【作者】 罗珂；

【导师】 刘玉田；

【作者基本信息】 山东大学 ， 电力系统及其自动化， 2010， 博士

【摘要】 大规模电力系统区域间的低频振荡已成为制约互联系统传输容量的瓶颈和影响安全稳定运行的重要因素。现有的电力系统稳定器(PSS)虽然对抑制功率振荡起到了重要作用,但由于局限于本地信号反馈的约束,不能直接利用相对角速度或相对功角构成闭环,不能很好地抑制互联电网区间低频振荡。广域测量系统(WAMS)的发展,给电力系统的监测、分析和控制提供了新的手段,为互联电网阻尼控制带来了新的契机。在采用本地信号设计阻尼控制策略中,由于时滞较小,忽略时延的影响是可行的。但是,在地理上广域分布的互联电网,远方信息的采集、处理和传输的时延可达几十甚至数百毫秒,是不能忽略的。信号传输时滞往往会恶化系统性能,降低系统的稳定性,使控制器达不到理想的效果。本文以现代互联电力系统中,由于阻尼不足产生的区间低频振荡现象为研究对象。重点研究计及时滞的广域附加区间阻尼控制,用现代控制理论的相关方法如基于模型的预测算法与LMI方法,克服广域信号的时滞对闭环系统稳定性的不良影响,丰富和拓展抑制系统区间低频振荡的方法。主要研究工作和取得的创新性成果如下：1)提出了基于模型预测的广域附加区间阻尼控制策略,克服无模型预测方法的可靠性差的不足。基于辨识得到的系统降阶状态空间模型,建立状态估计模型,然后以预测误差为校正环节的输入,建立输出预测模型。利用校正环节实时校正预测误差,由滞后输出量预测得到当前时刻的输出量,进而采用针对无时滞系统的控制理论设计反馈控制律。在校正环节中,采用固定参数或动态校正两种方法,其中动态校正根据预测误差,采用比例调节方法,进行误差校正。基于输出预测模型,提出了基于线性二次最优部分输出反馈的广域附加区间阻尼控制策略和基于滑模变结构控制的广域附加区间阻尼控制策略,以验证输出预测方法的有效性。本文的输出预测方法实现了沿系统状态轨迹,基于预测模型,根据预测误差,实时反馈校正的现代预测算法的主要功能。两区域四机算例系统上的仿真结果表明,输出预测模型能够实现对滞后输出量的预测估计,对不同的控制策略有较强的适应性。基于预测模型的广域阻尼控制器对时滞具有一定的不敏感特性,可以有效地抑制区间振荡模式。相对于仅施加本地PSS,基于预测模型的各种控制策略使系统区间阻尼得到明显增强。在输出预测模型中,相比于采用固定参数校正系数,采用动态校正方法,对抑制区间振荡更为有效。2)提出了可以直接求解滞后状态反馈矩阵的矩阵不等式定理,克服利用时滞闭环系统的稳定性判据设计广域附加区间阻尼控制策略的试探性本质和计算量大的不足。由两个已知的作为时滞系统稳定性判据的LMI定理,分别推导得到可以直接解出反馈控制律的矩阵不等式定理,对矩阵不等式中的非线性项做线性化处理,转化为LMI形式,进而将滞后状态反馈矩阵的求解转化为隶属于LMI的锥补问题,采用锥补线性化迭代算法进行求解。采用的两个LMI定理中,第二个LMI定理所含未知矩阵变量更少、算法计算量小、更易于收敛。基于上述求解滞后状态反馈矩阵的锥补算法,提出采用滞后状态观测器的滞后状态反馈广域附加区间阻尼控制策略。考虑广域输出量的时滞,改进并设计了滞后状态观测器,得到滞后状态估计,构建滞后状态反馈,并证明了闭环系统极点分离性的成立。由推导得到的第一个矩阵不等式定理,得到滞后状态反馈矩阵。提出了滞后状态直接反馈的广域附加区间阻尼控制策略。采用滞后状态直接反馈方法,直接推得滞后状态向量,构建滞后状态反馈；由推导得到的第二个矩阵不等式定理,得到滞后状态反馈矩阵。基于锥补算法的广域阻尼控制策略是实现直接利用滞后的广域信息进行附加区间阻尼控制的一种有效手段。两区域四机算例系统的仿真结果表明：基于锥补线性化迭代算法的广域阻尼控制器对时滞具有一定的不敏感特性,可以有效地抑制区间振荡。相对于仅施加本地PSS,控制器使系统区间阻尼得到明显增强。3)提出了一种时滞电力系统建模方法,以及广域附加区间阻尼控制的两层控制策略。克服目前在考虑时滞影响的电力系统广域附加区间阻尼控制研究中,通常将电力系统建模为一个无时滞系统,不能直接应用时滞系统控制理论的局限性。第一层控制即内层控制,对无时滞电力系统施加计及时滞的输出反馈控制,形成时滞闭环系统。第二层控制即外层控制,利用时滞系统的控制理论,进行反馈控制。在外层控制中,提出了动态输出反馈的控制策略,将状态反馈和状态观测器的设计统一考虑。依据一种时滞系统的二次型矩阵不等式形式的稳定性判据,采用LMI方法,求解动态输出反馈控制中状态反馈矩阵和观测器增益矩阵。提出了滞后状态直接反馈的控制策略,采用状态直接反馈方法,直接由滞后输出量得到滞后状态向量,进而依据一种时滞系统的二次型矩阵不等式形式的稳定性判据,采用LMI方法,求解得到滞后状态反馈矩阵。两层控制策略能够直接应用时滞系统控制理论,克服广域信号的时滞对闭环系统稳定性的不良影响,与将电力系统建模为一个无时滞系统,在反馈环节中处理时滞影响的单层控制策略相比,目的性更强、控制手段更直接。两区域四机系统和10机39节点算例系统的仿真结果表明：基于两层控制策略的广域阻尼控制器对时滞具有一定的不敏感特性,可以有效地抑制区间振荡。相对于仅施加本地PSS,控制器使系统区间阻尼得到明显增强。更多还原

【Abstract】 The inter-area low-frequency oscillation in large-scale power system has been a bottle neck limiting system’s transfer capacity and a key factor influencing system’s safe and stable operation. Although it plays an important role in suppressing power oscillation, limiting to the local feedback signals, the current power system stabilizer (PSS) cannot utilize the relative angular velocity or relative power-angle to form a closed loop and cannot effectively suppress the inter-area low-frequency oscillation in the interconnected power system. The wide area measurement system (WAMS) offers a new facility for the monitoring, analysis and control of power system and brings new opportunities to the damping control of the interconnected power system.In the damping control strategy that based on local signal, the influence of time delay is usually ignored as the delay is very small. However, in wide-area geographical distributed and interconnected power system, the time delay in collection, treatment and transfer of wide-area information reaches tens to hundreds of millisecond, which cannot be ignored. The signal transfer time delay usually deteriorates system performance, degrades system stability and make the controller unable to reach its ideal effect.This dissertation investigates the inter-area low-frequency