High-bandwidth Control Structure for Solid-State-Transformers with EtherCAT Protocol

This paper proposes a high-bandwidth control structure for solid-state-transformers (SSTs). To fabricate a medium-voltage (MV, 25 kV
rms
) SST, a 42-level AC/DC rectifier and forty-two dual-active-bridge (DAB) converters are required. However, it is challenging to simultaneously control these converters due to synchronization, propagation delay, and complexity. In this paper, an optimized structure for MV high-level SST controller is proposed. An industrial EtherCAT master PC and state-of-the-art micro-control-units (MCUs) TMS320F28388D are employed to fabricate the control environment. Using the serial-peripheral-interface (SPI) and EtherCAT protocols, a 10 kHz bandwidth data communication between controllers was achieved within a 100 μs delay. Based on the fast communication environment, a partially decentralized voltage balance control scheme, which reduces communication data size, is presented. The proposed controller is evaluated with a PLECS simulation model of the 42-level SST system.