Research on Dynamic Performance of Step-Down Converters with Input Perturbation

For PWM DC-DC converters, keeping the output voltage steady is very important. When the input voltage has a step change, up impulse or down impulse voltage will occur in the output. Both the magnitude and the duration time of the over voltage are severely influencing to the whole system, which will destroy or disorder the circuit. Step-down converter is used as an example to investigate the input perturbation phenomenon. Differential equations for inductor current profile and output voltage profile are established. The equations are based on the assumption that the frequency of inductor current profile and output voltage profile are much lower than the switching frequency of the converter. The condition leading to oscillation and impulse voltage in the output is obtained. The oscillation frequency, the time that the impulse voltage occurs and the max value of impulse voltage are also derived. Dynamic behavior of the PWM controlled buck converters in DCM is also discussed. The proposed method is tested by simulation. The simulation results show that the analysis is coherent with the analysis..