oscillation phenomenon caused by inadequate damping in modern interconnected power system, focusing on the wide-area supplementary inter-area damping control considering time delay. To overcome the adverse effect on stability of the closed-loop system caused by the wide-area signal time delay, relative methods with regards to the modern control theory, such as model based prediction method and linear matrix inequality (LMI) method, which enrich and expand the methods of suppressing the inter-area low-frequency oscillation.The main research work and innovative achievements are as follows:(1) An inter-area supplementary damping control strategy based on output prediction is proposed to overcome the poor reliability of the prediction method that does not use system model. The open-loop state observer is established based on the reduced-order system state space model. Then the output prediction model is built in which prediction error is used as input and a correction module is also contained. The module is used to correct the prediction error, and then the current predicted output can be obtained by the model from the delayed output. The feedback control law can be designed via the control theory for the system without time delay. In the correction module, both the fixed parameter and the dynamic correction method can be applied. The latter proportionally corrects the prediction error. Then two different wide-area supplementary inter-area damping control strategies based on the output prediction model are proposed, i.e., linear quadratic optimal part output feedback control and sliding-mode control.The simulation result of the two-area and four-machine test system proves the effectiveness of the output prediction model and the adaptability to various control strategies. The damping controllers based on this model are insensitive to time delay to some extent, and has better effect on suppressing the inter-area oscillation. Compared with the case that only local PSS is installed, the controller can enhance the inter-area damping significantly. Simulation results show that the dynamic correction is more effective in the aspect of suppressing the system oscillation than the fixed parameter correction method.(2) A cone complementarity linearization iterative algorithm which can directly solve the state feedback control law is proposed to overcome the shortcoming of the damping control strategy based on a class of stability criterion of time delayed closed-loop system which essentially is a tentative method and has large amount of computation. Two matrix inequality theorems based on state feedback as an asymptotic stability criterion on time-delay system are deduced from two known linear matrix inequality theorems. The damping controller design is converted to a cone complementarity problem subjecting to linear matrix inequalities (LMIs) and solved by cone complementarity linearization iterative algorithm. In the applied two known LMI theorems, the second one contains less unknown matrix variable, less algorithm calculation amount and is easier to converge.Based on the cone complementarity linearization iterative algorithm, firstly, the wide area inter-area supplementary state feedback damping control strategy adopting the delayed state observer is proposed. Considering the time delay of the wide-area output, the delayed state observer is designed to obtain the delayed state estimation which will be used to construct the state feedback. And the delayed state feedback matrix is solved