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An objective study of behavior of permanent magnet synchronous motor

under abnormal conditions

Article  in  International Journal of Engineering and Technology · September 2018

DOI: 10.14419/ijet.v7i4.15550

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 International Journal of Engineering & Technology, 7 (4) (2018) 1970-1976

International Journal of Engineering & Technology

Website: www.sciencepubco.com/index.php/IJET
doi: 10.14419/ijet.v7i4.15550
Research paper

An objective study of behavior of permanent magnet

synchronous motor under abnormal conditions
Zaid H. Al-Tameemi 1 *, Hayder H. Enawi 2, Karrar M. Al-Anbary 3,
Dalya H. Al-Mamoori 1, Hussam M. Almukhtar 4
1 Technical College /Al-Mussaib, Al-Furat Al-Awsat Technical University, Iraq
2 Engineering College, Babylon University, Iraq
3 Biomedical department, Warith Al-Anbiyaa University,Iraq
4 Middle Refineries, Najaf Refinery, Ministry of Oil, Iraq

*Corresponding author E-mail: zaid_altameemi@tcm.edu.iq

Abstract

Permanent magnet synchronous motors (PMSM) can be used directly in place of the induction motors (I.M) for several industrial appli-
cations since it is characterized by high efficiency, high power factor, and high power compared to I.M. However, this type of motor
suffers from some abnormal conditions that result in minimizing power quality such as voltage sags, temporary disturbances, and faults
within the network. In this paper, the behavior of PMSM has been studied under the above conditions in a Matlab/Simulink environment.
It was noticed that such problems caused an increase in the amount of torque and current in this motor which impacted negatively on the
motor speed and influenced the behavior of PMSM.

Keywords: PMSM; Short Interruptions; Faults; Broken Rotor Bar.

1. Introduction
2. Short interruptions
In the last few years, permanent magnet synchronous mo-
tors(PMSM) have gained a considerable attention in the industries A short interruption can be defined as the whole loss of voltage
and academic world [1]. Practically, PMSMs are considered more whether on single phase or more for certain periods ranging from
desirable than induction motors (IM) with respect to high duty 0.5 to 3 cycles [6]. A momentary disturbance always has the same
factor industrial applications such as pump, fan, and compressor cause as long disturbances, such as an inappropriate protection
because of its high efficiency, subordinate life cycle, high power intervention and a fault in clearing the protection. When a source
factor, and less sensitivity to supply frequency and voltage devia- is relinked automatically within 1 minute, the produced case is
tions [2,3]. It is worth mentioning that its use is increasing because called a short disturbance ; however, a manual restoration of the
of the decreasing cost of commercial magnets. The excitation of supply leads to long interruptions. Automatic reconnections can be
PMSM can be supplied partially by using the magnets that are implemented by closing the circuit breaker that cleared the result-
placed in the rotor and could be obtained partly by using the line ing fault [7]. These interruptions have a significant impact on
current. A squirrel cage is supplied to hasten PMSM from a PMSM which is designed to function in normal conditions such as
standstill when begun ‘across the line’ [4]. During the last three a balanced sinusoidal, periodic, steady-state voltage which can
decades, many researches have been implemented in order to test cause huge current and torque transients.
PMSM for eco-technique feasibility and stability in both transient
and steady states. Conversely, the researches carried out on the
reliability of PMSM in the reallife scenarios (subjection to high 2.1. Occurrence of voltage interruption
power quality challenges) are limited [5]. Currently, power quality
is a major concern in the electrical power utility field because of PMSM is designed to operate on sinusoidal, periodic, steady-state
modern equipment and other motors which are sensitive to chang- voltages. Short disturbances can increase the amount of torque and
es in frequency and voltage. Voltage sags, harmonics, and short current in this motor. When PMSM is disconnected from the
disturbances are the major problems related to power quality that source, the current in the stator circuit halts and flow into the
impact on motor performance. It should be clear that more than PMSM. This, in turn, contributes to the deceleration of the rotor.
80% of the power quality- related issues are concerned with the Once there is a supply disturbance, the PMSM is misplaced direct-
occurrence of short interruptions [6]. The previous studies focused ly; then, the rotating magnetic field produced by the stator current
only on the analysis of I.M under abnormal conditions and ignored disappears. On the other hand, the rotating magnetic field generat-
PMSM performance. Therefore, this paper will shed light on the ed by the magnets is maintained on the decelerating rotor.
behavior of PMSM under short-time disturbances and faults. A
Matlab/Simulink environment was used to conduct this study.

