Remote Negative-Sequence Voltage Fair Compensation in Grid-Forming Inverter-Based Islanded AC Microgrids

The presence of unbalanced loads in power systems creates voltage imbalances that perturb the operation of sensitive equipment like induction motors, power electronics converters, and adjustable speed drives. To address this issue, this article presents a novel control scheme to perform remote negative-sequence voltage fair compensation at any node of a grid-forming inverter-based islanded ac microgrid. The fair compensation reduces the voltage imbalance of the remote node by adjusting the negative-sequence output voltage of the inverters according to a predefined objective. For example, the goal could be to equalize the inverters’ negative-sequence output voltage. Alternatively, the aim could be to reduce this voltage at some inverters to perturb less the local loads at the expense of increasing it in other inverters. Therefore, the proposed controller achieves two control objectives: negative-sequence voltage reduction at a remote node and fair compensation through the inverters running this service. The controller also features inherent plug-and-play and parallel operation. Unlike state-of-the-art controllers on negative-sequence voltage compensation, the control scheme operation is accomplished by only broadcasting the remote node voltage measurement, thus significantly reducing the communication control data. The article presents the large-signal control design and stability analysis, and the performance in a laboratory microgrid with selected experimental results.