Yves Mollet

This paper presents a comparison of soft and hard
chopping on an 8/6 SRM in terms of noise, vibration and
harshness. Transient-state measurements are used to plot speedfrequency
signatures of current, vibration and acoustic noise of
the SRM for different load torques. With this technique speedrelated
frequencies can be distinguished from resonance
frequencies, and therefore, more information can be extracted
from the plots. The results show that hard chopping increases the
loudness of acoustic noise compared to soft chopping, with a
frequency shift to higher values. This however leads to an
attenuation of the vibration and noise amplitudes at the most
critical resonance of the SRM, situated at a relatively low
frequency.

Switched reluctance machines (SRMs) benefit from major advantages, such as cheap and robust construction and electrical fault tolerance, but also suffer from noise, vibration and harshness (NVH) issues. The present paper focuses on the NVH influence of the current hysteresis controller, which is generally used in SRM drives. The impact of changes in the controller sampling time is experimentally investigated on an 8/6 15 kW (30 kW peak) SRM. In practice the initial hysteresis controller, implemented on a dSPACE platform running at 10 kHz, is compared with an improved version running twenty times faster on external microcontrollers. Tests are performed in the form of run-ups, in order to study the drive in transient conditions and investigate a continuous speed range, while vibration, current and sound pressure waves are measured. Current waveforms are also simulated using AMESim software to compare with experimental measurements. Both controller implementations are modelled and both run-up and constant speed conditions are considered. To identify the frequency content related to the switching process, those simulation results are also analysed before and after having removed the current ripple due to switching through signal processing. Run-up results are plotted as waterfall diagrams, which both give a global overview of the frequency content for the considered speed range and allow distinguishing speed-order related harmonics and resonance frequencies. It is observed that the improved controller generates a shift of the spectrum towards higher frequencies with a global reduction of vibration and noise amplitude. Furthermore, the excitation of the dominating first ovalization mode of the SRM is considerably reduced.

The development of power converters has permitted the rise of switched reluctance machines (SRMs), due to their simple and cheap design and of their inherent fault tolerance. However, those machines suffer from torque ripple and noise and vibration issues, which constitute an obstacle to the extension of their application domain. This paper presents the influence of the bandwidth of a current-hysteresis controller on an 8/6 SRM in terms of noise, vibration and harshness. Simulations in AMESim environment and measurements on a 15 kW test bench are performed in transient state, based on continuous variation of the hysteresis bandwidth. Phase currents, acoustic noise and radial vibrations are measured without and with load, allowing for comparison of hysteresis-band-frequency plots. This transient state approach enables showing the evolution of a part of the frequency components with hysteresis bandwidth and distinguishing them from other components linked to speed or to structural behaviour of the motor. Results show that the current chopping by means of a hysteresis controller generates broadband frequencies in the phase currents that also appear in the vibration and sound pressure wave measurements. As the bandwidth increases, switching-related components are shifted towards lower frequencies, resulting in a higher excitation of the main resonance modes of the machine. Due to the higher current ripple in the case of hard chopping mode, the influence of the bandwidth is in general more important than in soft chopping mode. However, for the same bandwidth the ripple occurs at much lower frequencies in the latter case and therefore more attention has to be paid to possible interaction with the resonance frequencies.