Aggregation of exciter models for constructing power system dynamicequivalents

Constructing a dynamic equivalent for a power system involves several steps: the partition of the system into coherent areas, the coherent area aggregation, and the aggregation of the coherent generators and their control devices. In this paper we investigate the aggregation of exciter models. A trajectory sensitivity method is used to tune the aggregate exciter parameters of the reduced model. The optimal results are used to evaluate the aggregation from the DYNRED program and a weighted MVA method. A three-machine system with one coherent area satisfying the theoretical coherency conditions is used to investigate the impact of the variations of the individual generator, network, and exciter parameters on the aggregate exciter model parameters. The results are then applied to the exciter aggregation of a larger 48-machine system     

Fixed-order controller for reduced-order model for damping of power oscillation in wide area network

The interconnected power systems are complex and stabilizing control design still remains challenging task. The use of wide area monitoring system (WAMS) offers an integrated measurement-based and model-based control, which suits to the operation of large electric power system (EPS), along with online analysis. This paper presents a study on fixed-order controller design for equivalent network of coherent generator in order to stabilize inter-area electromechanical oscillations in the system. Firstly, the coherent generators in each area of large EPS are determined by mutual information theory, which represents the dynamic equivalence. Then network of each area with input–output variables of the selected generator that participates dominantly is reduced to lower size by square-root variant of balanced truncation algorithm. The dynamics and important oscillation modes are verified in equivalent representation of each area. Finally a local controller (decentralized) in each coherent area and a centralized controller between two coherent areas for selected generator are designed by reducing the H^∞ norm of its closed loop transfer function as much as possible. These controllers feed supplementary control signal in addition to one fed by local conventionally tuned PSS. The decentralized controller for selected generator is fed by local bus power or generator’s speed signal. On other hand, the centralized controller uses difference of power flow/speed of generators as input signal to dampen the oscillations between equivalent networks of two areas. The simulation results reveal effective damping of power/speed oscillations achieved by designed controller with respect to conventional PSS implemented. The robustness of controller is verified for heavy and light load operating conditions.     

Damping inter-area oscillation by generation rescheduling based on wide-area measurement information

Inter-area oscillations are inherent to power systems which can be caused due to oscillation of two coherent groups of generators against each other with low or negative damping. Poorly damped oscillations can pose various problems such as limiting transfer capabilities and in more severe cases can lead to uncontrolled islanding causing system blackout. In this paper, for damping inter-area oscillation a new method based on the wide area measurement system (WAMS) and using generation rescheduling (GR) is proposed. The proposed algorithm consists of three tasks; identification of inter-area mode, determination the most effective generators for rescheduling and enhancing damping of inter-area mode by GR. In this approach, first by means of Independent Component Analysis (ICA) and modified Random Decrement (RD) techniques and using on-line power and rotor angle oscillation data provided by WAMS, the frequency and damping of the inter-area mode is identified. In the case of low damping of oscillation, by using mode shape of the inter area mode, generation rescheduling is applied for improvement of damping. In this paper, a non-model based method is adopted for estimating mode shape from the measured data like generator rotor speeds. The proposed approach is applied on a two area small system and IEEE 39-bus test system and the results demonstrate effectiveness of the method for enhancing oscillation damping.     

Damping control of inter-area oscillations in the European power system using aggregated models

In the first part of the paper, a new approach to the reduction of large dynamic network models is presented. This method is implemented in the program package PSD and is used here in an exemplary fashion to reduce the model of the European power system to a model usable for the solution of a number of problems. In the second part, the paper describes a new damping concept of inter-area oscillations in large power systems. Additionally installed second-level damping controllers are acting on the voltage regulator reference inputs of selected generators. They are using global information about the swing profiles of the inter-area oscillations to be damped. The damping controllers are designed as a H_∞-norm optimal decentral control system based on both a topological and a frequency range decomposition of the control task. The solution is demonstrated for the reduced model of the European system. Received: 30 April 2001/Accepted: 8 June 2001     

