Study of Architecture for High-Power Color-Tunable LED Lighting System

Description

High-brightness light-emitting-diodes (LEDs) continue to reform the lighting industry with theincreased efficacy, reduced cost, and added versatility and intelligence they bring to generalillumination for both white-light and colored-light designs. These lighting systems offerdesigners flexibility to dynamically tune the color temperature in white-light applications.Alternatively, they allow dynamic color tuning to produce a broad spectrum of colored light.The light is synthesized by mixing appropriate proportion of primary colors. Historically, threeprimary colors including red, green, and blue were used. Due to non-homogenous colordistribution on the chromaticity diagram, many designs have also utilized more than threeprimary colors to synthesize the secondary color. Each primary color is produced by an LEDchannel. Each channel consists of multiple LED strings and each string has multiple LEDs orLED modules connected in series. The luminance of each channel is adjusted by a dimmingcontroller that controls the magnitude of electric current flowing through the associated strings.The channels are generally switched in time-division multiplexing or sequential manner.The architecture of a typical high-power LED lighting system consists of five major partsincluding central control unit (CCU), power processing unit (PPU), dimming and currentbalancing unit (DBU), color LED strings, and sensors. The strings are driven by the PPUthrough the DBU to regulate individual string current. The CCU reads the color and luminancecommand from the operators or peripherals on the system and the information from the sensors.It will then process the command to coordinate and control the operations of the PPU and theDBU to mix and regulate the output light.Different color LEDs have different forward voltages to operate. For example, the forwardvoltage of the blue LED is higher than the red LED. During the transition from one colorchannel to another, say from blue to red color, the output voltage of the PPU cannot reactinstantly due to the presence of the output capacitor. It will cause a transient current spikethrough the LED strings of low forward voltage (i.e., the red LED). Such current spike will giverise to undesired electromagnetic interference, spike heating, and reliability concern. It willadversely affect the lifetime and quality of the LED. Although there are several remedialtechniques for tackling such issue, they each have their own merits and limitations. This projectaims to investigate architecture for high-power color-tunable LED lighting system that can copewith wide variation in LED properties and abnormal LED condition, produces highly accuratecolored light, and has high operational reliability. Extensive theoretical and experimental workwill be conducted.