High-density power converters for sub-module photovoltaic power management

This work presents an overview of distributed submodule power electronics based on resonant and switched-capacitor topologies configured in a ladder architecture. We present a new resonant switched-capacitor topology, termed a `direct conversion´ topology because current flow is always uni-directional in the inductor component. The direct topology can be seen as a resonant version of the more common 3-level buck converter. We discuss some of the relevant theory for the direct topology compared to past work on the `indirect´ resonant switched capacitor architecture. We also present a high-density DC-DC converter that can be used in resonant or switched capacitor modes that is implemented in a 0.18 μm bulk CMOS integrated circuit. The presented topologies implement voltage equalization to mitigate power loss due to mismatch at the sub-module level in PV systems. We provide measurement results of key converter specifications based on laboratory testing and also with real PV setups. To test the chip-scale converter, we used a PV module built up from individual cells on a Lexan laminate to provide custom string lengths of 4-6 individual PV cells.