Study on the Topology and Control of Novel Multi-level Converter with Flying Capacitor Phase-leg to Form Dynamic Voltage Balancing

Diode-clamped multilevel converters employing capacitive voltage division suffer from dynamic imbalance in voltage distribution under complex operating conditions due to capacitor voltage fluctuations. Replacing capacitive voltage division with dynamically controlled voltage-sharing flying capacitor legs effectively resolves this issue. The topological evolution and control research is proposed based on this approach. Based on a three-level diode-clamped converter, the FC-NPC converter and its control methodology are introduced, with a prototype developed to achieve dynamic neutral point voltage balancing under various modulation schemes. Furthermore, to address 2 000 V photovoltaic/energy storage conversion requirements, a four-level FC-NPC topology and its control methodology are evolved. Within the FC-NPC converter topology, a novel modulation scheme optimized for electromagnetic interference mitigation is designed. Subsequently, for energy storage inverter applications employing the FC-NPC structure, a voltage disturbance method based on flying capacitors is proposed to achieve online battery impedance identification.