Converters with high boost, energy storage and bi-directional power flow in energy systems

This paper reviews the existing structures for converter stages in renewable energy and motor drive systems that offer high voltage gain at the input of an inverter. The inverter may also connect the DC supply to the utility grid. For traction motor drives in vehicle and rail transport and in high-frequency transformer connected grids, bi-directional power flow capability is also required. Cascaded high-boost non-isolated DC stage which offers multi-stage or multi-level DC inputs and output connections is the focus of attention in this paper. The high voltage DC supply to the inverter allows connections to inverters for motor drive and utility at the required voltage level. This arrangement may lead to reduced battery management issues and reduced size of storage elements, flexibility of connections with several input DC supplies at different levels, and improved reliability through series/parallel connection of converters with some redundancy. Several options for the high-boost stage which are currently available will be reviewed. This will be followed by considerations for energy storage elements and converters suitable for bi-directional power transfer capabilities. Converter topologies and control issues using a high-frequency link for bi-directional power flow between two AC grids will also be discussed.