This document discusses various methods for controlling the speed of AC induction motors, including stator-side control by varying voltage or frequency, and rotor-side control using cascade control, adding rotor resistance, or slip power recovery schemes. Stator-side control involves changing the stator voltage using autotransformers or resistors, or changing the frequency which varies the synchronous speed. Rotor-side control techniques include cascade control using two motors, adding external resistance in the rotor circuit, or recovering slip power using Kramer or Scherbius systems.

1. CONVENTIONAL AND SOLID STATE SPEED
CONTROL OF AC DRIVES

2. SPEED CONTROL OF THREE PHASE
INDUCTION MOTOR
 Stator side control
1.Stator voltage control
2.Stator frequency control
3.V/f control
4.Pole changing method
 Rotor side control
1.Adding external resistance in the rotor circuit
2.Cascade control
3.Slip power recovery scheme

3. Stator side control
Change in stator voltage
1.Using autotransformer
2.Primery resistors connected in series with stator
winding

4. Using autotransformers

5. Primary resistors connected in
series with stator winding

7. Change in stator frequency
 Synchronous speed of the motor
NS = 120f/P
f=supply frequency
P=number of poles

8. Change in stator frequency

9. Voltage/frequency control

10. Speed torque characteristics by
v/f method

11. Changing the number of poles
 Synchronous speed of the motor
NS = 120f/P
f=supply frequency
P=number of poles

14. Rotor side control
A. Cascade control
B. Rotor resistance control
C. Slip power recovery scheme
1.Kramer system
i.Conventional method
ii.Static method
2.Scherbius system
i.Conventional method
ii.Static method

15. Cascade control

17. DISADVANTAGES OF CASCADE CONTROL
 This method requires two motors
 More expensive
 Wide range of speed control is not possible
 It cannot be operated when
P1=P2 or P1<P2

18. Rotor resistance control

20. Slip power recovery scheme
 Used to speed control the slip ring induction motor
 Speed control by varying the stator voltage or
by controlling the power flow in the rotor circuit

21. Types of Slip power recovery scheme
1.Kramer system
i.Conventional method
ii.Static method
2.Scherbius system
i.Conventional method
ii.Static method

22. Conventional kramer system

23. Improved version of kramer
system

24. Improved version of kramer
system

25. Conventional scherbius system