Thesis defense of Unai Galfarsoro Anduaga
Thesis defense of Unai Galfarsoro Anduaga
Thesis defense of Unai Galfarsoro Anduaga
Title of the thesis: "Fault diagnosis in permanent magnet synchronous motors for elevator installations". Obtained the SOBRESALIENTE CUM LAUDE qualification.
- Title of the thesis: "Fault diagnosis in permanent magnet synchronous motors for elevator installations".
- Court:
- President: Jose Alfonso Antonino Daviu (Universitat Politècnica de València)
- Vocal: Daniel Moríñigo Sotelo (Universidad de Valladolid)
- Vocal: Leire Irazu Echeverria (Orona Elevation Innovation Center)
- Vocal: Jon Garcia Barruetabeña (Universidad de Deusto)
- Secretary: Gaizka Almandoz Larralde (Mondragon Unibertsitatea)
Abstract
The design, manufacturing tolerances, assembly problems and other defects have a direct influence on the comfort and reliability of Permanent Magnet Synchronous Motors (PMSMs), in the elevator sector where this thesis is focused. Therefore, the aim of this thesis is to develop a procedure to diagnose the most frequent mechanical (namely, cogging and eccentricity) and magnetisation faults faced in PMSMs, based on experimentally measured signals, to keep those imperfections under reasonable values in the end of the assembly line.
Considering the previously published researches on the faults of interest, the main conclusion is that several researches about eccentricity and magnetisation faults based on spectral analysis give confusing results and this needs to be studied. Local demagnetisation, where a single magnet is removed, is often studied, but further analysis of other more general and realistic magnetisation fault types is needed. Besides, the influence of tolerances is frequently ignored.
Regarding cogging torque, it is shown that its identification through vibration signals measured on the stator is not possible, but using the spectra of the rotational speed signals measured at low speeds the identification is successfully done.
Concerning eccentricities and tolerances, analytical and finite element calculations are used to gain knowledge on the effect of static and dynamic eccentricities, rotor and stator tolerances, and their combinations. Time signals and spectra of several signals (unbalanced magnetic pull, cogging torque and magnetic flux in the air gap) are considered in this analysis. Next, experimental measurements are carried out to verify the analytical and simulation calculations, obtaining the same trends. A novel test bench was designed and manufactured to generate any value of static and/or dynamic eccentricity in a continuous, fast and straightforward manner. Particularly, the mechanism designed to generate dynamic eccentricity is specially genuine and effective. By the experimental test bench, more types of signals (currents, voltages, vibrations, rotational speeds and magnetic fluxes through the teeth by means of search coils) are analysed. Based on all these results, an overall approach to assess static and/or dynamic eccentricity faults, together with rotor and/or stator tolerance faults, is established. For the machine analysed it is confirmed that diagnosing rotor tolerance faults is easier than diagnosing eccentricities. The strengths and weaknesses of each measured signal type and the analysis method to detect each kind of fault is explained. The importance of the configuration used to perform the Fast Fourier Transform (FFT) and its limitations are confirmed. It is verified that spectral analysis of time signals is not 100% reliable for diagnosis of electric machines when closely spaced harmonics need to be compared. Therefore, the order tracking technique is implemented to improve the results and avoid the effect of speed fluctuations. Alternatively, the use of statistical parameters is proposed and its reliability confirmed.
Regarding magnetisation faults, several cases are analysed: average and dispersion of the magnetisation level, and uniform or non-uniform magnetisation of the magnets. Indicators are derived to discern each of them. Particularly, the phase voltage is shown valuable to determine these faults.
Despite the fact that the frequency orders reported in bibliography as indicators of eccentricity and magnet magnetisation faults usually overlook tolerances, this research confirms that there is a clear coupling between eccentricities, tolerances and magnetisation faults, so tolerances cannot be ignored. In fact, those tolerances can be, to a certain extent, magnetisation faults or may induce eccentricities of the magnetic circuit.