基于虚拟复阻抗的低压微电网并联逆变器改进下垂控制策略研究

发布时间：2018-06-05 23:27

本文选题：低压微电网 + 并联控制　；参考：《江苏大学》2017年硕士论文

【摘要】：随着分布式发电系统的日益扩大,当今社会对微电网运行的稳定性及电能质量的要求越来越高,而微电网中各分布式电源并联运行的可靠性是决定微电网能否稳定运行的关键因素。逆变器作为分布式发电系统之间以及微电源与本地负载、大电网之间连接的桥梁,其并联运行的安全稳定至关重要。由于分布式电源大多靠近用户侧,电压等级较低,因此低压微电网中逆变器的并联运行成为当今研究领域的热点。本文主要对低压微电网中单相逆变器并联控制策略进行研究。在逆变器的并联控制中,无互联通信线的控制方法具有较高的冗余度及灵活性,该控制方法中最常用的是下垂控制。由于传统的fP-、VQ-下垂控制方法仅适用于中高压电网下系统阻抗为感性的场合,而低压微电网的线路阻抗为阻性,为解决低压微电网中系统阻抗为阻感性导致的有功功率和无功功率出现耦合的问题,本文引入虚拟复阻抗将系统等效输出阻抗设计为阻性,在此过程中通过矢量图分析法对引入的虚拟阻抗及逆变器的等效输出阻抗进行分析,从而提高所引入虚拟阻抗的精确性,使系统的有功功率和无功功率实现较好的解耦。在阻性系统阻抗下,系统的有功功率与电压近似成比例,无功功率与频率近似成比例,因此,相应的下垂控制方法由原来的fP-、VQ-下垂控制更改为VP-、fQ-下垂控制法。由于各微电源分布位置的不同,各分布式发电系统到负载端的距离也有所差异,这就导致彼此间的线路阻抗不同,而线路阻抗的不同就会使各分布式电源的输出功率无法均分,容易导致系统中有些电源出现过载的情况,从而影响微电网的稳定运行。因此本文提出一种应用于低压微电网的改进下垂控制方法,通过在VP-下垂控制中引入PI调节器,将原来的固定下垂系数改为变下垂系数,从而实现不同线路阻抗系统自适应调节下垂系数以使得有功功率得到较好的均分。最后本文通过Matlab/Simulink仿真软件对系统进行仿真。仿真结果表明,在负载突变以及系统线路阻抗出现不同程度差异的情况下,改进控制方法仍然可以更精确地实现逆变器系统输出功率的均分。
[Abstract]:With the increasing expansion of distributed generation system, the demand for the stability and power quality of microgrid is becoming higher and higher. The reliability of parallel operation of distributed power sources in microgrid is the key factor to determine whether the microgrid can operate stably. As a bridge between distributed generation systems, between micro-power and local load and large power grid, the security and stability of parallel operation of inverter is very important. Because most of the distributed power generation is close to the user side and the voltage level is low, the parallel operation of the inverter in the low-voltage microgrid has become a hot research field. In this paper, the parallel control strategy of single-phase inverter in low-voltage microgrid is studied. In the parallel control of inverter, the control method without interconnection communication line has high redundancy and flexibility. The most commonly used control method is droop control. Because the traditional fP-VQ- droop control method is only suitable for the case where the system impedance is inductive under the medium and high voltage power network, the line impedance of the low voltage microgrid is resistive. In order to solve the coupling problem of active power and reactive power caused by the impedance of low voltage microgrid, the virtual complex impedance is introduced to design the equivalent output impedance of the system as resistance. In the process, the introduced virtual impedance and the equivalent output impedance of the inverter are analyzed by vector graph analysis, so as to improve the accuracy of the introduced virtual impedance and to decouple the active and reactive power of the system. Under impedance of resistive system, the active power and voltage of the system are approximately proportional, and the reactive power is approximately proportional to the frequency. Therefore, the corresponding droop control method is changed from the original fP-VQ- droop control to the VP-fQ- droop control method. Because of the different distribution of the micro-power source, the distance from the distributed generation system to the load end is also different, which leads to the difference of the line impedance between each other, and the difference of the line impedance will make the output power of the distributed power source unevenly distributed. It is easy to cause overload of some power sources in the system, thus affecting the stable operation of microgrid. In this paper, an improved droop control method for low voltage microgrid is proposed. By introducing Pi regulator into VP- droop control, the original fixed sag coefficient is changed to variable sag coefficient. Thus, the sagging coefficient of different line impedance systems can be adjusted adaptively so that the active power can be well equalized. Finally, the system is simulated by Matlab/Simulink software. The simulation results show that the improved control method can achieve more accurate distribution of the output power of the inverter system under the condition of the sudden change of the load and the difference of the system line impedance.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464

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