Abstract
With global energy shortage and strong environment movements, many countries are encouraging and promoting the development of distributed alternative energy and renewable energy sources. It is well-known that bidirectional dc-dc converters (BDC) play an important role in the renewable energy generation systems. BDC has bidirectional power flow capability with flexible control between the source and load sides that can provide the backup power when the main source is not available or has failed. For this reason, the main objective of this dissertation is therefore to develop a high efficiency high conversion ratio BDC as an interface for DC-based nanogrid applications. In this dissertation, a novel interleaved high conversion ratio BDC with low switch voltage stress and uniform current sharing characteristics is proposed. As an illustration, a two phase interleaved NBDC with a new voltage quadrupler circuit configuration is first given for demonstration. Furthermore, topological extensions which include a four-phase interleaved NBDC, the extended six-phase NBDC, another two-phase interleaved IBDC and generalized configuration using the new voltage quadrupler module for higher bidirectional conversion applications. In these proposed converter topologies, based on the concepts of the voltage division of the capacitor voltage, the energy can be stored in the blocking capacitor set of the BDC converter for increasing the voltage conversion ratio and for reducing the voltage stresses of the switches. As a result, the proposed converter topology possesses the low switch voltage stress characteristic. This will allow one to choose lower voltage rating MOSFETs to reduce both switching and conduction losses, and the overall efficiency is consequently improved. In addition, due to the charge balance of the blocking capacitor, the converter features automatic uniform current sharing characteristic of the interleaved phases without adding extra circuitry or complex control methods. Finally, a 24V low voltage side, 400V high voltage side, and 500W output power prototype circuit is implemented in the laboratory to verify the performance.