【作者】 朱红萍；

【导师】 罗隆福；

【作者基本信息】 湖南大学 ， 电气工程， 2012， 博士

【摘要】 我国未来二十年的电力发展格局为：“西电东送、南北互供、全国联网”。直流输电工程在西电东送和全国联网中承担着主要任务，随着输送距离的增大和容量的增加，给直流输电技术提出了更高的要求，减少直流输电系统对交流系统的谐波注入，限制在各种工况下直流系统无功补偿对交流系统的影响，是直流输电技术的热点问题。我国南方电网是世界上最复杂的交直流并联电网，在交流系统故障时，利用直流系统的快速调节提高交流系统的暂态稳定水平，抑制交流系统的低频振荡，是研究交直流并联系统安全稳定运行的关键问题。在交直流并联输电系统中，直流系统对交流系统稳定性的影响主要由直流系统的拓扑结构和控制策略决定。基于感应滤波的直流输电系统中换流变压器结构有别于传统的换流变压器结构，而直流调制技术能改善交流系统的稳定性是一个众所周知的事实。因此，本文以这两个方面来研究直流输电系统如何改善交流系统的稳定性。本文依托“十一五”重大科技专项及国家自然科学基金，对基于感应滤波的直流输电系统在交流系统故障时，感应滤波换流变压器的滤波和无功补偿特性改善交流系统的稳定性进行了研究，对直流调制改善交流系统的频率及暂态稳定性进行了理论研究。研究重点及创新点主要体现在以下几个方面：(1)感应滤波换流变压器的短路阻抗是实现滤波的关键因素，设计者以遗传算法设计了短路阻抗，算法复杂，收敛较早。本文以换流阀最大短路冲击电流为原则优化设计了感应滤波换流变压器的短路阻抗，算法简单，易于实现。(2)分析了引起谐波不稳定的两个主要原因：幅值较大的低次非特征谐波电流流过谐波阻抗较大的系统引起正反馈；变压器铁芯的饱和现象。基于感应滤波的直流输电系统，对这两个原因已有研究，但是研究结果是建立在实验的基础之上，并没有从机理上进行本质的分析。本文在交流系统发生不对称故障时，将交流电压分解为正序谐波电压和负序谐波电压形式，并对直流输电系统交流侧的正序、负序谐波传递到直流侧的规律进行了推导。由于感应滤波换流变压器的作用，使得直流侧的谐波电压幅值比传统的直流输电系统有所降低。以正序、负序谐波在交、直流侧传递的规律为基础，分析了基于感应滤波的直流输电系统交流侧等值谐波阻抗的计算公式；直流侧等值谐波阻抗的计算公式。得出了基于感应滤波的直流输电系统的谐波等值阻抗比传统的直流输电系统要小，以上以正序、负序谐波电压在交直流侧传递的计算方法，很好的从机理上论证了基于感应滤波的直流输电系统在抑制谐波不稳定方面的优势。(3)对感应滤波换流变压器铁芯的饱和现象研究，目前都是基于实测数据和录波，本文以传统变压器铁芯饱和的研究方法为基础，考虑感应滤波换流变压器绕组布置的特殊性，用电路-磁路耦合模型建立了感应滤波换流变压器的绕组电磁关系，数值仿真和实验结果相一致。研究成果有助于进一步研究其本体特性。(4)对基于感应滤波的直流输电系统换流站的电压稳定性进行了计算，换流站交流系统的失稳常常是由于无功功率的欠补或过补造成的。基于感应滤波的直流输电系统的无功补偿特性使得逆变站的电压稳定性比传统直流输电有所改善。现有研究进行了感应滤波换流变压器的换相电抗和换相电压的跌落值这两个因数与传统直流输电的比较，而本文在此基础上对比了这两个因素对电压调节效应的评估计算的影响。验证了基于感应滤波的直流输电系统能增强换流站的电压稳定性。直流调制的调制信号和控制策略是研究的关键，针对目前两种主要的调节-交流系统的频率调节和交流系统的稳定性调节。在已有的线性与非线性变结构直流调制策略基础上进行控制器的改进研究。(1)着重研究了交直流并联系统中，受端系统出现负荷扰动时的频率控制问题，提出了变结构的直流调制线性控制器。建立了频率偏差、交流功率偏差与直流功率偏差控制的简单模型，采用了最优二次型切换面设计，与传统方法相比，该方法简单，状态变量少，容易实现，有利于抑制外部扰动，鲁棒性强。有利于在多端交直流并联系统中应用。(2)针对交直流并联系统的暂态稳定性问题，提出了非线性变结构直流调制控制器的设计新方法。本文与常规的变结构设计步骤相反，先设计了切换面，再设计控制器。该方法能使非线性系统的非线性变结构控制器的设计简单化。本文以交直流输电系统的应用需求为背景，以直流输电对交流系统稳定性影响为研究对象，研究了基于感应滤波的直流输电能在一定程度上改善交流系统的稳定性，研究成果有助于感应滤波换流变压器在直流输电中的推广应用。论文也对直流系统和交流系统的联合调节作了一定的研究，变结构直流调制器的设计新方法为交直流并联运行系统的控制器设计提供了有益的参考。更多还原

