Designs for ultra-high efficiency grid-connected power conversion

Abstract

Grid connected power conversion is an absolutely critical component of many established and developing industries, such as information technology, telecommunications, renewable power generation (e.g. photovoltaic and wind), even down to consumer electronics. There is an ever present demand to reduce the volume and cost, while increasing converter efficiency and performance. Reducing the losses associated with energy conversion to and from the grid can be accomplished through the use of new circuit topologies, enhanced control methods, and optimized energy storage. The thesis outlines the development of foundational methods and architectures for improving the efficiency of these converters, and allowing the improvements to be scaled with future advances in semiconductor and passive component technologies. The work is presented in application to module integrated converters (MICs), often called micro-inverters. These converters have been under rapid development for single-phase gridtied photovoltaic applications. The capacitive energy storage implementation for the double-line-frequency power variation represents a differentiating factor among existing designs, and this thesis introduces a new topology that places the energy storage block in a series-connected path with the line interface. This design provides independent control over the capacitor voltage, soft-switching for all semiconductor devices, and full four-quadrant operation with the grid.