Aggregated modeling and control of a boost-buck cascade converter for maximum power point tracking of a thermoelectric generator

For a wide output voltage ranged thermoelectric generator, it is necessary to have a dc-dc converter that allows voltage boost and buck functions. In this paper, a boost-buck cascade dc-dc converter is adopted to allow input voltage range from near 0 V to 25 V and output voltage range from 12.3 V to 16.5 V, needed for vehicle battery charging. To ensure a smooth operating mode change, a modified maximum power point tracking controller is used to control the first stage converter duty cycle while regulating the second stage output voltage. A conventional duty cycle controller is then used to control the second stage converter while regulating the middle dc bus voltage. In order to avoid intricate relationship between two controller duty cycles, a novel aggregated modeling approach is proposed. The small signal model is analyzed, and the design guidelines for the power converter and controller are provided. Experimental results indicate smooth transition between changes and load steps, and the effectiveness of the proposed modeling and the controller design is verified.