【Abstract】 In the next two decades, the pattern of the electric power development in Chinais:“the power transmission from west to east, north and south mutual supply andnationwide network”. HVDC (High Voltage Direct Current) transmission technologyundertakes the main task in the power transmission from west to east and nationwidenetwork. With increase of the transmission distance and transmission capacity,reliability of power system is higher standard for the DC transmission. The hotresearch field is how to reduce harmonic injection into AC system and how to reducethe influence that the reactive power compensation under various HVDC operatingconditions on the AC system.China Southern Power Grid is the most complex AC/DC hybrid systems.Utilizing the quick response of the DC system to improve the dynamic stability andsuppress the low frequency oscillations of AC grids under AC fault, which is a keyresearch issue for the security and stability operation of the AC/DC hybrid system.The effect of the DC system to AC system stability is mainly determined by theDC system topology and control strategy in the AC-DC parallel system. Based on thefact that the structure of the inductive filtering converter transformer of HVDCsystem is different from the structure of the traditional converter transformer,combined with the truth that the DC modulation can improve the performance of theAC system. Therefore, this thesis studied the DC system improved the stability of theAC system in these two aspects.Based on “the Eleventh Five” important scientific and technological specialFoundation and National Natural Science Foundation of China, this thesis studied thefiltering characteristic of inductive filtering converter transformer and its reactivepower compensation characteristic on improving AC system’s stability in case of ACsystem fault in the DC transmission system, and also carried out a theoretical researchon DC power modulation that improves the frequency and transient stability of ACsystem in the AC system fault. The fundamental research and the related innovativeachievement in this thesis can be summarized as follows:(1) The short-circuit impedance of the converter transformer is the key to filter,the designer using the genetic algorithm design short-circuit impedance, which makesthe algorithm complex and convergence earlier. This thesis takes the converter valve’sbiggest impact short circuit current as a design principle to optimize the short-circuitimpedance of inductive filtering converter transformer, the algorithm is simplified and can be realized easily.(2) The two main reasons that result harmonic instability are analyzed: thepositive feedback is occurred when the larger amplitude low-order harmonic passesthrough the system that owns larger harmonic impedance; and the transformer coresaturation phenomenon is another reason. Although these two reasons have beenstudied based on inductive filtering DC transmission system, the result was based onexperiment. Essence of this term has not been analyzed yet. In this term, the ACpower will be decomposed into positive sequence voltage and negative sequencevoltage when single phase fault occur in the AC system, the negative and positivesequence harmonic pass from the AC side to the DC side in HVDC system iscalculated. Because of the effect of inductive filtering converter transformer, the DCside harmonic voltage amplitude will be lower than the traditional DC transmissionsystem. Based on the transfer characteristic of the positive sequence, and negativesequence harmonics between AC-and DC-side, this thesis analyzed the equivalentharmonic impedance at the AC-and DC-side of the inductive filtering based HVDCsystem. The research result shows that harmonic equivalent impedance of theinductive filtering based HVDC converter station is smaller than the traditionalHVDC system. The above calculation method of the positive sequence, negativesequence harmonic voltage passing in AC to DC side, demonstrated the advantages ofthe DC transmission system based on the inductive filtering in the suppression ofharmonic instability in mechanism.(3) At present, the study of the inductive filter converter transformer coresaturation phenomenon are based on the measured data and the wave recording, basedon traditional method transformer core saturation, taking the special of inductivefiltering transformer winding arrangement into account. The electromagneticrelationship among windings of the inductive filtering converter transformer isestablished by using the circuit-magnetic coupling model. The simulation resultscoincide with the experimental results. The result contribute to the further study of itsbody features.(4) Calculating the voltage stability of inductive filtering based HVDC converterstation, it is found that the instability of AC system in converter station is often due toreactive power over compensation or de-compensation. Reactive power compensationcharacteristics of the inductive filtering converter transformer better stability of thevoltage in the inverter station than that of traditional HVDC. The former researchcompared commutation reactance and the dropping value of the commutation voltagewith the traditional DC transmission. On this basis, there is a comparison of these twofactors’ affection on the assessment of the voltage regulator. It verified that the inductive filtering based on HVDC transmission system can enhance the voltagestability of the converter station.Signal modulation and control strategies play the key role in the DC modulationresearch. For two main regulation-the AC system frequency regulation and stabilityregulation, the controller has some improvements in the existing linear and nonlinearvariable structure DC modulation strategies.(1) Variable structure DC modulation linear controller is proposed by focusingon researching frequency control when load disturbance occurred in the receiversystem in a parallel AC-DC interconnected power system. Using the optimal formswitching surface design in sliding mode, a simple model is built including offrequency deviation, the AC power deviation and DC power deviation. Using theoptimal quadratic form switching surface design in sliding mode. Compared withtraditional methods, this method is easy to achieve by its simplification with less statevariable, suppress external disturbances, the strong robustness. It also contribute toapplication in multi-terminal AC-DC parallel system.(2) In terms of the transient stability problems of the AC-DC parallel system, thenew design method of nonlinear variable structure DC modulation controller isproposed. Steps of the variable structure design are contrary to the conventional ones.First, the switching surface was designed, and then the controller is designed. Thismethod is easy to carry out make nonlinear variable structure controller in nonlinearsystems become simplified.Based on the background of the application requirements of AC-DC transmissionsystem and took the DC transmission’s impact on the stability of the AC system as thestudy object, this thesis makes a deep research on inductive filtering based HVDCtransmission system can improve the stability of the AC system, It provides a usefulpractical reference for the application of the inductive filtering converter transformer.the joint regulation of the DC system and AC system are also studied. The designmethod of variable structure DC modulator provides a useful reference for thecontroller design of AC-DC parallel operation system.更多还原