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 dc power grid. The CSCDCT owns the functions of the dc 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 loss of the CSCDCT are investigated in detail. The correctness of the analysis is validated through the experimental and simulation results.