Noise properties of pulse-width modulated power converters: open-loop effects

The pulse-width modulation (PWM) process in DC-DC and DC-AC power converters introduces characteristic nonlinear behavior. When PWM is performed in the presence of noise, specific effects are seen on the duty ratio and consequently on the output of the converter. Small-signal concepts do not model nonlinear noise issues. Here, the probability density function of the duty ratio and its implications are obtained analytically, given external noise that follows a Gaussian distribution. The results are verified with Monte Carlo simulation and confirmed by experiments. For a DC-DC converter, noise is shown to introduce a DC shift at the output. The degree of nonlinear effect on a converter depends on the noise derivative level. For an inverter, noise can produce significant DC offset at the output. Closed-form expressions from the analysis can be used to evaluate noise sensitivity of a design.