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Engineering, Technology & Applied Science Research Vol. 8, No. 6, 2018, 3585-3591 3585  
  

www.etasr.com Al-Barbarawi: Improving Performance of the Braking Process, and Analysis Torque-Speed … 

 

Improving Performance of the Braking Process, and 

Analysis Torque-Speed Characteristics of the 

Induction Motor 
 

Omar M. Al-Barbarawi 

Electric Power Engineering Department, 

Faculty of Engineering Technology 

Al-Balqa’ Applied University, As-Salt, Jordan 

omaralbarbarawi@yahoo.com 
 

 

Abstract—This study aims to investigate, analyze, discuss and 

illustrate an effective and reliable fast braking system used in a 

three-phase induction motor by combining two or more different 

conventional braking methods such as dynamic-plugging and 

electromagnetic-plugging. The plugging process is implemented 

by disconnecting one of the stator phases and connecting it with 

an electromagnetic brake while interchanging the other two 

phases. The dynamic process is executed by inserting high 

resistance in the rotor circuit of the motor. The performance of 

the torque-speed characteristics of the induction motor will be 

studied and analyzed through the dynamic process. 

Mathematical models have been developed and simulated. 

Results show that the braking process time is greatly reduced. 

Keywords-electromagnetic brake; plugging-dynamic brake; 

starting; torque-speed characteristics 

I. INTRODUCTION  

Induction motors (IMs) are commonly used in a wide 
variety of industrial applications, because of their high 
robustness, reliability, easy maintenance, low cost, high 
efficiency and good self-starting [1-12]. The most important 
control parameters in a motor drive system are starting, speed 
control and braking processes. Therefore, there is a need to 
deploy a fast braking system that brings the drive to a standstill 
after the completion of an operation. Electrical braking for the 
three-phase IM can be carried out by various methods. These 
include: regenerative braking, plugging braking, dynamic 
braking, DC dynamic braking, zero sequence braking etc. [6-8, 
9-11]. The braking system technique of an electric motor is 
basically the removal of the stored kinetic energy from the 
mechanical part of the system via the speed reduction of the 
rotating system and the transforming of the stored kinetic 
energy into another energy which dissipates through heat due 
to joule effect losses in the rotor bars. This paper presents a 
new braking method for IMs that integrates two conventional 
braking methods [6-13] mixing the plugging braking system 
with the electromagnetic braking system, or with the dynamic 
braking system. These methods are effective and efficient and 
employed in many industrial applications. The plugging 
braking system is achieved by the disconnection of one of the 

three phases which feed the motor and then connecting it to an 
electromagnetic braking coil, while, at the same time, the other 
two supply lines are interchanged. The switching processes are 
done in proper sequence and the time delays between the 
successive stages of switching are precise. For proper 
switching and proper time delay a microcontroller may be 
used. The plugging process leads to the development of a 
negative slip that is larger than one and acting on the opposite 
direction of the torque with respect to the motor rotation [10-
11]. This new method is effective in a variety of industrial 
applications for immediate motor stopping. Braking can be 
achieved by the use of the dynamic braking method by 
inserting a high resistance in the rotor circuit of the motor, with 
the plugging braking. The braking methods, namely: 
electromagnetic-plugging or plugging-dynamic of the 3-phase 
induction motor have been implemented analytically in a 
systematic manner. The aim of this contribution is to study and 
examine new methods of braking for this type of motor drive. 

II. ANALYSIS OF THE ROTATING MAGNETIC FIELD 

In this paper we will study the effect of the magnetic field 
on the behavior of the motor during braking process, especially 
when separating one phase from the power supply. Assume the 
stator of an IM is supplied by equal magnitude three phase 
currents with phase difference of 120

o
 between them: 

	 ���� = �� �	
��
�	���� = �� �	
��
 −	120������ = �� �	
��
 −	240�� � A   (1) 
where ���� ,����	, ����	are the instantaneous stator currents. 
These currents produce a constant magnitude rotating magnetic 
field (RMF), which will produce a rotating circular motion that 
rotates at an angular velocity ω [2, 4, 5]. The magnitude of the 
generated magnetic field (Bnet(t)), at any instant of time (t) is: 		������� = 0.5� !��	[�	
��
�ẋ- #$���
�ŷ]= 	= 	0.5� !��	 %		̶	 '( + �
*, ,-�.    (2) 
where Nph=2, 3, 4, 5 …, the number of phases.  



