Ripple control in PWM converters

The presentation “Ripple Control of PWM Converters” by Sam Ben-Yaakov explores an alternative approach to controlling pulse-width modulation (PWM) converters by utilizing ripple characteristics rather than average voltage feedback, which is common in traditional control methods. The speaker outlines the fundamental concept of ripple control, where the feedback relies on monitoring peak, valley, or hysteresis values of the ripple in the output voltage, instead of the average voltage. This technique offers advantages such as faster response times, as demonstrated in the presentation with examples of load step responses and AC signal tests. The concept is explained using a synchronous buck converter circuit, where the ripple created by the equivalent series resistance (ESR) of the capacitor is compared to a reference voltage. The presentation also touches on challenges like subharmonic oscillations at high duty cycles, which can be mitigated with slope compensation. However, this approach may slightly shift the average output voltage, which can be corrected by adding a feedback loop for the DC component.

To further improve the design, the presenter introduces techniques to reduce the dependence on high ESR capacitors, such as injecting an artificial ripple using additional circuitry. This method allows for precise ripple control even with low-ESR capacitors, resulting in smoother output with minimal ripple. The presentation emphasizes that ripple control mimics aspects of peak current mode control by indirectly monitoring inductor current through the ripple voltage. The educational session highlights the strengths and practical considerations of ripple control, which is employed in various commercial PWM controllers. With illustrative simulations and practical insights, the presentation provides an in-depth look at the mechanism and potential applications of this advanced control method in power electronics.