【作者】 李龙；

【导师】 谭永东；

【作者基本信息】 西南交通大学 ， 电气工程， 2014， 硕士

【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。更多还原

【Abstract】 Micro-grid is an independent power supply system, made up of distributed generation (DG) and local load, which can operate not only in grid mode but also in island mode. In addition, rational allocation of power between the DGs is an important goal in island mode. Since the droop control can achieve power allocation without communication system, it receives widespread attention. However, as the conventional droop control affected by the line impedance mismatch, partial load and other factors, it is difficult to achieve precise control of power allocation.Therefore, this dissertation focuses on the characteristics of power allocation and its improvement methods based on droop control strategy, and smooth switching method between two operating modes of micro-grid, the specific contents are as follows:Firstly, the inverter model is established; the outer voltage loop and inner current loop controller is designed; the droop controller model is also established. On the basis of the droop controller model, the stability of the active power-frequency and reactive power-voltage droop controller is analyzed and verified by a simulation.Secondly, the characteristics of power allocation in parallel inverter system are analyzed in this dissertation. What’s more, the influences of line impedance, sagging coefficient and partial load on the power allocation are researched.Thirdly, the dissertation has studied a virtual impedance control method based on Q-U droop characteristic in order to eliminate the effects of deviation of the equivalent output impedance on reactive power distribution through the control method, so as to improve the reactive power distribution characteristics And the validity of the control method has been testified.Finally, the smooth switching method in the micro-grid based on droop control is researched. This method can achieve smooth switching between grid mode and island mode without changing the control method. The simulation results verify the correctness and validity of this method. In this dissertation, theoretical analysis and simulation verification show that: virtual impedance can effectively compensate for the effect on reactive power allocation, caused by line impedance mismatch. Thus the accuracy of reactive power allocation is improved. The smooth switching method based on droop control in micro-grid reduces the complexity and increases the flexibility, as it does not need to change the control mode. This conclusion has some value for power allocation strategy and smooth switching method based on droop control in micro-grid.更多还原