Cascaded DC–DC Converter Connection of Photovoltaic Modules

TLDR

New residential‑scale photovoltaic arrays are typically connected to the grid by a single dc‑ac inverter linked to a series string of panels or by many small dc‑ac inverters that connect one or two panels directly to the grid. This paper proposes an alternative topology of nonisolated per‑panel dc‑dc converters connected in series to form a high‑voltage string that feeds a simplified dc‑ac inverter. The authors evaluate cascaded nonisolated per‑panel dc‑dc converters—buck, boost, buck‑boost, and Cu/spl acute/k—using Matlab simulations to compare efficiencies, costs, and complexity for different string lengths. The simulations show that buck and boost converters are the most efficient, with buck preferred for long strings and boost for short strings, while buck‑boost and Cu/spl acute/k converters are consistently less efficient or more costly.

Abstract

New residential scale photovoltaic (PV) arrays are commonly connected to the grid by a single dc-ac inverter connected to a series string of pv panels, or many small dc-ac inverters which connect one or two panels directly to the ac grid. This paper proposes an alternative topology of nonisolated per-panel dc-dc converters connected in series to create a high voltage string connected to a simplified dc-ac inverter. This offers the advantages of a "converter-per-panel" approach without the cost or efficiency penalties of individual dc-ac grid connected inverters. Buck, boost, buck-boost, and Cu/spl acute/k converters are considered as possible dc-dc converters that can be cascaded. Matlab simulations are used to compare the efficiency of each topology as well as evaluating the benefits of increasing cost and complexity. The buck and then boost converters are shown to be the most efficient topologies for a given cost, with the buck best suited for long strings and the boost for short strings. While flexible in voltage ranges, buck-boost, and Cu/spl acute/k converters are always at an efficiency or alternatively cost disadvantage.