Parallel multicell converters for high current: Design of intercell transformers

Duality rules show that the multilevel output voltage of series multicell converters transposes in the form of a multilevel input current in parallel converters. However the duality of these families of converter is only partial and parallel converters offer an extra advantage which is multilevel output behavior. When the inductors are coupled together, it is even possible to reduce the ripple of internal quantities, i.e. individual cell currents. The magnetic components at the heart of these converters obey very particular rules and need a specific design procedure. The leakage inductance of this component plays an important part in this design and because it involves flux trajectories in the air it is difficult to predict its value and optimize the design. It is also required to evaluate the core losses, the copper losses and the heat exchange surface to determine which number of cells should be used to minimize total weight. Such a procedure is described and used to compare designs with coupled and uncoupled inductors.