Energization and Start-Up of CHB-Based Modular Three-Stage Solid-State Transformers

Abstract

This paper discusses the energization and start-up process of modular three-stage Solid State Transformers (SSTs) based on a cascaded H-bridge (CHB) topology. A key element of the SST is the Auxiliary Power Supply (APS) feeding the auxiliary circuitry. Redundancy and simpler implementation can be achieved by powering the APSs from the cells DC-link capacitors, but at the expense of a more challenging start-up process of the SST. The first steps of this process must be performed before APSs are operative. This can result in undesired transient events (inrush currents, voltage sags in the capacitors voltages, etc.) which could prevent proper start-up of the SST or even jeopardize the power devices or other elements. A simple strategy for the energization and start-up of SSTs using this APSs structure is proposed. The method is valid both for grid-forming and grid-feeding operation of the SST, regardless of the energization port and without the addition of any extra circuitry. Simulation and experimental results are provided.

SiC-Based High Efficiency High Isolation Dual Active Bridge Converter for a Power Electronic Transformer

“…where the HV and LV sides have separate APSs [32]. Commercial APSs can be used for voltages under 1 kV, otherwise, custom solutions must be implemented, such as the modular ISOP topology proposed in [29].…”

Flexible and Fault Tolerant Distributed Control Structures for Modular Power Electronic Transformers

“…The PET topology considered in this paper is a threestage topology, based on a Cascaded H-bridge (CHB) converter, interfacing a HVAC and a LVAC grids [9], [15] (see Fig. 1), though, the concepts being discussed can be applied to other modular configurations [15].…”

“…This is considered the most challenging case for two reasons: (1) the module power devices becomes uncontrolled and only the diodes conduct blocking the power transfer through the module which implicates disconnecting the PET from the grid, and (2) once fault is cleared, the ride-through process has to re-energize and start-up the module with no monitoring or control (i.e. the FPGA and communication ring are not powered) [9]. The reconfiguration process when a fault of this type occurs must be therefore carefully designed.…”

“…However, this is at the price of higher complexity during energization and start-up process and during the reconfiguration in the event of a module failure. Discussion of energization and start-up process in modular PETs using distributed APSs was presented in [9].…”

Energization and Start-up of Modular Three-stage Solid State Transformers

“…What specially distinguish the energization and start-up of the modular three-stage SSTs from other SST structures is the isolation requirements. It not only requires isolation between its two ports but also between series stacked modules/cells at the HV side AC/DC converter stage which can be several kV over the LV side reference [21], [22]. Another important fact for practical SST application is the possibility of starting-up the SST with both grids available or with just one of them (i.e.…”