Study On The Digital V~2 Control Of Switching-Mode Power Supply With Pulse-Frequency Modulation

Compared with conventional analog control, digital control has got much attention due to its ability to interface with digital systems, flexibility to using different arithmetic without changing hardware circuit, and so on.Digital V2 Control technique with pulse frequency modulation is studied in this thesis. Pulse frequency modulation technique includes constant on-time (COT) modulation and constant off-time (CFT) modulation, meanwhile digital V2 control includes digital peak voltage (DPV) control and digital valley voltage (DVV) control techniques. COT-DPV, COT-DVV, CFT-DPV and CFT-DVV control algrithms are investigated and compared based on buck converter in continuous conduction mode (CCM) and discontinuous conduction mode (DCM). Comparison results shows that the required sampling and calculation time of CFT-DPV control and CFT-DVV control is much more than others. Moreover, it is found that CFT-DPV control law in DCM without sampling inductor current is easiest among them. What's more, stability analysis of them shows that all of them are stable without sub-harmonic oscillation in the whole range of duty ratio, and simulation results are given to verify the analysis results.Simulation model is established based on Matlab/Simulink software, which includes main circuit module, analog-to-digital converter module, digital compensator module, and digital control law module. For comparing their input and load transient performance, small-signal model in CCM is derived according to different control algorithms, and main Bode diagrams are given to analyze their differences. Comparitions show that all of them have fast transient performance, but COT-DPV control low is slowest, and CFT-DVV control low is fastest. Based on simulation model, main transient simulation waveforms are given to verify the analysis results.To futher prove the analysis results, experimental prototype is designed based on FPGA, and the main circuit parameter, circuit elements, design method, and control flow chart are introduced. Take the COT-DPV control and CFT-DVVcontrol as an example, experiment waveforms of them are given to prove that both of them have fast load transient performance, but in contrast the transient performance COT-DPV control is slower, which is agreeable to the theoretical analysis.