Design and Control of Single-Phase WBG Based Grid Connected Inverter in Photovoltaic Applications

The solar energy generation technology has been considered as a very effective way in decarbonization and energy saving. In order to connect the solar energy to the power grid more flexibly, grid connected inverters play a paramount role in the system. However, the performance improvement (weight, volume, efficiency, etc.) of grid connected inverters is directly related to the evolution of power semiconductor devices. Nowadays, due to high efficiency, high temperature and high frequency capabilities, the power electronics devices based on Wide Band Gap (WBG) semiconductors, like Silicon Carbide (SiC) and gallium nitride (GaN) are paid common attention and widely considered as the foundation of next-generation power electronics converters. According to a report provided by 4E Power Electronic Conversion Technology Annex, the average efficiency of WBG based PV (Photovoltaic) inverters is 98.8%, while that of Si based PV inverters is 96.8%, which means an increased energy production of 10.3 TWh/year. Meanwhile, the size of the inductors and capacitors in the inverters could also be reduced due to the high switching frequency, which means higher power density. Consequently, WBG devices could improve the performance of grid connected inverters significantly.
Although the WBG devices have plenty of advantages, there are still some challenges to meet to make full use of such devices in grid connected inverters. When applying WBG devices in those hard-switching inverters, good efficiency only remains at 50 - 250 kHz switching frequency, which is slightly better than Si-based inverters. Therefore, the power density improvement is limited. Further, high dv/dt and di/dt would bring serious EMI (electromagnetic interference) issues. It is necessary to analyze the generated EMI noise and its propagation path when designing a WBG based inverter. In addition, compared to traditional Si devices, the power rating of WBG devices is limited, how to extend the application of these devices also needs to be considered.
This PhD project would focus on the design and control of grid connected inverter with Wide Band Gap devices in photovoltaic applications, including the following aspects:
1) Adopt soft-switching strategy for single-phase grid connected inverter to improve the efficiency and power density.
2) Design for EMC (electromagnetic compatibility) while maintaining energy efficiency.
3) Integrated magnetic components to boost the power density further.
4) Modular design to provide more flexibility and reliability.

Finally, the conducted theoretical and simulation analysis will be validated through hardware prototypes and experimental measurements.