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An Analysis of Vibration and Acoustic Noise of BLDC Motor Drive
Conference Paper · August 2018
DOI: 10.1109/PESGM.2018.8585750
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An Analysis of Vibration and Acoustic Noise of
BLDC Motor Drive
R. M. Pindoriya, Student Member, IEEE, A. K. Mishra, B. S. Rajpurohit, Senior Member, IEEE and R. Kumar
Indian Institute of Technology Mandi, Himachal Pradesh, India
pindoriya_rajesh@students.iitmandi.ac.in
Abstract—This paper presents a comprehensive analysis of the
vibration and acoustic noise for brushless direct current (BLDC)
motor drive. BLDC motor finds several applications due to their
cost efficiency and simple construction. The major advantages of
BLDC motors are low maintenance, high efficiency, long life, low
weight and compact construction. However, few applications are
acoustic noise and vibration sensitive. Hence, research has
started concentrating on the acoustic/vibrational performance of
the machines. In this work, a digital pulse width modulation
(PWM) based control technique has been used to drive the BLDC
motor to perform an analysis of vibration and acoustic noise
experimentally. Simulation and experimental results have been
presented.
Index Terms— Acoustic noise, brushless direct current
(BLDC) motor drives, field-programmable gate arrays (FPGA),
pulse width modulation (PWM) and vibration.
I. INTRODUCTION
The brushless direct current (BLDC) motor has find its
place in its increased utilization in medical, aerospace and
industrial automation and other applications. Some of the
submarine and under water vehicle applications, permanent
magnet (PM) motors are able to find its increasing use because
of its high torque density and high efficiency. Acoustic noise
and vibration are the major problem in applications of
underwater vehicles for BLDC motor drive. The acoustic
noise and vibration reduction methods are analysed and
classified into two categories. First one is mechanical
structural development and the other is voltage and current
control approaches [1]. For mechanical structural
improvement, there are many examples such as a rotor hole at
the poles in order to reduce the radial force, and a segment
rotor structure, which expands the radial force acting on the
stator [2]. In voltage and current control schemes, there is an
active vibration cancellation (AVC) which focuses on the
reduction of vibration at the natural frequency. AVC
introduces a two-step voltage waveform with a constant period
of zero-voltage excitation that corresponds the natural
frequency [3]. In the case of AVC, large diameter motors have
low mechanical resonance frequency, thus zero voltage
termination becomes considerably long.
The BLDC drive controller generally gives better steadystate and transient responses. The parameters of the motor
system do not change during operating conditions, but in
practical applications the mechanical load parameters changes
978-1-5386-7703-2/18/$31.00 ©2018 IEEE
continuously with respect to time, such as inertia and friction
[4]. Power electronic converters (PEC) are used with control
of BLDC motor which increases the cost and complexity of
the system and is one of the major disadvantages with BLDC
motor drive used for operation of drives [5-7]. Another
disadvantage, as mentioned earlier, is creation of complex
acoustic noise and vibration through the operation of the drive.
The speed of the BLDC motor is directly proportional to the
applied voltage across the stator winding. The speed can be
changed, by varying the ON-OFF period of the pulse width
modulation (PWM) signal [8].
The electromagnetic torque of the BLDC motor narrates to
the three functions, like product of phase, back electromotive
force (EMF) and current. The back EMF of each phase is
trapezoidal in shape and it is displaced 120 electrical degrees
with respect to each other in three phase machines [9] - [10].
In this work, a digital PWM technique for speed control
using proportional integrator (PI) controller and analysis of
vibration and acoustic noise for different operating point is
investigated for BLDC motor drive. Computer simulations
were used for proof-of-concept and application of the digital
PWM controller with the rapid prototyping and real-time
interface system with Spartan 3AN field programmable gate
array (FPGA) board for experimental investigations. The
organization of this paper is as follows. Section II discusses
the analysis of vibration and acoustic noise sources in BLDC
motor drive. The digital control strategy of the BLDC motor is
explained in section III. Section IV describes the results and
discussion on simulation and experimental results. Section V
ends with conclusion.
