Resonant Switched-Capacitor Converters for Sub-module Distributed Photovoltaic Power Management

Abstract

This paper discusses the theory and implementation of a class of distributed power converters for photovoltaic (PV) energy optimization. Resonant switched-capacitor converters are configured in parallel with strings of PV cells at the sub-module level to improve energy capture in the event of shading or mismatch. The converters operate in a parallel-ladder architecture, enforcing voltage ratios among strings of cells at terminals normally connected to bypass diodes. The balancing function extends from the sub-module level to the entire series string through a dual-core cable and connector. The parallel configuration allows converters to handle only mismatch power and turn off if there is no mismatch in the array. Measurement results demonstrate insertion loss below 0.1% and effective conversion efficiency above 99% for short-circuit current mismatch gradients up to 40%. The circuit implementation eliminates large power magnetic components, achieving a vertical footprint less than 6 mm. The merits of a resonant topology are compared to a switched-capacitor topology.Index Terms-Maximum power point tracking (MPPT), microinverter, resonant converter, solar energy, switched-capacitor.

Differential diffusion charge redistribution for photovoltaic cell-level power balancing

“…Differential power processing have been implemented at different levels of integration using a variety of architectures and topologies [3][4][5][6][7]. However, these approaches typically consist of a single modular functional block capable of achieving DPP and MPPT simultaneously, hence requiring these blocks with either parallel current steering inductors or voltage balancing capacitors at the desired level of MPPT granularity.…”

“…A few underperforming cells can cause significant loss in energy capture in a large string because series-connected cells must carry the same current, and are therefore constrained by the lowest-performing cell. Mismatches caused by partial shading, dirt accumulation, manufacturing tolerances, and different aging characteristics can severely limit the overall power extraction from a string and the negatively impact the longterm project economics [2][3][4][5][6][7][8][9][10][11][12][13].…”

“…The main disadvantage of cascaded architectures is the necessity to process the full power from each PV element, resulting in high insertion loss. The differential power processing schemes address the insertion loss problem by placing converters in parallel to only process the mismatch power [3][4][5][6][7]. However, all these approaches are subject to the high costs of intermediate energy storage components, such as discrete inductors and capacitors.…”

Two-Switch Voltage Equalizer Using an LLC Resonant Inverter and Voltage Multiplier for Partially Shaded Series-Connected Photovoltaic Modules

“…However, increased cost and complexity due to multiple micro-inverters/converters are very likely. In addition, the lower power utilization due to the efficiency penalty of the added power conversion stage is also considered a major drawback [3], [17].…”

“…2. Most conventional topologies are based on individual multiple bidirectional dc-dc converters such as buck-boost converters [3]- [10] (and some extended topologies [11]- [14]), multi-stage buck-boost converters [15], [16], and switched capacitor converters [17], [18], shown in Figs. 2(a)-(c), respectively.…”