太陽能LED之色彩控制技術研究

Abstract

本研究探討採用三原色RGB-LED為燈源之獨立型太陽能蓄電池直驅全彩照明技術，可適用於植物工廠等環境溫度穩定之長時間穩態色彩照明。藉由設計一個24V之全彩照明燈具系統，並配合一微處理機，採用廻授控制技術建立一個PWM定功率控制系統，分別控制與R、G、B三原色LED串接的金氧半場效電晶體(MOSFET)之開關訊號，來調整其平均電流與功率。調整電源供應器之驅動電壓源，在26V至23V間來模擬蓄電池之放電電壓變化，最大的燈源驅動功率誤差控制於2.7%內。並探討R、G、B三原色LED燈源在PWM開關訊號驅動下產生的色彩照明特性，分析驅動電壓與PWM之責任週期變化對主波長偏移、色度座標改變之影響。根據測試資料與數據建立一開路(Open-Loop)色彩模型並用以混色控制，在固定驅動電壓下可產生之混色座標達1000種。燈具混色實測數據顯示，紅光測試點Rt之實測混色座標與目標值之色差飄移皆在Δu'v'=0.00203之內，而綠光測試點Gt最大的色差飄移為Δu'v'=0.00273，藍光測試點Bt實測之色差飄移皆小於Δu'v'= 0.00083，表示建立之混色數據資料應用PWM定功率技術來驅動LED燈具，有良好的色差飄移控制效果。而針對白光色溫6500K之混色目標，透過最小平方誤差演算，求得RGB-LED混光開路控制之最佳近似參數，在驅動電壓23V、24V、25V與26V時，不需光度感測回授，可控制與6500K混色目標之色差飄移在Δu'v'=0.00526之內。本研究建立之太陽能RGB-LED色彩控制技術，可減低設計與感測器成本，增加實際應用於植物工廠燈具之可行性。

A 24V stand-alone solar direct battery driving full-color lighting system with tri-chromatic RGB-LED as lighting source has been built in this study. The lighting system could be suit for the plant factory which is stable with temperature and for long-term lighting. Useing a microprocessor and PI feedback control technology to create a PWM constant power control system. The microprocessor could control the switch signal of the MOSFET which is in series with R, G, B LED to adjust the average current and power stability. In the change of the driving voltage of 26V to 23V, the maximum controlled driving power error is below 2.7%. Through exploring the illumination characteristics of R, G, B LED, as chromaticity coordinates and spectrum shift, under different driving voltage while PWM duty cycle is changed, a constant power PWM mixing-color technology has been developed. A thousand kinds of mixing color can be generated by the mixing-color data at a fixing RGB-LED driving voltage. Comparing the measured data with the three test points, the results show that the maximum offset between the measured value and the target point Rt is Δu'v'= 0.00203, and point Gt is Δu'v'= 0.00273, and point Bt is Δu'v'= 0.00083. It means the constant power PWM mixing-color system consists of the mixing-color data can reach the wanted chromatic coordinates within criterion drift Δu'v'= 0.0035. The established constant power PWM mixing-color technology provide a evaluation of mixing-color target error by least squares error analysis. While the driving voltage are 23V, 24V, 25V, and 26V, the constant power PWM mixing-color technology control the color difference under Δu'v'=0.00526 from the white light of color temperature 6500K without illumination and chromatic feedback. The technic in this study realize a mixing-color control system with low cost and could be feasible.