II. ANALYSIS OF VIBRATION AND ACOUSTIC NOISE SOURCES
IN BLDC MOTOR DRIVE
Acoustic noise is an audible sound which is undesirable.
Vibrations may be perceived directly where they are
transmitted to the body through. However, in most of the parts
the sound radiated from a vibrating body is very important in
terms of acoustic noise. The selection of machine which
defines the fundamental acoustic characteristics in terms of the
machine inherent noise components. The switching frequency
associated harmonics can become the leading noise
components when the frequency lies within the audible range.
Fig. 1 gives an overview of noise sources in electrical
machines and their transmission towards airborne sound. This
classification is introduced by Timar et al. in [11]. The sound
level can be described using the sound pressure with the aid of
the sound wave resistance, which is assumed to be a real
number, and the averaging time Tm;
𝜌
𝐿𝑝 = 20log⁡( )dB
𝑃0
1
𝑇𝑚
𝜌 = √( ) ∫0
𝑇𝑚
𝑃2 𝑑𝑡
cycle and back EMF waveforms and generate PWM pulses for
three-phase inverter bridge.
(1)
(2)
where, P0 is threshold level of sound, P is actual sound
level, Tm is average time slot and 𝜌 is sound pressure. BLDC
motor commutate every 60° in one electrical cycle. The
current variation gives rise to electromagnetic noise, and the
fundamental frequency of the acoustic noise from the current is
the commutation frequency of the BLDC motor [12]. The
frequency of the harmonics of the electromagnetic acoustic
noise should be:
𝑛
𝑓𝑖 = 𝑖 ∗ 𝑘 ∗ 𝑝 ∗
(3)
60
Where, i number of the harmonic order, k is the number of
step commutation in one electric cycle, p is number of rotor
poles and n is rotor speed in RPM. A transmission path is the
path over which the vibration is carried from the motor to
sensor [11].
Fig. 2. Flowchart for speed control of BLDC motor drive.
IV. EXPERIMENTAL INVESTIGATION
Fig. 1. Noise sources in electrical machines and drives.
III. DIGITAL SPEED CONTROL STRATEGY FOR BLDC MOTOR
DRIVE
Modeling of the three-phase star connected BLDC motor
drive, fed with three-phase voltage source inverter has been
done by standard equations [12-14]. PWM technique is the
most popular speed control techniques for electrical motors.
This technique performs by comparing a high frequency signal
with specific duty cycle is multiplied by switching signals of
inverter [8]- [9]. Flowchart for speed control of BLDC motor
drive is shown in fig. 2. In this technique compare the duty
The aforementioned control strategy for BLDC motor
drive is implemented in simulation as well as experimentally.
The schematic diagram and actual picture of experimental
setup is shown in fig. 3 and fig. 4, respectively. Table I list the
parameters and specifications used for simulation and
experimental step-up.
Simulation studies have been performed using
MATLAB/Simulink model. This has been done using a
variation of the PWM duty cycle, according to the error signal.
The simulation results are shown in fig. 5. Fig. 5 (a) shows
the waveform of three-phase back-EMFs⁡(⁡𝐸𝑎 , ⁡⁡𝐸𝑏 , ⁡⁡𝐸𝑐 ) of
BLDC motor drive, each phase is 120-degree phase shifted
with respect to each other. When voltage of any two phases is
constant means these are connected to positive and negative
DC link voltage respectively at that time interval, the voltage
transition take place in the floating phase. Fig. 5 (b) shows the
rotor speed of BLDC motor at a rated torque and gain value
of⁡⁡𝐾𝑝 = 2⁡&⁡⁡𝐾𝑖 = 8, for the speed reference set at 1000
RPM. The steady state error in the speed response is zero due
to the effective control action taken by the speed PI controller
as shown in Fig. 5 (b). The peak overshoot in each speed
reference is not more than 5%. The settling time for the speed
response is less than 0.02 seconds. Based on these
performance indices values, the studied BLDC motor drive
qualifies to be called as high-performance motor drive.
