Medium-Voltage Electric Spring Based on Modular Multilevel Cascaded Converter with Multiple-Outputs

The latest medium-voltage electric spring (MV-ES) incorporated into a solid-state transformer provides a possible solution for future electric vehicle charging infrastructure in multistorey car parks and can enhance the stability of the power system in the meantime. The first generation of MV-ES provides only one output port to feed all the loads, lacking flexibility and compromising user experience. This paper proposes a multiple-output MV-ES based on a modular multilevel cascade converter (MMCC) and dual active bridges. The design of multiple outputs enables an extra degree of freedom for separating critical and non-critical loads and is suitable for applications that demand multiple voltage level outputs. The controller design is discussed including the balance of capacitor voltages and the ES functions. The proposed system is verified with microgrid simulation in MATLAB.