含多类分布式电源微网小信号稳定性分析

发布时间：2019-04-25 07:48

【摘要】：微网是集成多类分布式电源(光伏发电、太阳能热发电、风力发电、微型燃气轮机等)、负荷(常用负荷、可切除负荷和敏感负荷)、储能系统、控制装置、保护装置及能量管理系统构成系统。微网相对传统电网容量较小,但其输出功率与负荷的变化功率较大,独立运行时易受扰动影响。分布式发电的间接性、波动性导致功率输出波动,影响了微网的稳定性;大量的电力电子设备接入微网,导致微网具有低惯性、弱阻尼。在多类分布式电源接入微网的条件下,选用可靠的控制方法有利于微网的安全运行,研究其稳定性可了解不同接口类型的分布式电源对微网稳定性的影响。本文围绕这一主题,本文首先从建模角度研究了逆变型接口分布式电源稳定性;然后从分布式电源的角度,研究了含逆变器接口与同步电机接口分布式电源的微网小信号稳定。本文第一部分工作是对比了下垂控制的逆变型分布式电源的不同建模方法,并研究了其稳定性。首先分别建立采用下垂控制的受控电压源简化模型的小信号模型和三环下垂控制的逆变器接口分布式电源的全阶小信号模型。基于这两类小信号模型,分别对下垂增益变化、线路阻抗变化、负荷阻抗变化进行稳定性分析,并画出特征值变化的根轨迹。最后根据PSCAD/EMTDC进行时域仿真及相似特征值根轨迹进行比较的结果显示,当研究三环下垂控制的逆变器接口分布式电源稳定性,不考虑电压电流内环动态过程时,两个分布式电源的特征值的根轨迹具有相同趋势,因此研究三环下垂控制的逆变器接口分布式电源的稳定性可用基于下垂控制的受控电压源简化模型的小信号模型代替,简化了部分稳定性研究中阶数庞大的问题。第二部分是研究并分析了基于下垂控制的含同步发电机与电压源型逆变器接口分布式电源的独立运行的微网稳定性。模型在建立时,既考虑了同步电机定子磁链变化和逆变器电压电流环变化等快动态过程,也考虑了同步电机转子变化等相对较慢的动态过程。建模时,首先在各自的dq坐标系下建立两个分布式电源及控制系统的小信号模型,其次取同步电机的dq坐标系作为参考坐标系,并将逆变器极其控制器数学模型、负荷模型、网架结构模型通过坐标变化转换到同步电机坐标系下,最终建立了含着两类分布式电源的全阶模型。计算结果表明,合理选择低通滤波器惯性时间常数,增大同步电机惯性时间常数,适当增大线路阻抗中的电感有利于增强系统稳定;增加系统的下垂增益会降低系统的稳定性;加入同步电机接口的分布式电源后,系统的稳定性增强。
[Abstract]:Microgrids are integrated with multiple types of distributed power sources (photovoltaic, solar thermal, wind, micro gas turbine, etc.), loads (common loads, removable loads and sensitive loads), energy storage systems, control devices, etc. The protection device and the energy management system constitute the system. The capacity of micro-grid is smaller than that of traditional power grid, but its output power and load power change greatly, so it is easy to be affected by disturbance when it operates independently. Because of the indirectness of distributed generation, the fluctuation of power output results in the fluctuation of power output, which affects the stability of micro-grid, and a large number of power electronic devices are connected to micro-grid, which results in low inertia and weak damping of micro-grid. Under the condition that many kinds of distributed power are connected to the micro-grid, the reliable control method is beneficial to the safe operation of the micro-grid. The research on the stability of the micro-grid can understand the influence of the distributed power supply of different interface types on the stability of the micro-grid. In this paper, firstly, the stability of distributed power supply with inverter interface is studied from the point of view of modeling, and then the stability of micro-grid with distributed power supply with inverter interface and synchronous motor interface is studied from the point of view of distributed power supply. In the first part of this paper, the different modeling methods of sag controlled inverter distributed power supply are compared, and its stability is studied. Firstly, the small-signal model of controlled voltage source simplified by drooping control and the full-order small-signal model of three-loop drooping inverter interface distributed power supply are established respectively. Based on these two kinds of small-signal models, the stability analysis of droop gain, line impedance and load impedance is carried out, and the root trajectory of eigenvalue variation is plotted. Finally, the time domain simulation based on PSCAD/EMTDC and the comparison of similar eigenvalue root trajectories show that when the distributed power supply stability of the inverter interface controlled by three-loop droop is studied, the dynamic process of voltage-current inner loop is not considered. The root trajectory of the eigenvalues of the two distributed power sources has the same trend. Therefore, the stability of the inverter interface distributed power supply with three-loop drooping control can be replaced by the small signal model of the simplified controlled voltage source model based on the droop control. The problem of large order in the study of partial stability is simplified. In the second part, the micro-grid stability of distributed power supply with interface between synchronous generator and voltage source inverter based on drooping control is studied and analyzed. When the model is built, the fast dynamic processes, such as the change of stator flux of synchronous motor and the change of voltage and current loop of inverter, are considered, as well as the relatively slow dynamic process such as the change of rotor of synchronous motor. In modeling, two small signal models of distributed power supply and control system are established in the respective dq coordinate system, then the dq coordinate system of synchronous motor is taken as the reference coordinate system, and the mathematical model and load model of inverter and controller are taken as the reference coordinate system. The grid structure model is transformed into synchronous motor coordinate system by coordinate change. Finally, the full-order model with two kinds of distributed power supply is established. The results show that selecting the inertia time constant of low pass filter reasonably, increasing the inertia time constant of synchronous motor and properly increasing the inductance in line impedance are beneficial to enhance the stability of the system, and increase the droop gain of the system will reduce the stability of the system. The stability of the system is enhanced by adding distributed power supply with synchronous motor interface.
【学位授予单位】：天津工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM727

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