Auto
Transformer
3
Inverter
V&I
sensors
V: Voltage sensors
I: Current sensors
Accelerometer
FPGA
Controller
Encoder
3
Rectifier
Microphone
BLDC
motor
(a)
Computer
Comput
Fig. 3. Schematic diagram of experimental setup.
(b)
Fig. 5. Simulation results of BLDC motor drive: (a) stator phase back-EMFs,
(b) speed response in RPM (refer. speed is 1000 RPM).
Fig. 4. Experimental setup of BLDC motor drive.
TABLE. I. E XPERIMENTAL SET -UP SPECIFICATION
Specification Item
Power
Rated speed
No. of poles
Torque cont. stall
Current cont. stall
Rated bus voltage
Resistance
Inductance
Rotor inertia
Spartan 3AN FPGA kit
Value
1.07
3000
04
3.6
6.29
300
3.07
6.57
1.4-1.8
20
Peak current
Torque constant
IGBT based inverter stack
16
0.49
600
30
N-m
A
V
Ohms
mH
Kgm2
kHz Clock
frequency
A
Nm
V
A
10
mV/g
20
kHz
Accelerometer sensitivity
(PCB Piezotronics 352C03)
Microphone (1/2" free-field)
(National Instrument USB 4432)
Unit
kW
RPM
For experimental investigations, Spartan 3AN FPGA
board is used to generate digital PWM signal and fed to direct
three-phase inverter bridge. National instrument (NI) based
development platform is used to capture vibration and acoustic
noise for BLDC motor drive as shown in fig. 4 and
specifications of sensors are given in Table I.
The inverter is using power IGBT modules, rated at 30 A,
600 V, with a switching frequency of 10 to 20 kHz. Reference
speed was set at different values to see the dynamics of drive
and PI based speed loop was used to compare the actual speed
and the reference speed and based on error to determine the
duty cycle for the next period.
Results obtained experimentally are shown in fig. 6. The
three-phase stator phase current with amplitude 2 A is shown in
fig. 6 (a). It is quasi square waveforms and 120 electrical
degree phase shift to each other. Speed response of BLDC
motor shown in fig. 6 (b) and (c). Step speed reference of 500
RPM has been applied at the time instant of 11th second. It
takes approximate to 6 second to settle the speed response.
The experimental speed response shows no steady state error.
Both vibration and acoustic noise analysis provide
important information that can be used to improve the motor
design, and to devise and implement other noise suppressing
or control methods. Signals can be analysed for the
mechanical vibration and acoustic noise in two domains. One
is time domain measurement; this analysis gives the real-time
signal and extract the signal characteristics like the value of
magnitude of signal. Another one is a frequency domain
measurement, the various information like amplitude, phase,
power spectrum can be analysed in this case.
a
f
Fig. 6. Experimental investigation of BLDC motor drive: (a) stator phase
current, (b) low speed response (c) high and variable speed response (d)
frequency spectrum of vibration at 1000 RPM (e) frequency spectrum of
acoustic noise at 1000 RPM and (f) bode plot of acoustic noise.
b
c
d
Time and frequency spectrum of vibration signal for BLDC
motor drive at experimental speed of 1000 RPM is shown in
fig. 6 (d). Vibration sensors were located horizontally on the
end of the body of the motor. It is important to consider
ambient noise also for experimental conditions, as it can have
a decisive impact on whether the subject perceives the noise
that is to be evaluated as being in the ranges as prescribed by
standards such as ISO 7919-2: 2001 [15]. Fig. 6 (d) presents a
vibration spectrum of the motor in frequency range, from 0 Hz
to 2.5 kHz. The high vibration peak at around 300 Hz with
magnitude 3500 m/s, it could be due to mechanical resonance
of mechanical parts like fan blades or end cap. As per the ISO
7919-2: 2001, the allowable vibration signal range for up to 15
kW machine at rated speed and rated load conditions is 0.9 to
1.19 mm/s.
