Digital Ripple-based Control For Switching Converter With Pulse Frequency Modulation

With the rapid development of power electronic devices,the performance demand for switching converter is becoming increasingly strict.Due to its high light-load efficiency and fast transient response,pulse frequency modulation(PFM)technology has attracted much attention.However,the output voltage regulation accuracy of switching converter with traditional PFM is poor,which is difficult to apply to the electronics equipments requiring high voltage regulation accuracy,such as computer,microprocessors,etc.In addition,it suffer stability problem resulting in unstable phenomenon when the equivalent series resistor(ESR)of output capacitor is too small.Therefore,it is necessary to study the high voltage regulation accuracy of switching converter with PFM and the solution to its stability problem.In order to improve the voltage regulation accuracy of switching converter with PFM,a digital ripple-based control technology for switching converter with PFM is proposed.This paper introduces the principle and control algorithm of digital ripple-based controlled buck converter with PFM.Furthermore,its voltage regulation accuracy,stability problem and conditions to eliminate the switching cycle delay are analyzed and verified by simulation.The research results indicate that the dual-edge PFM has good voltage regulation accuracy,but it is poor in single-edge PFM.When ESR is too small,both the single-edge and dual-edge PFM have stability problem.In addition,if the conditions to eliminate switching cycle delay is not satisfied,its transient performance will deteriorate.In order to solve the stability problem of digital ripple-based controlled buck converter with PFM,a capacitor current compensation technology for digital ripple-based control with PFM is proposed,and its control principle and control algorithm are introduced in detail.By sampled-data modeling,the stability analysis of digital ripple-based controlled buck converter with PFM and its capacitor current compensation is completed,and the explicit expression of stability condition is derived.The proposed digital ripple-based control with PFM are summarized,and the best PFM method is recommended.By simulation and experimental platform based on field programmable gate array(FPGA),the stability analysis is verified,and the influence of introducing capacitor current compensation technology on transient performance is investigated by experiment.The research results indicate that the stability range of dual-edge PFM is wider than single-edge PFM,and the capacitor current compensation can not only further broaden the stability range of the system,but also improve its transient performance.In order to expand the application of digital ripple-based control with PFM,simplify the design process of control loop in traditional PFC converter,a digital ripple-based controlled power factor correction(PFC)converter with dual-edge PFM is proposed.Its limitation of slow transient response is analyzed in detail,and a new method to acquire reference signal of input current is researched.Further,an improved digital ripple-based controlled PFC converter with dual-edge PFM is proposed,which has rapid transient response.And its stability analysis is completed.Simulation results and experimental results from experimental platform based on digital signal processing(DSP)indicate that the improved digital ripple-based controlled PFC converter with PFM has faster transient response and smaller voltage fluctuation.