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This equation is the final expression for the total magnetic 
flux density (Bnet) produced in the stator. The magnetic field 
will have a magnitude equal to 0.5Nph.Bm. The result of these 
waves is a sinusoidal wave distributed in the gap of the motor 
that continues to rotate in a circular motion at an angular 
velocity (ω) in clockwise or in counterclockwise direction 
depending on the phase sequence, and it starts rotating at angle ∠±900 as shown in Figure 1. If one of the three phases in the 
stator of an induction motor is disconnected, the other two 
phases’ currents will produce a magnetic field with variable 
magnitude. Supposing that a phase of a (0AA′) current from (1) 
has been disconnected, the other two phases’ currents will 
produce the following magnetic flux density : 

������� = ������� + ������� = 
 0.5�� �	
��
� ) 1.5�� #$���
� ∟ ̶

2
23  ,

�4
5(3  �3� 

where ����	 , ����	, ����  are the instantaneous values of the 
magnetic field intensities for the different phases. This equation 
determines the total magnetic flux density presented in the 
stator, with total value distributed in a sinusoidal wave in the 
gap. This field begins to rotate in an elliptical form by an angle 
of -90

0
. The outcome of the field is distributed as a sinusoidal 

wave in the gap of the motor. The field lines are concentrated 
in a long axis of the phase AA′ on the vertices of the elliptic, 
and we can notice that the field value changes from 0.5Bm in 
the middle of the elliptic up to 1.5Bm on the vertices of the 
elliptic as shown in Figure 2. Figure 3 shows the results of the 
simulation aiming to illustrate torque-speed characteristics of a 
3-phase IM. In both, motoring and braking regions when one of 
the three phases in the IM stator is separated from the power 
supply and a variable external resistance is inserted to the rotor 
circuit then decrease in motor speed and torque occurs. 

 

 

 
Fig. 1.  The sine, cosine and net waves of the magnetic density 

III. BREAKING SYSTEMS 

From the above analysis of the rotating magnetic field, it 
can be noticed that if any phase is disconnected, the total 
magnetic flux density presented in the stator, will consist of 
two parts that are changing in sine and cosine waves as shown 
in Figure 2. The total value of the flux is distributed in a 

sinusoidal wave, and it rotates clockwise or counterclockwise 
in an elliptical form. The total value of the flux density in these 
cases will vary from 0.5Bm at middle zone of the ellipse up to 
1.5Bm as shown in Figure 2. The field lines are concentrated 
on the vertices zone of the ellipse and are weakened in the 
middle zone of the same ellipse [2-4]. This causes a high 
magnetic attraction on the vertices (between the stator and 
rotor), which consequently decreases the speed of the motor. 
Integrating the two conventional braking systems [5], the 
electromagnetic braking and plugging braking, is an effective 
and efficient way to turn off the induction motor causing it to 
stop. During the braking process of the electromagnetic brake 
shown in Figure 4, a knife switch as shown in Figure 5 
separates one phase from the motor supply and directly 
connects to the coil of the electromagnetic brake [6-7]. 

 

 
Fig. 2.  The net sinusoidal wave field, and space vector of the rotating field 

when phase current 0AA fails 

 
Fig. 3.  Torque-speed characteristic for a phase failure, in both motoring 

and braking 

 
Fig. 4.  Electromagnetic brake 

While the other two phases have been interchanged using 
the plugging process, this will energize the coil of the 
electromagnetic brake which will cause brake shoes to press on 
the brake drum that is installed on the motor shaft as shown in 
Figure 5. The attraction force (Fatt) between the cores (shoes) 
of the electromagnetic brake coil can be defined by (4): 

78�� = 9:	.�( � 9(    (4) 
where K1 depends on the number of turns of the brake coils, the 
air gap length, the effective area and the reluctance of the 



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www.etasr.com Al-Barbarawi: Improving Performance of the Braking Process, and Analysis Torque-Speed … 

 

armature. K2 is the restraining force usually produced by a 
spring, while I is the rms current of the armature coil. 

