During voltage sags, distributed generation systems must fulfil specific grid-code requirements for reactive current injection. This ancillary service can produce overvoltage problems in networks operating in unbalanced conditions when the amplitude of one of the phase voltages is higher than the others and a balanced reactive current is injected through large grid impedance. This study proposes a control scheme to avoid these overvoltage problems, thus reducing the risk of cascade disconnection that this incident may produce. The derivation of the control scheme starts from the flexible oscillating-power control, introduces the necessary modifications so that this control meets the grid-code requirements for current injection and combines it with a slope voltage control to achieve a good voltage regulation. A theoretical analysis is included to determine the expressions that quantify the voltage support characteristics of the proposal. Finally, selected experimental results are reported to validate the characteristics of the proposed control.

中文翻译：

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在不平衡电压骤降期间避免三相分布式发电系统中的过电压问题

在电压骤降期间，分布式发电系统必须满足无功电流注入的特定电网规范要求。当相电压之一的幅度高于另一相电压并且通过大的电网阻抗注入平衡的无功电流时，这种辅助服务可能会在不平衡条件下运行的网络中产生过电压问题。这项研究提出了一种避免这些过电压问题的控制方案，从而降低了此事件可能引起的级联断开的风险。控制方案的推导从灵活的振荡功率控制开始，进行了必要的修改，以使该控制满足电流注入的电网规范要求，并将其与斜率电压控制相结合以实现良好的电压调节。包括理论分析以确定可量化建议电压支持特性的表达式。最后，报告选定的实验结果以验证所提出控制的特征。