Chapter 8 Switch-Mode DC-AC Inverters

1. Chapter 8 Switch-Mode DC-AC Inverters • converters for ac motor drives and uninterruptible power supplies Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

2. Switch-Mode DC-AC Inverter • Block diagram of a motor drive where the power flow is unidirectional Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

3. Switch-Mode DC-AC Inverter • Block diagram of a motor drive where the power flow can be bi-directional Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

4. Switch-Mode DC-AC Inverter • Four quadrants of operation Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

5. One Leg of a Switch-Mode DC-AC Inverter • The mid-point shown is fictitious Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

6. Synthesis of a Sinusoidal Output by PWM Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

7. Details of a Switching Time Period • Control voltage can be assumed constant during a switching time-period Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

8. Harmonics in the DC-AC Inverter Output Voltage • Harmonics appear around the carrier frequency and its multiples Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

9. Harmonics due to Over-modulation • These are harmonics of the fundamental frequency Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

10. Output voltage Fundamental as a Function of the Modulation Index • Shows the linear and the over-modulation regions; square-wave operation in the limit Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

11. Square-Wave Mode of Operation • Harmonics are of the fundamental frequency Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

12. Half-Bridge Inverter • Capacitors provide the mid-point Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

13. Single-Phase Full-Bridge DC-AC Inverter • Consists of two inverter legs Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

14. PWM to Synthesize Sinusoidal Output • The dotted curve is the desired output; also the fundamental frequency Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

15. Analysis assuming Fictitious Filters • Small fictitious filters eliminate the switching-frequency related ripple Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

16. DC-Side Current • Bi-Polar Voltage switching Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

17. Output Waveforms: Uni-polar Voltage Switching • Harmonic components around the switching frequency are absent Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

18. DC-Side Current in a Single-Phase Inverter • Uni-polar voltage switching Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

19. Sinusoidal Synthesis by Voltage Shift • Phase shift allows voltage cancellation to synthesize a 1-Phase sinusoidal output Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

20. Single-Phase Inverter • Analysis at the fundamental frequency Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

21. Square-Wave and PWM Operation • PWM results in much smaller ripple current Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

22. Push-Pull Inverter • Low Voltage to higher output using square-wave operation Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

23. Three-Phase Inverter • Three inverter legs; capacitor mid-point is fictitious Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

24. Three-Phase PWM Waveforms Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

25. Three-Phase Inverter Harmonics Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

26. Three-Phase Inverter Output • Linear and over-modulation ranges Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

27. Three-Phase Inverter: Square-Wave Mode • Harmonics are of the fundamental frequency Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

28. Three-Phase Inverter: Fundamental Frequency • Analysis at the fundamental frequency can be done using phasors Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

29. Square-Wave and PWM Operation • PWM results in much smaller ripple current Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

30. DC-Side Current in a Three-Phase Inverter • The current consists of a dc component and the switching-frequency related harmonics Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

31. Square-Wave Operation • devices conducting are indicated Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

32. PWM Operation • devices conducting are indicated Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

33. Short-Circuit States in PWM Operation • top group or the bottom group results in short circuiting three terminals Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

34. Effect of Blanking Time • Results in nonlinearity Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

35. Effect of Blanking Time • Voltage jump when the current reverses direction Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

36. Effect of Blanking Time • Effect on the output voltage Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

37. Programmed Harmonic Elimination • Angles based on the desired output Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

38. Tolerance-Band Current Control • Results in a variable frequency operation Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

39. Fixed-Frequency Operation • Better control is possible using dq analysis Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

40. Transition from Inverter to Rectifier Mode • Can analyze based on the fundamental-frequency components Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters

41. Summary of DC-AC Inverters • Functional representation in a block-diagram form Chapter 8 Switch-Mode DC- Sinusoidal AC Inverters