Voltage balancing algorithm of a MMC-like topology for pulsed power applications

The Modular Multilevel Converter (MMC) has become one of the most attractive topologies for high-power applications, such as power supplies for nuclear fusion generators. MMC is composed by identical Submodules (SMs), permitting an easy scalability, and provides a multilevel output voltage, thus it represents a promising alternative to replace the system supplied by the Flywheel Generator (FG) that provides electrical power to ASDEX Upgrade (AUG) Toroidal Field (TF) coils. Due to the pulsed DC operation of these coils and their high-power needs (up to 150 MW) for each experiment, an adapted version of the MMC has been modeled with some differences compared to conventional ones: SMs’ capacitors have been replaced with Supercapacitor (SC) modules to increase the amount of available stored energy while SMs belonging to different "arms" are interconnected to simplify their control and increase the reliability of the converter. Two of the main challenges of this topology consist in keeping balanced the series-connected SMs’ voltages and the parallel-connected SMs’ currents during its operation, which leads to an increase of components’ lifetime. This paper gives an overview of the modeled converter, showing the adopted control strategy and highlighting the developed voltage balancing algorithm.