Comparison and design of InterCell transformer structures in fault-operation for parallel multicell converters

Parallel multicell converters are now widely used in many high performance applications. In this paper, an exhaustive sizing and weight comparison is detailed for several Inter-Cell Transformer (ICT) structures at a normal operation or for a reduced number of phases due to fault-occurrence or Maximum Power Point Tracking strategy in Photovoltaic applications. Results are then compared with the classical uncoupled inductors topology. In the first part, authors present the analytic pre-design methodology of ICTs structure under normal operation. This methodology is extended taking into account the imbalance operation of ICTs considering different phases-disconnections. Afterwards, ICTs weight evolution related to the number of commutation cells in parallel is plotted and studied. An air-gap insertion is presented and discussed in order to avoid an over-sizing for ICTs. Finally, a 6-phase ICT set-up including air-gaps was built and presented. Magnetic and electric results clearly show the robustness capability of such a device for an operation with a reduced number of phases, due to the air-gap. The restarting of one phase is also performed in a safe condition, in order to change dynamically the number of phases for improve the converter efficiency.