This paper proposes a novel control structure for a 4 red-green-blue (RGB) LED lighting system, and applies multivari-5 able robust control techniques to regulate the color and luminous 6 intensity outputs. RGB LED is the next-generational illuminant for 7 general lighting or liquid crystal display backlighting. The most 8 important feature for a polychromatic illuminant is color adjusta-9 bility; however, for lighting applications using RGB LEDs, color 10 is sensitive to temperature variations. Therefore, suitable control 11 techniques are required to stabilize both luminous intensity and 12 chromaticity coordinates. In this paper, a robust control system 13 was proposed for achieving luminous intensity and color consis-14 tency for RGB LED lighting in a three-step process. First, a mul-15 tivariable electrical-thermal model was used to obtain RGB LED 16 luminous intensity, in which a lookup table served as a feedfor-17 ward compensator for temperature and power variations. Second, 18 robust control algorithms were applied for feedback control de-19 sign. Finally, the designed robust controllers were implemented to 20 control the luminous and chromatic outputs of the system. From 21 the experimental results, the proposed multivariable robust con-22 trol was damned effective in providing steady luminous intensity 23 and color for RGB LED lighting. 24 Index Terms-Color difference, luminous intensity, red-green-25 blue (RGB) LEDs, robust control, thermal-electrical-luminous 26 model. 27 I. INTRODUCTION 28 R ECENTLY, LED has been drawing much attention as a 29 state-of-the-art illuminator because of its numerous ad-30 vantages, including energy savings, long lifetime, and environ-31 mental friendliness. Red-green-blue (RGB) LEDs can provide a 32 wide color gamut for liquid crystal display (LCD) backlighting, 33 as well as full color adjustability for general lighting applica-34 tions [1], [2]. This newly developed illuminant is the only light 35 source currently capable of this type of vivid and dynamic light-36 ing performance. However, the tunable light outputs have been 37 found to induce light consistency issues for RGB LED light-38 ing, because the luminous intensity and color outputs are easily 39 influenced by junction temperature variations caused by self-40 heating of the LEDs and disturbances in ambient temperatures. 41 Therefore, proper control strategies are required to stabilize light 42 output in order to counteract temperature variations.

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The concept of red-green-blue (RGB) light-emittingdiode (LED) lighting has gained wide attention during recent years and is now one of the targets for future lighting solutions. However, the self-heating of LEDs and environmental temperature variation lead to luminous intensity droop and lighting color drift. The main purpose of this research is to investigate a novel flux feedback and temperature feed-forward (FFB&TFF) control structure for RGB LED lighting control system, in order to provide a wide color range of input commands and regulation of both luminous and color outputs. The work in this paper was carried out in three main steps. First, a thermal-electrical-luminous-chromatic model was derived and identified for RGB LED luminaire. Second, a converter and a compensator were derived and applied to input command conversion and temperature compensation, respectively. Finally, a diagonal proportional-integral controller designed by the decentralized control approach was implemented to regulate the lighting outputs of luminous intensity and chromaticity coordinates in CIE 1976 Uniform Chromaticity Space (UCS) diagram. The results of transient and steady-state experiments showed that the proposed control system was effective.Index Terms-Decentralized control approach, flux feedback and temperature feed-forward (FFB&TFF), red-green-blue (RGB) light-emitting-diodes (LEDs), system identification, thermalelectrical-luminous-chromatic model. I. INTRODUCTIONL IGHT-EMITTING diodes (LEDs) are a highly effective lighting technology. Energy saving and long lifetimes are the main advantages in lighting applications. Red-green-blue (RGB) LED lighting is one of the most popular techniques for white light in the application of LCD backlighting, video projection and general lighting. Its chromatic changeability and wide color range can provide unique lighting experiences [1]. However, the luminous and color outputs are easily affected by self-heating of LEDs as well as environmental temperature variations [2], [3]. Thus, a control system for RGB LEDs is called for to regulate both luminous and color outputs. The key issue of effective regulation is a proper control structure design.