【作者】 陈厚合；

【导师】 李国庆；

【作者基本信息】 华北电力大学 ， 电力系统及其自动化， 2012， 博士

【摘要】 我国已跨入复杂交直流混合大系统发展阶段。HVDC由于其独特的优点,在远距离输电和大型互联电网中起着十分重要的作用,但HVDC也对大型互联系统的运行提出了新的挑战。复杂交直流混合系统中,如何协调系统运行的安全性和经济性的研究迫在眉睫。电力系统区域间可用输电能力(ATC)这一经济技术指标,在维持系统的安全稳定运行、输电阻塞的管理、引导市场交易进行等方面具有特别重要的意义。因此,交直流混合输电系统区域间ATC的评估已成为电力市场环境下一项十分重要而又有许多问题亟待解决的研究课题。为此,本文紧紧围绕着这一中心课题,对其静态及动态约束下混合系统区域间ATC的相关问题展开了详细分析和深入研究。首先,针对现有混合系统潮流计算方法存在的可改进空间,改进了交直流混合系统潮流计算方法。考虑在换流器不同控制方式下交直流系统的相互影响,提出一种能够满足换流器控制方式转换策略的潮流计算方法。以交替迭代法为基础,对交流系统雅可比矩阵的特殊节点元素进行有效修正；结合换流器控制方式转换策略合理选取换流器关键状态变量,并将控制角余弦值和变压器分接头变比乘积作为一个状态变量处理,有效地避免了迭代过程中控制角余弦值和变压器分接头越限情况发生。改进的交替迭代法数学概念清晰、易于实现、可移植性强,提高了交直流系统潮流计算的鲁棒性。针对现有电压稳定性指标的局限性,本文以局部电压指标(L指标)为基础,结合实际输电网线路电抗远大于电阻、母线电压相位小的特点,提出一种可适应大规模电网快速计算的简化L指标(Lsimple指标)及分析母线间电压稳定关联信息的L-Q灵敏度分析方法。借助Lsimple指标的全微分方程分析系统参数变化对电压稳定影响作用的基础之上,定义电力系统的Lsimple-Q灵敏度,并阐明了其物理意义；简化L指标与Lsimple-Q灵敏度相结合,可提供系统电压稳定在线监控的多元信息,有利于系统运行人员全面掌握系统电压运行状态,采取合理措施改善系统电压稳定性,具有一定的工程实用价值。结合改进的交替迭代法和Lsimple指标,基于计及常规静态安全约束的ATC优化模型,充分考虑了HVDC系统的特点,并将Lsimple指标加入不等式约束,构建了基于OPF法的混合系统ATC计算模型。采用非线性原-对偶内点法对优化模型进行求解,分析了L指标约束值的变化对混合系统ATC和电压稳定性的影响,指出了对于一确定的交直流混合系统具有相同ATC优化结果的条件下,具有Lsimple指标约束的ATC模型电压稳定性优于无Lsimple指标约束的ATC模型。针对目前动态等值方法的不足,对同调等值方法做了改进,定义发电机的动态响应因子,并以动态响应因子为权系数推导并定义了大区互联电网机组动态稳定性指标,应用该指标可定量评价振荡后区域内各发电机的动态稳定性。借助于机组动态稳定性指标对区域互联系统进行同调等值计算,在有效地提高等值精度的前提下,减少了计算量。将大区互联电网机组动态稳定性指标用于电力系统同调等值能够有效跟踪系统运行方式变化,准确识别惯量中心主导机群,更符合电力系统动态等值中的发电机聚合思想,为提高非线性直流附加功率控制效果提供了有力的理论支持。针对HVDC的附加功率调制可改善交流系统的动态稳定性这一特性,提出一种新的非线性直流附加功率调制控制策略。采用改进的同调等值方法对各系统区域内发电机组进行等值,并根据等值后交直流系统的特点,将交直流系统的微分反馈线性化模型扩展为微分代数反馈线性化模型,有效计及了电力系统强非线性代数方程的影响,采用线性最优理论进行模型求解；为克服系统全状态反馈条件难以实现的不足,采用等值系统主导机群的状态变量作为调制输入信号,在保证控制效果的前提下,降低了控制策略实现的难度。本文的直流附加功率调制控制策略与传统的线性化的控制策略相比,更加有效地改善了交直流混合系统的动态稳定性。本文最后,针对系统区域间传输功率显著影响互联系统的动态稳定性,可能引发系统区域间低频振荡,从而限制ATC这一问题,构建了计及系统动态稳定约束的交直流系统区域间ATC评估模型。将阻尼比作为衡量系统的动态稳定性的指标加入ATC优化模型,并采用连续潮流法进行模型求解；模型通过直流附加功率调制策略,有效地改善系统动态特性的同时显著提高了系统的区域间ATC,在提高并满足了系统稳定性要求的前提下又兼顾了经济性的需要。计及系统动态稳定约束的交直流系统ATC计算模型,为混合系统区域间ATC的研究开辟了新的途径。更多还原

