【作者】 肖朝霞；

【导师】 王成山；

【作者基本信息】 天津大学 ， 电力系统及其自动化， 2009， 博士

【摘要】 微网是一种可将各种小型分布式电源组合起来为当地负荷提供电能的低压电网。它具有联网和孤岛两种运行模式,能提高负荷侧的供电可靠性。微网中的分布式电源常采用电力电子接口连接到微网,这增加了分布式电源接口控制的灵活性,减少了系统的惯性。微网缺少惯性和运行模式的多样性增加了系统在维持能量平衡及频率稳定等方面的控制难度。如何连接多种不同类型的分布式电源形成微网是微网必须解决的问题。本文研究了分布式电源通过逆变器接口形成微网的微网控制策略,并在该控制策略下分析了微网的运行特性。主要工作如下:首先,总结和比较了现存的两种微网控制策略及每种控制策略中的主要控制方法的优劣性。其次,分析了微网中多个分布式电源采用P-f和Q-V下垂控制时,微网的频率稳定性。在考虑微网中分布式电源的分散性以及不同分布式电源容量不同等特点下,论述了当微网中多个不同容量的分布式电源采用下垂控制时,下垂增益的确定方法。分析了微网联网运行时的频率稳定性,并且比较了它与大型同步发电机在功角稳定性方面的异同。采用小信号状态空间模型研究了多个分布式电源同时参与系统频率调节时孤岛运行微网的频率稳定性。计算了负荷阻抗变化、等效线路阻抗变化和下垂控制器下垂增益变化时的系统特征值,分析了它们对微网频率稳定的影响,并给出了相应的时域仿真结果。然后,根据微网内分布式电源的输出特性和负荷需求特性,设计了一种分布式电源层对等控制与主从控制相结合的微网控制策略。在该控制策略中,对于适合采用P-f和Q-V下垂控制的分布式电源,设计了基于该控制方法的多环反馈控制器。在该多环反馈控制器中,外环为P-f和Q-V下垂控制器,内环为电压电流双环控制器。通过采用内环控制器,减少了负荷和其它分布式电源扰动对其接口逆变器输出电压的影响,保证分布式电源接口逆变器输出的端口电压等于其外环控制器输出的参考电压。同时通过对内环控制器参数的设计,使逆变器闭环输出阻抗呈感性,减少了传输的有功和无功功率受线路阻抗影响的耦合程度。对适合采用恒功率控制(PQ)的分布式电源,设计了适用于电流源逆变器和电压源逆变器接口的PQ控制器,该控制器确保了分布式电源的输出功率等于其参考功率。最后,进行了不同运行状况下微网的暂态特性分析。分析了感应电动机负荷对微网暂态稳定的影响和微网有目的的孤岛运行、断开分布式电源、分布式电源输出功率变化、负荷功率变化及微网联入主电网时微网的暂态响应。同时,分析了不同故障类型和不同故障点对微网暂态稳定的影响。更多还原

【Abstract】 A MicroGrid is a low voltage network with different micro generators (micro sources) and loads operating to supply electric power for the local area. It can operate in grid-connected or islanded, which has the ability to enhance the reliability of electrical energy supply. Most of micro sources in a MicroGrid are interfaced through power electronic converters. The interfaces of converters increase the flexibility of control but reduce the inertia of the MicroGrid. Lack of inertia and two operation modes pose difficulties in maintaining a power balance between generation and consumption and controlling the network frequency of an islanded MicroGrid. The connection of different types of micro sources to form a MicroGrid is an important task. This thesis concentrates on a control strategy and operation characteristics of an inverter-interfaced MicroGrid. The main jobs of the thesis are as the following.Firstly, the various control techniques and different control approaches in a MicroGrid used to date are summarised and comparied.Secondly, the frequency stability of a MicroGrid, in which the frequency is regulated by different micro sources using P-f & Q-V droop control,was analyzed. Considering the decentralization and the capacity difference of micro sources in a MicroGrid, how to choose the right droop gains is investigated when different micro sources use P-f&Q-V droop controllers. Then the frequency stability of a grid-connected and an islanded MicroGrid is investigated based on the right droop gains. The differences between the frequency stability of a grid-connected MicroGrid and the power angle stability of the conventional generator are analyzed. Moreover, a small-signal state-space model is used to explore the frequency stability of an islanded MicroGrid in which the frequency is regulated by different micro sources using P-f&Q-V droop controllers. The eigenvalues are calculated when the load resistance and impedance, the equivalent line impedance and the droop gains change. And the factors that induce the frequency unstable are analysed.Thirdly, the control scheme of inverter-interfaced MicroGrid based on the peer-to-peer and master-slave is designed considering the generation characteristics of micro sources and the characteristics of the load power demand. A multi-loop feedback controller is obtained to control the micro sources that are controlled by the P-f&Q-V droop. The outer loop of the multi-loop feedback controller is P-f&Q-V droop controller. The inner voltage controller and current controller insure the output voltage of the inverter of the micro source equal to the output voltage of the outer P-f&Q-V droop controller by reducing the effect of the disturbances of loads or other micro sources. The closed-loop output impedance of the interfaced inverter can be inductive by designing the parameters of the inner controller that can decouple the transferred active power and reactive power. Difference PQ controllers for the interface of current source inverter and the voltage source inverter, are designed to control the output power of the micro sources equal to the reference power.Finally, the transient characteristics of the MicroGrid are investigated in different operation conditions based on the control scheme. The impact of induction machine loads on the transient stability of the MicroGrid, and the transient response of the intentional islanding, the disconnection of a micro source, the output power change of the micro source using PQ control, the change of load power and the connection with the main grid, are shown in this thesis. The impact of different types of faults and the different locations of faults on the transient stability of the MicroGrid are also investigated.更多还原