Transparent DC-Bus Voltage Control for Grid-Forming Converters

A transparent DC-bus voltage control structure is proposed in this paper, to operate grid-forming converters while ensuring under- and over-voltage regulation of the DC bus. If another converter is already regulating the DC bus voltage, then the converter with the proposed method behaves as a grid-forming converter. The control system switches seamlessly to dual-voltage-forming mode to regulate both AC-side and DC-bus voltages if the DC-bus voltage goes beyond the lower or upper limits. This seamless operation is allowed by the disturbance observer structure used in both DC-bus voltage control and grid-forming control modes. The performance of the proposed method is studied experimentally using a$12.5-\text{kVA}$setup.