【Abstract】 China has entered a large complex system with AC and DC era. Because of its unique advantages, HVDC plays an important role in the long-distance power transmission and large interconnected power system. But new challenges are also raised in large-scale interconnected system operation. In complicated AC and DC systems, the research to coordinate the system safety and economic operation is imminent. Available transfer capability (ATC) is applied as the economic and technical indicator in inter-regional electric power system, it is of great importance in maintaining security and stability of the system, managing transmission congestion, and guiding the conduct of market transactions and other aspects. Therefore, the assessment and decision-making of ATC in regional AC-DC hybrid electricity transmission system has become a very important research issue, which still has many problems to be solved, under electricity market environment. As a result, tightly connected with this central theme, the paper gives detailed analysis and conducts in-depth research for ATC related problems in inter-regional systems under static and dynamic constraints.Firstly, aiming at existing space which still can be proved in nowadays power flow calculation method for hybrid systems, this paper improved the power flow calculation method in AC-DC hybrid systems. Considering the interaction between AC and DC systems under different control strategies, it brings us a power flow calculation method satisfying inverters changing controlling strategies. It is based on alternating iterative method, giving effective correction for the special nodes in AC system Jacobian matrix. Key state variables of the converter is choosen reasonably according to its changing controlling strategies, and deals with the cosine value of the control angle and the transformation ration product as a state variable. It effectively avoids the cosine value and transformation ration form crossing the limitation during the iterative process. The refined alternating iterative method has clear mathematical concepts, and is easy to be implemented and transferred. It improves the robustness of the power flow calculation method in AC-DC hybrid systems.There are some limitations of Voltage stability index. A simplified formula of local voltage stability L-index is proposed in this paper. It is based on the actual grid line with reactance is much greater than resistance, the characteristics of a small bus voltage phase. It is proposed a fast calculation can be adapted to large-scale grid L-index (LSimple indicators) and voltage stability analysis of bus related information among the LSimPle_Q sensitivity. The differential equation of the simplified L-index is developed to obtain the sensitivity of LSimpe respect to parameters, such as LSimple-Q sensitivity. The physical meaning of LSimple-Q sensitivity is comprehensively presented. Combining simplified L index with LSimple-Q sensitivity online monitoring system to provide multi-voltage information. It can help system operators complete control system voltage running condition and take reasonable measures to improve the system voltage stability. It has some practical value.The ATC optimization model based on conventional static security constrained, combined the improved alternating iterative method and LSimple index,fully considered characteristics of the HVDC system, and join the LSimple index in inequality constraints, constructed a new ATC calculation method, which is based on the OPF hybrid system. The proposed model is solved by primal-dual interior point method, at the same time, this paper analysis the change of the LSimple value constraints and its influence on ATC of AC-DC hybrid system and voltage stability. Finally pointing out that for a certain AC-DC hybrid system with the same ATC optimization results, the votlage stability of ATC model with LSimple index constraints is better than the one who doesn’t have LSimple index constraints.As the prerequisite for realizing the nonlinear additional power control strategy, an improved coherency-based equivalence method is proposed to make up for the current deficiency of dynamic equivalence method. The generator dynamic response factor is defined by the combination of coherency-based equivalences and model equivalences, the generator dynamic stability index is deduced and obtained by the dynamic response factor, and the generator dynamic stability after oscillation can be quantitatively evaluated by using the index. By means of the generator dynamic stability index to calculate coherency-based equivalences of the regional interconnected grid, the accuracy of the equivalence can be effectively improved and the amount of computation can be reduced. The improved coherency-based equivalence method can effectively trace the system operating mode changes and accurately identify the dominant cluster in the center of inertia, which is more accord with generator polymerization concept in dynamic equivalence of power system.This method offers a strong theoretical support for the nonlinear additional power control.According to the additional power characteristic of HVDC that its modulation can improve the dynamic stability of the AC system, a rational DC nonlinear additional power control strategy is proposed. A new dynamic equivalent method is proposed to enhance the accuracy of equivalent system. According to the characteristics of the equivalent strategy, a rational nonlinear optimal supplementary control strategy is proposed for the DC modulation. The feedback linearization of differential systems is easily extended to differential-algebraic systems by proposed approach. Utilizing the equivalent strategy, a rational nonlinear optimal supplementary control strategy is proposed for the AC-DC system. The control strategy only requires the critical clusters’speeds and angles as modulation signals, which ensures the control effect and reduces the difficulty of control strategy implementation. Compared with the traditional control strategy, the proposed control strategy can effectively improve the dynamic stability of the AC-DC hybrid system.At last, against the problem that inter-area transmission power for the system can significantly affect the dynamic stability of the interconnected system, and may lead to inter-area low-frequency oscillation, thereby limiting the ATC. Taking system dynamic stability constraints into account, ATC evaluation model is constructed for inter-area AC-DC systems, which makes the damping ratio join ATC optimization model as an indicator to measure the system dynamic stability, and uses the continuous power flow method to solve the model. By additional DC power modulation strategies, the model effectively improves the system dynamic characteristics and significantly raises the of inter-area system ATC, which takes the economic needs into account and meets the premise of the stability of the power system. The AC-DC systems ATC calculation model considering the dynamic system stability constraints opens up a new way for the research of ATC in hybrid inter-area system.更多还原