The MMC Based DC Transformer With Reshaped Circulating Current

Inhalt:
In this article, the modular multilevel converter based dc transformer (MMC-DCT) is proposed, which is constructed by modular multilevel arms, a transformer, and diode valves. Compared with other promising dc transformers, MMC-DCT can achieve high step-up ratio with MW level power transmission via intermediate medium-frequency transformer. The circulating current is reshaped into the trapezoidal wave instead of conventional dc wave, so that the capacitor voltage ripple can be suppressed significantly. Furthermore, by controlling three-phase currents of transformer into interleaved trapezoidal waves as well, smooth dc currents can be synthesized without bulky filters. The effectiveness is validated in simulation model and scaled-down laboratory prototype.