For time domain measurements, as given in Table- II
shows the values of vibration level in term of velocity in the
RMS (mm/sec) at various speeds. As per the ISO 7919-2:
2001 guidelines for vibration measurement, vibration values
are in the acceptance range at all speeds and load conditions of
2 N-m. From the analysed values of vibration signal of time
domain measurement, it has been found that vibrations are
reasonably lower side at loaded condition. The main
advantage of using frequency domain measurement has been
analyzed the accurate noise level over a frequency ranges
using the power spectrum graph. As further studies, authors
will analyse and will establish the correlations for the
mechanical resonance frequency of experimental set-up with
measured frequency spectrum.
TABLE. II. VIBRATION MEASURED FOR BLDC DRIVE
e
Speed
(RPM)
100
300
500
800
1000
1500
2000
2500
RMS
(mm/s) for
vibration level
0.1959
0.1996
0.1920
0.1856
0.1953
0.1923
1. 1214
0.9872
Acoustic noise analyses are useful for evaluating the
available machine conditions and diagnosing the fault
associated with the operational machine. As per the IEEE
Standard 85-1980, “IEEE Test Procedure for Airborne Sound
Measurements on Rotating Electric Machinery for acoustic
noise measurement, it should be in the 20 – 25 dB for 15 kW
machine [16]. The sensor used for experimental measurement
in lab. is ½ inch free-field microphone from National
Instruments, to sense the acoustic noise of the BLDC motor
drive. A microphone always picks up the entire noise pattern.
For industrial applications, when performing measurements
using a microphone, background noise can-not be avoided.
The maximum acoustic noise generated at 1.5 kHz frequency
and amplitude is 5.2 mV/Pa or 82 dB shown in fig. 6 (e). The
values has been measured at a speed of 1000 RPM for load of
2 N-m. For different speed range, measured acoustic noise is
given in Table III. However, after getting acoustic noise by
making adjustment for background noise, the acoustic noise
from BLDC motor drive is considerably higher range. For
rated speed of 2500 RPM, it is almost double of allowable
limits.
TABLE. III. ACOUSTIC NOISE MEASURED FOR BLDC DRIVE
Speed
(RPM)
100
300
500
800
1000
1500
2000
2500
Back ground noise
level (dB)
48
48. 3
49. 48
47. 56
50
48. 5
49. 23
52. 45
Motor noise level
(dB)
72. 29
75
73. 54
77
82
86. 52
89. 2
91. 26
Difference
(dB)
24. 29
26. 7
24. 06
29. 44
32
38. 02
39. 97
38. 81
The fig. 6 (f), shows bode plot and frequency response of
acoustic noise for BLDC motor drive. The magnitude and
phase plots show that the speed gain is -40.1 dB at 2.41 Hz.
The system has the phase of -7.47 degree at 1.99 Hz.
V. CONCLUSION
In this paper an experimental study has been presented for
varying operating conditions of a brushless direct current
(BLDC) motor drive and effect of such changes on the acoustic
noise and vibration produced by the drive has been measured
and analyzed. The electromagnetic forces are the main cause of
vibration and acoustic noise for BLDC motor drive, rather than
the torque ripple and cogging torque. Simulation of the digital
PWM method is carried out by using MATLAB/Simulink and
that results are investigated by experimental setup. Measured
vibrational signal and acoustic noise of BLDC motor drive has
been analyzed and it is observed that vibration signals are well
in range as per the ISO 7919-2: 2001 guidelines however
acoustic noise signals are almost double of higher side of
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prescribed range as per the IEEE Standard 85-1980.
Therefore, it is required to understand and develop the
methods to supress the acoustic noise from the BLDC drive.
Further design of BLDC drive will be taken up by the authors
for low acoustic noise as well as to develop models to
understand resonance of different mechanical components.
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