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Braking Methods of Induction Motors

Braking Methods of Induction Motors
The induction motor is a rugged, reliable, low
maintenance and less expensive machine. Braking
is one of important questions in electrodynamics
machine system. During production, in order to
decrease auxiliary work time, to raise production
efficiency, to realize halt exactly, to improve
product quality, to ensure personal safety and so
on, a great deal of machines require effective
braking. The braking is the process of reducing the
speed of an induction motor. In braking, the
motor works as a generator developing a negative
torque which opposes the motion of a motor. The
braking of an induction motor is mainly classified
into three types. They are;
Regenerative Braking
Plugging or reverse voltage braking
Dynamic Braking
Regenerative Braking
With the growing concerns towards the
environmental protection and energy
conservation, the development of Electric
Vehicles (EV) and Hybrid Electric Vehicles (HEV)
has been the acceptable challenges for research
and development. Regenerative braking is an
important aspect to improve the efficiency of EV
and HEV. Regenerative braking used in addition
with the traditional mechanical braking is more
apt to the driver's braking requirement while
improving the operating range of the vehicle.
During regenerative braking, the electrical
traction motor provides negative torque to the
driven wheels and converts the kinetic energy into
electrical energy for recharging the battery.
The energy is being dissipated in plugging and
dynamic braking whereas in the regenerative
braking the energy is recovered back into the
system. Thus many researchers have coined new
strategies and designed numerous control
algorithms so as to reduce the complicacy in the
development of regenerative braking. The basic
problem regarding incorporation of regenerative
energy storage in case of ac drive systems is high
dc link voltage at the inverter input side. This
requires a dc-dc converter for charging the
battery at a specific charging rate. In the
applications of hybrid electric vehicle (HEV) user
applies brakes repeatedly. This causes a lot of
energy loss in friction and heating. However, this
energy can be stored in ultra-capacitor and then
battery can be charged with help of it. This
increases the life span of the battery.
Plugging or Reverse Voltage Braking
The deceleration stopping method requires
careful selection of the deceleration time to
achieve optimum stopping performance . It is
sometimes necessary to stop quickly or decelerate
the induction motor under controlled condition as
when lowering a load in a crane or hoist. Such
retardation is effected to by providing a braking
torque. Plugging is one of the electrical braking
methods applicable in the case of induction
motor. The principle of traditional plug braking is
that changing the direction of revolving magnetic
field to oppose the direction of former magnetic
field by changing the phase sequence of threephase voltage, then the motor will be braked by
opposing torque in a short time. If the leads on
the stator windings are reversed suddenly, the
direction of rotation for the stator field is
reversed. The resulting slip is larger than one. The
motor will come to an abrupt stop. The motor
must then disconnected from the voltage source
before it starts to rotate in the reverse direction,
this method of bringing motors to a quick stop is
commonly known as plugging. Reverse-current
braking (plugging) is very effective but consumes
approximately three times the stored kinetic
energy of the system in reducing the speed to
zero, and would run up as a motor in reverse
rotation unless prevented.
Dynamic braking
This braking method involves dissipation of the
kinetic energy of the rotor as heat in resistors
after cutting off supply. This method is widely
used in industrial applications where running
motors can be brought to a halt quickly without
any mechanical tear. After the supply has been
cut off, the rotor of the induction motor, having
some residual magnetic flux, continues to rotate
due to inertia. Hence, the motor acts as a
generator supply electrical energy to the stator.
This energy needs to be dissipated and different
methods have been suggested to do this.
Conventional Dynamic Braking Methods
A. Capacitor self excitation braking
In this method of dynamic braking, capacitors
connected to the stator terminals are used to
consume the kinetic energy of the rotor. When
the supply is cut, the rotor continues to rotate
due to the inertia of the load. The residual
magnetic flux present in the rotor induces emf in
the stator windings and the machine now acts as a
generator. This emf induced excites the three
phase capacitors connected to the stator
windings. The capacitors store this energy coming
from the rotor. The electric power generated is
dissipated as heat in the winding resistances.
Braking is enhanced if external resistors
connected in parallel with the capacitors are used.
from the DC supply. When the rotor is at a
standstill, the emf induced in the stator becomes
zero thereby allowing the full current from the DC
supply to flow through the stator.
D. Zero sequence braking
Zero sequence braking is achieved by connecting
the stator terminals of the induction motor in
series and supplying either AC or DC voltage
across the two terminals This produces a static
field in the stator windings thereby opposing the
rotation of the rotor. One advantage of this
method over the DC injection method is that the
heating is more uniform in zero sequence braking
due to equal currents in the three windings.
B. Magnetic braking
When two or all of the three terminals of the
stator are shorted after switching off main power
supply, magnetic braking is achieved. After the
supply is cut off, the residual magnetic flux of the
rotor rotating due to inertia induces currents in
the short circuit . These induced currents oppose
the motion of the rotor according to Len’s law. In
this way, magnetic braking is achieved.
C. DC injection braking
DC injection braking is achieved when a DC
supply is connected between two stator terminals
with the third being kept open and the main
supply being switched off. This results in zero
frequency current in stator windings and the
induction motor gets inverted into a synchronous
generator with the stator as the field and rotor as
the rotating armature. This stops the rotation of
the rotor with the rotor current becoming zero at
standstill condition. One disadvantage of this
method is that a separate DC source is required.
The analysis of DC injection method has been
done well in where at first, both the DC supply
voltage and speed is varied and then the speed is
kept constant and the DC supply voltage is varied.
The standstill current observed in the both the
cases is found to be greater than the braking
current. This can be attributed to the fact that
initially during braking, the rotor rotates due to
inertia and the residual flux present in it induces
emf in the stator windings to oppose the current
R. Singh, S. Umashankar, D. Vijaykumar and D. P.
Kothari, "Dynamic braking of induction motor Analysis of conventional methods and an efficient
multistage braking model," 2013 International
Conference on Energy Efficient Technologies for
Sustainability, Nagercoil, 2013, pp. 197-206, doi:
A. A. Mahapatra and S. Gopalakrishna,
"Regenerative braking in induction motor drives in
applications to Electric Vehicles," 2014 IEEE
Students' Conference on Electrical, Electronics
and Computer Science, Bhopal, 2014, pp. 1-5, doi:
S. K. Agrawal, V. Kumar, A. Alam and P. Thakura,
"Regenerative braking for induction motor drive,"
2014 6th IEEE Power India International
Conference (PIICON), Delhi, 2014, pp. 1-6, doi:
H. A. Hairik, R. H. Thejel and W. A. Kadhem,
"Proposed scheme for plugging three-phase
induction motor," Melecon 2010 - 2010 15th IEEE
Mediterranean Electrotechnical Conference,
Valletta, 2010, pp. 1-5, doi: