Controlling HID lamps by intelligent power electronics Geert

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

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 © K. U. Leuven - ESAT/ELECTA 2

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

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

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 § © K. U. Leuven - ESAT/ELECTA 5

High pressure discharge lamps • higher luminance § compact discharge tube • high intensity discharge (HID) lamps • typical 80 -200 lm/W, up to 25000 hr © K. U. Leuven - ESAT/ELECTA 6

HID lamp © K. U. Leuven - ESAT/ELECTA 7

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 © K. U. Leuven - ESAT/ELECTA 8

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 (k. V) • limit current to correct levels § discharge lamps have negative resistance • ‘ballasts’, auxiliaries © K. U. Leuven - ESAT/ELECTA 9

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

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

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

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

Electronic ballasts • operate at higher frequencies 40 -60 k. Hz for low-pressure discharge lamps § 100 -400 Hz for low wattage HID lamps § 100 -130 k. Hz 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 +8. . 12 % above 10 k. Hz © K. U. Leuven - ESAT/ELECTA 14

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 15

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 16

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 e. g. 200 K over lamp life o also when lamp is ageing o also for incoming voltage changes (surges / sags) o • 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 17

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 18

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 © K. U. Leuven - ESAT/ELECTA 19

Power supply for HID lamps • HID lamps require a high ignition voltage 1 to 4 k. V in cold condition § up to several tens of k. V 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 20

Approach • power electronics power supply • continuous sine-wave output voltage adjustable frequency (<300 k. Hz) § variable amplitude ( <15 k. V) § low harmonic contents, no switching noise research purposes § • control and protection mechanisms • automated measurements of hot-restrike characteristics © K. U. Leuven - ESAT/ELECTA 21

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

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

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

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

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

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

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

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

Test setup lamp ballast in series with the igniter circuit © K. U. Leuven

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 © K. U. Leuven - ESAT/ELECTA 31

Test procedure cold breakdown experiments • amplitude waveform generator produces repeating linear ramps § ramp rate (k. V/s) • when breakdown occurs: a scope image is recorded § further pulses are blocked § • after given sample time (5 s), voltage ramp restarts © K. U. Leuven - ESAT/ELECTA 32

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

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. VBD and actual breakdown § © K. U. Leuven - ESAT/ELECTA 34

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

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 © K. U. Leuven - ESAT/ELECTA 36

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 37

Measurement results hot restrike experiments • 39 W metal halide arc tube only • f. RES = 50 k. Hz, ramp rate = 4. 4 k. V/s (slow) - High initial VBD - High statistical spread < Steady state VBD © K. U. Leuven - ESAT/ELECTA Steady state VBD 38

Measurement results hot restrike experiments • 39 W MHD lamp § arc tube + jacket, single-ended • f. RES = 50 k. Hz, ramp rate = 4. 4 k. V/s (slow) External breakdown < Steady state VBD © K. U. Leuven - ESAT/ELECTA Steady state VBD 39

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

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 © K. U. Leuven - ESAT/ELECTA 41

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 o less statistical spread o © K. U. Leuven - ESAT/ELECTA 42