High-efficient Soft-Switching Converter for Three-Phase Grid Connections of Renewable Energy Systems

Despite their high efficiency, soft-switching three-phase inverters ca have disadvantages like higher conduction losses (resonant pole inverter), voltage stress and sub-harmonics (resonant DC-link inverter) or the need for additional components (auxiliary resonant commutated pole inverter). In contrast to single-phase grid connection, the three-phase grid connection provides a continuous power flow without the need for large energy storage devices. If the inverter is fed by a constant power source, it is possible to overcome these disadvantages by using the novel double 120deg flattop modulation, which results in an inverter with low conduction losses, small dc-link capacitance and soft-switching operation without the need for additional components. The developed inverter prototype in the kW-range operates with a total dc-link capacitance of only 10 muF. All these characteristics make it promising for grid-connection of renewable energy systems