Direct Current Control and Compensation of Non-Linearity for the Impovement of Quality Parameters of the LED Lamp
2015
Oļegs Tetervenoks

Defending
13.05.2015. 13:00, Rīgas Tehniskās universitātes Enerģētikas un elektrotehnikas fakultātē, Āzenes ielā 12/1, 212. telpā.

Supervisor
Iļja Galkins

Reviewers
Oskars Krievs, Enrique Romero-Cadaval, Eino Tetri

The present Doctoral Thesis is devoted to the study and development of energy efficient drivers of LED lamps for smart lighting systems. LEDs have already proved themselves as highly efficient light source with many benefits for use in modern high quality lighting systems. However, LEDs also have significant drawbacks. One of the main drawbacks is high initial costs when moving to a new LED based lighting system. High initial costs must be compensated by lower system maintenance costs (lower electrical power consumption, longer service life) in order to motivate consumer to implement LED based lighting system. At the same time, the service life of such lighting system depends on many factors, but there are two main problematic elements to highlight. LED by itself, which is temperature sensitive element (faster degradation under high temperature conditions) and LED driver, the service life of which usually is limited by presence of electrolytic capacitors. The issue of high temperature can be solved relatively easily: applying known procedure for thermal design calculations and appropriate heatsink in accordance with these calculations. The issues related to LED driver are more complicated. Thus, the main attention in this research is focused on the problems related to LED driver and proper application of LED. A brief summary of the conventional lighting technologies is given in the introductory section of the Doctoral Thesis, as well as their main benefits and drawbacks are discussed. The main tasks and hypotheses of the research have been defined. The second section of this Doctoral Thesis is devoted to general issues related to LEDs. The main benefits of LEDs are high efficiency, long service time and dimming (light regulation) possibility in a wide regulation range. However, the quality of the light can be affected by the dimming: the change in the light color temperature or the light fluctuations and related undesirable optical effects may appear. Therefore, the main light quantities have been also briefly considered in this section, as well as the issues related to photometry and colorimetry: light quality quantities. There are several dimming techniques, which have been described in this section in detail. Selected dimming approach in a large extent affects not only the light quality parameters, but also the structure of LED driver. From the point of view of efficiency and light quality parameters, the most appropriate dimming technique for general purpose lighting is fluent or amplitude mode light regulation technique. Slight color shift can be observed using this dimming technique, at the same time light fluctuations are minimal. Therefore, in the next two sections have been considered topologies and operation modes of the converters, which allow simplifying implementation of amplitude mode dimming technique in microcontroller based systems. The compensation of nonlinearity of LED curves by nonlinear transfer function of the converter has been considered in the following section of this research. For this purpose the family of tapped-inductor converters has been studied, as well as operation of the converter in a discontinuous conduction mode. During these studies it was found and confirmed (by analytical calculations and experiments) that both nonlinearity compensation approaches in case of amplitude mode dimming approach allows obtaining controllability curves with better parameters (lower nonlinearity and higher dimming resolution) in comparison with traditional converter topologies. Direct current control and current fed converters have been considered in the fourth section of this Doctoral Thesis. These converters have been previously considered in other works as well. The main drawback has been specified there: the constant current source is necessary at the input of current fed converter for its proper operation, but the prevalent electrical power sources by their nature are voltage sources. The solution of the described problem has been proposed in this section: non-inverting buck-boost converter has been considered as combination of constant current source and current fed converter. Thus, special control algorithm allows obtaining properties of the converter with the direct current control using non-inverting buck boost converter. This allows improving the parameters of controllability curves (lower nonlinearity and higher dimming resolution) in comparison with the traditional converter topologies. Conclusions summarize the results of this research and their accordance with the hypotheses. The Doctoral thesis has been written in English. It consists of 5 chapters including introduction and conclusions, bibliography with 139 reference sources and 17 appendices. The volume of the present Doctoral Thesis is 135 pages. It has been illustrated by 85 figures and 11 tables.


Keywords
LED apgaismojums, LED draiveri, strāvas tiešie pārveidotāji, nelinearitātes kompensēšana

Tetervenoks, Oļegs. Direct Current Control and Compensation of Non-Linearity for the Impovement of Quality Parameters of the LED Lamp. PhD Thesis. Rīga: [RTU], 2015. 135 p.

Publication language
English (en)
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