Improved Three-Terminal Model for PWM Converters with Current-Mode Control

The two nonlinear components in a PWM converter are power switches and PWM modulator. In a voltage-mode control, they were modeled separately due to the sufficient low-pass filtering from both power stage and feedback compensator. In more advanced controls such as peak current-mode, constant on-time, or $\mathrm{v}^{2}$ controls, more state variables are fed-back into the control loop with less or no filtering in order to achieve a better dynamic performance. Consequently, power stage and feedback control must be considered as one entity to properly account for contribution from harmonics. J. Li derived the corresponding models based on describing function method, and the mathematical model was then approximated with an equivalent-circuit form by Y. Yan. However, the perspective of the current feedback was lost since power stage and feedback were lumped together. Moreover, the average-model based power stage cannot address the contribution from harmonics. This paper proposes an equivalent circuit model that preserves the current feedback information, and is accurate at half switching frequency at all terminals due to the improved power stage model.