Research On Electrolytic Capacitor-less LED Driver And Control Strategy

With the development of economy and the increasing demand for lighting,electricity consumption for lighting accounts for about one fifth of the total annual electricity consumption in the world.As a new type of solid-state cold light source,light emitting diode(LED)has been gradually praised for its long lifetime,small size and environmental friendliness.At the same time,the technology of LED driver has developed.However,the traditional LED driver usually contains electrolytic capacitors,which results in mismatch between the lifetime of LED driver and LED.The methods of eliminating electrolytic capacitors in AC/DC LED driver are researched in this paper.In order to ensure that the power consumption of LED driver does not pollute the grid voltage,the input current needs to follow the input voltage in a sinusoidal form,so the input power is in the form of twice line frequency pulsation.LED needs constant power,so there will be fluctuation difference between input and output power.Traditional LED driver uses large capacity electrolytic capacitor to balance the power pulsation,but there is a mismatch in lifetime,which will affect the improvement of power density of LED driver.Therefore,it is necessary to study the electrolytic capacitor-less LED driver.Firstly,an improved electrolytic capacitor-less LED driver is proposed in this paper.DCM flyback converter is adapted to realize function of power factor correction(PFC).The bidirectional cuk converter is connected in parallel with the output of PFC stage.The pulsating power is temporarily stored in the auxiliary energy storage capacitor through the bidirectional cuk converter,and the capacitance value of the energy storage capacitor can be reduced by increasing the ripple of the auxiliary energy storage capacitor,thus replacing short lifetime electrolytic capacitors with long lifetime CBB capacitors.Secondly,the working principle and mode of the proposed electrolytic capacitor-less LED driver are analyzed in detail,and the principle of PFC function is analyzed.Thirdly,the control strategy of bidirectional cuk converter in the new topology is researched.Hysteresis current control is analyzed and simulated in this topology.At the same time,in order to overcome the shortcomings of hysteresis current control,the model predictive control strategy is proposed to be applied in the new topology.The modeling and implementation are analyzed in detail,and simulation results are given and analyzed.Finally,parameters of the new topology are deduced and calculated in detail,and the basis for selecting the device is given.A 24 V,3A prototype is designed for experimental verification.The experimental results verify the correctness and feasibility of the improved electrolytic capacitor-less LED driver topology and the corresponding control strategy.