Power converters for distributed photovoltaic power conversion systems

Distributed architectures mitigate partial shading, module mismatch, uneven ageing and soiling problems in small and medium scale photovoltaic power conversion systems. While micro inverters interface PV panels to a common AC bus in distributed PV power conversion systems, micro converters integrate single PV panels to a common DC system bus. Extensive details about PV system architectures and associated power converter topologies which are based on high-frequency operation are presented in Chapters 1 and 2 with a comprehensive literature review. Soft-switching techniques known as zero-voltage-switching and zero-current-switching are utilized to reduce switching losses of high frequency switching converters. Their realization in power converters depends on power converter topology and associated power modulation scheme. Details of the soft-switching operation of di erent power converter topologies are presented throughout this thesis with a basic introduction provided in Chapter 2. Several micro inverter topologies based on resonant power converters are presented in Chapters 3, 4, 5, and 6 along with their power modulation methods, namely, phase shift and pulse width modulations. Micro inverters presented in Chapters 3, 5 and 6 are high-frequency-link or DC-link-less type and micro inverters presented in Chapter 4 have a DC-link. Furthermore, a switching control strategy for a micro converter is presented in Chapter 7. That micro converter is based on a current-fed converter topology. The realization of soft- switching operation of power switches in di erent power conversion modes of these power converters and their steady state operation are presented along with their power modulation methods in Chapter 7. The soft-switching operation of all micro inverter topologies with the proposed power modulation schemes is validated using simulation and experimental results. Moreover, the soft switching operation of the current-fed push-pull converter with the proposed switching control strategy is also validated using simulation and experimental results. A comprehensive comparison between the proposed micro inverter and micro converter topologies is presented at end of this thesis with some conclusions and recommendations which are useful to improve operational capabilities of these power converters before they are used in real world applications.Doctor of Philosophy (EEE