The Design Of The DCM Mode Power Factor Corrector

Reducing the high-order harmonic pollution generated by AC-DC converter andimproving the power factor become hotspot, so power factor corrector is used more and moreapplications. Digital control technology, for its simplicity and greater flexibility to realizesophisticated algorithms, is getting more and more researched in the range of digital power.In this paper, a DCM mode digital power factor correction is designed for the mediumand low power applications. This paper proposes a duty cycle control strategy for DCM mode,which is different from the traditional double-loop control and easy to implement. Duty cyclecontrol is divided into two parts: the control of switch on-time and the control of switchingcycle. Switch on-time calculation in each switching cycle is derived to replace the traditionalcurrent loop, and the voltage feedforward items and voltage loop output is introduced in theswitch on-time calculation formula. Also, the switching frequency strategy in DCM mode isdesigned to optimize EMI and efficiency. In order to improve the dynamic response rate ofthe voltage loop, the comb filter is designed to eliminate twice the power frequency and itsharmonics in the output voltage ripple component, and then design a high-bandwidth digitalPI controller. The small-signal model derived in situations with bandwidth less than twice theline frequency does not apply to the design of high-bandwidth voltage loop. This paper usethe nonlinear time-varying systems analysis methods to analyze the high-bandwidth voltageloop stability. In order to resolve the contradictions of the clock frequency and resolution inthe counter based DPWM, a second-order Delta-Sigma modulator with pole and zerooptimization is utilized to process the switch on-time signal.Finally, the parameters of the peripheral circuit components of the DCM mode PFC isdesigned. And with the tool of Matlab\Simulink and modelsim cosimulation, experimentalverification of the design show the results to achieve the purpose of power factor correctionand output voltage stable at400V DC value, through steady state and dynamic analysis.