Special Electrical Machines

1. PERMANENT MAGNET SYNCHRONOUS MOTOR
-It is an electronically
commutated motor powered by
DC Supply
-This DC supply is used by the
means of switching power supply
to drive each phase of the motor
by a closed loop controller.
- The controller provides pulses
of current to the motor winding .
-These pulses further control the
speed and the torque of the
motor.

2. PARAMETER MECHANICAL COMMUTATOR ELECTRONIC COMMUTATOR
Type of
Commutation
Brushed commutation because
of the mechanical contact
between the brush and the
commutator
Electronic Commutation using
the power semiconductor
devices like the
MOSFET,transistor etc
Position of
Commutator
Commutator are arranged on
the rotor
Commutator are arranged on
the stator
Speed Range Low High
Maintenance High Low
Control Difficult to control Easy to control
Life Shorter Life Longer Life

3. Construction of a PMBLDC Motor:

4. Operating Principle/Operation:
● Self-start motors don’t require any external force for starting.
● As power is supplied the armature winding draws current and flux is produced by the permanent magnets.
● The armature conductors experience a force by the Fleming’s left hand rule.
● This force being reactive in nature develops a torque for rotor rotation.
● If the produced torque is greater than the opposing frictional and load-torque,then the motor starts to
rotate.

5. ● As the speed increases there exists a relative angular velocity between the
permanent field and the armature conductors.
● This relative speed produces as emf in the armature conductors.
● Due to the lenz's law this back emf opposes its cause,that leads to the
reduction in the armature current and the developed torque.
● The rotator attains the steady state speed when the developed torque gets
exactly equal to the opposing frictional and load torque.
● On increase in the load torque, the rotor speed starts decreasing and back emf
generated in the armature winding also starts decreasing.
● And since,the supply voltage remains constant the supply is increased
● The increase in the armature current increase the torque in the motor
● Motor attains a new equilibrium position when the motor torque is equal to
the new load torque.

6. Classification of PMBLDC Motors:
One-phase
One-Pulse
One-Phase
two-pulse
Two-phase
two-pulse
Three-phase
three-pulse
Three-phase
six-pulse
1)This uses only one
semiconductor switch
2)Has only one armature
winding
3)Rotor position sensor gets
turned on and off on being
influenced by the N and S pole
respectively
4)Torque is only developed for
half cycle
1)Has one armature winding
2)Two-static switches used
3)It requires a 3-phase DC
supply
4)Requires a position sensor,
two switching position sensor
and 2 switching devices S1
and S2.
5)S1 is tuned on and off on
the influence of the N and S
pole and the reverse
happens in the case of S2
1)It has 2 armature windings
each displaced by 180.
2)Two semiconductor
switches are used.
3)It requires 2 independent
Phase windings
1)It has 3-phase windings
displaced by an angle of 120
electrical apart.
2)It has 3 switching devices.
3)3 position sensors are
required.
1)It has three-phase
windings.
2)It requires 6
semiconductor switches.
ADVANATGES:
1)The utilization of switch and
winding is 50%
2)Inertia is such that the rotor
rotates contionously
ADVANTAGES
1)Winding Utilization is better
2)A more uniform torque is
devloped
ADVANTAGE:
It produces a better torque
waveform
Multi-phase
Multipuse
1)It has embedded
permanent magnet rotor
2)The stationary armature
has parallel and
independent phase
windindgs

7. Control of PMBLDC Motors:

8. PMBL 120 Degrees Square-wave commutated DC-Motor:
● Three-phase bridge inverter composed of six-switching
devices is used.
● High-side device turned on in one phase and low-side
device is in another phase.
● Both high & Low side devices are turned off in the
remaining phase.
● This commutation technique always conducts electric
current through 2 windings at any one-time
● The phase voltage remaining to a motor’s neutral point
always becomes Vdc/2.

9. PMBL 180 degrees Square-Wave Commutated DC-Motor:
● 3-phase bridge inverters composed of six-switching devices is used.
● At once, only either the upper side or the lower side of the same arm
are turned on.
● Value of the phase voltage here is Vdc/3 or 2Vdc/3.
● Current here flows from the positive to the negative end of the DC bus.
● It produces a current ,4/3 times and torque 35% greater than
commutation in 120 degrees ,if operated on the same voltage.

10. MICROCONTROLLER BASED PMBLDC MOTOR:
● BLDC motor supplied with a power converter having 6
static devices
● Tachometer mounted on shaft to obtain the speed feedback
signal
● Hall-sensors used to provide position signal
● Stator current identified by Current sensor
● Amplitude identified by Optically Isolated Amplifier
● Output signals are multiplexed and converted into digital
form by ADC.
● During normal operation,Input-output terminals sent to
command and the line current,rotor position and speed are
sensed and fed to the CPU.
FUNCTIONS OF A MICROPROCESSOR:
● Receives current signal,position
signal,speed signal and current
references
● Processes the input signals and gives
the appropriate triggering signals to the
switches.
● After the Process, Issues control to
base/gate drive circuit where the signals
are amplified.

11. TORQUE EQUATION OF A PMBLDC MOTOR:

12. EMF EQUATION OF A PMBLDC MOTOR:

13. APPLICATIONS OF PMBLDC MOTORS
Computer Hard Drive, DVD/CD Player
ELECTRIC VEHICLES INDUSTRIAL ROBOTS WASHING MACHINE COMPRESSORS/DRYERS
FANS/PUMPS/BLOWERS

14. THANK YOU