【摘要】：隨著廣州電網(wǎng)網(wǎng)架結(jié)構(gòu)的完善,其供電能力及可靠性逐步提高,同時,在電源不斷投產(chǎn)、負荷水平持續(xù)增長等影響下,電網(wǎng)的短路電流呈持續(xù)增長的趨勢。利用柔性直流輸電系統(tǒng)能夠獨立控制所傳輸?shù)挠泄蜔o功的能力,提高電網(wǎng)供電可靠性、動態(tài)無功補償能力和電網(wǎng)調(diào)度運行的靈活性。但協(xié)調(diào)控制系統(tǒng)的控制方式靈活多變,針對交流系統(tǒng)故障可以設(shè)計其控制系統(tǒng),抑制負序分量,改變傳統(tǒng)故障的故障特性,對交流線路上的傳統(tǒng)保護可靠性產(chǎn)生了影響。因此,針對電網(wǎng)交流線路發(fā)生故障時,研究柔性直流輸電系統(tǒng)的控制方式及其對交流保護的影響變得尤為迫切。首先,本文對MMC換流器的拓撲結(jié)構(gòu)、工作原理及調(diào)制控制策略等方面進行了研究,基于基本理論搭建相應(yīng)的系統(tǒng)穩(wěn)態(tài)仿真模型;接著,針對交流線路發(fā)生故障時,依據(jù)信號延遲法提取電網(wǎng)電壓和電流的dq軸正負序分量,提取正序分量進行鎖相的改進,對負序分量進行數(shù)學(xué)建模并設(shè)計負序電流控制器,仿真結(jié)果表明,該負序電流控制器可以抑制掉負序電流分量,使得換流器輸出的交流電流具有三相對稱的特性;然后,基于距離保護的基本原理,推導(dǎo)了柔性直流輸電系統(tǒng)的控制系統(tǒng)中負序電流控制器的投入運行對其測量阻抗不產(chǎn)生影響,得出了不改變其動作可靠性的結(jié)論,由于負序電流控制器投入運行影響了負序網(wǎng)絡(luò),進而影響了零序電流大小;最后,針對交流線路發(fā)生故障時,控制系統(tǒng)中的負序電流控制器投入運行后,抑制掉負序電流,三相電流突變量相等,從而電流突變量的故障選相元件失效。基于故障相的相電壓降低的故障特性,選擇了低電壓故障選相元件。本文針對交流電網(wǎng)發(fā)生故障的工況,設(shè)計了控制系統(tǒng)的負序分量控制策略,理論推導(dǎo)分析了該控制策略對交流線路距離保護、零序電流保護、電流突變量選相元件等保護的影響,在仿真軟件上搭建相應(yīng)的模型驗證理論結(jié)論。本文結(jié)論為柔性直流輸電系統(tǒng)的接入交流系統(tǒng)的保護配置和整定提供一定的理論基礎(chǔ),為電網(wǎng)的安全穩(wěn)定運行提供保障。
[Abstract]:With the improvement of the grid structure in Guangzhou, the power supply capacity and reliability are improved gradually. At the same time, under the influence of power supply and load level, the short-circuit current of power grid is increasing continuously. The flexible direct current transmission system can independently control the active and reactive power transmission, improve the reliability of power supply, dynamic reactive power compensation and the flexibility of power dispatching. But the control mode of the coordinated control system is flexible and changeable. The control system can be designed for the fault of AC system, which can suppress the negative sequence component and change the fault characteristic of the traditional fault, which has an impact on the reliability of the traditional protection on the AC line. Therefore, it is urgent to study the control mode of flexible DC transmission system and its influence on AC protection. Firstly, the topology, working principle and modulation control strategy of MMC converter are studied, and the corresponding steady state simulation model is built based on the basic theory. Then, according to the signal delay method, the positive and negative sequence components of the dq axis of the grid voltage and current are extracted, and the phase-locking improvement is carried out. The mathematical model of the negative sequence component is established and the negative sequence current controller is designed. The simulation results show that the negative sequence current controller can suppress the negative sequence current component and make the AC current output of the converter have the characteristic of three-phase symmetry. Then, based on the basic principle of distance protection, it is deduced that the operation of negative sequence current controller in the control system of flexible direct current transmission system has no effect on its measuring impedance, and the conclusion is that the reliability of its operation is not changed. Because the negative sequence current controller is put into operation, the negative sequence network and the zero sequence current are affected. Finally, the negative sequence current controller in the control system can suppress the negative sequence current when the fault occurs in the AC circuit, and the three-phase current mutation amount is equal, so the fault phase selection element of the current mutation quantity is invalid. Based on the fault characteristics of the phase voltage reduction of the fault phase, the low voltage fault phase selection element is selected. In this paper, the negative sequence component control strategy of the control system is designed for the fault condition of AC power network, and the control strategy for AC line distance protection and zero sequence current protection is deduced and analyzed theoretically. The effect of current sudden change phase selection element on the simulation software is built to verify the theoretical conclusion. The conclusion of this paper provides a certain theoretical basis for the protection configuration and setting of the access AC system of the flexible direct current transmission system, and provides the guarantee for the safe and stable operation of the power network.
【學(xué)位授予單位】：華北電力大學(xué)(北京)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM721.1;TM77

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