交流微电网孤岛模式下无功功率均分控制策略研究

发布时间：2019-05-12 06:24

【摘要】：为解决分布式微源并网稳定性问题,学者提出了微电网理论。随着微电网的发展,难点问题层出不穷,比如微网在孤岛运行模式中的无功功率均分问题,以及微网接入不平衡负载时输出端和公共耦合点(Point of Common Coupling,PCC)电压不平衡问题。因此,研究逆变器接口控制技术解决上述问题具有重要意义。下垂控制能够利用本地信息,对通讯要求较低,是实现并联逆变器均分无功功率的重要控制方法,但是微网线路阻抗呈阻性导致逆变器输出的有功功率和无功功率耦合,影响下垂控制分配无功功率效果,此外逆变器等效输出阻抗的阻性分量和感性分量无法严格按照容量比匹配也会造成逆变器输出的无功功率无法均分。基于虚拟阻抗无功功率均分控制方法可以解决传统下垂控制无法均分无功功率问题,但是如何整定虚拟阻抗一直是个难点。虚拟阻抗包括虚拟电阻和虚拟电抗。针对虚拟电阻整定问题,本文提出一种虚拟负电阻的方法,通过添加同线路电阻大小相同的虚拟负电阻,抵消线路电阻产生的压降;针对虚拟电抗整定问题,本文提出了一种利用逆变器输出参数整定虚拟电抗的无功功率均分控制策略。选取线路结构简单的逆变器作为参考逆变器,其他逆变器作为目标逆变器。利用参考逆变器和目标逆变器的输出电压、下垂系数、线路电抗来整定目标逆变器的虚拟电抗,参考逆变器的虚拟电抗根据滤波电感进行整定。在平衡负载和不平衡负载两种情况中,该方法可以提高传统下垂控制均分无功功率精度。针对不平衡负载条件下系统电压不平衡问题,本文给出一种同时补偿逆变器输出端和PCC点电压不平衡度协调补偿控制策略,该方法优先补偿逆变器输出端电压,在输出端电压不平衡度满足供电要求前提下,对PCC点电压不平衡度进行补偿。此方法可同时改善逆变器输出端和PCC点电压不平衡问题。在MATLAB/Simulink软件环境的仿真结果验证了上述控制策略的有效性。
[Abstract]:In order to solve the stability problem of distributed microsource grid connection, scholars put forward the theory of microgrid. With the development of microgrid, difficult problems emerge in endlessly, such as the sharing of reactive power in isolated island operation mode, and the voltage imbalance between output and common coupling point (Point of Common Coupling,PCC when microgrid is connected to unbalanced load. Therefore, it is of great significance to study the inverter interface control technology to solve the above problems. Drooping control can make use of local information and has low communication requirements. It is an important control method to realize the equal sharing of reactive power of parallel inverter, but the impedance of microgrid line is resistive, which leads to the coupling of active power and reactive power of inverter output. The effect of sag control on reactive power distribution is affected. In addition, the resistive component and inductive component of equivalent output impedance of inverter can not be matched strictly according to the capacity ratio, which will also cause the reactive power output of inverter to be unevenly divided. The method based on virtual impedance reactive power sharing control can solve the problem that traditional drooping control can not divide reactive power evenly, but how to adjust virtual impedance has always been a difficult point. Virtual impedance includes virtual resistance and virtual reactance. In order to solve the problem of virtual resistance tuning, a method of virtual negative resistance is proposed in this paper, which can offset the voltage drop caused by line resistance by adding virtual negative resistance with the same size of line resistance. In order to solve the problem of virtual reactance tuning, a reactive power sharing control strategy using inverter output parameters to adjust virtual reactance is proposed in this paper. The inverter with simple circuit structure is selected as the reference inverter and the other inverters as the target inverter. The output voltage, sag coefficient and line reactance of the reference inverter and the target inverter are used to adjust the virtual reactance of the target inverter, and the virtual reactance of the reference inverter is adjusted according to the filter inductance. In the case of balanced load and unbalanced load, this method can improve the accuracy of the traditional sag control. In order to solve the problem of system voltage imbalance under unbalanced load, this paper presents a coordinated compensation control strategy for simultaneous compensation of inverter output and PCC point voltage imbalance. This method gives priority to compensation of inverter output voltage. On the premise that the output voltage imbalance meets the requirements of power supply, the voltage imbalance of PCC point is compensated. This method can improve the voltage imbalance of inverter output and PCC at the same time. The simulation results in MATLAB/Simulink software environment verify the effectiveness of the above control strategy.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM727

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