High-Efficiency Quad-Mode Parallel PV Power Optimizer for DC Microgrids

The paper introduces a new parallel photovoltaic (PV) power optimizer intended for direct integration of PV modules into a dc bus or microgrid. The topology is derived from a typical galvanically isolated buck series resonant dc-dc converter (SRC) to the buck-boost SRC recently proven as a parallel PV power optimizer (PO). By applying the topology morphing control, this two-mode converter is extended to the quad-mode parallel PV PO. Its operation modes defined by changing modulation of switches are detailed, and gain expressions are provided. The proposed concept provides enhanced performance in the region where global power maximum could occur due to partial shading. Accordingly, a significant efficiency improvement is achieved at voltages below the nominal value that targets the most probable PV module operating point without shading. An experimental prototype was built to demonstrate the benefits of the proposed quad-mode PV PO and compare it to the existing two-mode buck-boost SRC. Thermal stress analysis is supported with power loss breakdown calculations to demonstrate component thermal stresses in critical operating points.