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

© K.U.Leuven - ESAT/ELECTA 2Outline 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

© K.U.Leuven - ESAT/ELECTA 3 Discharge lamps breakdown and arc between electrodes in tube collisions ionising / elastic / inelastic collisions Plancks law discrete spectrum

© K.U.Leuven - ESAT/ELECTA 4 Discharge voltage vs. discharge current

© K.U.Leuven - ESAT/ELECTA 5 Low pressure discharge lamps fluorescent lamps (TL) mercury, sodium, … lm/W, 8000 hr compact fluorescent lamps energy saving lm/W, hr

© K.U.Leuven - ESAT/ELECTA 6 High pressure discharge lamps higher luminance compact discharge tube high intensity discharge (HID) lamps typical lm/W, up to hr

© K.U.Leuven - ESAT/ELECTA 7 HID lamp

© K.U.Leuven - ESAT/ELECTA 8Outline 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

© K.U.Leuven - ESAT/ELECTA 9 Role of control gear ballasts provide power supply correct starting and operating voltage and current o initiate & sustain arc discharge between lamp electrodes ignition: high voltage required (kV) limit current to correct levels discharge lamps have negative resistance ballasts, auxiliaries

© K.U.Leuven - ESAT/ELECTA 10 Starter and ballast for TL-lamp

© K.U.Leuven - ESAT/ELECTA 11 Ballast characteristics ballast factor power factor lamp current crest factor total harmonic distortion

© K.U.Leuven - ESAT/ELECTA 12 Ballast types passive magnetic ballasts core & coil at net frequency active electronic ballasts at higher frequency often integrated starter

© K.U.Leuven - ESAT/ELECTA 13 Electronic ballast

© K.U.Leuven - ESAT/ELECTA 14 Electronic ballasts operate at higher frequencies kHz for low-pressure discharge lamps Hz for low wattage HID lamps 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 o flux % above 10 kHz

© K.U.Leuven - ESAT/ELECTA 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

© K.U.Leuven - ESAT/ELECTA 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

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

© K.U.Leuven - ESAT/ELECTA 18 Electronic ballasts disadvantages higher capital cost sometimes lower power quality (depends on components, e.g. PFC) harmonics filters required o but also for magnetic ballasts interference o filters required

© K.U.Leuven - ESAT/ELECTA 19Outline 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

© K.U.Leuven - ESAT/ELECTA 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 o output voltage, output voltage for a given restrike time… given ballast: estimation of restrike time,…

© K.U.Leuven - ESAT/ELECTA 21Approach 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

© K.U.Leuven - ESAT/ELECTA 22 Test setup

© K.U.Leuven - ESAT/ELECTA 23 Test setup asymmetrical H-bridge LC resonance circuit comprising T, L and C high sinusoidal voltage across C

© K.U.Leuven - ESAT/ELECTA 24 Test setup lamp connected in parallel with C high-bandwidth, high-voltage 1:1000 probe Rogowski coil current sensor

© K.U.Leuven - ESAT/ELECTA 25 Test setup switching rate controlled by pulse generator adjust to resonance frequency of LC circuit

© K.U.Leuven - ESAT/ELECTA 26 Test setup DC bus voltage output voltage amplitude programmable waveform generator

© K.U.Leuven - ESAT/ELECTA 27 Test setup optional resistor R lim limits breakdown current (omitted when LC tank energy is small)

© K.U.Leuven - ESAT/ELECTA 28 Test setup DSO: records voltage, current and timestamp at each breakdown

© K.U.Leuven - ESAT/ELECTA 29 Test setup Res. Diss. ENABLE Res.Diss.Off detect the first breakdown event, and inhibit further control pulses

© K.U.Leuven - ESAT/ELECTA 30 Test setup lamp ballast in series with the igniter circuit

© K.U.Leuven - ESAT/ELECTA 31Outline 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

© K.U.Leuven - ESAT/ELECTA 32 Test procedure cold 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

© K.U.Leuven - ESAT/ELECTA 33 Measurement results cold breakdown experiments context 39 W metal halide lamp room temperature, f RES = 50 kHz ramp rate = 762 V/s (slow) 300 measurement samples

© K.U.Leuven - ESAT/ELECTA 34 Measurement results cold 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. V BD and actual breakdown

© K.U.Leuven - ESAT/ELECTA 35 Measurement results cold breakdown experiments 762 V/s 1550 V/s

© K.U.Leuven - ESAT/ELECTA 36Outline 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

© K.U.Leuven - ESAT/ELECTA 37 Test procedure hot 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

© K.U.Leuven - ESAT/ELECTA 38 Measurement results hot restrike experiments - High initial V BD - High statistical spread < Steady state V BD Steady state V BD 39W metal halide arc tube only f RES = 50 kHz, ramp rate = 4.4 kV/s (slow)

© K.U.Leuven - ESAT/ELECTA 39 Measurement results hot restrike experiments 39W MHD lamp arc tube + jacket, single-ended f RES = 50 kHz, ramp rate = 4.4 kV/s (slow) External breakdown < Steady state V BD Steady state V BD

© K.U.Leuven - ESAT/ELECTA 40 Measurement results hot restrike experiments 39W MHD lamp f RES = 100 kHz, ramp rate = 348 V/ms (high)

© K.U.Leuven - ESAT/ELECTA 41Outline 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

© K.U.Leuven - ESAT/ELECTA 42Conclusions 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 = o lower mean breakdown voltage o less statistical spread

© K.U.Leuven - ESAT/ELECTA 43Questions?