A VUF Constrained Neutral Current Reduction Strategy for 4-Leg Grid Forming Inverter

The landscape of power distribution networks is undergoing a significant transformation with the increasing penetration of distributed energy generators (DGs). These DGs include single phase solar and wind based generator. While this integration offers environmental and economic benefits, it also introduces challenges related to unbalanced load conditions. The inherent unbalance in distribution networks is further exacerbated by integration of single phase inverters, leading to excessive neutral currents. These high neutral currents pose significant challenges, including overloading of distribution feeders and transformers, common mode noise, flat-topping of voltage waveforms, and potential wiring failures. To address this critical issue, three-phase four-leg (3P4L) grid-forming inverters (GFMs) offer a promising solution. The fourth leg in these inverters can be employed to actively regulate the neutral current while maintaining grid codes. This paper delves into the control strategy for a 3P4L GFMs and proposes a novel neutral current reduction (NCR) control algorithm. The proposed control strategy demonstrates a significant reduction in neutral current, achieving up to 34% decrease compared to a scenario without any reduction mechanism. The effectiveness of the proposed algorithm is further validated through simulations conducted on a benchmarked low voltage CIGRE test network and in scenarios with multiple DGs supplying power. These results showcase the adaptability and flexibility of the proposed control approach in practical grid configurations.