Hybrid Direct Power Converters with Increased/Higher than Unity Voltage Transfer Ratio and Improved Robustness against Voltage Supply Disturbances

Variable voltage and variable frequency conversion of electrical energy from an AC source to an AC load is done in traditional power converters via a DC-link where an energy storage element (electrolytic capacitors) is situated. Despite its well-known benefits, it has the disadvantage of being bulky and to limit the converter lifetime. On the other hand, direct power conversion (DPC) is an attractive concept, which doesn´t need an energy storage buffer, but has two main disadvantages: reduced voltage transfer ratio (<0.86) and low immunity to voltage supply disturbances. This paper proposes a new method to improve both the voltage transfer ratio and the robustness against voltage supply unbalance by employing a new concept of power conversion based on hybrid structures while the installed power and energy storage in the auxiliary converters remain low