微电网平滑切换的控制策略研究
发布时间：2019-03-27 07:57
【摘要】：在实现智能电网为核心的低碳能源背景下,微电网被认为是降低能耗、提高电力系统可靠性和灵活性的智能电网的重要的组成部分。微电网实现其技术性、经济性优势的关键就是并网与孤岛两种模式的运行能力。两种运行模式间的平滑切换是保证微电网持续稳定运行的关键技术。 本文针对微电网结构及并网与孤岛运行方式的特点,提出了一种实现微电网两种运行方式平滑切换的控制策略。在并网运行时,微电网内的功率波动由大电网进行平衡,此时微电源采用PQ控制来保证输出功率的恒定,实现能量管理,而储能装置则处于充电备用状态；当大电网发生故障或者主动与微电网解列时,孤岛检测装置检测到之后,微电网切换到孤岛模式运行,储能装置中的蓄电池采用改进的V／f下垂控制策略,主要用来弥补功率缺额,实现能量供需平衡,同时也为系统提供电压和频率支撑,超级电容则采用恒压恒频的V／f控制,主要是在微电网两种模式切换时快速为系统提供电压和频率支撑。其它的微电源保持PQ控制状态,用以缩短系统电压和频率的过渡时间。对于再并网的情况,因蓄电池有下垂控制环节,微电网的电压会与大电网电压产生偏离,直接重合闸并网可能引起巨大的冲击电流,因此设计增加了预同步处理单元,该单元分别采用了两种方法进行控制,包括直接法和间接法,间接法更能有效的较少冲击电流,它基于三相软件锁相环(SPLL)来控制逆变器输出电压跟踪大电网电压,包括电压幅值跟踪和相位(频率)同步,以降低重合闸过程的冲击,最终实现微电网系统由孤岛模式到并网模式的平滑切换。在整个过程中,充分考虑了储能容量的优化配置和可靠保护,以较小的容量满足控制目标,提高微电源的发电效率,降低燃料及污染排放水平。利用MATLAB/Simulink仿真软件进行建模和仿真实验分析,其结果验证了所提出平滑切换控制策略的有效性。通过对储能和微电源的控制,确保微电网在孤岛运行、并网运行、离网／并网模式切换等过程中能够保持良好的电压和频率稳定性以及微电源输出功率的稳定性,有效减小可再生能源发电输出功率间歇性和随机性等不足,从而保证了微电网内敏感负荷的供电可靠性,对未来智能电网的发展有巨大的推动作用。
[Abstract]:Under the background of low carbon energy with smart grid as the core, microgrid is considered to be an important part of smart grid, which can reduce energy consumption and improve the reliability and flexibility of power system. The key to realize the technicality and economic advantage of microgrid is the operation capability of grid-connected and island-connected modes. The smooth switching between the two operation modes is the key technology to ensure the continuous and stable operation of the microgrid. In this paper, according to the structure of microgrid and the characteristics of grid-connected and island-connected operation mode, a control strategy for smooth switching between two operation modes of microgrid is proposed in this paper. When connected to the grid, the power fluctuation in the micro-grid is balanced by the large power grid. At this time, the micro-power supply adopts PQ control to ensure the constant output power and realize the energy management, while the energy storage device is in the state of charging and standby. When a fault occurs in a large power grid or an active detach from the microgrid occurs, after the isolated island detection device is detected, the microgrid is switched to islanding mode, and the storage battery in the energy storage device adopts an improved control strategy of Vxf droop. It is mainly used to make up the shortage of power, realize the balance of energy supply and demand, at the same time provide voltage and frequency support for the system, and the supercapacitor is controlled by constant voltage and constant frequency. It mainly provides voltage and frequency support for the system when switching between two modes of microgrid. Other micro power supplies maintain PQ control to shorten the transition time of system voltage and frequency. In the case of regrid connection, due to the drooping control of the battery, the voltage of the microgrid will deviate from the voltage of the large grid, and the direct reclosing of the grid may result in a huge impulse current, so the pre-synchronous processing unit is added to the design. The unit adopts two kinds of control methods, including direct method and indirect method. The indirect method can effectively reduce the impact current. It is based on the three-phase software phase-locked loop (SPLL) to control the output voltage of the inverter to track the large power grid voltage. It includes voltage amplitude tracking and phase (frequency) synchronization in order to reduce the impact of reclosing process and finally realize smooth switching from island mode to grid-connected mode in microgrid system. In the whole process, the optimal configuration of energy storage capacity and reliable protection are fully considered to meet the control target with smaller capacity, improve the power generation efficiency of micro-power supply, and reduce the fuel and pollution emission level. Modeling and simulation experiments are carried out with MATLAB/Simulink simulation software, and the results show that the proposed smooth switching control strategy is effective. Through the control of energy storage and micro-power supply, the microgrid can maintain good voltage and frequency stability and output power stability in the process of island operation, grid-connected operation, off-grid / grid-connected mode switching, and so on. By effectively reducing the intermittent and random output power of renewable energy generation, the reliability of sensitive load supply in microgrid is guaranteed, and the development of smart grid in the future will be greatly promoted.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM732
