Controlling HID lamps by intelligent power electronics

1. Controlling HID lamps by intelligent power electronics Geert Deconinck, Peter Tant K.U.Leuven-ESAT 8 November 2007

2. Outline • discharge lamps • role of ballasts for discharge lamps • variable frequency high-voltage power supply for hot-restrike modelling of HID lamps • cold breakdown experiments • hot restrike experiments • conclusions

3. Discharge lamps • breakdown and arc • between electrodes in tube • collisions • ionising / elastic / inelastic collisions • Planck’s law • discrete spectrum

4. Discharge voltage vs. discharge current

5. Low pressure discharge lamps • fluorescent lamps (TL) • mercury, sodium, … • 50-100 lm/W, 8000 hr • compact fluorescent lamps • energy saving • 35-70 lm/W, 10000 hr

6. High pressure discharge lamps • higher luminance • compact discharge tube •  high intensity discharge (HID) lamps • typical 80-200 lm/W, up to 25000 hr

7. HID lamp

8. Outline • discharge lamps • role of ballasts for discharge lamps • variable frequency high-voltage power supply for hot-restrike modelling of HID lamps • cold breakdown experiments • hot restrike experiments • conclusions

9. Role of control gear • ballasts provide power supply • correct starting and operating voltage and current • initiate & sustain arc discharge between lamp electrodes • ignition: high voltage required (kV) • limit current to correct levels • discharge lamps have negative resistance • ‘ballasts’, auxiliaries

10. Starter and ballast for TL-lamp

11. Ballast characteristics • ballast factor • power factor • lamp current crest factor • total harmonic distortion

12. Ballast types • ‘passive’ magnetic ballasts • core & coil • at net frequency • ‘active’ electronic ballasts • at higher frequency • often integrated starter

13. Electronic ballast

14. Electronic ballasts • operate at higher frequencies • 40-60 kHz for low-pressure discharge lamps • 100-400 Hz for low wattage HID lamps • 100-130 kHz for high wattage HID lamps • higher frequency allows smaller size of coils • avoid interference and resonance in arc • no stroboscopic effects • smaller, lighter, more efficient • more ionised gas • flux +8..12 % above 10 kHz

15. Electronic ballasts • compensate lamp characteristics • at start-up: ignition (breakdown) + warm-up • in steady-state • sometimes separate start-up device • higher voltage is less statistical lag time • often many consequent start-up pulses • typical HID – ballast • PFC (power factor correction) + H-bridge • typically 400 Hz (no resonance) blockwave

16. Electronic ballast advantages:lamp protection • can allow protection of lamp • e.g. at end of life, to ensure that if inner tube breaks, no external arc is established • based on measuring low or erratic voltages • output short-circuit protection • thermal protection within ballast • internal fusing

17. Electronic ballast advantages (ctd.) • better colour output • colour output depends on operating point (power) • (e.g. ceramic HID) • maintaining current for optimal operating point • e.g. 200K over lamp life • also when lamp is ageing • also for incoming voltage changes (surges / sags) • allows dimming • continuous dimming for 50%-100% of lamp power • automatically after 15’ warm-up period • allows integration with domotics (IED)

18. Electronic ballasts disadvantages • higher capital cost • sometimes lower power quality • (depends on components, e.g. PFC) • harmonics  filters required • but also for magnetic ballasts • interference • filters required

19. Outline • discharge lamps • role of ballasts for discharge lamps • variable frequency high-voltage power supply for hot-restrike modelling of HID lamps • cold breakdown experiments • hot restrike experiments • conclusions

20. Power supply for HID lamps • HID lamps require a high ignition voltage • 1 to 4 kV in cold condition • up to several tens of kV in hot condition, hot-restrike • trend mercury-free HID lamps: higher ignition voltages • characterization of (cold lamp) ignition properties • = statistical analysis • characterization of hot-restrike properties • ballast design • output voltage, output voltage for a given restrike time… • given ballast: estimation of restrike time,…

21. Approach • power electronics power supply • continuous sine-wave output voltage • adjustable frequency (<300 kHz) • variable amplitude ( <15 kV) • low harmonic contents, no switching noise  research purposes • control and protection mechanisms • automated measurements of hot-restrike characteristics

22. Test setup

23. Test setup asymmetrical H-bridge LC resonance circuit comprising T, L and C high sinusoidal voltage across C

24. Test setup lamp connected in parallel with C high-bandwidth, high-voltage 1:1000 probe Rogowski coil current sensor

25. Test setup switching rate controlled by pulse generator adjust to resonance frequency of LC circuit

26. Test setup DC bus voltage  output voltage amplitude programmable waveform generator

27. Test setup optional resistor Rlim limits breakdown current(omitted when LC tank energy is small)

28. Test setup DSO: records voltage, current and timestamp at each breakdown

29. Test setup Res. Diss. Res. detect the first breakdown event, and inhibit further control pulses ENABLE Res. Diss. Off

30. Test setup lamp ballast in series with the igniter circuit

31. Outline • discharge lamps • role of ballasts for discharge lamps • variable frequency high-voltage power supply for hot-restrike modelling of HID lamps • cold breakdown experiments • hot restrike experiments • conclusions

32. Test procedurecold breakdown experiments • amplitude waveform generator produces repeating linear ramps •  ramp rate (kV/s) • when breakdown occurs: • a scope image is recorded • further pulses are blocked • after given sample time (5s), voltage ramp restarts

33. Measurement resultscold breakdown experiments • context • 39 W metal halide lamp • room temperature, fRES = 50 kHz • ramp rate = 762 V/s (slow) • 300 measurement samples

34. Measurement resultscold breakdown experiments • discussion • distribution of breakdown voltage:long right tail (not a normal distribution). • a free electron must be available • statistical time lag between exceeding min. VBD and actual breakdown

35. Measurement resultscold breakdown experiments 762 V/s 1550 V/s

36. Outline • discharge lamps • role of ballasts for discharge lamps • variable frequency high-voltage power supply for hot-restrike modelling of HID lamps • cold breakdown experiments • hot restrike experiments • conclusions

37. Test procedurehot restrike experiments • lamp burns at nominal power for 15 min. • at t = 0, the lamp is switched off • output voltage rises until lamp ignites • when breakdown occurs: • a scope image is recorded • further pulses are blocked

38. Measurement resultshot restrike experiments • 39W metal halide arc tube only • fRES = 50 kHz, ramp rate = 4.4 kV/s (slow) - High initial VBD- High statistical spread < Steady state VBD Steady state VBD

39. Measurement resultshot restrike experiments • 39W MHD lamp • arc tube + jacket, single-ended • fRES = 50 kHz, ramp rate = 4.4 kV/s (slow) External breakdown Steady state VBD < Steady state VBD

40. Measurement resultshot restrike experiments • 39W MHD lamp • fRES = 100 kHz, ramp rate = 348 V/ms (high)

41. Outline • discharge lamps • role of ballasts for discharge lamps • variable frequency high-voltage power supply for hot-restrike modelling of HID lamps • cold breakdown experiments • hot restrike experiments • conclusions

42. Conclusions • versatile & simple power supply for testing purposes • output: high voltage & continuous wave • avoid saturation of output inductors • avoid excessive power dissipation in output capacitor • multiple, subsequent lamp breakdowns avoided • lamp temperature and electrodes are affected • detection of breakdown • voltage ramp rate is an important parameter • lower ramp rate = • lower mean breakdown voltage • less statistical spread

43. Questions?