| LED,as the fourth generation lighting source,is a kind of semiconductor solid state lighting device.Compared with the incandescent and energy-saving lamps,LED has the advantages of high efficiency,long service life,small size,short response time,good modulation performance,and so on.Using such high-speed modulation characteristics,can achieve both good lighting characteristics and information transmission,so as to realize the dual purpose of LED lighting and communication,VLC(Visible Light Communication)technology was born.Compared with radio frequency,visible light communication has no electromagnetic radiation,electromagnetic interference,no occupation of the radio spectrum resources high safety and other unique advantages,has received more and more extensive attention in domestic and abroad.Therefore,the visible light communication technology has great development prospects,and it has significance for the study of indoor visible light communication.When the LED driver is connected to the power grid,the harmonics produced by the driver will cause pollution to the power grid,in order to meet the low-frequency harmonic restriction standard,the circuit needs to have the function of PFC(Power Factor Correction).Due to the simple control,high efficiency and high reliability,the single stage circuit is widely used in the indoor occasions of small and medium power driver.Therefore,study of high efficiency,high reliability,low THD,single stage buck LED driver circuit has great engineering application value.A single-stage buck LED drive circuit with unit power factor is presented in this paper.The circuit is composed of buck and buck-boost,according to the relationship between input voltage and intermediate DC bus voltage,the work is divided into two stages.The working principle,working process and characteristics of the circuit are analyzed in detail,and the key parameters are designed and analyzed.For the proposed circuit,A nonlinear control strategy of digital control is derived,and the control design and simulation analysis are carried out,a switching frequency is 50kHz,the output for the 80V/0.5A experimental prototype is design and set up.In the 175V-265V input voltage range,the efficiency is maintained at more than 85%,THD is less than 10%,the input current accurately tracks the input voltage,and realizes the unit power factor correction.Three kinds of VLC modulation methods issued by IEEE802.17.5 standard were analyzed in this paper,and the basic principle of OFDM modulation strategy was analyzed in depth.Combined with the advantages of external modulation method and the advantages of OFDM modulation,an OFDM modulation method using network transformer is designed,the experimental research on the dimming and communication of the designed method is carried out.For the problem of bipolar OFDM signal cut off,in the PWM dimming mode,when the dimmer switch tube is off.A new strategy combined with PWM lighting dimming and OFDM communication is proposed,and its working process is analyzed in detail,and related experiments are carried out,the experimental results verify the effectiveness of the proposed method.In the end,a VLC system using indoor LED to realize lighting communication is designed base on the MSE500 chip of Mstar company,the design method of the transmission circuit and the receiving circuit is analyzed in detail.The experimental results show that the system can realize the communication rate of 70Mbps under the distance of 1.5m. |
PDF Full Text Request