基于三电平DC-DC变换器的风储双极性直流微电网运行控制策略研究

发布时间：2018-01-06 16:36

本文关键词：基于三电平DC-DC变换器的风储双极性直流微电网运行控制策略研究　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：直流微电网作为新的能源结网形式,集成风力、光伏等新能源发电单元、储能单元及本地负荷,实现可再生能源的高效利用,成为当前国内外研究热点。目前直流微电网主要采用单极性结构,系统的运行效率较低。本文研究了基于三电平DC-DC变换器接入的双极性直流微电网结构,该结构减小了母线对地电压,提高了系统运行效率,且可满足不同变换器和负荷对各电压等级的要求,并基于此结构提出了相应的运行控制策略,主要研究内容包括:第一,详细研究了双极性直流微电网中三电平变换器的拓扑结构和工作原理,根据能量双向流动特性将其分为三电平Boost变换器和三电平Buck变换器,并分析其工作状态与输入输出关系。研究了风电单元中的三电平Boost变换器,同时建立该变换器的状态空间数学模型。第二,重点研究了基于三电平Boost变换器的风电单元控制策略。建立了风电单元中各部分的模型,分析了风电机组在不同风速下的运行特性。在此基础上,提出风能利用系数恒定区域的最大功率跟踪控制(maximum power point tracking,MPPT)与高风速区域的恒转速、恒功率控制策略。根据三电平Boost变换器输出特性,设计了中点电位平衡控制以保证分裂电容电压平衡。最后通过Matlab/Simulink仿真验证了风电单元策略的有效性。该控制策略保证了风机在各个风速区域内稳定运行,实现了区域间平滑切换,提高了风能的利用效率。第三,着重研究了基于三电平双向DC-DC变换器的储能单元控制策略。分析了超级电容器的工作原理和等效电路模型,建立了电压下垂特性关系。根据直流母线电压波动范围,将超级电容器的运行分成不动作、下垂控制、恒流充放电三个阶段,并提出一种充放电模式分离的控制策略。最后通过Matlab/Simulink仿真验证了储能单元控制策略的合理性。该控制策略在充电模式或放电模式时只需两个开关管导通,降低了控制的复杂性。第四,提出了风储双极性直流微电网母线电压分区间运行控制策略。分析了风储双极性直流微电网结构和功率平衡关系,并根据微电网不同状态将母线电压分成四个运行区间。通过风电单元的风电特性控制与基于下垂特性的限功率控制、储能单元的充放电分离控制配合负荷单元的减载控制,实现了各状态的稳定运行与各区间的平滑切换。第五,搭建了含风电单元、超级电容储能装置和直流负荷的双极性直流微电网实验平台,通过实验验证了控制策略在不同母线电压下运行与不同状态间切换的表现。结果表明,母线电压分区间运行控制策略可以调节母线电压和平衡系统功率,从而确保了风储双极性直流微电网稳定运行。
[Abstract]:DC microgrid as a new form of energy grid integration of wind photovoltaic and other new energy generation units energy storage units and local load to achieve the efficient use of renewable energy. At present, DC microgrid mainly adopts unipolar structure. The structure of bipolar DC microgrid based on three-level DC-DC converter is studied in this paper, which reduces the bus voltage to the ground and improves the efficiency of the system. And it can meet the requirements of different converter and load on each voltage level. Based on this structure, the corresponding operation control strategy is proposed. The main research contents are as follows: first. The topology and working principle of three-level converter in bipolar DC microgrid are studied in detail. According to the characteristics of bi-directional energy flow, it is divided into three-level Boost converter and three-level Buck converter. The three-level Boost converter in wind power unit is studied, and the state space mathematical model of the converter is established. Second, the relationship between the operation state and the input and output of the converter is analyzed. Second, the three-level Boost converter in the wind power unit is studied. The control strategy of wind power unit based on three-level Boost converter is studied emphatically. The model of each part of wind power unit is established, and the operating characteristics of wind turbine unit under different wind speed are analyzed. The maximum power point tracking control (MPPT) in the region of constant wind power utilization coefficient and constant speed in high wind speed region are proposed. Constant power control strategy. According to the output characteristics of three-level Boost converter. The midpoint potential balance control is designed to ensure the voltage balance of split capacitor. Finally, the effectiveness of wind power unit strategy is verified by Matlab/Simulink simulation. Stable operation in the wind speed zone. The smooth switching between regions is realized and the utilization efficiency of wind energy is improved. Third. The control strategy of energy storage unit based on three-level bi-directional DC-DC converter is studied, and the working principle and equivalent circuit model of supercapacitor are analyzed. According to the voltage fluctuation range of DC bus, the operation of supercapacitor is divided into three stages: no action, droop control, constant current charge and discharge. A control strategy of charging and discharging mode separation is proposed. Finally, the rationality of the control strategy of energy storage unit is verified by Matlab/Simulink simulation. The control strategy is in charge mode or discharge mode. It only takes two switches to switch on. The complexity of the control is reduced. In 4th, the operation control strategy of wind storage bipolar DC microgrid bus is proposed, and the structure of wind storage bipolar DC microgrid and the power balance relationship are analyzed. According to the different states of microgrid, the bus voltage is divided into four operation areas. The wind power characteristic control of wind power unit and the power limit control based on droop characteristic are carried out. The charge / discharge separation control of the energy storage unit and the load reduction control of the load unit realize the stable operation of each state and the smooth switching of each interval. 5th, the wind power unit is built. The performance of the control strategy under different bus voltages and switching between different states is verified by experiments on supercapacitor energy storage device and bipolar DC microgrid with DC load. The busbar voltage division operation control strategy can adjust the bus voltage and balance the system power, thus ensuring the stable operation of the wind storage bipolar DC microgrid.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM46;TM727

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