Input-Series and Output-Series High Voltage Converter with Active Balancing Circuit for N-1 Operation

An input-series/output-series converter dedicated to high power applications is presented. The converter is composed of plural MF transformers based on DC-DC sub-converters. The series connection allows reaching input-voltage levels in the range of several tens or hundreds of kV. The power level can be increased by modularity, even if the size of one MF transformer is generally limited by the size of the available magnetic cores. Each sub-converter has at its primary side a 3-Level Half-Bridge inverter that generates the MF intermediary voltage. The output circuit of each subconverter is a simple diode rectifier. The series input circuit is completed by an active balancing circuit which allows the N-1 operation of the installed channels with unmodified input voltage conditions. The paper presents the new topology together with the adopted control structure. The performance of the proposed architecture and its possible mode of operation with one or more disabled sub-converters is verified with a small-scale demonstrator.