Download Discharge lamps

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
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Discharge lamps
• breakdown and arc

anode
between electrodes in tube
• collisions

kathode

ionising / elastic / inelastic collisions
• Planck’s law h. f  W2  W1
• discrete spectrum
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Discharge voltage vs. discharge current
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Low pressure discharge lamps
• fluorescent lamps (TL)
mercury, sodium, …
 50-100 lm/W, 8000 hr

Straling in het
zichtbare gebied
Ultraviolette straling
Fluorescerend
poeder
• compact fluorescent lamps
Kwikatoom
Elektronen
Elektrode
(gloeidraad)

energy saving
 35-70 lm/W, 10000 hr
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High pressure discharge lamps
• higher luminance

compact discharge tube
•  high intensity discharge (HID) lamps
• typical 80-200 lm/W, up to 25000 hr
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HID lamp
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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
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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
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Starter and ballast for TL-lamp
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Ballast characteristics
• ballast factor
• power factor
commercial ballast light output
BF 
laboratory reference ballast light output
PF 
total power
input voltage  input current
• lamp current crest factor
peak current
CF 
RMS current
• total harmonic distortion
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Ballast types
• ‘passive’ magnetic ballasts

core & coil
 at net frequency
• ‘active’ electronic ballasts

at higher frequency
 often integrated starter
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Electronic ballast
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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
o
flux +8..12 % above 10 kHz
© K.U.Leuven - ESAT/ELECTA
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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
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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
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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
o
o
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
o
automatically after 15’ warm-up period
• allows integration with domotics (IED)
© K.U.Leuven - ESAT/ELECTA
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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
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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
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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
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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
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Test setup
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Test setup
asymmetrical H-bridge
LC resonance circuit comprising T, L and C
high sinusoidal voltage across C
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Test setup
lamp connected in parallel with C
high-bandwidth, high-voltage 1:1000 probe
Rogowski coil current sensor
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Test setup
switching rate controlled by pulse generator
adjust to resonance frequency of LC circuit
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Test setup
DC bus voltage  output voltage amplitude
programmable waveform generator
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Test setup
optional resistor Rlim limits breakdown current
(omitted when LC tank energy is small)
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Test setup
DSO: records voltage, current and timestamp at each breakdown
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Test setup
Res.
Diss.
Res.
detect the first breakdown event,
and inhibit further control pulses
Res.
Diss.
Off
ENABLE
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Test setup
lamp ballast in series with the igniter circuit
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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
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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
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Measurement results
cold breakdown experiments
• context

39 W metal halide lamp
 room temperature, fRES = 50 kHz
 ramp rate = 762 V/s (slow)
 300 measurement samples
© K.U.Leuven - ESAT/ELECTA
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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
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Measurement results
cold breakdown experiments
762 V/s
1550 V/s
© K.U.Leuven - ESAT/ELECTA
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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
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Measurement results
hot 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
© K.U.Leuven - ESAT/ELECTA
Steady state VBD
38
Measurement results
hot 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
© K.U.Leuven - ESAT/ELECTA
Steady state VBD
39
Measurement results
hot restrike experiments
• 39W MHD lamp
• fRES = 100 kHz, ramp rate = 348 V/ms (high)
© K.U.Leuven - ESAT/ELECTA
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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 =
o
o
lower mean breakdown voltage
less statistical spread
© K.U.Leuven - ESAT/ELECTA
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Questions?
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