ACOUSTIC NOISE AND VIBRATIONS OF ELECTRIC …€¦ · Some specificities of electric vehicles NVH ... tonality, Tone-to-Noise and Prominence Ratios (tonal metrics), sharpness (sound
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• Switching frequency of most converters goes up to 20 kHz, but switching is lowered under light-load and no-load to reduce switching losses and switching frequency
• Buck-boost converter include a capacitor and an inductor
Name Function Operation mode Components
3-phase DC-AC inverter / rectifier
ESS HV to AC voltage to power electric motors in traction, the opposite in braking
Traction / Braking DC link capacitor
AC-DC rectifier Mains AC 50/60 Hz to ESS Charging Filter capacitors
DC-DC converter ESS HV to onboard LV conversion (ex from 400 V to 12V) = buck/boost converter
Traction / Braking / Parking
Capacitors / inductorsHF transformer
DC-DC converter Mains DC to ESS Charging Filter capacitors
• Mechanical imbalance of the rotor creates dynamic eccentricity, enriching magnetic force spectrumboth in frequency (sidebands) and space domaines (modulation of wavenumbers with +/-1)
• Dynamic eccentricity transforms pulsing forces in unbalanced magnetic forces, generating shaftbending vibrations and structure borne noise
• Couple imbalance occurs when 2 equal masses are placed symmetrically (static balance but dynamicunbalance)
• Couple imbalance is found frequently in EV/HEV when rotor is connected to imbalanced powertraincomponents [R1]
• ICE start-up & shup down vibration is a significant contributor to overall vehicle vibration
• Special noise reduction techniques can be applied at neutral or park mode on conventional ICE
• However in HEV, ICE start-up does not always occur at neutral or park mode, it depends of many factors (e.g. state of charge of battery, driver torque demand)
• Dedicated noise reduction techniques are implemented on ignition timing, valve opening/closingtiming, piston stop position etc. [R1]
• In HEV special noise & vibration control techniques are based on compensating ICE torque pulsation during starts using fast response characteristics of the electric motor to mechanical torque ripples[R1]
• Rubber isolation in more effective on high frequency vibration of electric motors compared to ICE, acoustic absorption materials are also more effective
• New balance between electric motor noise, tire/road noise and wind aerodynamic noise
• Modified moments of inertia & eigen-frequencies in the powertrain, lower torque ripple on the shaft line compared to ICE
• Importance of mass/stiffness of batteries in EV lighter body structure
• High directivity, highly integrated components (ex: L, C, generator + motor), high sensitivity to temperature
• Low reproductibility: +/- 10 dB in electric motor or passive components manufactured according to same specification
Psychoacoustics of electromagnetically-excited noise
• Objective psychoacoustic metrics often used in EV/HEV: loudness (sound intensity), roughness and fluctuation strength (frequency modulation), tonality, Tone-to-Noise and Prominence Ratios (tonal metrics), sharpness (sound timbre and energy at high frequency), Articulation Index (tone detectability) [R8]
• Subjective psychoacoustic evaluation: hearing tests and subjects surveyfor annoyance judgement, pleasantness judgement, detectability and sound design