基于改进下垂法的光伏微网并网控制策略研究

发布时间：2018-08-09 20:48

【摘要】：日益凸显的能源和环境问题,使得风能、太阳能等洁净可再生能源受到了人们的广泛关注。分布式发电是开发利用可再生能源的有效途径,但由于分布式发电的随机性和分散性,使得分布式电源接入电网时会对系统的运行产生影响,这制约了分布式发电技术的发展。微网是将分布式电源与储能装置相结合,为当地负荷提供电能的一个可控的系统,它的出现不但能够很好的解决这一问题,同时还可以与电网互补,提高供电可靠性。微网的运行具有联网和孤岛两种模式,在不同的运行模式下选择合适的控制策略是保证微网系统发挥其诸多优势的前提。因此,建立以光伏电池为分布式电源的微网系统运行控制仿真模型具有重要的意义。文章首先从光伏微网并网系统拓扑结构出发,建立了光伏电池的仿真模型,并采用扰动观察法实现了光伏电池的最大功率跟踪控制；考虑到在微网系统中由分布式电源接口逆变器输出的电流中含有大量的谐波,为降低谐波含量,通过对不同类型滤波器的分析比较,最终选择了LC型滤波器且对其参数进行了整定。其次对微网的下垂控制原理展开研究；分析了两台分布式电源并联运行在孤岛模式时影响无功功率分配的因素,在传统下垂控制方法的基础上提出了补偿线路压降的改进下垂控制法,改进后的方法对于分布式电源运行在孤岛模式下的无功功率分配有明显的改善；设计了并网预同步控制器以减少系统联网瞬间产生的冲击电流对电网的影响。再次,针对微网系统与电网并网运行时的需要,通过在改进的下垂控制器中引入电压、频率参考值调整环使电源的输出功率保持恒定,实现了微网系统在并网运行时的恒功率(PQ)控制。最后,在Matlab/Simulink仿真环境下搭建了含有光伏电池的小型微网模型,将改进的下垂控制策略、并网预同步控制器和改进的恒功率控制策略应用到设计的算例中,通过对运行模式切换和负荷变化时的运行特性进行分析,结果证明了改进控制策略的有效性。
[Abstract]:Increasingly prominent energy and environmental problems, such as wind energy, solar energy and other clean renewable energy has received widespread attention. Distributed generation is an effective way to develop and utilize renewable energy. However, due to the randomness and dispersion of distributed generation, the distributed generation will affect the operation of the system when it is connected to the power network, which restricts the development of distributed generation technology. Microgrid is a controllable system which combines distributed power source with energy storage device to provide local load with electric energy. Its appearance can not only solve this problem but also complement the power grid and improve the reliability of power supply. The operation of microgrid has two modes of networking and islanding. Choosing appropriate control strategy under different operation modes is the prerequisite to ensure the microgrid system to give full play to its many advantages. Therefore, it is of great significance to establish the simulation model of microgrid system with photovoltaic cells as the distributed power source. In this paper, the simulation model of photovoltaic cell is established based on the topology of photovoltaic microgrid grid-connected system, and the maximum power tracking control of photovoltaic cell is realized by perturbation observation method. Considering that there are a lot of harmonics in the current output from the inverter of distributed power interface in the microgrid system, in order to reduce the harmonic content, the different types of filters are analyzed and compared. Finally, LC filter is selected and its parameters are adjusted. Secondly, the droop control principle of microgrid is studied, and the factors that affect reactive power distribution when two distributed power sources are running in island mode in parallel are analyzed. Based on the traditional droop control method, an improved droop control method for compensating line voltage drop is proposed. The improved method can obviously improve the reactive power distribution of distributed power generation running in isolated island mode. A presynchronous controller is designed to reduce the impact of the impulse current on the power grid. Thirdly, according to the need of the microgrid system running in parallel with the grid, by introducing the voltage into the improved droop controller, the output power of the power supply can be kept constant by the frequency reference adjusting loop. The constant power (PQ) control of microgrid system in grid-connected operation is realized. Finally, a miniature microgrid model with photovoltaic cells is built in Matlab/Simulink simulation environment. The improved droop control strategy, grid-connected presynchronous controller and improved constant power control strategy are applied to the design example. The results show that the improved control strategy is effective by analyzing the characteristics of operation mode switching and load changing.
【学位授予单位】：宁夏大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM615

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