Copyright © 2018 Zaid H. Al-Tameemi et al. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
International Journal of Engineering & Technology 1971

3. Effect of broken rotor bar on PMSM ed under different cycle interruptions (2 - 6 cycles) as shown in
the figures below. The speed is observed to greatly reduce because
of the 2,4,6, and 8 interruption cycles carried out in the supply. A
In the last two decades, many researchers studied some of the
synchronism of the motor is achieved after 0.04 to 0.16 seconds
faults that occur in machines, including broken rotor bar faults.
which is less than the starting time of the motor .Figures2, 3, and 4
Since 1980, several studies have been carried out in the field of
showed the stator currents falling to zero after all the interruptions.
broken rotor detection. Douglas (2003)studied this type of fault in
the rotor using FFT method and Discrete Wavelet Transformer in
a transient state by changing the load [8]. A discrete pack trans-
former has been reportedly used to detect broken rotor bar faults
[8].It is worth mentioning that rotor failures account for about
10% of total faults that occur in machines[9]. In this regard, many
reasons can contribute to damaging rotor bars, such as thermal
stress,mmanufacturing defects, magnetic and mechanical stresses.

4. Impact of fault on PMSM

This type of fault is deemed as a power-related electrical problem
which leads to the loss of one or more phases that supply a motor
[10]. This situation impacts negatively on the behavior of motors,
as demonstrated in Case3.

5. Impact of fault on PMSM within grid

Power quality is considered as an essential branch of electric power
engineering. It plays a significant role in delivering quality power
for industrial use. Many problems can contribute to decreasing the
power quality in a system, such as voltage sag caused by some
faults during specific periods, thereby, costing several millions of
dollars [11]. Therefore, this section sheds light on some system
problems in the presence of PMSM during faults.

6. Simulation results
Fig. 2: Speed, Torque and Stator Current at 2 Cycle Interruption.
To understand the impact of the aforementioned faults, different
cases have been considered. The motor data are given as shown in
each case.
Case1: short interruption
A PMSM with specific parameters given in Table 1 is simulated in
a Matlab/Simpower system.

Table 1: Motor Parameters

Voltage in volt 220 Flux linkage 0.1852
Frequency in Hz 50 No. poles 8
Stator resistance (ohm) 1.6
Armature inductance (H) 0.000395

Fig. 3: Speed, Torque and Stator Current at 4 Cycle Interruption.

Fig. 1: PMSM Under Short Interruptions.

Fig. 4: Speed, Torque and Stator Current at 6 Cycle Interruption.
A three-phase supply is disconnected at 0.2 seconds once the
Case2: Broken Rotor Fault
PMSM reached a steady state. The behavior of PMSM is evaluat-
1972 International Journal of Engineering & Technology

The dynamics of a sudden torque change on the PMSM is consid-

ered. The PMSM is connected to three-phase sources with a small
resistive load integrated into the network. This motor is initiated
with a load of 1 p.u. When the motor has reached a steady state
condition, the torque was suddenly increased from 1 to 20 at 1
second. This increment led to an accelerated torque and a decreas-
ing motor speed as shown in Figure 7.

Fig. 8: PMSM Under Fault Condition.

Fig. 5: PMSM Under Sudden Change in Torque.

Fig. 6: PMSM Under Normal Torque.

Fig. 9: Torque and Speed Under No.Load Condition.

Fig. 7: PMSM Under Sudden Change in Torque.

Case3: Impact of fault on PMSM

PMSM model are created in a Matlab environment as shown in

Figure 8. This mode is utilised to comprehend the impact of a
three phase fault on the performance of PMSM, including torque
and speed. The Simulink model comprises of 100(peak) and 50 Hz
3-phase source and three levels inverter. Two scopes are placed in Fig. 10: Torque and Speed Under Constant Load Condition.
the system to monitor the torque and speed under different load
conditions in the presence of a three-phase fault. The fault is ap-
plied during 0.01 to 0.1s.
 Fig. 11: Torque and Speed Under Variable Load Condition.

Case4: Impact Of Fault On PMSM Within Grid

Different scenarios are performed to understand the influence of faults on PMSMs that run within power networks, as demonstrated be-
low.

a) Normal condition
The PMSM used here consists of 30 MVA, 11 KV, and a 50 Hz 3-phase source. The feeder has a transformer of 11/0.4 KV, 1MVA del-
ta/star. Two scopes were situated at 0.4 and 11 KV bus to monitor the voltage waveforms and other waveforms including the rotor speed,
rotor theta, and stator current under various situations. In this case, the model runs under a normal case

Fig. 12: PMSM under Fault within Grid.

