A Two-Switch Forward Partial Power Converter for Step-Up/Down String PV Systems

This letter proposes a novel step-up/down series-connected partial power converter (S-PPC) for string photovoltaic (PV) applications. The proposed bidirectional two-switch forward (BFwd) dc–dc S-PPC performs partial power processing, reducing component stresses and losses. The PV active power is unidirectional, but the BFwd alone operates with bidirectional active power flow; with bidirectional current at the input and bipolar voltage at the output, characterizing two distinct modes of operation. To validate the analysis, a 950-W system prototype of the novel BFwd S-PPC was implemented experimentally for a realistic PV application example, where the transformer turns ratio was designed to decrease the nonactive power processed, resulting in a high power factor (
$ >\text{0.75}$
). The prototype reached a rated/peak system efficiency of 98.68%/99.48%. Compared with previously published step-up/down S-PPCs, the BFwd S-PPC employs fewer active switches (and gate drivers), which reduces its complexity and cost; but moreover, increases its performance. In fact, the proposed BFwd S-PPC presents higher efficiencies than most step-up/down S-PPCs in the literature.