Inter-cluster balancing of Solid-State Transformer Based on a Feedforward Negative-Sequence Power Control

This paper proposes an inter-cluster balancing of an input-parallel output-series modular multilevel cascaded solid-state transformer (SST) based on a feedforward negative-sequence power control. An imbalanced energy flow into each cell of the SST would cause the dc-capacitor voltage of each cell to diverge if the outflow of energy were not regulated to be equal to its inflow. The proposed method distributes the DC-input power to the three clusters corresponding to the AC output power imbalance among the three clusters. This enables the SST to prevent the divergence of the dc-capacitor voltage of each cell without the zero-sequence voltage injection. Simulation results are presented to validate the effectiveness of the proposed control.