A switching strategy for multiple-input DC-DC converters

Abstract

This paper presents and analyzes a switching strategy for multiple-input converters (MICs). With this technique, the effective duty ratio of each switch is an integer multiple of a common-duty-ratio (CDR), which is generated at a higher frequency by frequency division. In general, the frequency of the common duty ratio is dictated by power-budgeting requirements—a higher CDR frequency corresponds to more flexibility with respect to power budgeting. Switching functions can then be generated with relative ease for MICs that have a large number of input legs. Another benefit of this scheme is that it allows an MIC's output voltage to be stabilized by adjusting all the effective duty ratios of its input-leg switches at once. This stabilization is achieved by employing the CDR as the only control variable, irrespective of the number of input legs. Essentially, the strategy transforms an MIC into an equivalent single-input single-output (SISO) system for analysis, which simplifies controller design. Without loss of generality, this technique is demonstrated by analyzing a multiple-input buck-boost (MIBB) converter. A PI-controller is shown to stabilize the MIC's operating point. The analysis is verified by simulations and experiments.