Investigating the Robustness of Sliding Mode Control Applied to NPC Rectifier-Based Smart Transformer

In recent years, the Smart Transformer (ST), defined as an advanced type of power electronic transformer incorporating sophisticated communication and control systems, has received increasing attention in the power distribution system. Its power circuit is a combination of High Frequency (HF) transformers and power electronic converters. In power distribution systems, the three-stage ST topology comprising a medium voltage AC-DC power stage, a HF DC-DC power stage, and a low voltage DC-AC power stage, is selected as the most appropriate due to the availability of DC buses on the medium and low voltage sides. However, it has a low efficiency as multiple power converters are integrated. To enhance the performance of this topology, an ST model comprising a 3-level Neutral Point Clamp (NPC) rectifier, a dual active bridge power electronic converter, and a 3-phase inverter is proposed in this manuscript. To optimize the performance of the studied ST model, the sliding-mode controller is implemented at the NPC rectifier and the 3-phase inverter, while the soft-switching technology is used for the dual active bridge converter. Furthermore, several simulations under disturbed operating modes, including voltage flicker, overvoltage, voltage sag, and parametric variations, are performed to demonstrate the good performance of the ST model under study and the great robustness of the proposed control strategy.