Low-Frequency Sampled-Data Models of Switched Mode DC-DC Converters

Practical implementation of low cost digital controller for switched mode converters is feasible if the sampling rate is lower than the switching frequency. However, a prerequisite for the development of control algorithms for this mode of operation is the availability of a low-frequency sampled-data model of the converter. A sampled-data model of switched mode converter applicable for the low frequency range is presented. The assumption made is that the sampling rate is sufficiently high as dictated by the sampling theorem. It is shown that the models are linear for small signal operation but represent a bilinear system under large signal conditions. The models could be useful for the design of microprocessor based controller for switched mode converter, with improved transient response. Two examples of possible applications of the model are discussed: as a fast and efficient time domain simulator and as a tool for the analysis and design of a fast turn-on boost converter.