【作者】 陈磊；

【导师】 唐跃进；

【作者基本信息】 华中科技大学 ， 电工理论与新技术， 2010， 博士

【摘要】 随着电力系统装机容量的逐渐增加,电网互联范围的逐步扩大,系统中短路电流呈不断增长趋势。一旦短路电流超过当前断路器的遮断容量,断路器将无法有效地切除故障,这会严重威胁到电力设备乃至整个电力系统的安全运行。为提高系统运行的安全性、稳定性及可靠性,降低短路电流对电力设备的冲击,控制短路电流、限制过大短路电流的技术已成为一种迫切需求。目前研究的各种故障电流限制技术中,利用超导材料的超导限流器(SFCL)依靠自身独特的优越性,成为了限流技术领域中发展主线之一。本文提出了一种电压补偿型有源超导限流器,从理论分析、策略构架、仿真建模、性能比较、协调运行到动模样机的研制等方面对其开展了较为系统的研究工作,为促进该型SFCL在中高压系统等级的推广应用,给出了10kV级电压补偿型有源SFCL的概念设计方案,并初步探讨了工程化问题。论文第2章首先介绍了电压补偿型有源SFCL的单相拓扑结构及运行原理,它由空心超导变压器和脉宽调制(PWM)变流器组成。超导变压器的一次侧线圈串联接入系统主回路,二次侧线圈与PWM变流器相联。当系统正常运行时,通过PWM变流器控制变压器二次侧的注入电流,使其与系统电流满足一定关系,超导变压器一次侧的两端电压被补偿为零,限流器对系统无影响。当短路故障发生时,通过改变二次侧注入电流的幅度和相位,实现调节限流器等效接入系统的限制阻抗,以达成限流目的。根据电流调节目标的不同,此有源SFCL有三种限流工作模式。利用MATLAB仿真和小型单相样机的短路试验研究,限流机理的正确性及空心超导变压器的实用性得到了有力证实。论文第3章在单相结构的基础上,给出了完整的三相组成结构,并解析了不同类型短路故障下其工作特性的差别。为实现三相电压补偿型有源SFCL在各种短路工况下的限流性能,对于其组成结构中带分裂电容的三相四线制PWM变流器,设计了一种结合电容电压平衡控制的双闭环PI控制策略。基于仿真分析结果,肯定了控制策略的有效性。关于空心超导变压器参数的变化对限流器性能的影响也做了相应分析,得出如下结论：增大变压器一次侧自感有利于加强限流能力；增加变比会导致初始补偿电流的上升；提高耦合系数有助于降低变流器的无功功率输出。论文第4章以暂态稳定性、距离保护及电压跌落为研究目标,分析了电压补偿型有源SFCL对电力系统原有设备及运行特性的影响。首先,从单机无穷大系统的功角特性出发,研析了此有源SFCL的引入对发电机输出电磁功率的作用,继而采用等面积法则,阐述了其对暂态稳定性的具体影响机理。依靠仿真分析平台,模拟了不同的限流模式、短路类型、故障切除时间下发电机的功角特性曲线。仿真结果表明,电压补偿型有源SFCL可一定程度上消耗发电机的输出电磁功率,使得发电机转子的加速面积减少而增强系统暂态稳定性。接着,从修正阻抗继电器测量阻抗的角度着手,实现消除电压补偿型有源SFCL对距离保护的影响。针对其各种模式下的限制阻抗,给出了测量阻抗的匹配修订公式,并以含有源SFCL的双端电源系统为分析对象,证明了修订公式的适用性。最后,就不同限流参数、故障点位置下的特性分析为例,研究了电压补偿型有源SFCL对短路瞬间同步电机机端电压跌落的改善效果,从中得知有源SFCL的装设能够显著地抑制电压跌落,提高系统的动态电能质量。在国家863计划的支持下,完成了220V／30A电压补偿型有源SFCL动模样机的研制。作者在该项研究工作中重点承担了系统分析、参数设计、动模试验以及数据分析处理等任务。论文第5章就该试验样机的总体结构、基本特性及试验运行情况进行了介绍。试验结果表明,有源SFCL动模样机在系统发生三相短路后能有效地投入,自动地对故障电流加以约束,限流过程中没有过电压现象产生,且能对故障电流的稳态水平实施调控。论文第6章选取国内实际的10kV配电网线路,将电压补偿型有源SFCL安装于其中一条常发生短路故障的馈线处,就其结构中的空心超导变压器及变流器设计了基本参数。出于促进10kV级有源SFCL工程化的考虑,简要讨论了超导装置交流损耗的影响、低温绝缘技术的选取及大容量变流器中开关器件的应用,所得结论为将来的工程样机制作奠定了技术基础。更多还原

