Analysis of boundary control for a multiple-input DC-DC converter topology

This paper studies boundary control for a multiple-input buck-boost (MIBB) converter topology with equal voltages at each input leg. In addition to not requiring different input voltages as in previously suggested MIBB converters, when input voltages are equal the proposed controller eliminate the need for forward-conducting bidirectional-blocking switches (FCBBs) also present in previous MIBB topologies. The prescribed controller makes the closed loop MIBB system to behave as a single-input buck-boost converter so that a solution to in the sense of Filippov can be defined in reflective mode. Large-signal asymptotic stability of the desired operating point is subsequently established using Lyapunov´s direct method. The state-dependent switching strategy presented ensures that the system avoids certain limitations that occur when multiple-input converters that operate based on switching period-sharing. These restrictions include different input voltages, and limited number of input legs. A lower parts count and better efficiency may then be achieved. Robustness and other attributes of boundary control make the proposed strategy favorable. Both pros and cons of the proposed scheme are discussed and design recommendations are given. The analysis is verified by simulations and an experimental setup with four input legs.