11 describes a method that employs distributed intelligent power electronics to mitigate the effects of cell mismatch. Unfortunately, any irradiation mismatch between cells will limit the current through a series-connected string of cells to that of the weakest cell, causing a lower output power than what is theoretically possible. The extraordinarily small size of the overall system in this work makes it particularly difficult to ensure perfect TPV cell-current matching, owing to cavity reflections and uneven irradiation across the different cells. This step is important because the generator operating conditions (i.e., incident irradiation and the cell junction temperature) can vary over time and must therefore be continuously tracked to ensure that maximum power is extracted from the cells at all times. In the final conversion step, the raw output of the TPV cell is dynamically converted into useful current and voltage levels via a low-power power electronics converter known as the maximum power-point tracker (MPPT). The system was demonstrated to operate up to 800 ☌ (silicon microcombustor temperature) with an input thermal power of 13.7 W, generating 344 mW of electric power over a 1-cm 2 area. The μTPV experimental system that was built and tested comprises a silicon propane microcombustor, an integrated high-temperature photonic crystal selective thermal emitter, four 0.55-eV GaInAsSb thermophotovoltaic diodes, and an ultra-high-efficiency maximum power-point tracking power electronics converter. Even with a much-simplified μTPV system design with theoretical efficiency prediction of 2.7%, we experimentally demonstrate 2.5% efficiency. Although considerable technological barriers need to be overcome to reach full performance, we have performed a robust experimental demonstration that validates the theoretical framework and the key system components. The approach is predicted to be capable of up to 32% efficient heat-to-electricity conversion within a millimeter-scale form factor. The challenging problem of ultra-high-energy-density, high-efficiency, and small-scale portable power generation is addressed here using a distinctive thermophotovoltaic energy conversion mechanism and chip-based system design, which we name the microthermophotovoltaic (μTPV) generator.
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