【Abstract】 With the continual development of power system installed capacity, and the expansion of interconnected network, the level of short-circuit current increases constantly. Once the short-circuit current is greater than the interrupting capacities of existing circuit breakers, the fault cannot be cleared effectively, and further the safeties of power equipments and whole power system may be threatened seriously. In order to enhance the security, stability and reliability of power network, and to reduce the burden induced by the fault current, it’s urgent to suppress the fault current to a certain level. Among the proposed curren-limiting technologies, superconducting fault current limiter (SFCL), due to its some special advantages, has been one of the current-limiting technical field’s main research directions. In this thesis, a voltage compensation type active SFCL is proposed. This dissertation systematically studies the proposed voltage compensation type active SFCL, including the issues of theoretical analysis, strategy frame, simulation verification, performance comparison, coordinated operation, prototype development and short-circuit test in a dynamic simulation power system. To drive the application of this type SFCL to the medium and high voltage power network, the basic parameter design about a 10kV voltage compensation type active SFCL is carried out and some corresponding engineering problems are discussed briefly.In chapter 2, the structure and principle of the single-phase voltage compensation type active SFCL are firstly introduced. The single-phase active SFCL is composed of an air-core superconducting transformer and a pulse-width modulation (PWM) converter. The superconducting transformer’s primary winding is in series with AC main circuit, and its second winding is connected with the PWM converter. In normal state, the injected current in the secondary winding will be adjusted to ensure that the primary voltage of the transformer is compensated to zero. As a result, the SFCL has no influence on the main circuit. When the fault happens, the current-limiting impedance in series with main circuit can be changed by adjusting the injected current in the amplitude and phase angle, and further the current through the fault line can be limited. According to the difference in the regulating objectives of the converter’s output current, there are three operation modes. Based on the simulation analysis and the short-circuit test for a small-scale protype, the correctness of the current-limiting principle and the practicability of the air-core superconducting transformer can be proved.In chapter 3, on the basis of the single-phase structure, the integrated three-phase topology structure is proposed, and its operational characteristics under the different types of faults are investigated. In order to realize the three-phase active SFCL’s current-limiting characteristics, it is needed to control its component, namely the three-phase four-wire PWM converter with split-capacitors, flexibly and reasonably. The double closed loop control, consisting of capacitor-voltage balance control, is proposed. According to the simulation results, the validity of presented control strategy is fully affirmed. In additon, the influence of the air-core superconducting transformer’s parameter variation on the integrated three-phase active SFCL’s performance is also investaged, and conclusions are shown as follows:raising the self-inductance of primary winding is beneficial to the current-limiting capacity; enhancing the transformation ratio can lead to the increase of initial compensation current; increasing the coupling coefficient is helpful to reduce the reactive power output of converter.In chapter 4, taking the power system transient stability, distance protection and voltage sag for examples, the influences of the voltage compensation type active SFCL on the existing equipments and operating characteristics of power system are analyzed. Firstly, based on the power-angle characteristic of the single-machine to infinite bus power system, the effect of the active SFCL on the generator’s electromagnetic power is researched, and then its influence on the transient stability is studied by adopting the equal area rule. According to the simulation platform, the power-angle swing curves are simulated under the different current-limiting modes, fault types and fault clearance times. It can be found that, the installation of the active SFCL can consume the electromagnetic power, reduce the energy acceleration area, and then enhance the transient stability. From the point of view of revising the distance relay’s measured impedance, the effect of the active SFCL on the distance relay can be eliminated. Based on the three different operation modes of the active SFCL, this chapter presents the corresponding modified formulas. The model of the dual-source power system with the active SFCL is built to evaluate the validities of the modified formulas, and the results are positive. In the final part of this chapter, according to the simulation analyses under the different current-limiting parameters and fault locations, the impact of the active SFCL on the synchronous machine’s terminal voltage sag due to short circuit is researched. It is observed that the active SFCL can help to reduce the voltage sag and improve the dynamic power quality.The author participated in the research on the 220V/30A three-phase voltage compensation type active SFCL supported by the 863 program, and took charge of the system analysis, parameter design, dynamic experiments and experimental data processing. In chapter 5, the configuration of the 220V/30A three-phase active SFCL and the part of important test results are presented. In the dynamic simulated experiment of power system, the SFCL prototype can not only effectively suppress the fault current under the three-phase short-circuit, but also adjust its steady level. In addition, there is no overvoltage during the current-limiting process.In chapter 6, a practical lOkV distribution network is chosen, and the voltage compensation type active SFCL is applied to a feeder where the fault often occurs. For the air-core superconducting transformer and the PWM converter of the 10kV active SFCL, the basic parameters are designed. In view of the 10kV active SFCL’s engineering application, the AC loss of superconducting coil, the low temperature insulating technique, and the converter’s switching element are selected to be investigated briefly, and the conclusions can provide the technical foundation for the future engineering protype fabrication.更多还原