Abstract:
This thesis presents a detailed design and control methodology of a single-stage multi-color or multi CCT fly-back LED driver with dimming option. Multi CCT LED lighting is required for various applications especially street lighting for different seasons or maintaining CCT in the class or office room lighting. However, in most of the reported multi CCT LED lighting applications, it was found that dual number drivers are used for controlling different CCT of LED lighting with limited variations of CCT of LED lighting. Unlike the existing multi CCT LED driver system, the proposed single driver will be used for producing multi CCT or multi-color LED lighting systems with dimming control. In the proposed driver, feedback circuit with power factor correction unit is incorporated to achieve desired power factor and reduction of total harmonic distortion of the input current. Furthermore, single-stage methodology is used in the circuit design where AC-DC rectification and DC-DC conversion take place in a single stage with the positive and negative cycle of input voltage thereby reducing power loss in the primary side of the driver. Flyback DC-DC converter is also used to achieve galvanic isolation between supply voltages and load. Hence, it ensures the safety of the circuit from the abnormal fluctuation of the input voltage. In the proposed driver, multi-string LED lights are connected in parallel. So maintaining current balancing in each string was challenging due to the different characteristics of LEDs. However, this challenge is addressed by controlling the LED string currentby switching. In this work, a hybrid control scheme is developed which combines pulse width modulation (PWM) technique along with microcontroller control scheme in the LED strings to control the input and output current efficiently. Here red, yellow, and blue color LED lights have been mixed to produce the desired color. The look up table is used here to control the duty ratio of different color mixing. Applying the same methodology, warm white (3000K ) and cool white (7000K) LED lights are also mixed to produce different CCTs of output lights. The timing sequence corresponding to color mixing ratios and CCTs is also explained. The dimming of the multicolor LED driver has been achieved by changing the current gain of the feedback circuit. Finally, the optimal parameters of the proposed circuit are determined for the best performances by analysing the key performance factors such as efficiency, power factor and THD. The resulting design gives better performance in terms of power factor (0.88), acceptable (40%) THD, and maximum efficiency which reaches up to 80%.
