High Gain DC-DC Multilevel Boost Converter to Enable Transformerless Grid Connection for Renewable Energy

Abstract

The solid state transformer (SST) is a new technology that will result in the replacement of traditional line frequency transformers in applications demanding high-power density and greater level of control. This paper describes a new form of boost converter to support the development of SST to enable the grid connection of renewable energy sources, such as wave energy and photovoltaics. SST contains the initial low voltage AC-DC converter, a high gain transformer based DC-DC converter, and the output high voltage DC-AC converter. A transformerless DC-DC Multilevel Boost Converter (MBC) is proposed, which combines the traditional boost converter with switched capacitor topology to realise a high voltage gain with only one driven switch and passive components. The main advantages of the proposed converter are the ability to realise high voltage gain without the need for an extreme (>80%) duty cycle, resulting in low voltage stress on the switching device and the creation of three self-balanced voltage levels at the output. The simulation results of the proposed topology are compared to the experimental results to validate the analyses. Thus, a 1 kW prototype MBC converter operating at 75 kHz is reported that resulted in a voltage gain of 10, with an experimental efficiency of 92.4% at a duty cycle of 71%, which compares favourably with the simulated efficiency of 94.5% under the same operating conditions.