 

 

Fig. 5.  Torque-speed characteristic for a phase failure, in both motoring, 

braking and generating 

Once one phase of the motor is disconnected from the 
motor supply, and connected to the electromagnetic brake coils, 
a strong magnetic attraction will be created between the coil 
cores (brake shoes). At the same time the plugging brake of the 
motor will be used by changing the direction of the RMF to 
oppose the direction of the former magnetic field by 
interchanging the connections of the other two phase currents 
of stator with respect to the supply terminals [9]. This leads to a 
decrease of the maximum torque, by 33.3% of its original 
value, as shown in Figure 3 and as a result, the motor 
decelerates to zero before reversing. The resulting slip during 
plugging is (2-S), and the original slip of the running motor is 
(S). Then (S) can be given in the following equation: 

; = <=>	<=?=>       (5) 
where Ns is the synchronous speed and Nm the mechanical 
speed. 

As a result the two supply lines are interchanged, the motor 
speed will decelerate to zero before starting to rotate in the 
opposite direction, and the braking torque is not zero at zero 
speed [8, 9]. A speed sensor can be used to provide a signal to 
circuit breaker to disconnect the two phases from the power 
supply when the speed reaches zero. As a result of activating 
the electromagnetic brake, the motor will stop automatically 
and immediately in a very short time. Braking process will 
work automatically with the appropriate arrangement of the 
switching circuit and a giving appropriate delay time [5]. For 
the proper switching procedure and proper time delay, a 
microcontroller can be used so that switching and time delay 
are easy and reliable. The combined braking system can stop 
the motor in less than 1s, safely, without any over voltage, over 
current or overheating in the motor windings. The illustration 
of the natural torque-speed characteristic for 3-phase, and 2-
phase (when one phase is separated from the motor feed), in 
three regions, motoring, generating and braking is shown in 
Figure 5. The opposite direction of the torque characteristic and 
plugging curve are shown in Figure 7, while Figure 6 illustrates 
the control circuit. 

IV. SIMULINK IMPLEMENTATION OF THE INDUCTION MOTOR 

A simple block diagram is simulated to show how to drive 
an IM and how to use plugging and dynamic braking [10, 11]. 
The simulation is used to study the effects of variation of the 
IM’s parameters and to determine the behavior of any IM at 

plugging process. The simulation model is built up 
systematically by selecting a 3-phase 5hp IM (Table I).  

 

 

Fig. 6.  Control circuit of the electromagnetic-plugging brake 

(a) 

 

(b) 

 
Fig. 7.  (a) Natural torque-speed and (b) opposite direction 

torque-speed characteristics and plugging process 

The mathematical model used to calculate and simulate 
these models has been implemented with the use of 
Matlab/Simulink. The construction of the basic block diagram 
and the mathematical model for the plugging and dynamic 
braking process are based on the ratio between the 
conventional electromagnetic torque equation (Tem) and the 
maximum electromagnetic torque equation (Tmax). Equation (9) 
is the critical slip equation [5]. The effect of various parameters 
such as the variation of the rotor resistance and the variable 
voltage were also used. 

@�� = A BCDE	. F�G.�HGIJ� 	�KLM∗OP	[�GQH�G.�HGIJ� 	�	/KLM�.H�S>T	�.U  (6) 



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@�8V = A BCDE	.(OP	[	AGQHWGQ.HS>T. 	U	   (7) 
X��X?IY = (ZLM∗KTKLM. HKT. = @∗�[\�	   (8) 		;� = �](� + ]8^� � _]:( + K̀�(⁄     (9) 

where Vph is the Voltage, SFL, SC are full load slip and critical 
slip, bc	 the angular velocity, R1, ](�  are the stator and rotor 
resistances while K̀� = :̀ + (̀�  are the stator and rotor 
inductances. ]8^�  is the external resistance.  

