Control of an MMC-based Hybrid Transformer with Star-point Voltage Injection

Inhalt:
Hybrid transformers (HTs) can provide both voltage and current compensation in the utility grid. HTs include a line-frequency transformer and a converter rated for partial transformer power. This paper presents a HT using a modular multilevel converter (MMC) connected at the medium-voltage (MV) side of the transformer, which allows scaling to a wide range of power and voltage ratings. The application in a HT requires an unconventional control approach for the MMC, as its output voltages have equal phase angles, but different amplitudes.