This document discusses voltage source inverter (VSI) and current source inverter (CSI) fed induction motor drives. It explains that the torque produced by an induction motor is proportional to the slip at stable operation, and inversely proportional to the slip at unstable operation. It also notes that induction motors should always be operated at or near zero slip for normal operation. The document describes how VSI and CSI topologies work, including using PWM inverters to vary frequency and voltage. It discusses reasons why MOSFET or IGBT devices are preferred over SCRs. In addition, it explains that CSI drives control torque by varying the DC link current to change output voltage.

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VSI and CSI
fed induction motor drives
Dr. A. Ravi
Professor/EEE
FRANCIS XAVIER ENGINEERING COLLEGE
TIRUNELVELI
Tamil Nadu - India

2. TORQUE EQUATION
Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli
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Slip =0
Slip =1

3. TORQUE EQUATION
Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli
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4.  Stable
 T α s (AB)
 Unstable
 T α1/s (BC)
 Normal Operating Region (AD)
 Always operate the motor at zero slip. 4
Always
operate the
near zero slip

5. VSI FED INDUCTION MOTOR DRIVES
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Voltage
Source
Inverter
Variable frequency
variable voltage
DC
PWM
Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

6. VSI FED INDUCTION MOTOR DRIVES
6Transistor Inverter fed Inductor motor
Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

7. VSI FED INDUCTION MOTOR DRIVES
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Six
Stepped
Inverter
• Control of DC input voltage
• Control of the ac output voltage by use of multiple inverters

8. VSI FED INDUCTION MOTOR DRIVES
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Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

9. VSI FED INDUCTION MOTOR DRIVES (PWM INVERTER)
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Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

10. VSI FED INDUCTION MOTOR DRIVES
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Torque can be calculates considering only for Fundamental voltage,
All tripplen harmonics
absent

11. VSI FED INDUCTION MOTOR DRIVES
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•Because of low frequency harmonics, the motor
losses are increased at all speeds causing derating of
the motor.
•Motor develops pulsating torques due to fifth,
seventh, eleventh and thirteenth harmonics which
cause jerky motion of the rotor at low speeds.
•Harmonic content in motor current increases at low
speeds. The machine saturates at light loads at low
speeds due to high (Vlf ) ratio.
• These two effects overheat the machine at low
speeds, thus limiting lowest speed to around 40% of
base speed.

12. WHY MOSFET OR IGBT IS PREFERRED
 SCR or thyristor is preferred in inverter, because it
need commutation circuit.
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ON- Firing
Circuit
OFF-
Commutation
Circuit
Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

13. WHY MOSFET OR IGBT IS PREFERRED
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Whenever gate supply is there it will
conduct , otherwise no conductoin
Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

14. CSI FED INDUCTION MOTOR DRIVES
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What is current
source
current source
Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

15. CSI FED INDUCTION MOTOR DRIVES
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High value of Inductor Current Source
Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

16. CSI FED INDUCTION MOTOR DRIVES
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The fundamental component of motor phase current
For a given speed, torque is controlled by
varying dc link current Id by changing the
value of Vd.
Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

17. CSI FED INDUCTION MOTOR DRIVES
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Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli

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