Modeling And Stability Analysis Of Digital Current-mode Controlled DC-DC Switching Converters In Z-domain

The mode of digital control is flexible, programmable, and has possibilities to improveperformance using more advanced control schemes. Thus, digital controlled power switchingconverters are gradually replacing analog ones. However, it is more complex to study thecharacteristics of digital controlled DC-DC switching converters than analog controlled, dueto time delays, sampling and quantization error and other factors. So it is essential to establishthe model of digital controlled DC-DC switching converters for analyzing theircharacteristics.This work was supported by The National Natural Science Foundation of China (NO.51077057)——Modeling and stability analysis of digital controlled switching powerconverters, their applications. And this paper deeply researches on digital current-modecontrolled DC-DC converters. The main contents of this paper are as follows.(1) We derived and analyzed the sampling and quantization model of digital controlledDC-DC Converters. The simulation results have shown that, resolution of DPWM moduledetermines the highest performance of digital controlled system.(2) We established a more complete discrete z-domain model of digital current-modecontrolled DC-DC Converters. Firstly, we analyzed the performance of digital peak currentmode control algorithms. Then we obtained its main power stage circuit model, the peakcurrent controller model and control algorithm model based on the state-space averagingmethod and small signal model. Finally, we deduced the discrete z-model, which contains thetime delay and sampling and quantization.(3) We analyzed the influence of sampling and holder module and time delay module onthe system. The theoretical analysis shows that, the stability of digital current-mode DC-DCconverters is not only related with the circuit parameters, but also limited by the samplingperiod. The time delay module generates a phase delay lag to affect the stability of the system.(4) We designed digital PI controller and established matlab/Simulink simulation modelof the system and analyzed the steady and load disturbance, based on the simulation model.The simulation results have shown that, this digital controlled system has good performancein steady-state and anti-load disturbance. Further, we verified the correctness of the theoreticalstability analysis and the validity and accuracy of the simulation model.(5) We also found the potential low frequency oscillation in digital current-modecontrolled Boost Converter by simulation. Then we proposed a new way that is more clearand intuitive to reveal the mechanism of this phenomenon by analyzing eigenvalues of closed-loop system.