多区域单机等效法分析和控制故障后区间振荡

针对故障后系统的区间振荡,提出改进的单机等效法分析不同区域间的相互作用,并制定相应的控制措施。根据故障后各发电机功角的振荡轨迹,将系统划分为若干个主导振荡区域和非主导振荡区域,并将多区域系统进一步等效为单机无穷大母线(one machine infinite bus,OMIB)系统。定义并计算不同区域间的相对动能及OMIB系统动能,用于分析不同区域间的非线性相互作用。采用傅里叶频谱分析和Prony分析辨识OMIB系统参数,得到故障后系统的主导振荡模式及相应的阻尼比。基于上述分析,提出调整故障前各区域发电机出力的方法以减少区间的相对动能,抑制互联区域振荡。算法用于分析和控制IEEE5区域16机标准测试系统的故障后区间振荡。仿真结果表明,算法不但能准确辨识故障后的主导振荡模式,且能分析多种区间模式的非线性相互作用;控制措施显著地提升了系统阻尼,抑制了故障后系统的区间低频振荡。     

基于广域测量信息在线辨识低频振荡

全国电网的互联使区域间的低频振荡成为威胁系统稳定的关键因素之一,而基于全球定位系统（GPS）的广域测量系统（WAMS）的发展和应用为在线分析区间低频振荡模式乃至控制提供了新契机.因而,研究区间低频振荡模式的在线辨识算法成为实现低频振荡在线监测以及进行阻尼控制的重要理论问题.该文在讨论Prony方法本质的基础上,给出了一种新的模型阶数估计方法,提出根据广域测量系统（WAMS）的测量信息,采用多机组的功角及转速变量进行低频振荡辨识.结合工程实际提出了基于（WAMS）的研究低频振荡问题的实现方案,包括启动判据、数据预处理、阶次估计、模式提取和综合分析等步骤.8机36节点的算例结果表明：该方案具有系统性、直接性、噪声干扰小的特点,为低频振荡的监测和控制创造了条件.     

Optimal location of PWM based series compensator in a power system

This paper proposes a new approach for optimal placement of PWM based Series Compensator (PWMSC) in large power systems. The proposed approach is based on the Selective Modal Analysis (SMA) and dynamics index to damp out the inter-area oscillation modes. For this reason, first, SMA is used to calculate the low frequency modes of oscillation, and then Most Dominant Line (MDL) Table based on the dynamic index is proposed which shows the influence of active power flows of the transmission lines on inter-area modes of the power system. The parameters of the PWMSC damping controller are designed by optimization based approach for the purpose of damping inter-area oscillations in practical system. Optimal PWMSC placement is validated by comparing different candidate placements based on the total damping that they provide for system. The effectiveness of the proposed method is demonstrated on the 16-machine five-area power system for various network conditions.     

H∞ damping controller design in large powersystems

The design of an H_∞ controller for a thyristor controlled series VAr compensator to enhance the damping of an inter-area oscillations in a large power system is presented. The paper describes a comprehensive and systematic method of applying the H_∞ control design algorithm in power systems. Two methods to obtain a satisfactory reduced order system model, which is crucial to the success of the design, are described     

大区电网互联对电力系统动态稳定性的影响

研究了由区域电网间互联形成的互联电网动态稳定性的特点、低频振荡产生的原因，提出了互联系统动态稳定性的控制策略，并提出以下结论：励磁系统中自动电压调节器的负阻尼作用仍然是互联电网发生低频振荡的主要原因；PSS 已被证明是阻尼低频振荡的最有效、经济的装置，对本地振荡模式和区域间振荡模式均有很好的效果；直流调制、可控串补及可控静补对改善系统阻尼可有重要作用，今后应对这些领域进行更多的研究。     

