Control and Driving Methods for LED Based Intelligent Light Sources

Research output: Book/ReportPh.D. thesisResearch

Abstract

High power light-emitting diodes allow the creation of luminaires capable of generating saturated colour light at very high efficacies. Contrary to traditional light sources like incandescent and high-intensity discharge lamps, where colour is generated using filters, LEDs use additive light mixing, where the intensity of each primary colour diode has to be adjusted to the needed intensity to generate specified colour.

The function of LED driver is to supply the diode with power needed to achieve the desired intensity. Typically, the drivers operate as a current source and the intensity of the diode is controlled either by varying the magnitude of the current or by driving the LED with a pulsed current and regulate the width of the pulse. It has been shown previously, that these two methods yield different effects on diode's efficacy and colour point.

A hybrid dimming strategy has been proposed where two variable quantities control the intensity of the diode. This increases the controllability of the diode giving new optimisation possibilities. It has been shown that it is possible to compensate for temperature drift of white diode's colour point using hybrid dimming strategy. Also, minimisation of peak wavelength shift was observed for InGaN diodes.

Control of trichromatic luminaires, dimmed with either pulse-width modulation or amplitude modulation, cannot be optimised. Introduction of hybrid dimming mechanism creates three additional degrees of freedom therefore luminaire parameters such as luminous flux, efficacy and colour quality can be maximised. Simulations show that the gamut of the device can be increased, especially in the cyan colour range for \rgb{} luminaires.

A current-voltage model of light-emitting diode is presented. It utilises the fact that instantaneous values of diode's current and voltage correspond uniquely to a set of diode's colorimetric properties, like tristimulus values. This model can be used for colorimetric feedback in colour control loop. The model was created in thermal steady-state conditions and its validity has been tested with a diode driven with a pulsed current. The model can also be used to create highly accurate luminaire model.

Finally, a dual interleaved buck converter has been proposed for driving high power light-emitting diodes. Interleaving two converters lowers the output ripple current thus lowering the requirement on the output capacitor. It has been shown that at the expense of cost and increased complexity an efficient design can be created for supplying high current to LEDs without the need for electrolytic capacitors.
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High power light-emitting diodes allow the creation of luminaires capable of generating saturated colour light at very high efficacies. Contrary to traditional light sources like incandescent and high-intensity discharge lamps, where colour is generated using filters, LEDs use additive light mixing, where the intensity of each primary colour diode has to be adjusted to the needed intensity to generate specified colour.

The function of LED driver is to supply the diode with power needed to achieve the desired intensity. Typically, the drivers operate as a current source and the intensity of the diode is controlled either by varying the magnitude of the current or by driving the LED with a pulsed current and regulate the width of the pulse. It has been shown previously, that these two methods yield different effects on diode's efficacy and colour point.

A hybrid dimming strategy has been proposed where two variable quantities control the intensity of the diode. This increases the controllability of the diode giving new optimisation possibilities. It has been shown that it is possible to compensate for temperature drift of white diode's colour point using hybrid dimming strategy. Also, minimisation of peak wavelength shift was observed for InGaN diodes.

Control of trichromatic luminaires, dimmed with either pulse-width modulation or amplitude modulation, cannot be optimised. Introduction of hybrid dimming mechanism creates three additional degrees of freedom therefore luminaire parameters such as luminous flux, efficacy and colour quality can be maximised. Simulations show that the gamut of the device can be increased, especially in the cyan colour range for \rgb{} luminaires.

A current-voltage model of light-emitting diode is presented. It utilises the fact that instantaneous values of diode's current and voltage correspond uniquely to a set of diode's colorimetric properties, like tristimulus values. This model can be used for colorimetric feedback in colour control loop. The model was created in thermal steady-state conditions and its validity has been tested with a diode driven with a pulsed current. The model can also be used to create highly accurate luminaire model.

Finally, a dual interleaved buck converter has been proposed for driving high power light-emitting diodes. Interleaving two converters lowers the output ripple current thus lowering the requirement on the output capacitor. It has been shown that at the expense of cost and increased complexity an efficient design can be created for supplying high current to LEDs without the need for electrolytic capacitors.
Original languageEnglish
PublisherDepartment of Energy Technology, Aalborg University
Number of pages133
StatePublished - 2012
Publication categoryResearch

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