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  1. Power electronic inverters for photovoltaic (PV) systems over the years have trended towards high efficiency and power density. However, reliability improvements of inverters have received less attention. Inverters are one of the lifetime-limiting elements in most PV systems. Their failures increase system operation and maintenance costs, contributing to an increased lifetime energy cost of the PV system. Opportunities exist to increase inverter reliability through design for reliability techniques and the use of new modular topologies, semiconductor devices, and energy buffering schemes. This paper presents the implementation and design for reliability for a GaN-based single-phase residential string inverter using a new topological and control scheme that allows dynamic hardware allocation (DHA). In the proposed inverter architecture, a range of identical modules and control schemes are used to dispatch hardware resources within the inverter to variably deliver power to the load or filter the second harmonic current on the DC side. This new approach more than triples the lifetime of GaN-based inverters, reducing system repair/replacement costs, and increasing the PV system lifetime energy production. 
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  2. This paper presents the design and implementation of a boundary current mode (BCM) modulated GaN-based single phase inverter using a combination of bipolar and unipolar switching. Both unipolar and bipolar BCM-switched full bridge inverters are explored in detail in the context of efficiency, output current distortion and leakage current. Although the unipolar switched BCM inverter results in a higher efficiency in comparison to the bipolar switched inverter, it leads to a higher output current distortion at the low frequency zero crossing. On the other hand, the bipolar switched BCM inverter yields a low leakage current and reduced output current distortion, but exhibits lower efficiency. To overcome the low frequency zero crossing current distortion while maintaining a high efficiency, a combination of bipolar and unipolar switching in a BCM inverter is proposed. An experimental prototype has been built to validate the proposed control technique and modulation scheme. The proposed approach achieves a 2% efficiency improvement in comparison to the standard bipolar switched BCM inverter and a THD of 1.15%. 
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