不接地配电网具有无零序电流通路、端点元件无中性点或虽有中性点但无引出线两个特点.由于无零序电流通路,端点注入电流满足零序分量为0的约束;由于无中性点或中性点引出线,端点元件具有相-中性点电压不可测或不宜控制相-地电压的特点.因此,实际不接地配电网中的电源端点通常以线电压作为测量和控制对象,即电源具有线电压控制特性.文中同时考虑不接地配电网的上述两个特点,提出以线电压为控制对象,通过构造平衡端点等值中性点作为全网的电压参考点,建立平衡端点和有功功率-电压端点的改进模型;在此基础上,进一步结合不同接线方式负荷的潮流模型,建立考虑电源线电压控制特性的不接地配电网改进三相潮流模型.最后,用IEEE 13节点修正系统验证了所提模型对不接地配电网三相潮流计算的适应性和有效性.%Ungrounded distribution networks have two main features: 1) there is no path for zero-sequence current;2) the endpoint element either has no neutral point or, even if with one, is without a neutral line.Because of the first feature, zero-sequence input current of an endpoint must be equal to 0, and because of the absence of neutral point or neutral line, the endpoint element is characterized by immeasurability of the phase-neutral point voltage or inadvisability of control on the phase-to-ground voltage.Therefore, the endpoint of power source in an ungrounded distribution network usually takes the line-to-line voltage as the objects of measurement and control rather than the phase-to-ground/phase-to-neutral point voltage of the endpoint in an actual ungrounded distribution network, which is called the line-to-line voltage controllability.By taking both features into consideration, this paper tries to improve the existing three-phase power flow model for ungrounded distribution network.First, an equivalent neutral point of the slack node is obtained and treated as the common reference point for phase voltages to serve as an improved model for the slack node.Then an improved model for active power-voltage node with the total active input power and line-to-line voltages as control objects is proposed based on the two watt-meter method.Finally, the improved three-phase power flow model with line-to-line voltage controllability and wye-connected/delta-connected load is proposed.The modified IEEE 13-bus distribution network is tested to verify the improved three-phase load model proposed.
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