Study On High Power Factor Single Switch Isolated PFC Converter

With the wide application of power electronics equipment,AC-DC switch converter brings serious harmonic pollution into public power grid.Power factor correction(PFC)technology has been applicated widely in AC-DC switch converter,because it can eliminate harmonic pollution in power system,and improve input power factor effectively.Single-switch isolated PFC converter is very popular in the field of PFC technology,due to its advantages as input-output isolation,low cost,and simple structure,especially flyback PFC converter.In general,in order to avoid high voltage and current spikes in cuicurt,energy of transformer leakage inductance must be consumed by RCD buffer circuit.Therefore,efficiency of flyback PFC converter will be restricted because of its RCD buffer circuit.This paper is devoted to study on single-switch isolated PFC converter with high power factor and high efficiency.Peak current of switch for traditional peak current controlled(PCC)critical continuous mode(CRM)flyback PFC converter follows the input sinusoidal half-wave voltage,and its input current is distorted seriously.A sine square compensated peak current control(S2C-PCC)technology is proposed in this paper.A sine square term is compensated to peak sinusoidal half-wave current of switch for PCC-CRM flyback PFC converter,and its coefficient is determined by amplitude of input voltage,output voltage and turns ratio between primary and secondary of transformer.The compensated converter has sinusoidal input current,and can obtain unit power factor over entire input voltage range.Finally,simulation and experiment verify the theoretical analysis results.In order to reduce energy loss of transformer leakage inductance,and improve the efficiency of CRM flyback PFC converter,resonant tank is introduced intoconstant on time(COT)controlled CRM flyback PFC converter in this paper firstly.A resonant tank consisting of resonant capacitor,leakage inductance and freewheeling diode,is added into CRM flyback PFC converter,which can transfer energy of leakage inductance into load,improve efficiency of converter,and reduce voltage stress of switch and diode.Moreover,the CRM single-switch resonant isolation PFC converter can obtain sinusoidal input current with only simple COT technology.Finally,simulation and experiment verify the theoretical analysis results.Similarly,adding resonant tank into discontinuous conduction mode(DCM)flyback PFC converter,solves the problem of low efficiency for DCM flyback PFC converter,it also distorts original sinusoidal input current.Therefore,in order to eliminate the adverse effects which resonant tank brings to DCM flyback PFC converter,variable on time(VOT)controlled technology is introduced into DCM single-switch resonant isolated PFC converter in this paper.By using input voltage and output voltage to modulate the switch on time,VOT-DCM single-switch resonant isolated PFC converter not only has advantages as high efficiency,low voltage stress of devices,but also can maintain power factor as high as COT-DCM flyback PFC converter.Finally,simulation and experiment verify the theoretical analysis results.