Standalone Clamping Switched Capacitor-Based Modular DC Transformer for MVdc Application

This article introduces a standalone clamping switched capacitor-based dc transformer (CSCDCT) for the medium-voltage de power grid. The CSCDCT owns the functions of the de fault isolation and the online redundant design, and hence, the power distribution reliability can be guaranteed. It is also shown that the additional advantages of the CSCDCT are the matching regulation of the high-frequency ac voltages and the voltage self-balance of the dc capacitors. The coupling effect of ac voltage amplitudes and dc voltages can be eliminated by the matching regulation, and the action of dc voltages will not alter the amplitude of high-frequency ac voltages in CSCDCT, improving the soft-switching performance, efficiency, and control stability of the DCT system. Besides, by the self-balance capability, the dc capacitor voltage balancing mechanism is not required for the individual unit although two capacitors are used in each submodule. This simplifies the control system of the CSCDCT. The topology, operating mode, voltage matching modulation, current characteristic, switching performance, and power lass of the CSCDCT are investigated in detail. The correctness of the analysis is validated through the experimental and simulation results.

Automated summary

This article introduces a standalone clamping switched capacitor-based dc transformer (CSCDCT) for the medium-voltage de power grid. The CSCDCT has the functions of de fault isolation and online redundant design to ensure power distribution reliability. In addition, it achieves matching regulation of high-frequency ac voltages and voltage self-balance of dc capacitors, eliminating the coupling effect and improving the soft-switching performance and control stability of the system. The article thoroughly investigates the topology, operating mode, voltage matching modulation, current characteristic, switching performance, and power loss of the CSCDCT, and validates the analysis with experimental and simulation results.