter 4. The physical background of SLM operation is described and its advantages as well as disadvantages are listed. An equivalent circuit for 3-phase PMSM has been adapted for v 6-phase PMSM, where iron loss has been included as well. This enables us to better explain power circulation between the sets operating in motor and generator mode. The measurement system, the practical implementation of the SLM, and the measurement procedure are described in Chapter 5. The loss measurements were performed using a 3-phase power analyzer in 2-wattmeter configuration. Thus, only two wattmeters were needed to measure the input power of the 3-phase winding set, whereas the third wattmeter was used to simultaneously measure the DC power covering the losses of the entire drive. Since only one power analyzer was available, the measurements were made separately for each winding set operating in generator and motor mode, respectively. It was necessary to ensure the same operating conditions for both cases, what we achieved by setting the operating points identically via the user interface. Additionally, we simultaneously measured the DC power as well as the converter and machine temperature. This information served as an additional confirmation that we were at the same operating points. To thermally stabilize the drive component during the measurements, the machine and the converter were connected to a common liquid cooling system. The measurement results for SLM are presented in Chapter 6. Based on phase current waveforms of the motor and generator set, we have confirmed the predictions that the magnitude of the currents of the motor winding set is higher than that of the generator set. Because of the way the synthetic load control loop is implemented, this is only true as long as machine operates in constant torque region. Namely, in field-weakening region the current of the motor winding set becomes lower than the current of the generator winding set. From the power measurement of 3-phase winding sets and the DC circuit, the losses of the machine and converter were determined. It can be seen from the results that the machine losses increase with speed and increasing load. The losses of the inverter do not change with increasing speed up to the field-weakening region and only change with increased load. To confirm the performance of the SLM, the results would have to be directly compared with those obtained with the NLM, which could not be realized within the scope of the master's thesis. Nevertheless, based on the measurements, we can conclude that SLM is a good alternative to NLM. The machine losses are mainly affected by the losses in the stator winding, which depend on the stator current, the iron losses, which are due to a large magnetic field density and the rotational speed, as well as the losses due to friction in the bearings. Because of vi the way the machine is driven in the SLM, we conclude that the magnetic field density in the iron is lower than during NLM, hence the SLM somewhat underestimates iron losses. Due to the increased radial components of the magnetic force resulting in additional bearing load, we assume that the frictional losses in the SLM are higher than in the NLM.

Keywords:synthetic loading, unbalanced magnetic pull, magnetostatic analysis, efficiency measurement, permanent magnet synchronous machine, multiphase machine, 6-phase machine

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