Comparison between Ramp Pulse Modulation (RPM) and constant frequency modulation for the beat frequency oscillation in voltage regulators

In the voltage regulator (VR) applications, the load frequency varies in a very wide range from several kHz to several MHz. When the load transient frequency approaches to the switching frequency of VR, there is a low frequency oscillation in the system, which is the beat frequency oscillation between the load transient frequency and the switching frequency of VR. When this low frequency oscillation becomes significant, the system may be hurt. The root cause of this beat frequency oscillation is constant frequency operation of the VR. In order to resolve this problem, Ramp Pulse Modulation (RPM) method is proposed. A Ramp Pulse Modulation control is one of the ripple based control methods, which is generally used in the single phase voltage regulators. In this paper, RPM method is reviewed and it is compared to the constant frequency control method with experiments.