TABLE I.  3-PHASE INDUCTION MOTOR PARAMETERS 

P-Power (Watt) 5×746 

Voltage (V) 380 

Frequency (Hz) 50 

R1-Stator resistance (Ω) 1115 

L1s-Stator inductance (H) 0.005974 

R2-Rotor resistance (Ω) 1083 

L2r-Rotor inductance (H) 0.005974 

Lm-Mutual inductance (H) 0.2037 

Inertia, friction factor (kg) 0.02-0.005752 

Pole pairs 2 
 

V. PLUGGING-ELECRTOMAGNETIC BRAKING SIMULATION 

Equations (6)-(9) were simulated in Matlab/Simulink. 
Figure 8 shows the block diagram model used to implement 
how the three phase IM can be driven at normal operation and 
the simulation of the normal plugging and plugging brake. 

 

(a) 

 

(b) 

 
Fig. 8.  Block diagrams of (a) normal operation and (b) plugging 

dynamic braking process 

Figures 9-11 show the obtained results of the dynamic 
behavior of the motor, the oscillating torques as a function of 
speed, the oscillatory stator currents as a function of time 
during startup at normal operation and normal plugging with 
load, without brakes, without phase failure, and its effect upon 
the speed as a function of time and voltage. 

(a) 

 

(b) 

 

(c) 

 
Fig. 9.  Simulation results during normal operation, and its 

effect upon current, torque and speed. 

(a) 

 

(b) 

 
Fig. 10.  Simulation results during normal plugging operation, 

and its effects upon current and torque 

Figures 12 and 13 show the results of the stopping process 
of the motor by using plugging brake, in Matlab/Simulink. The 
source will be disconnected when the speed reaches zero to 
satisfy the plugging braking. It is needed to set the breaker 
parameters on the stator side, to activate the braking when the 
speed reaches zero by using a speed sensor to provide a signal 
to the breaker to automatically and immediately stop it. 

VI. DYNAMIC-PLUGGING BRAKING 

The moment that one of the three phases is separated, the 
plugging brake and dynamic brake of the motor are used 



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instantly while the separate phase is connected to the contactor 
coil in the control circuit in order to insert high resistance with 
the rotor circuit as shown in Figure 1. 

 

(a) 

 

(b) 

 

Fig. 11.  The simulation results during the plugging operation, 

and its effects upon speed and voltage 

(a) 

 

(b) 

 

(c) 

 
Fig. 12.  Simulation results during plugging brake, and its 

effects upon current, torque and speed 

Dynamic braking which has been integrated with the 
plugging brakes is a process in which the kinetic energy of the 
rotor is dissipated in the internal and external resistor as heat 
energy after the main supply separation [9-13]. Dynamic 
braking process is implemented when the motor operates at the 
other two phases, which makes the motor act as a single phase 

motor supplied in the opposite direction as a result of the 
plugging process, which leads to reduction of the braking 
torque. In this case, the motor operation as shown in Figure 6. 
The resistance inserted in the rotor circuit to decelerate the 
motor speed can be obtained by (10): 

]�d8e� =	_]:( + � :̀ − (̀��(	−	](�    (10) 
Figure 14 illustrates the control circuit diagram of the 

plugging and dynamic braking process. 

 

(a) 

 

(b) 

 
Fig. 13.  Simulation results during plugging brake, and its 

effects upon voltage and torque when one phase fails 

 
Fig. 14.  Control circuit of the dynamic-plugging braking with external 

resistances 

As a result of the single phase separation from the motor 
feed, this leads to maximum torque reduction. When the 
plugging brake is used, the magnetic field from the other two 
phases’ currents rotates in an elliptical form on the opposite 
direction. As a result of the plugging and the dynamic process, 
inserting a high external resistance in the rotor circuit makes 
the critical slip increase to one. At this case the speed of the 
motor decreases to reach zero, while the torque is not zero at 
zero speed. Near zero speed, we can use a speed sensor to 
provide a signal to the breaker to automatically operate with the 
appropriate arrangement of the switching circuit and a giving 
appropriate delay time by using the microcontroller switch. The 



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combined braking system can stop the motor very quickly (in 
less than 1s) and safely.  

VII. SIMULATION OF THE DYNAMIC BRAKING 

A Matlab/Simulik implementation approach similar to the 
model discussed above has been used to model the dynamic-
plugging braking for the induction motor by using (6)-(9). 
Figure 15 shows the block diagram model used to implement 
and simulate the motor drive and the dynamic-plugging brake 
using Matlab/Simulink for a three phase IM, to illustrate the 
performance dynamic- plugging brake on the braking process 
of the motor at load, when inserting an external resistance in 
the rotor circuit, with and without disconnection of any phase 
from the motor feed. 

