微电网无缝切换控制策略与特性研究

发布时间：2018-06-21 11:16

本文选题：微电网 + 非计划孤岛　；参考：《华北电力大学(北京)》2017年硕士论文

【摘要】：常规能源如煤炭、石油等的消耗所带来的环境问题日益严峻,而当前社会对能源的需求日益增加。在此背景下,分布式能源如风能、太阳能的消耗越来越多,而且它们的特点是清洁可持续,对环境危害很小,将分布式能源以及储能和控制设备结合而构成小容量的微电网,在满足本地负载的同时,与主电网连接进行功率交换,其应用场合越来越广。并网时,微电网一般控制为电流源与主电网进行功率交换,如果非计划孤岛发生导致主电网断电,此时微电网中的敏感负载可能会因为主电网断电而导致供电质量受损。因此有必要研究相应的控制策略实现PCC点的无缝切换,以完成并网到孤网切换过程中PCC点电压的平滑过渡,保障敏感负载的良好供电质量。首先,本文对现有的微电网并网、孤网和两者间切换的控制策略做了充分研究。其次,通过对已有文献的分析,提出一种基于PCC点电压的无缝切换控制策略。并设计电压、频率限幅器和电感电流环、电压外环、前馈电压环的PI控制器参数,通过开环Bode图来说明参数选取的效果。在PISM中对不同阻值的负载进行并网到孤网的切换与孤网到并网重连仿真分析,在实验室的微电网实验平台中,根据仿真内容,完成并网到孤网的切换与孤网到并网重连物理实验,仿真和物理实验结果验证了基于PCC点电压的无缝切换控制策略的正确性。然后,提出一种基于电感参数设计的无缝切换控制策略。根据并网时输出电流与电网电压的夹角的不同,微电网变流器与主电网交换的功率以及流动方向也不同。通过查询国际协会与各国出台的PCC点电压对电网异常响应时间的标准,给出本章所采用的切换时PCC点电压允许波动的范围,基于该标准,考虑到实际工程中电感纹波与基波压降要求,根据微电网有功容量等参数给定变流器输出电感参数值,在该电感参数值下不改变控制策略也可完成无缝切换过程。最后,微电网含有多个变流器时,可以采用下垂控制来完成并网到孤网的无缝切换。并网时微电网运行于PQ控制,限幅器不起作用;孤网发生时,由于给定功率可能会与负载功率不匹配,使得限幅器起作用,电压和频率的限制值根据下垂关系修改功率参考指令值,完成PCC电压的无缝切换。孤岛检测到孤网后,状态运行开关切换到下垂控制,根据微电网容量与负载大小关系,合理分配功率,优化能源利用。并在PSIM软件中验证基于下垂控制的无缝切换控制策略。
[Abstract]:The environmental problems caused by the consumption of conventional energy, such as coal and oil, are becoming more and more serious, and the demand for energy is increasing day by day. In this context, distributed energy sources, such as wind and solar energy, are consuming more and more, and they are characterized by clean and sustainable, very little harm to the environment, the combination of distributed energy and energy storage and control equipment to form a micro-grid of small capacity. At the same time, the power exchange with the main power grid is more and more widely used. When the microgrid is connected to the grid, the power exchange between the current source and the main grid is usually used. If the unplanned isolated island occurs and the main grid is cut off, the sensitive load in the microgrid may damage the power supply quality due to the power failure of the main grid. Therefore, it is necessary to study the corresponding control strategy to realize seamless switching of PCC points, in order to complete the smooth transition of PCC point voltage in the process of grid-connected switching to isolated network switching, and to ensure the good power supply quality of sensitive load. Firstly, the existing control strategies of microgrid grid-connected, isolated network and switching between them are fully studied in this paper. Secondly, a seamless switching control strategy based on PCC point voltage is proposed. The Pi controller parameters of voltage, frequency limiter, inductor current loop, voltage outer loop and feedforward voltage loop are designed. The effect of parameter selection is illustrated by open-loop Bode diagram. In PISM, the load with different resistance values is switched from grid to grid and the reconnection of grid to grid is simulated. In the experiment platform of microgrid in laboratory, according to the content of simulation, The physical experiments of grid-to-solitary-network switching and reconnection are completed. The results of simulation and physical experiments verify the correctness of the seamless switching control strategy based on PCC voltage. Then, a seamless switching control strategy based on inductance parameter design is proposed. According to the difference of the angle between the output current and the voltage, the power and flow direction of the microgrid converter and the main grid are different. By querying the standard of PCC point voltage response time to power network, which is issued by the International Association and other countries, the paper gives the range of the PCC point voltage which is allowed to fluctuate when switching, based on this standard, Considering the requirements of inductance ripple and fundamental wave voltage drop in practical engineering, the seamless switching process can be completed without changing the control strategy according to the output inductance parameter value of the converter according to the parameters such as active power capacity of microgrid. Finally, when microgrid contains multiple converters, sagging control can be used to complete seamless switching from grid-connected to isolated grid. When the microgrid is connected to the grid, the limiter does not work because of PQ control. When the isolated network occurs, because the given power may not match the load power, the limiter works. The limiting value of voltage and frequency is modified according to the droop relation to change the power reference instruction value to complete the seamless switching of PCC voltage. After the isolated network is detected, the state operation switch is switched to droop control. According to the relationship between the capacity of the microgrid and the load, the power is allocated reasonably and the energy utilization is optimized. The seamless switching control strategy based on droop control is verified in PSIM software.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM727

【参考文献】