It is shown how distributed inverters can be applied to increase the fault tolerance of switched reluctance drives. The simulated and measured results show that it is possible to compensate for the torque loss and torque ripple in case of faults of single modules. If the controller detects the fault, a simple fault tolerant control strategy can be applied which, first, turns off additional modules to reduce the excitation of certain eigenfrequencies and, second, increases the currents in the remaining active modules. For the given machine, in case one complete phase fails, the available torque with fault tolerant control is reduced by 10 % compared to no fault. This is half of the reduction if no fault tolerant control is applied. To determine the maximum available torque, a current limit has been set for each module to prevent thermal damages. It is obvious that this limit strongly influences the maximum available torque after a fault. Due to the lack of an excitation source on the rotor of the SRM, the short-circuit of single coils during operation of the drive is not critical. It has been illustrated that the induced current in the coil is far below the nominal current of the coil and can be neglected for this machine. The simulation and the experimental results have shown that additional eigenfrequencies and, hence, vibration modes appear in the spectrum according to different faults. The vibration modes, resulting from faults, inherently increase the noise of the machine. Moreover, vibration mode 1 is excited which causes a net radial force on the bearings. If one, two or three modules fail within one phase, mainly mode 1, 2 and 3 are excited. In normal operation, only mode 0 and 4 are excited for the given five-phase 20/16 configuration of the SRM. The drawback of exciting mode 1, 2 and 3, is that the corresponding eigenfrequencies of these modes are all below 1000 Hz. Therefore, a fault of a module leads to a significant increase in noise in a well audible frequency region. In particular, the excitation of mode 1 has to be avoided for two reasons: first, mode 1 causes the net radial force, which periodically stresses the bearings. Second, the eigenfrequency of mode 1 is 43 Hz for the analyzed prototype. This resonance is directly excited by the fundamental electric frequency at a common operating speed of 160 rprn. Although the eigenfrequencies of mode 2 and 3 are higher than the maximum fundamental electric frequency, those modes are excited as well by multiples of the fundamental frequency, in the case of different faults. For instance, the fault of two opposite modules, leads to a significant excitation of mode 2. Nevertheless, m case one module fails, turning off the opposite module prevents the excitation of modes 1 and 3. However, it is advisable to turn off the complete phase if the application does not require maximum torque. Thereby, neither mode 1 nor mode 2 are excited. The remaining modules of the faulty phase should only be used if the maximum available torque with four phases needs to be increased. The presented measurement results prove the concept of the distributed inverter, the proposed simulation model, the vibration analysis in case of different faults and the simple fault tolerant control strategy. The measured currents, torque and vibrations in case of different faults are in good agreement with the simulation results.


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    Titel :

    Analysis of the fault tolerance of a switched reluctance machine with distributed inverter


    Beteiligte:

    Erschienen in:

    Erscheinungsdatum :

    2012


    Format / Umfang :

    12 Seiten, 20 Bilder, 1 Tabelle, 19 Quellen



    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch






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