In a three-phase four-wire low voltage (LV) distribution system, unbalanced loads lead to neutral current (NC) looping resulting in increase of power losses and variation of neutral potential. Compared to the conventional power transformer, smart transformer (ST) has strict current limitations to avoid overcurrent. However, its advantages on the downstream LV grid voltage regulation can provide the capability to regulate excessive NC. This article proposes a closed-loop NC optimization control in order to, on the one hand, minimize the NC current in the normal operation satisfying the standard EN 50160 requirement, on the other hand, suppress the NC current in extreme cases to avoid the overcurrent damage of the ST. The proposed control strategies are validated by experimental tests via the hardware-in-the-loop setup and a case study based on a 350-kVA, 10-kV/400-V, ST-fed distribution network under unbalanced loading profile according to the three-phase four-wire distribution grid in the Manchester area. The results clearly prove the effectiveness and flexibility of the proposed NC optimization control strategies on the NC suppression and minimization.

中文翻译：

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不平衡负载下智能变压器供电配电系统的中性点电流优化控制

在三相四线低压（LV）配电系统中，不平衡负载会导致中性线电流（NC）环路，从而导致功率损耗增加和中性线电位变化。与常规电源变压器相比，智能变压器（ST）具有严格的电流限制，以避免过电流。但是，其在下游LV电网电压调节方面的优势可以提供调节过多NC的能力。本文提出一种闭环NC优化控制，以便一方面在满足标准EN 50160要求的正常运行中最小化NC电流，另一方面在极端情况下抑制NC电流以避免过电流ST的损坏。所提出的控制策略通过硬件在环设置的实验测试和基于350 kVA，10 kV / 400 V，ST馈电配电网络的非平衡负载情况下的案例研究进行了验证，具体方法如下：曼彻斯特地区的三相四线配电网。结果清楚地证明了所提出的NC优化控制策略在NC抑制和最小化方面的有效性和灵活性。