直流微网中变流器的控制技术研究

发布时间：2018-07-17 22:21

【摘要】：近年来,我国不断面临一次能源短缺的威胁,面对日益严峻的环境问题,开发新能源并解决新能源发电接入电网的一系列问题显得十分重要。为了避免分布式能源并网对大电网造成的冲击,而提出的既可为区域内负荷提供冷热电联供,也能与电网并联运行的小型电网被称为微网。其中由微电源、电力电子接口、储能及负荷组成的以直流方式传输的微电网就是直流微电网。该文针对直流微电网中主要电力电子变流器的控制方法展开了讨论与研究。首先,为了应对离网运行时的不平衡交流负载,该文在三相DC/AC逆变器原有的拓扑结构上增加了一条零序电流分量的通路,形成一种新型中线拓扑结构,这种添加了中线的三相逆变器能够在负载不平衡的情况下保证逆变器输出电压不发生畸变。其次,当直流微电网作为直流微源并入大电网的时候需要其能够友好平滑地接入大电网,采用虚拟同步发电机控制方法的并网接口逆变器可以自动的参与配网调节,在实现分布式电源并网的同时改善接入点电能质量,并且能消除本地负荷大量切投引起的电压波动,保证输出电压质量。与大电网并联运行时,能够抑制大电网电压畸变时产生的影响维持逆变器直流侧电压基本稳定。最后,针对直流微电网中最常见直流负荷——电动汽车的充电问题提出了一种基于虚拟直流发电机的柔性直流变换器控制方法,通过这种方法控制的双向直流变换器在恒压充电模式时,能稳定负荷侧电压不受母线电压发生扰动时的影响实现恒压充电,同样在恒流充电模式中也能过滤母线波动影响使输出电流恒定,且由于考虑了直流发电机的惯性环节,因此负荷侧电压、电流的变化是一个缓和震荡过程,有效提升了电动汽车充电的稳定性。该文在PSCAD/EMTDC中搭建了一个简单的直流微电网模型,该模型中包含了带不平衡负载的三相四桥臂逆变器、基于虚拟同步发电机的并网接口逆变器、以及基于虚拟直流发电机的双向直流变换器。通过仿真和实验,验证了虚拟同步发电机及虚拟直流发电机控制策略的可行性以及中线拓扑结构针对不平衡负载的有效性,为直流微电网的进一步研究奠定基础。
[Abstract]:In recent years, China is facing the threat of primary energy shortage. In the face of increasingly severe environmental problems, it is very important to develop new energy and solve a series of problems of new energy generation connected to power grid. In order to avoid the impact of distributed energy grid connection on large power grid, the proposed small power grid, which can not only provide the combined cooling and heat supply for the local load, but also run in parallel with the power grid, is called microgrid. The DC microgrid, which consists of micro-power supply, power electronic interface, energy storage and load, is DC microgrid. In this paper, the control methods of main power electronic converters in DC microgrid are discussed and studied. First of all, in order to deal with the unbalanced AC load in off-grid operation, this paper adds a zero-sequence current component path to the original topology of three-phase DC / AC inverter, and forms a new midline topology. The three-phase inverter with neutral line can ensure that the output voltage of the inverter is not distorted when the load is unbalanced. Secondly, when the DC microgrid is incorporated into the large power grid as a DC microsource, it is necessary that the DC microgrid can be connected to the large power grid in a friendly and smooth manner, and the grid-connected interface inverter using the virtual synchronous generator control method can automatically participate in the distribution network regulation. The power quality of the access point can be improved while the distributed power supply is connected to the grid, and the voltage fluctuation caused by the local load cutting can be eliminated, and the output voltage quality can be guaranteed. When running in parallel with large power grid, the DC side voltage of inverter is basically stable when the influence of voltage distortion in large power grid can be restrained. Finally, a flexible DC converter control method based on virtual DC generator is proposed for charging the most common DC load-electric vehicle in DC microgrid. The bidirectional DC / DC converter controlled by this method can stabilize the load side voltage in constant voltage charging mode and realize constant voltage charging without the influence of bus voltage disturbance. In the same constant current charging mode, the output current is constant by filtering the effect of bus fluctuation, and because the inertia link of DC generator is considered, the variation of load side voltage and current is a mild oscillation process. Effectively improves the electric vehicle charging stability. In this paper, a simple DC microgrid model is built in PSCAD / EMTDC. The model includes three-phase four-leg inverter with unbalanced load and grid-connected interface inverter based on virtual synchronous generator. And the bidirectional DC converter based on virtual DC generator. Through simulation and experiment, the feasibility of control strategy of virtual synchronous generator and virtual DC generator and the validity of midline topology for unbalanced load are verified, which lays a foundation for further research on DC microgrid.
【学位授予单位】：长沙理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM46

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