Synchronous motor drive

1. Presentation
on
Synchronous motor Drive

2. Self controlled drive empoying load
commutated inverter
• Each phase of a synchronous motor is
represented by an internal voltage in series
with the motor inductance assuming a non-
sailent pole motor.
• The dc output voltage of the controlled
converter can be controlled by changing the
firing angle α.
• The load inverter is a converter operating in
the inverter mode with α greater than 90°.

4. • The three phase motor voltages are measured
using the measurement transformer,to
calculate the position of the rotor field current
as a function of time as shown in fig...
• These voltages are then rectified to provide a
dc signal proportional to the instantaneous
rotor speed.
• Keeping If and toff constant,the actual speed
is compared with the reference speed.
control circuit for load commutated
inverter based synchronous motor drive

6. • Show in the fig. At the time of starting and at
low speeds the induced emf in synchronous
motor is not sufficient to ensure the current
commutation of the load inverter thyristor.
• The frequency and phase current should be
changed in synchronization with the rotor
position.
• The fillter inductance reduces the current
harmonics and ensures that the input to the
load inverter and hence to the motor appears
to be a current source.

7. • The actual DC link current is sensed by a current
sensor.
• If the actual value of Id is less than the reference
value,then the line converter increases the dc
voltage applied to the link thus increasing Id and
the torque produce by the motor.
• The torque producing of the motor is
decreases,but the motor can supply the rated
power .
• The rated speed ,the field flux needs to be
weakened by reducing If ,this region is called as
flux weakening region.

8. closed loop control of load
commutated inverter synchronous
motor

9. • Shown in the fig..there are two feedback loops.
• The outer loop is the speed loop while inner loop
is the current loop.
• The inner control loop are some circuits are
emplay only the speed feedback.
• The motor is required to operate at a desired
speed but it has to meet the load torque
requirement ,which depends on motor current
Idc.

10. Speed sensing
• As shown in the fig..the terminal voltage
sensor senses the stator voltage and
generates a pulsed waveform the frequency
of which is same as the machine induced
voltage.it is proportional to the speed of the
rotor.
• The speed error signal is applied to the speed
controller as shown in figure..

11. Current sensing
• The feedback signal is applied to a comparator
which compares it with the current reference
signal produced by the speed controller ,to
produce Vc to the control the firing angle of
the source side converter shown in fig ..

12. 1.speed controller:
• The speed controller is a (P+I) type controller
which produces an output voltage
proportional to the error between the set or
desired speed and the actual speed.
• The output of the speed control is called as
torque reference.

13. 2.current controller
• This is also a controller which generates the
control voltage that decides the firing angle of
the converter.
• The input to the current controller is the error
signal between the torque reference signalat
the output of speed controller and the current
feedback signal.

14. Properties
• Used for the synchronous motor in very large
HP rating.
• The load commutated inverter is simple and
has lower compared to the inverter used in
CSI -induction motor drives .
• The power switches used in the LCI may not
have the self commutation capacity.

15. Thank you…