Dynamic behavior of PWM DC-DC converters in starting process

Closed loop PWM DC-DC switching converter is strongly nonlinear, and the analytical solution is difficult to be achieved. Oscillation and impulse voltage will probably occur in the output during the starting period in DC-DC converters. In this paper, a pulse-width-modulation(PWM) buck converter is used as an example to discuss such problems so as to predict them in the course of design, and reduce or even avoid above harmful phenomena by modifying the parameters. In order to investigate the dynamic behavior in the output voltage of the converters, 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 occur and the max value of impulse voltage are also derived. The proposed approach is verified by PSPICE simulation and experiment results.