Study And Stability Analysis Of Digital Peak Current Mode Controlled Boost Converters

With the rapid development of power electronics technology,various industries need to use electronic products,and switching power supplies are constantly developing in the direction of high frequency and digitalization.The digital control of switching converters gradually replaces the analog control.Due to the time delay in digital control,the Digital Pulse Width Modulator(DPWM)and Analog-to-Digital Converter(ADC)in the digital control loop have some problems such as quantization effect and resolution of DPWM,which may cause lowfrequency oscillation and limit cycle oscillation of the system,thus affecting the stability of the switching converter and increasing the difficulty of modeling and analysis.In order to verify the accuracy of the small-signal model and the effect of parasitic parameters on the inductor current,the basic small-signal model and the accurate small-signal model were developed in continuous conduction mode(CCM)and discontinuous conduction mode(DCM)for the Boost converter.The study of the Boost converter model in CCM and DCM provided a theoretical basis for the design of digital peak-current-mode controlled(PCMC)controllers.In the CCM,the operating principle of the digital peak-current-mode controlled Boost converter was first analyzed,and then the s-domain model of the Boost converter was obtained by using the state-space averaging method,and the z-domain model of the system was established by considering the effects of time delay,quantization effect and resolution of DPWM.Since the traditional small-signal modeling method ignored the nonlinear characteristics of the DC-DC converter,the constructed model was not accurate enough.Therefore,the z-domain model of the PCMC Boost converter and its stability criterion were established in the thesis based on the descriptive function method.The proposed model allowed a clear analysis of the time delay from ADC and DPWM and the effect of DPWM module resolution.In the transition zone from the steady state to unsteady state of the digital PCMC Boost converter,the range of this transition zone could be determined based on the descriptive function method analysis.For the appearance of low-frequency oscillation phenomenon,the nonlinear behavior of the digital PCMC Boost converter was confirmed by using the eigenvalues to determine the critical resolution between the stable and unstable operation of the converter.Finally,the Simulink simulation model was built,and this model was simulated and analyzed in terms of steady state and transient,which proved the excellent characteristics in terms of stability and resistance to load disturbance,and the stability of the proposed z-domain model of the descriptor function was analyzed systematically and its correctness was verified,showing that the proposed z-domain and descriptor function models could describe the trailing edge modulated digital PCMC Boost converter.The proposed z-domain and descriptor function models were shown to describe the operating characteristics of the trailing edge modulated digital PCMC Boost converter.In DCM,the two controllers in digital peak current mode control strategy have observed current error and reference current error respectively,and their errors are caused by parasitic parameters in the accurate small signal model,so a current compensation strategy was proposed to compensate the observed current error and reference current error.This control strategy improveed the current accuracy and cleared the steady-state error of the output voltage.