Two-Part Controller Design for Switched-Capacitor Based Buck–Boost Converter

Many of the buck–boost topologies have lower duty ratio range per unit voltage gain (DMR). In this article, controller design aspects, multi-mode operation of a switched-capacitor bridge based buck–boost converter (SCBDBBC) exhibiting better DMR is investigated. Presence of switched-capacitor bridge enhances the duty ratio range for bucking operation while the existence of two switches offers degree of freedom to realize multi-mode operations. These are: 1) buck–boost; 2) standalone boost; and 3) standalone buck operation. By exercising the degree of freedom associated with two switches, under the buck–boost operation three different multi-mode operations are feasible which are: 1) equal duty ratios with synchronized gate signals (D_S1 = D_S2); 2) unequal duty ratios with synchronized gate signals (case-1: D_S1 > D_S2); and 3) unequal duty ratios with synchronized gate signals (case-2: D_S1 < D_S2). Mathematical analysis is established for both the cases (case-1 and case-2). From voltage gain point of view both of these schemes result in identical gain, but the D_S1 < D_S2 operation results in low source current ripple compared to equal duty ratio operation. Hence, detailed investigations are given for SCBDBBC under case-2 control. Since there are two controlling inputs (D_S1, D_S2) and one controlled output (v_o), two controllers are designed using two-input single-output (TISO) control theory. To demonstrate the SCBDBBC operation and TISO based two-part controller design, a 48 to 24 V (in bucking)/ 60 V (in boosting) with power rating 24 ∼ 60 W is chosen for experiments. The SCBDBBC multi-mode operation in standalone buck and boost operations are demonstrated in addition to buck–boost conversion. The analytical findings are in close agreement with experimental observations.