微电网功率分配及平滑切换方法研究

发布时间：2018-10-08 09:23

【摘要】：微电网是一种集分布式电源、局部负荷为一体的独立供电系统,可以在并网和孤岛两种模式下运行。孤岛运行时,在并联分布式电源之间合理分配功率是一个重要的控制目标。由于下垂控制可实现无通信系统的功率分配,因而受到了广泛关注。然而,传统下垂控制器受到线路阻抗不匹配、局部负荷等因素影响,难以实现精确的功率分配控制。因此,本文重点研究基于下垂控制策略的功率分配特性及其改进方法以及平滑切换方法,具体研究内容如下：首先,本文建立了逆变器模型；设计了电压外环电流内环控制器；建立了下垂控制器模型,在此基础上分析了有功-频率和无功-电压下垂控制器的稳定性,并进行了仿真验证。其次,本文分析了逆变器并联系统的功率分配特性；研究了线路阻抗、局部负荷对功率分配的影响。再次,本文研究了一种基于Q—U下垂特性的虚拟阻抗的控制方法,通过该控制策略消除等效输出阻抗的偏差对无功功率的分配影响,从而改善无功功率分配特性,并进行了仿真验证。最后,本文研究了基于下垂控制的微电网平滑切换方法。该方法可以在不改变控制模式的情况下实现并网和孤岛模式的平滑切换,仿真结果验证了该方法的正确性和有效性。本文理论分析及仿真验证表明：虚拟阻抗可以有效弥补线路阻抗不匹配对无功功率分配的影响,从而改善无功分配精度。基于下垂控制的微电网平滑切换方法由于不改变控制模式,从而降低了复杂性,提高了灵活性。该结论对基于下垂控制的功率分配策略和平滑切换方法有一定的应用价值。
[Abstract]:Microgrid is an independent power supply system with distributed generation and local load, which can be operated in two modes: grid-connected and isolated island. The reasonable distribution of power between parallel distributed power sources is an important control objective when the island is running. Because droop control can realize power distribution of no communication system, it has been paid more and more attention. However, the traditional droop controller is affected by the line impedance mismatch and local load, so it is difficult to achieve accurate power allocation control. Therefore, this paper focuses on the power allocation characteristics based on droop control strategy and its improvement method and smooth switching method. The specific research contents are as follows: first, the inverter model is established in this paper; The voltage outer loop current inner loop controller is designed, and the sagging controller model is established, and the stability of active power frequency and reactive power voltage droop controller is analyzed and verified by simulation. Secondly, the power distribution characteristics of parallel inverter system are analyzed, and the influence of line impedance and local load on power distribution is studied. Thirdly, this paper studies a control method of virtual impedance based on Q-U droop characteristic. By using this control strategy, the influence of the deviation of equivalent output impedance on the distribution of reactive power is eliminated, so as to improve the distribution characteristics of reactive power. The simulation is also carried out. Finally, this paper studies the smooth switching method of microgrid based on droop control. The method can realize smooth switching between grid-connected and islanding mode without changing the control mode. The simulation results show that the method is correct and effective. Theoretical analysis and simulation results show that virtual impedance can effectively compensate for the effect of line impedance mismatch on reactive power distribution and improve the accuracy of reactive power distribution. Because the smooth switching method of microgrid based on droop control does not change the control mode, it reduces the complexity and improves the flexibility. This conclusion has certain application value to power allocation strategy and smooth switching method based on droop control.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM727

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