by the first matrix inequality theorem. Secondly, the state direct feedback wide-area supplementary inter-area damping control strategy is proposed. The state direct feedback method is applied to deduct the delayed state vector directly to be used to construct the state feedback. And the delayed state feedback matrix is solved by the second matrix inequality theorem.The damping control strategy based on cone complementarity linearization iterative algorithm is an effective method to implement this idea that can directly use the delayed wide-area signals to actualize the supplementary inter-area damping control. The simulation result of the two-area and four-machine test system proves the damping controller based on cone complementarity linearization iterative algorithm is insensitive to time delay to some extent, and has better effect on suppressing the inter-area oscillation. Compared with the case that only local PSS is installed, the controller can enhance the inter-area damping significantly.(3) A time delay system modeling method is proposed, and then a two-layer control strategy of wide-area inter-area supplementary damping control strategy is put forward to overcome the limitation of current wide-area supplementary inter-area damping control method in which power system is modeled without time delay and cannot directly apply the time delay system control theory. The first layer is the inner control, which applies the output feedback control considering time delay to the power system without time delay to constitute the time delayed closed-loop system. The second layer is the outer layer, which carries out feedback control aiming at the time delayed system model by using the control theory of time delayed system. For the outer control, firstly, the dynamic output feedback control strategy is proposed. The state feedback matrix and observer gain matrix in the strategy are solved by the LMI method based on a stability criterion of time delay system with quadratic matrix inequality type. Secondly, the delayed state direct feedback control strategy is proposed. The delayed state vector is obtained from the delayed output directly, and then the delayed state feedback matrix is solved by LMI method based on a stability criterion of time delay system with quadratic matrix inequality type.The two-layer control strategy can directly apply the time delayed system control theory to overcome the adverse effect on the closed-loop system stability caused by the time delay of wide-area feedback signals. Compared with the single-layer control strategy in which the controlled power system is established as a system model without time delay, and the time delay influence is treated in the feedback phase, the proposed two-layer control strategy is more direct and effective.The simulation results of the two-area and four-machine test system and 10-machine 39-bus New England test system prove the damping controllers based on the two-layer control strategy are insensitive to time delay to some extent and has better effect on suppressing the inter-area oscillation. Compared with the case that only local PSS is installed, the controllers can enhance the inter-area damping significantly.The simulation results of the two-area and four-machine test system show that the time delay stability margins provided by the two-layer damping controller and the damping controller based on cone complementarity algorithm are greater than that provided by the damping controller based on the output prediction.更多还原