| In order to meet the requirements of harmonic standards for lighting products,the light emitting diode(LED)driving power supply supplied by municipal power supply must have the function of power factor correction(PFC).Because the output of PFC converter contains two times the power frequency voltage and current ripple,it will affect the effect of LED lighting.In the situation of high quality requirements,it can not directly supply power to the LED load.In order to reduce the ripple effect,the current LED drive power supply is divided into two-stage and single-stage structure.Compared with the two-stage structure,the control of single-stage structure is simpler and cheaper,but it has the problems of lower power factor and larger output voltage ripple.In addition,electrolytic capacitors with short service life are used as energy storage elements in both structures,which affect the overall service life of the power supply.Therefore,it is of great significance to study a single-stage LED driver with high power factor and long life.In this thesis,a single-stage variable conduction control flyback PFC parallel active decoupling circuit of LED constant current drive power supply is proposed.Flyback converter realizes PFC function.Without using electrolytic capacitor,active decoupling circuit realizes the function of balancing double power difference of PFC converter.Among them,single-stage flyback PFC works in the mode of inductor current boundary conduction.In the case of high-voltage input,the average input current will be seriously distorted,which is difficult to meet the requirements of high power factor.In order to solve this problem,the input voltage feedforward circuit structure is added to the peak current control strategy,which changes the on time of PFC circuit switch in half a power frequency cycle.The problem of low power factor in high voltage input is solved.The performance of the system before and after the improvement is analyzed and compared.The simulation results show that the improved control method can achieve the good effect of PFC close to unit 1 in the full input voltage range while maintaining the original performance and efficiency of the system,which verifies the correctness and feasibility of the improved control strategy.Secondly,the flyback of the parallel active decoupling circuit is analyzed in detail.According to the working mode of PFC converter,by giving the amplitude and phase of the reference current of the decoupling circuit,and adopting the method of hysteresis current control,setting the appropriate hysteresis bandwidth,the double ripple power decoupling function can be better realized.The simulation results show that the average current of the inductance in the decoupling circuit can well follow the change of the given reference current.It can replace electrolytic capacitor with long-life thin-film capacitor and keep the output current and voltage constant to meet the requirements of LED power supply. |
