1. ECE 442 Power Electronics1 Series-Resonant Inverter

2. ECE 442 Power Electronics2 Operation T 1 fired, resonant pulse of current flows through the load. The current falls to zero at t = t 1m and T 1 is “self – commutated”. T 2 fired, reverse resonant current flows through the load and T 2 is also “self-commutated”. The series resonant circuit must be underdamped, R 2 < (4L/C)

3. ECE 442 Power Electronics3 Operation in Mode 1 – Fire T 1

4. ECE 442 Power Electronics4

5. 5 To find the time when the current is maximum, set the first derivative = 0

6. ECE 442 Power Electronics6 To find the capacitor voltage, integrate the current The current i 1 becomes = 0 @ t=t 1m

7. ECE 442 Power Electronics7

8. 8 Operation in Mode 2 – T 1, T 2 Both OFF

9. ECE 442 Power Electronics9 t 2m

10. ECE 442 Power Electronics10 Operation in Mode 3 – Fire T 2

11. ECE 442 Power Electronics11

12. ECE 442 Power Electronics12

13. ECE 442 Power Electronics13

14. ECE 442 Power Electronics14 Summary -- Series Resonant Inverter

15. ECE 442 Power Electronics15 To avoid a short-circuit across the main dc supply, T 1 must be turned OFF before T 2 is turned ON, resulting in a “dead zone”. This “off-time” must be longer than the turn-off time of the thyristors, t q. The maximum possible output frequency is

16. ECE 442 Power Electronics16 Series Resonant Inverter Coupled Inductors

17. ECE 442 Power Electronics17 Improvement in performance When T 1 turned ON, voltage @ L 1 is as shown, voltage @ L 2 in same direction, adding to the voltage @ C This turns T 2 OFF before the load current falls to 0.

18. ECE 442 Power Electronics18 Half-Bridge Series Resonant Inverter Note: L 1 = L 2 C 1 = C 2

19. ECE 442 Power Electronics19 This configuration reduces the high-pulsed current from the dc supply Power drawn from the source during both half-cycles of the output. Half of the current is supplied from the associated capacitor, half of the current is supplied from the source.

20. ECE 442 Power Electronics20 Full-Bridge Series-Resonant Inverter

21. ECE 442 Power Electronics21 Characteristics of the full-bridge inverter This configuration provides higher output power. Either T 1 -T 2 or T 3 -T 4 are fired. Supply current is continuous but pulsating.

22. ECE 442 Power Electronics22 Example 8.1 – Analysis of the Basic Resonant Inverter L 1 = L 2 = L = 50μH C = 6μF R = 2Ω V s = 220V f o = 7kHz t q = 10μs

23. ECE 442 Power Electronics23 Determine the resonant frequency The resonant frequency in Hz

24. ECE 442 Power Electronics24 Determine the turn-off time t off

25. ECE 442 Power Electronics25 Determine the maximum permissible frequency

26. ECE 442 Power Electronics26 Determine the peak-to-peak capacitor voltage

27. ECE 442 Power Electronics27 Determine the peak load current

28. ECE 442 Power Electronics28 Sketch the instantaneous load current, capacitor voltage, and dc supply current

29. ECE 442 Power Electronics29 Calculate the rms load current

30. ECE 442 Power Electronics30 Using MATHCAD, I o = 44.1Amperes

31. ECE 442 Power Electronics31 Determine the output power

32. ECE 442 Power Electronics32 Determine the average supply current

33. ECE 442 Power Electronics33 Determine the average, peak, and rms thyristor currents

34. ECE 442 Power Electronics34 rms Thyristor Current Using MATHCAD