1. 14-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Chapter 14 Induction Motor Drives Extremely large potential as adjustable speed drives

2. 14-2 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Pump Application: Adjustable Flow rate Fixed versus adjustable speed drive

3. 14-3 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Per-Phase Representation Assuming sinusoidal steady state

4. 14-4 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Important Relationships in an Induction Machine Not necessary for our purposes to know the exact expressions for constants used here

5. 14-5 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Torque-Speed Characteristics The linear part of the characteristic is utilized in adjustable speed drives

6. 14-6 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Plot of Normalized Rotor Current It increases with slip and slip frequency

7. 14-7 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Acceleration Torque at Startup Intersection represents the equilibrium point

8. 14-8 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Torque Speed Characteristics at various Frequencies of Applied Voltage The air gap flux is kept constant

9. 14-9 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Adjusting Speed of a Centrifugal Load The load torque is proportional to speed squared

10. 14-10 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Frequency at Startup The torque is limited to limit current draw

11. 14-11 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Increasing Speed at Startup The ramp rate of frequency depends on load inertia

12. 14-12 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Phasor Diagram at Small Value of Slip Frequency The rotor branch is assumed to be purely resistive

13. 14-13 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Voltage Boost to Keep Air Gap Flux at its Rated Value Depends on the torque loading of the machine

14. 14-14 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Induction Motor Drive Capability Curves Mainly two regions

15. 14-15 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Generator Mode of Operation Rotor speeds exceed the synchronous speed

16. 14-16 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Regenerative Braking Mode to Slow Down Machine is made to go into the generator mode

17. 14-17 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Per-Phase Equivalent Circuit at Harmonic Frequencies The magnetizing branch is ignored

18. 14-18 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Torque Pulsations due to Harmonics Rotations of fields due to the fifth and the seventh harmonics are in opposite directions

19. 14-19 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Classification of Converter Systems PWM-VSI is now most commonly use

20. 14-20 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives PWM-VSI System Diode rectifier for unidirectional power flow

21. 14-21 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives PWM-VSI System Options for recovered energy during regenerative braking

22. 14-22 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives General-Purpose Speed Controller High dynamic performance is not the objective here

23. 14-23 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Change in Switching Frequency based on the required Fundamental Frequency Can be significant in large power ratings

24. 14-24 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Field-Oriented Control A concise coverage is presented in “Advanced Electric Drives: Analysis, Control and Modeling using Simulink” by N. Mohan (www.MNPERE.com)

25. 14-25 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Square-Wave VSI Waveforms Large peak-peak ripple in currents

26. 14-26 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives CSI Drives Mostly PWM-VSI drives are used

27. 14-27 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Comparison of Three Types of Inverter Systems PWM-VSI is by far the most commonly selected system now

28. 14-28 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Speed Control by Adjusting the Stator Voltage Highly inefficient in most cases

29. 14-29 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Controlling the Stator Voltage Magnitude Results in distorted current and torque pulsations

30. 14-30 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Torque-Speed Curves for Wound-Rotor Machines Highly energy-inefficient unless using energy recovery schemes

31. 14-31 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 14 Induction Motor Drives Static Slip Recovery Applications in very large power ratings where the speed is to be adjusted over a very limited range