Copyright © 2018 Zaid H. Al-Tameemi et al. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
 ta/star transformer with 10 kW resistive load in the line between
the motor and a 0.4 KV bus. Two scopes were placed at 0.4 and
11 KV buses to monitor the voltage waveforms and other wave-
forms, including rotor speed, rotor theta, and stator current in the
presence of a three-phase fault. The fault block was placed at 11
KV bus to simulate a three-phase fault. In this part, the perfor-
mance of PMSM was investigated by applying a three-phase fault
as shown in the figures below. Figures 17 and 18 show voltage sag
waveforms resulting from a three-phase fault at 11 KV feeder
during the period of 0.15-0.25 s. It is noted that the 11 kV bus
faces big voltage sags at all phases because of the low fault re-
sistance between the three faulted lines as shown in the figures
below:

Fig. 13: PMSM under Normal Condition within Grid

Fig. 16: Voltage Sag Caused by Three Phase Fault at 11 Bus Line.

.
Fig. 14: Voltage Sag at RMS Scope.

Fig. 15: Speed and Torque under Normal Condition. Fig. 17: Voltage Sag at RMS Scope.

b) Three phase fault It can be noted that voltage sag impacts negatively on the rotor
A line fault mode is created in a Matlab environment as shown in speed, rotor angle theta, and stator current. Most of the values
Figure 12. This mode is used to simulate a voltage sag due to line witnessed reductions and vibrations during this period while the
faults. The Simulink model comprised of a 30 MVA, 11 KV, 50 stator current –q faces swelling as shown in the figure below.
Hz 3-phase source block feeding through 11/0.4 KV, 1MVA del-

Copyright © 2018 Zaid H. Al-Tameemi et al. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
International Journal of Engineering & Technology 1975

Fig. 20: Voltage Sag at RMS Scope.

Fig. 18: Speed, and Torque under Three Phase Fault.

c) Line to line fault

In this section, the performance of PMSM is investigated by ap-
plying an L-L fault as shown in the figures below. Figures 19 and
20 show voltage sag waveforms caused by L-L faults that oc-
curred at 11 kV feeder during the period of 0.15-0.3 s. It is noted
that the 11 bus faces two voltage sags at different voltage magni-
tudes because of the high fault resistance (8 ohms) between the
two faulted lines as shown in figure 20. The faulted phase at 0.4
KV bus faces a small voltage swell because there is no ground
point in this type of fault, as well as the high fault resistance.

Fig. 21: Speed and Torque under L-L Fault Line to Ground Fault.

d) Line to ground fault

In this section, the performance of PMSM is investigated by apply-
ing an L-G fault as shown in the figures below. Figures 22 and 23
show voltage sag waveforms caused by an L-G fault at an 11 kV
Fig. 19: Voltage Sag Caused by L-L Fault at 11 Bus Line. feeder during the period of 0.15-0.3 s. It was noted that the 11 bus
faced small voltage sags at the faulted line because of the high fault
In this study, voltage sag waveforms are presented in RMS scope. resistance (8 ohms) between the faulted line and the ground point.
It represents the analysis of an L-L fault voltage sag waveform in The phases at 0.4 KV bus also faced a small voltage swell and sag
the figure above. The voltage sag magnitudes for each phase are because of the presence of a ground point and a high fault re-
visualized. Small oscillations are observed to arise at the pre-sag sistance in this type of fault [13].
and post-sag, as well as swells because of a phase shift during the
fault [12].
 1976 International Journal of Engineering & Technology

7. Conclusion
A PMSM is designed to work on the sinusoidal, periodic, steady-
state voltage; hence, it is important to study the behavior of
PMSM under different abnormal conditions such as short interrup-
tions and sudden changes in the mechanical torque and faults. In
these conditions, the torque, speed, and current are monitored to
understand their impacts on the performance of PMSM. It is ob-
served that short time interruptions contribute significantly to
increasing the torque and currents which result in decreasing the
motor speed. It is also noticed that resistance plays a vital role in
reducing voltage sags during faults that occur in the power net-
works (including PMSM). The broken rotor bar is also found to
play a negative role on the performance of PMSM, especially in
accelerating the torque to an undesirable level.

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Fig. 24: Speed And Torque.

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