 

(a) 

 

(b) 

 

Fig. 15.  Block diagrams of the IM model 

As highlighted above, when one of the three phases is 
disconnected from the motor feed and simultaneously a 
resistance is added to the rotor circuit, as a result the motor 
speed decelerates to zero. At this instant, a speed sensor is 
activated and provides a signal to breaker to stop the motor 
automatically and to disconnect all current phases. Figure 16 
shows the Matlab/Simulink simulation results regarding 
oscillatory currents during start-up at normal operation, at load 
and at dynamic-plugging brake with and without added 
resistance. 

Figure 17 shows the Matlab/Simulink simulation results 
regarding the effects of the dynamic-plugging brake on the 
braking process of the motor during start-up at normal 
operation at load and at dynamic plugging braking process, 
when inserting external resistance in the rotor circuit, with and 
without disconnection of a phase. 

Another advantage of the added external resistances is that 
it decreases the high oscillatory currents in starting and braking 
process. The mathematical model used is described by (6) and 
(7) or (8) and (9). Figure 18 shows the effect of inserting 
variable external resistance in the rotor circuit, on the torque-
speed characteristics, in motoring and braking regions.  

(a) 

 

(b) 

 

Fig. 16.  Simulation results of the oscillatory currents with and 

without added external resistance 

(a) 

 

(b) 

 
Fig. 17.  Simulation results of the oscillatory currents with and 

without added external resistance 

VIII. CONCLUSIONS 

Experimental and analytic results show that a most reliable 
induction motor fast braking system can be designed through 
the integration of two or more different traditional braking 
methods with utilization of all their properties. We can use a 
microcontroller switch to provide suitable arrangements of the 
switching circuit and to give appropriate time delay between 
stages, which makes the braking system stop safely and 
quickly. This paper shows the experimental and analytic results 
done by the integration of two pairs of conventional braking 
techniques, plugging brake with electromagnetic brake, and 



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plugging brake with dynamic brake. Plugging-electromagnetic 
brake can be done by disconnecting any phase from the power 
supply, and connecting it with an electromagnetic brake which 
will press on the brake disk of the motor.  

 

(a) 

 

(b) 

 
Fig. 18.  Programming results illustrating the effect of the 

added external resistance on the torque-speed characteristics, in 

both regions  

At the same time the connections of the other two phase 
currents of the stator will interchange with respect to supply 
terminals (plugging brake). The plugging braking will develop 
braking torque in the opposite direction of the rotating motor, 
which leads to deceleration to zero, while the braking torque is 
not zero at zero speed. The speed sensor provides a signal to 
circuit breaker to disconnect the two phases from the power 
supply, to make the motor stop automatically and in very short 
time. After that all the phases will disconnect from the voltage 
source before the motor starts to rotate in the reverse direction. 
This braking method provides simple and fast braking action 
but with high braking current and losses during the plugging 
process. 

Dynamic-plugging braking is done by disconnecting one 
phase from the power supply, and connecting it with a control 
circuit that energizes the contactor coil which inserts an 
external resistance in the rotor circuit. This procedure leads to 
increase the braking torque to maximum and the critical slip to 
reach one, which leads to motor speed deceleration to zero. The 
plugging brake procedure is done as above. As a result of 
inserting a resistance in the rotor circuit, the plugging process 
becomes very slow, which activates the speed sensor to provide 
a signal to circuit breaker to disconnect the two phases from the 
power supply in order to stop the motor automatically and 
immediately. Then, all the phases which feed the motor are 
disconnected. 

The presented braking methods are improving the power 
factor by reducing braking current and losses. These methods 
are quicker, more effective and efficient than the conventional 
ones. In the same reasoning, we also can implement a braking 
system by integrating three conventional braking systems, 
plugging braking, dynamic braking and electromagnetic 
braking, which also is effective and efficient. 

REFERENCES 

[1] M. S. Alshamasin, “Control of Zero Sequence Braking for a Three-phase 
Induction Motor Operating from Single-phase Supply with a Controlled 
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