Date of Award

5-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Electrical Engineering

Committee Member

Dr. Edward R. Collins, Jr., Committee Chair

Committee Member

Dr. Elham Makram

Committee Member

Dr. Richard Groff

Committee Member

Dr. Pierluigi Pisu

Committee Member

Dr. Math H.J. Bollen (Honorary)

Abstract

Consumer electronic devices employing active power electronic switching have been increasingly used in the last decade. With the rise in number of these devices, the emission of harmonic currents by these devices has changed both in magnitude and character. The effects of harmonic frequencies up to 2000 Hz on various electrical and electronic devices has been the subject of considerable scrutiny over the past decade. However, newer consumer devices employ switched mode power electronic circuits that switch in the multiple kilohertz range. The emission from these devices, along with power line communication, are sources of high frequency currents in the range of 2 to 150 kHz. As a result, there has been an appreciable rise in the amount of conducted emission in the frequency range 2 to 150 kHz. One of the important outcomes of rising emission in this frequency range is that there have been reported cases of interference with various consumer electronic devices. Among the devices in which interference has been reported are the new generation of solid state LED lamps which have become popular in the last 3-5 years. Considerable research has been done in the past about the effects of light flicker and the modulation of light output from incandescent lamps, on human beings. However, the utilization of power electronic converters changes this paradigm considerably. Unlike incandescent bulbs, where low frequency modulation of input voltage resulted in visible flicker, observations and reports have shown that LED lamps may be susceptible to flicker from frequencies above the 2 kHz mark. As a result, old methods of predicting flicker and studying it may no longer be applicable. This thesis attempts to shorten this gap in knowledge by exploring the topic of LED flicker due to high frequency distortion, and the factors that affect it. This was achieved by exposing LED lamps of various sizes and from various manufacturers, to realistic voltage distortion signals, recorded in the power system. Signals with high-frequency distortion superimposed on to the fundamental, were used. The test set-up used, allowed for the testing of light equipment with various types and levels of distortion at different points on wave. For the first time, experimental results showed that not only does high frequency voltage distortion cause changes in average value of light output and the modulation of light output, but that this change depends upon the point-on-wave at which the high frequency distortion appears. The mathematical tool of cross-correlation was proposed to quantify the effect of point-on-wave of high frequency distortion on light output. The utilization of this tool showed that LED lamps are susceptible to distortion appearing near the peak or near the zero crossing of the input voltage. In order to understand the dependence of LED flicker on the topology of the LED driver, five LED driver development boards available commercially were also subjected to the above mentioned high frequency voltage distortion. The results showed that light flicker from LED lamps is not necessarily a by-product of LED driver topology. The utilization of discontinuous conduction mode of operation and an isolation transformer in the LED driver is not sufficient to disconnect the LED load from input voltage variations. LED drivers of the same topology can behave completely different, likely due to the control methodology employed by each manufacturer. Finally, a simulation model of a popular LED driver solution: a flyback DC-DC converter with primary side regulation was developed to verify the experimental results and perform root cause analysis for the observed phenomena. Changes in control methodology and circuit design were suggested to overcome this flicker problem and evidence of the degradation of circuit components due to excess heat generated by high frequency distortion was shown.

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