【作者】 刘杨华；

【导师】 吴政球；

【作者基本信息】 湖南大学 ， 电气工程， 2010， 博士

【摘要】 全球正面临着能源危机和环境污染、气候变化的压力。应用新能源发电随之成为电力工业发展的时代课题。本文选择燃料电池中最具有商业前景的固体氧化物燃料电池SOFC(Solid Oxide Fuel Cell)作为研究对象,对其发电系统建模、并网控制仿真以及微电网孤岛运行的潮流计算分析进行研究,旨在为SOFC等分布式发电在电力系统中广泛应用提供理论参考。根据SOFC发展趋势,选择平板式阳极支撑的中高温SOFC(以下简称电池)为研究对象。首先介绍其材料及结构,分析电池单体及堆栈的发电原理,用基于电极的微观动态电化学电势(Electrochemical Electric potential model,ECE)模型得到发电输出及控制特性。单体工作电压在06V-09V范围即稳态输出时,电池单体及其堆栈输出特性呈线性。基于线性化理论和电路等效原理,对输出外特性曲线进行简化,提出了对应操作条件下的电压源串联电阻(Voltage Source Series Resistance,VSSR)模型和基于实验响应时间常数的可调控多级电压源串联电阻(Multi-Voltage Sources Series Resistances - MVSSRs)模型。提出的等效模型简单有效、易于接口,为含电池发电的系统稳态运行分析提供电路理论基础。根据电池发电系统的特点,采用PI调节、电流滞环跟踪和PWM控制等手段,通过对并网接口——三相逆变器的控制,实现对电池发电系统接入大电网的并网控制。基于Matlab软件平台,以5kW的电池系统与大电网并网为例,进行动态控制仿真。结果表明,经电池系统的反馈调节及并网逆变器门极电路的控制,可实现该分布式电源逆变器输出侧的电压/电流/功率等调节,以平衡系统负荷波动的功率需求;尽管电池系统仅能发出有功,经逆变器控制还可实现其无功输出控制;从仿真结果并结合电池发电材料要求及控制响应时间等特性可知,电池并网发电时,适于为系统基础负荷供电,不适于系统频率或电压稳定调节。传统潮流计算需要设定系统平衡节点。然而目前分布式电源(以下简称电源)的输出功率极其有限,且微型电网中电源一般无独立二次调频设备,故在孤岛运行的微电网中无一电源能承担传统电力系统调频电厂的角色。基于上述控制仿真研究,提出一种新的改进潮流计算方法,去掉平衡节点的设定,将电源视为松弛PQ节点。以三相对称的孤岛系统为例,推导出改进潮流算法的功率平衡方程和牛顿-拉弗逊法求解过程中雅可比矩阵各元素的表达式。用环网结构的5节点系统和树形结构的配电网33节点系统验证算法的合理有效性及不同拓扑结构的适应性。线路不完全换位或者不平衡负荷等因素,往往造成实际潮流的三相不平衡。采用相分量法对孤岛运行的三相不平衡潮流算法进行研究,考虑了变压器移相角对潮流的影响以及线路参数的相间耦合,推导出三相不平衡潮流的功率平衡方程以及雅可比矩阵各元素的表达式,并用5节点系统进行验证。三相平衡/不平衡潮流计算分析采用多种方案,详细比较不同分布式电源及其有功/无功调节能力、电源不同出力及位置、不同负载条件,以及采用不同的负荷模型及其电压/频率静态调节特性等各种情况。与传统潮流算法的计算结果比较表明,改进潮流算法物理意义明确,计算简单,计算潮流的同时反映系统频率的变化,比传统的潮流算法更适于孤岛运行微电网的三相平衡/不平衡潮流计算。同时可知电池应用于孤岛运行的微电网发电时,特别是在三相不平衡系统中,需要与其他供电形式配合,更有利于系统的稳定运行。更多还原

【Abstract】 Electrical power demanding is increasing with the development of the whole society. More and more energy consumption causes depletion of fossil fuels comparing with their growing speed. At the same time, the whole world is facing the pressure of circumstance pollution and global warming caused by industry. To solve these issues, new energy and electricity generation are taken out to be researched and applied. In this paper, solid oxide fuel cell (SOFC) is chose to be studied for it has the best future among all fuel cells. The research includes electrical modeling SOFC, control and simulation of connecting with the main grid, and the power flow calculation of islanding systems. It aims to give a reference for analysis and control of the system with SOFC and other distributed generation resources (DGRS) widely used.Planner anode-supported high/intermediate-temperature solid oxide fuel cell (P-A-H/M-T SOFC) is studied in this paper for it is mostly popular in the power system. Firstly, the material and structure of P-A-H/M-T SOFC and its stack are introduced. Based on the principle of its power generation, the output characteristics of the cell and it control is studied with electrochemical electric potential model (ECE). With the help of linearization and equivalence principle, voltage source series resistance (VSSR) model and multi-voltage sources series resistances (MVSSRs) model are proposed for the simplification of the model application in static analysis. The linear equivalent electric circuit models proposed are simply and effective for applications of P-A-H/M-T SOFC in system control and analysis.Based on the analysis of the power generation characteristics, PI control, Pulse Width Modulation (PWM) control with current relay track as a feeder back, and other control ways are used to control the three-phased inverter of the cell stack to the main grid. With an example of a 50kW SOFC power generation system link to a main grid, the dynamic power control of the fuel cell stack is simulated with Matlab software. The simulation shows that it is possible to control the power (includes both active power and reactive power) of the distributed generation (DG) system by controlling its inverter to the main grid. And it shows that P-A-H/M-T SOFC is suitable for power supplying to basic load.Current DGRs are so limited that in an independent micro-grid, known as‘islanding’system, no current DGR is big enough to balance the power demand and to stabilize the frequency of the micro-grid. It means that there is no swing bus of an islanding micro-grid can be managed as that set in the traditional calculation. Setting DGRs as slack PQ nodes, a new power flow calculation method based on the above research, is proposed to accommodate the lack of a swing bus in an islanding system. With this method, balanced power calculations are discussed with IEEE-5 bus system (ringing topological structure) and distributed 33-bus system (radial structure). It is solved with Newton-Raphson method). The method proposed is valid by comparing its results with those got with the traditional method. It shows that the new method is adapted to networks with different topological structures.Three-phase power flow of power system is normally unbalanced causing by the shifting of lines, single-phase loads and other factors. Using phase component analysis, a new power flow calculation method is proposed for unbalanced power calculation of islanding micro-grids. The phase shifting in power flow between primary and secondary windings of the transformer, caused by the transformer winding connection, and the coupling of the lines are also discussed in unbalanced three-phase power flow calculation. It is valid with IEEE-5 bus system by comparing he results with those of the traditional power flow calculation method.In the balanced/unbalanced three-phase power flow, different DG systems with various adjustment coefficients, different load demanding level, different load models with various adjustment coefficients are discussed in details. The improved method with good convergence addresses power flow results and the frequency of the whole system and is more appropriate for islanding systems with mesh topology and for micro-grid management with no swing bus. The power flow calculation shows that to improve the stability of the islanding micro-grids, especially that of an unbalanced system, P-A-H/M-T SOFC needs to work together with other DGRs which can change their power output quickly.更多还原