柔性交直流电网潮流算法的研究

发布时间：2018-06-06 22:41

本文选题：直流电网 + 交直流网络　；参考：《山东大学》2017年硕士论文

【摘要】：高压直流输电因输送容量大、不受输送距离限制、无稳定性问题且可实现异步互联等优点,已在电能大规模、远距离输送和大区电网互联中广泛应用。其中,直流电网是以柔性直流输电技术为基础,由大量直流线路互联组成的能量系统,与常规的直流输电系统相比,可以提供更高的供电可靠性和设备的冗余性,适应性更强的供电模式,灵活和安全的潮流控制。现如今,交直流电网快速发展,交流与直流的关联与耦合程度越来越强,但显然,无论是常规的交直流电网,还是柔性交直流电网,或者是二者混合的形式,潮流分析都是一个基础的理论问题,对揭示交直流电网运行特性、控制机理和策略制定都具有重要意义。经过电力科技工作者们几十年的研究,纯交流系统的潮流算法现在已经相当成熟,相比之下,交直流混合电网潮流算法却没有发展到相同的高度。因此,本文以柔性交直流电网为例,对交直流混合电网潮流算法进行研究,具体内容如下:首先,简单概述换流站的模型结构以及VSC的基本特性,在此基础上,对换流站的控制机理进行定性分析。从同步电网角度出发,交直流电网潮流的本质依然显现交流电网的特性,从交流系统支撑能力对交直流电网运行状态的影响入手,论证对交直流电网进行有机统一处理的必要性。为使交直流算法可以有效衔接原有经典的交流潮流算法,以直流节点电压作为直流电网的状态变量,并对直流节点进行分类,在换流站公共联接点电压变量给定的情况下,给出了基于牛顿-拉夫逊法的直流电网潮流算法,为交直流混合电网进一步的统一计算奠定基础。其次,提出了一种考虑节点电压关联的交直流电网潮流算法,通过换流站的功率关系对换流站进行稳态建模,以交流网络和直流网络的节点电压为最小状态集,推导换流站仅关联状态变量的功率方程,在不同的控制方式下演绎相关节点潮流方程的修正,实现对其用牛顿-拉夫逊方法的求解。修正方程式中的雅克比矩阵体现了交直流的耦合关系且维持良好的稀疏规律,可以实现在算法中沿用稀疏技术,有利于进一步分析和研究交直流电网性能。最后,换流站内部的主要器件VSC在性能上与变压器类似,仍然是电压的变换,只是电压还在交流向量和直流标量之间变换。基于以上思路,提出一种基于复变比描述换流站数学模型并用于潮流计算的新思路,其核心在于将VSC等效为非标准变比为复变量形式的理想变压器模型,进而引入换流站对两侧节点的等效注入功率,再对换流站支路进行戴维宁模型和诺顿模型的等效,在诺顿模型下交直流电网可以得到计及换流站支路的与网络拓扑一致的对称的节点导纳矩阵。在此模型下使用牛顿-拉夫逊法对交直流混合电网潮流进行求解,此种算法对原有交流潮流算法有良好的继承性,编制程序的工作量小。
[Abstract]:High voltage direct current (HVDC) transmission has been widely used in large-scale, long-distance transmission and power grid interconnection for its advantages of large transmission capacity, no restriction of transmission distance, instability and asynchronous interconnection. Among them, DC network is an energy system based on flexible DC transmission technology, which is composed of a large number of DC lines interconnected. Compared with conventional HVDC transmission system, DC network can provide higher reliability of power supply and redundancy of equipment. More adaptable power supply mode, flexible and safe power flow control. Nowadays, with the rapid development of AC / DC power grid, the correlation and coupling between AC and DC is becoming stronger and stronger. But obviously, whether it is conventional AC / DC network or flexible AC / DC network, or the combination of the two, Power flow analysis is a fundamental theoretical problem, which is of great significance to reveal the operating characteristics of AC / DC power network, control mechanism and strategy formulation. After decades of research by power science and technology workers, the power flow algorithm of pure AC system has been quite mature now, but the hybrid power flow algorithm of AC / DC power system has not developed to the same height. Therefore, this paper takes the flexible AC / DC power grid as an example to study the AC / DC hybrid power flow algorithm. The specific contents are as follows: firstly, the model structure of converter station and the basic characteristics of VSC are briefly summarized. The control mechanism of converter station is analyzed qualitatively. From the point of view of synchronous power grid, the nature of AC / DC power flow still shows the characteristics of AC power grid, starting with the influence of AC system support capacity on the operation state of AC / DC power network. The necessity of organic unified treatment of AC / DC power network is demonstrated. In order to link up the classical AC power flow algorithm effectively, the DC node voltage is taken as the state variable of DC network, and the DC node is classified. When the voltage variable of commutator common connection point is given, A power flow algorithm for DC networks based on Newton-Raphson method is presented, which lays a foundation for further unified calculation of AC / DC hybrid networks. Secondly, an AC / DC power flow algorithm considering the connection of node voltage is proposed. The steady state of converter station is modeled by the power relation of converter station, and the node voltage of AC network and DC network is taken as the minimum state set. The power equation of the converter station is derived which only correlates the state variables. The power flow equation of the correlated node is deduced under different control modes. The Newton-Raphson method is used to solve the power flow equation. The Jacobian matrix in the modified equation embodies the coupling relationship between AC and DC and maintains a good sparse law. It can be realized by using sparse technique in the algorithm and is helpful to further analyze and study the performance of AC / DC power network. Finally, the VSC, the main device in the converter station, is similar to the transformer in performance. It is still a voltage conversion, but the voltage is still changing between AC vector and DC scalar. Based on the above ideas, a new idea is proposed to describe the mathematical model of converter station based on complex variable ratio and to apply it to power flow calculation. The core of this idea is to equivalent VSC to an ideal transformer model with a non-standard variable ratio as a form of complex variable. Then the equivalent injection power of the converter station on both sides of the node is introduced, and the equivalent of the Davining model and the Norton model for the branch circuit of the converter station is carried out. In the Norton model, a symmetric node admittance matrix, which is consistent with the network topology, can be obtained by taking into account the branch of the converter station. In this model Newton-Raphson method is used to solve the AC / DC hybrid power flow. This algorithm has good inheritance to the original AC power flow algorithm and the workload of programming is small.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1;TM744

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