Unified small-signal model for PCM control in CCM: unterminated modeling approach

Teuvo Suntio^* and Mikko Hankaniemi

The small-signal modeling of peak-current-mode (PCM) controlled switched-mode converters has attracted the researchers and caused lively discussions since the invention of the control mode. The application of the PCM control makes the converter to resemble a current source at open loop rather than a voltage source, what it actually is, when the feedback loop is connected. The current-source nature has caused problems to study the converter dynamics and the anomalies it has, such as the limited duty ratio. As a consequence, generally accepted small-signal models are not available but only a variety of models serving the interests of different schools. In this paper, we will show definitively that the models including infinite duty-ratio gain form the basis for the accurate small-signal modeling as well as explain fully the phenomena characteristic to PCM control.

Keywords: Peak-current-mode control, switched-mode converter, mode limit, CCM