本文编号：2448014
[Abstract]:Under the background of low carbon energy with smart grid as the core, microgrid is considered to be an important part of smart grid, which can reduce energy consumption and improve the reliability and flexibility of power system. The key to realize the technicality and economic advantage of microgrid is the operation capability of grid-connected and island-connected modes. The smooth switching between the two operation modes is the key technology to ensure the continuous and stable operation of the microgrid. In this paper, according to the structure of microgrid and the characteristics of grid-connected and island-connected operation mode, a control strategy for smooth switching between two operation modes of microgrid is proposed in this paper. When connected to the grid, the power fluctuation in the micro-grid is balanced by the large power grid. At this time, the micro-power supply adopts PQ control to ensure the constant output power and realize the energy management, while the energy storage device is in the state of charging and standby. When a fault occurs in a large power grid or an active detach from the microgrid occurs, after the isolated island detection device is detected, the microgrid is switched to islanding mode, and the storage battery in the energy storage device adopts an improved control strategy of Vxf droop. It is mainly used to make up the shortage of power, realize the balance of energy supply and demand, at the same time provide voltage and frequency support for the system, and the supercapacitor is controlled by constant voltage and constant frequency. It mainly provides voltage and frequency support for the system when switching between two modes of microgrid. Other micro power supplies maintain PQ control to shorten the transition time of system voltage and frequency. In the case of regrid connection, due to the drooping control of the battery, the voltage of the microgrid will deviate from the voltage of the large grid, and the direct reclosing of the grid may result in a huge impulse current, so the pre-synchronous processing unit is added to the design. The unit adopts two kinds of control methods, including direct method and indirect method. The indirect method can effectively reduce the impact current. It is based on the three-phase software phase-locked loop (SPLL) to control the output voltage of the inverter to track the large power grid voltage. It includes voltage amplitude tracking and phase (frequency) synchronization in order to reduce the impact of reclosing process and finally realize smooth switching from island mode to grid-connected mode in microgrid system. In the whole process, the optimal configuration of energy storage capacity and reliable protection are fully considered to meet the control target with smaller capacity, improve the power generation efficiency of micro-power supply, and reduce the fuel and pollution emission level. Modeling and simulation experiments are carried out with MATLAB/Simulink simulation software, and the results show that the proposed smooth switching control strategy is effective. Through the control of energy storage and micro-power supply, the microgrid can maintain good voltage and frequency stability and output power stability in the process of island operation, grid-connected operation, off-grid / grid-connected mode switching, and so on. By effectively reducing the intermittent and random output power of renewable energy generation, the reliability of sensitive load supply in microgrid is guaranteed, and the development of smart grid in the future will be greatly promoted.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM732
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