Multi-Channel Adjustable LED Driver Based On Uniform Light Control

In recent years,LED(Light-Emitting Diode)light sources have gradually been recognized in the field of plant factory lighting due to their advantages such as narrow spectral range,high luminous efficiency,long life,and high controllability.However,unlike sunlight under natural conditions,due to the placement of the light source being restricted by the size of the cultivation rack,uneven lighting exists in the indoor environment where plants grow,which can easily cause inconsistent harvest quality.The current research on uniformity of supplementary lighting mostly focuses on changing the emission angle of the light source or improving the layout of LED chips on the light board.As plants grow,the area of light reception gradually changes.Simply adjusting the angle and layout of the light source cannot maintain uniformity of lighting during plant growth,which may lead to the problem of not being able to timely regulate the light environment.As the LED driver directly connected to the power grid,in addition,its design needs to meet the grid’s requirements for harmonic wave and avoid large energy loss.Therefore,this paper designs an LED driver and its control program.Based on the cultivation rack data and the LED light information in the existing plant factories,this paper derived the calculation formula and control conditions for achieving uniform light control.The circuit design of the LED driver and the programming of the control program were completed,which can achieve control of lighting uniformity that follows the plant growth.After simulation and experimentation,the lighting uniformity and power stability both met the design goals.The proposed control method and power supply design have certain research value and significance.The main contents of this study are as follows:(1)Analyzed and introduced the physical structure and light-emitting principle of LEDs,studied the light source model and voltammetry characteristic curve of LEDs,and according to the dynamic light requirements during the plant growth process,the proportion relationship between each LED branch under the uniform illumination control target is derived using the Lambert formula.Through the improved Shockley equation,the mathematical model of LED current-illuminance in practice is obtained.The aim is to meet the dynamic light requirements of plants and achieve interlayer uniform illumination control of the cultivation rack by controlling the output current of the LED driver and the duty cycle of different LED branches.(2)Analyzed and selected constant current as the driving mode for LEDs,The two-stage structure of the front stage active power factor correction circuit and the back stage half-bridge LLC resonant converter as well as the sampling feedback control circuit are designed.The parameters of each component in the driving power are calculated in detail.According to the national standards,the requirements of high power factor of LED driving power supply and wide adjustment range of illuminance in plant factories are completed.In the output control part,the multi-channel output,feedback control and PWM dimming of the incubator LED light group are completed.The simulation results show that the control system can achieve accurate dimming by changing the PWM duty cycle.(3)The hardware system design of optical control is completed.The ICL5102 grid driver chip is selected as the driver chip of the switch tube in the drive power supply and the peripheral circuit is designed.The peripheral circuit includes resistance attenuation sensing circuit,THD optimization circuit,high side grid driver circuit and overvoltage protection circuit.STM32F103 is selected as the chip of multi-channel output and sampling feedback control part,and the sampling feedback control program is written.RS-GZ-N01-2 illuminance sensor is selected to collect illuminance and serial communication is carried out by Modbus-RTU protocol.Its communication program is written.(4)The prototype of the LED driving power was completed.Finally,the light equalization control test was carried out in different light source distances and different light ranges.The test results showed that the control method proposed in this study significantly improved the light uniformity and basically achieved the design goal.