【作者】 刘青；

【导师】 曲小慧； 陶以彬；

【作者基本信息】 东南大学 ， 电气工程（专业学位）， 2020， 硕士

【摘要】 半导体发光二极管(Light Emitting Diode,LED)具有寿命长、效率高、绿色环保等优点,已被广泛应用于室内照明、汽车照明、显示屏、和智能照明等领域。LED是电流型器件,LED驱动电源需提供其所需的恒定电流。在交流供电场合,为减小对交流电网的谐波干扰,LED驱动电源还应实现高功率因数,即采用功率因数校正(Power Factor Correction,PFC)电路。由于PFC电路的输入交变功率和输出恒定功率之间不可避免存在差值,通常采用容量大的电解电容来平衡,但电解电容寿命短,难以匹配LED光源的长寿命。因此,本项目提出采用有源功率解耦的方式,实现输入和输出功率的平衡,避免使用电解电容,同时保证输入端的高功率因数。有源功率解耦方法本质上是通过在电路中增加有源开关器件和储能元件,将输入交流侧的低频脉动功率转移到非输出端储能元件中,由于非输出端口的平均电压或纹波电压不受负载特性限制,因此其输出电容容值可以减少,从而避免使用电解电容。此外,不同有源功率解耦电路可避免能量的二次流动,提高效率。因此,本文基于此原理,从具有近似PFC功能的断续模式(Discontinuous Current Mode,DCM)下Boost变换器出发,推导出改进型Boost PFC变换器,包括两个输出端口,一个端口用于将有功功率直接传递到负载,另一个端口在输入功率大于输出功率时,将低频脉动功率转移到中间储能电容中;在输入功率小于输出功率时,中间储能通过Buck-Boost变换器功率解耦电路,将能量传递给负载。通过以上方式,实现输入端的高功率因数,保证LED输出功率恒定,去除电解电容,且二倍频脉动功率仅流经功率解耦电路一次,提高效率。本文详细介绍了该无电解电容的AC-DC LED驱动电路的推导过程,并对解耦后的输入功率进行了功率流通路径分析,从拓扑角度证明其具有更高转换效率。针对该电路,本文亦提出载波叠层控制策略来实现LED驱动电源的恒定电流输出,即在同一个载波上叠加两个不同的直流电压源可以形成两个叠层的载波,因此,该控制方法仅需一个反馈环即可实现输出电流恒定,无需乘法器、逻辑门电路等器件,具有控制电路简单、响应速度快等特点。最后,本文在实验室搭建了一台实验样机,并给出了主电路及控制电路中参数设计,验证了所提出的LED驱动电源拓扑及控制策略的有效性。更多还原

【Abstract】 Semiconductor light-emitting diodes(LEDs)have the advantages of long life,high efficiency,and no environmental pollution,and thus they have been widely used in indoor lighting,automotive lighting,display,intelligent lighting and other fields.LEDs are typically current-driven devices,and the LED drivers should provide the required constant current.In the AC power supply situation,in order to reduce harmonic interference to the AC power grid,LED drivers should achieve a high input power factor,by using a power factor correction(PFC)circuit.Also,since there is inevitable power difference between input alternating power and output constant power,the electrolytic capacitors with large capacity are usually used as energy balance.However,the lifetime of electrolytic capacitors are usualy much lower than that of LED light sources.Therefore,the active power decoupling method is used in this paperto achieve a balance of input and output power,while avoiding the use of electrolytic capacitors and achieving high power factor.The active power decoupling method is essentially to use active switching devices and energy storage elements to the circuit to transfer the low-frequency pulsating power from the input AC side to the energy storage element in the non-output end.Because the average voltage or ripple voltage of the non-output port is not limited by the load characteristics,its output capacitance value can be reduced,thereby avoiding the use of electrolytic capacitors.In addition,different active power decoupling circuits can avoid the secondary flow of energy and improve efficiency.Therefore,based on this principle,starting from the Boost converter in the discontinuous current mode(DCM)with automatic PF function,an improved Boost PFC converter is proposed in this paper,which includes two output ports.One port is used for transferring active power to the load directly.When the input power is larger than the output power,the other port transfers the low-frequency pulsating power to the intermediate energy storage capacitor.When the input power is less than the output power,the intermediate energy storage passes through the Buck-Boost converter power decoupling circuit to transfer energy to the load.In this way,the high power factor at the AC input side is achieved,and the output power of the LED is kept constant without electrolytic capacitors.The doublefrequency ripple power can only flow once through the power decoupling circuit,which guarantees efficiency enhancement.This paper analyzed the derivation process of the AC-DC LED drive circuit without electrolytic capacitors in detail.The power flow path of the decoupling input power is also given,proving high conversion efficiency from the perspective of topology.To control this circuit,a carrier stack control strategy is also proposed in this paper to achieve the constant current output of the LED driver,that is,two different DC voltage sources can be stacked on the same carrier to form two stacked carriers.Therefore,this control method has only one feedback loop to achieve constant output current,without the need for multipliers,logic gate circuits and other devices.It is simple and fast responsing.Finally,a 40 W experimental prototype was built in the laboratory,and the parameter design of the main circuit and control circuit was also given.Experimental results verify the proposed LED drive power topology and control strategy well.更多还原