NVH of Electric Vehicles

INTERNAL PUBLIC SECRET CONFIDENTIAL

NVH of Electric Vehicles

Juan J García.

9/11/2020


What characterises electric powertrain sound , sound quality and

how can it be described with acoustic metrics?

Contents:


Comparison of Energy Efficiency of powertrains


New components to take into account


EV Powertrain configuration


Drive Control System – Architecture for one EM


EV Global arquitecture


Types of electric machines


Properties of electric machines

Maximum torque available at start-up

Can be designed with any shape or size

• Several possibilities to design stator and rotor for the same technology

High power density

High efficiency

• Several operating points with an efficiency higher than 90%


Masker

Masked high

frequency

region

The hidden ‘electric’ sounds

40 dB

60 dB

80 dB

Masker

level


Noise and vibration of electric motors

Although electric powertrain is quieter that internal

combustion engines (ICE), the sound character is

different and not more acceptable.

The noise signature from an electric traction motor is

characterised by speed-dependent high frequency

tonal components form the dominating electromagnetic

harmonics covering a wide r.p.m range

With a relative low levels of broad band masking noise

from tyres and wind, the tonal components can be

accented in a large frequency range and contribute to

perceived annoyance in the car

Good coupling

for bending

waves

generation on

stator surface

Segment of a PMSM with surface mounted

permanent magnet with radial and tangential

components of the electro-magnetic field


Noise and vibration of electric motors

Concept Observation Interpretation

ODS allows the definition of

the circumferential order that

dominates the radiation

efficiency.


ICE

EM

A new soundscape…

Relative distribution of excitation orders:

ICE v.s EM


ICE v.s. EV noise and vibration: Observations

ICE

EM


Inverter noise

The conversion of DC to AC voltage takes place in the inverter by pulse-width

modulation (PWM)

In order to produce a sinusoidal-like output voltage with a certain frequency to the electric

motor, a switching-frequency is required to control the duration of the pulsed voltage

The output voltage from the inverter contains the fundamental frequency component

distorted with the switching frequency and respective harmonics.

During run-ups, the switching frequency component induces adjacent side bands.

Pulse width modulation speed control works by driving the motor with a series of “ON-

OFF” pulses and varying the duty cycle, the fraction of time that the output voltage is “ON”

compared to when it is “OFF”, of the pulses while keeping the frequency constant.


Inverter + magnetic motor noise

Pulse-width modulation (PWM) frequency lines including side-bands

and magnetic harmonics during motor run-up of an electric vehicle.

Stator housing radial

velociy

v


WOT: 0-100 km/h

Volvo C3: 82 kW

1000 – 9000 Hz

200 – 2000 Hz

Sound quality evaluation in EV


High tonal levels for frequencies > 1kHz, the results in higher perceived

annoyance, sharpness, aggressiveness and a low sound quality.

Increasing levels of high of frequency (1kHz-9kHz) tonal components and

decreasing mid frequency tonal components (200Hz-2kHz) from electric

motor and transmission gives high rankings on sharpness, annoyance,

toughness and powerfulness

Lowering the same high frequency components improves sound acceptability

Sound quality evaluation in EV


101

102

103

104

105

101

102

103

104

Center frequency (Hz)

Crit

ical

ban

d w

idth

The bandwidth of the critical bands are similar to 1/3 octave

bands, but in contrast they do not have fixed frequency limits

Bark 1

Bark 24

Sound quality evaluation in EV: Critical bands


Prominence ratio is calculated from the sound pressure level of the critical band of

the tone and the adjacent critical bands.

The critical band is the frequency range of a noise, centred at the frequency of a

tone, which effectively can mask the same tone

For the calculation of the PR, the critical band containing the tone or tones is

compared to the adjacent two critical bands:

𝑃𝑅 (𝑑𝐵) = 10 log10

𝐿𝐵

𝐿𝐴 + 𝐿𝑐 2

Sound quality evaluation in EV: Prominence ratio


In steady state and acceleration conditions the psycho-acoustic metrics

prominence ratio (PR) , which quantifies the tones levels relative to the

adjacent background noise is well correlated to sound quality in EV

PR ≤ 2dB, the perceived annoyance was similar and independent on

frequency range

Increased PR-level (PR ≥ 3) provides high probability of detecting the

tones and increases the perceived annoyance, particularly for tones

above 2.5 kHz

Sound quality evaluation in EV : Some criteria


02000

40006000

800010000

0

5

10

0

0.2

0.4

0.6

0.8

1

Frequency (Hz)PR - value (dB)

Audib

le

Poor order

evolution

Good order

evolution

Application: projection of order evolution on the PR-f plane

Order

projection

Order Audibility

PR-f plane


0.9

0.7

0.5

0.3

Low audibility

Mid audibility

High audibility Run-up

order Seady state

order

𝑡𝑖 𝑡𝑓

Application: projection of order evolution on the PR-f plane


With the absence of acoustic emissions from an operating internal combustion

engine, the presence of high pitched tonal components from the electric

traction motor can be pronounced in many driving conditions

There is a robust relationship between the psychoacoustic metric PR and the

threshold of detecting the tones and the perceived annoyance, for both

constant speed and acceleration of EV

The perceived noise annoyance in EV is low for tonal noise with PR ≤2 dB.

With higher audibility (PR≥3dB), the perceived annoyance is significantly

increased above 5 kHz compared to frequencies below 800 Hz (constant speed

and acceleration)

Conclusions


Thank you for your attention


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Second Public Technical Course: Fundamentals of Electric Vehicle NVH

Time Title

09:00 - 10:00 NVH of Electric Vehicles

10:00 - 11:00 Target setting for Electric Vehicles NVH

11:00 - 11:15 Coffee

11:15 - 12:15 Effect of motor controller on Electric Vehicles NVH

12:15 - 13:00 Effect of driveline design on Electric Vehicles NVH

13:00 - 14:00 Lunch

14:00 - 15:00 Early Damage Detection of electric motors based on modal energy vibration

15:00 - 15:15 Coffee

15:15 - 16:30 NVH objectives for powertrain in-vehicle integration: experimental and simulation approach

16:30 - 17:00 Close

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NVH of Electric Vehicles

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