抑制区域间低频振荡的FACTS阻尼控制

随着电力系统规模的不断扩大,区域间低频振荡正成为限制电网传输能力的瓶颈。对少数发电机组安装PSS来抑制区域间低频振荡很难有好的效果。但FACTS因其安装地点的灵活性及良好的动态性能而给抑制区域间振荡提供了新的手段。为此,利用相角补偿原理,设计控制器持续减小区域间的振荡能量,以此来实现区域间阻尼控制。以SVC为例详细说明附加阻尼控制器的设计,通过PSASP软件下的仿真结果表明,具有附加阻尼控制作用的SVC能有效地抑制区域间低频振荡。另外,对其它几种常用的FACTS器件也设计了阻尼控制器,并同样通过了PSASP下的仿真验证,阻尼效果很好。以上结果证明利用FACTS可实现区域间低频振荡的阻尼控制。     

A new approach for online coherency identification in power systems based on correlation characteristics of generators rotor oscillations

In this paper, a new approach for identifying coherent groups of generators in power systems based on the correlation coefficients between rotor angle/speed oscillations of generators is presented. The method uses a newly proposed clustering index based on the correlation coefficients of generators oscillations which is able to classify any number of generators into coherent groups. The proposed approach uses real time data of generators oscillations via VAMS/PMUs, so it is able to easily take into account the effect of system detailed modeling, generators and system controllers and type of events. The proposed correlation index evaluated from the real time behavior of generators in time-domain following disturbances are used to evaluate the degree of coherency between any pair of generators. The generators’ rotor angles and speeds can be obtained from synchronized measurements of system quantities using PMUs. Hence, the proposed method could be integrated into a wide-area measurement system enabling fast identification of coherent groups of generators. It is shown that by using COI of the aggregated in-phase coherent groups, the frequency of the inter-area mode can be evaluated. The proposed method is tested on the IEEE 39-bus with 10 generators and realistic power system of Iran with 405 generators.     

Coordinated design of STATCOM and excitation system controllers for multi-machine power systems using zero dynamics method

FACTs devices are being used in transmission networks for increasing the power transfer limit and stability improvement. They also help damp out both local and inter-area low frequency oscillations. However, uncoordinated design of these devices with excitation systems may deteriorate the power system performance. Moreover, power system is a large, complex and nonlinear system, and the controllers that are designed based on linear control theories may have a detrimental effect on the system performance, especially when there are large disturbances occurring in the system. The design method of a nonlinear control technique, named zero dynamics is given in this paper to design the controllers of STATCOM and excitation systems coordinately for multi-machine power systems. This technique is able to provide the stability of both external and internal dynamic performances of the system. Simulations results clearly verify that the proposed method improves the power system stability.     

ILP-based multistage placement of PMUs with dynamic monitoring constraints

This paper addresses two aspects of the optimal Phasor Measurement Unit (PMU) placement problem. Firstly, an ILP (Integer Linear Programing) model for the optimal multistage placement of PMUs is proposed. The approach finds the number of PMUs and its placement in separate stages, while maximizing the system observability at each period of time. The model takes into account: the available budget per stage, the power system expansion along with the multistage PMU placement, redundancy in the PMU placement against the failure of a PMU or its communication links, user defined time constraints for PMU allocation, and the zero-injection effect. Secondly, it is proposed a methodology to identify buses to be observed for dynamic stability monitoring. Two criteria, which are inter-area observability and intra-area observability, have been considered. The methodology identifies coherent groups in large power systems by using a new technique based on graph theory. The technique requires neither full stability studies nor a predefined number of groups. Also, a centrality criterion is used to select a bus for monitoring each coherent area and supervise inter-area oscillations. Then, PMUs are located to ensure complete observability inside each area (intra-area monitoring). Methodology is applied on the 14-bus test system, the 57-bus test system with expansion plans, and the 16-machine 68 bus test system. Results indicate that the optimization model finds the optimal number of PMUs when the PMU placement by stages is required, while the observability at each stage is maximized. Additionally, it is shown that expansion plans and particular requirements of observability can be considered in the model without increasing the number of required PMUs, and the zero-injection effect, which reduces the number of PMUs, can be considered in the model.     

A new methodology for identification of critical lines using damping sensitivity analysis

When an inter-area mode dominates a low-frequency oscillation in a stressed condition, control of the active power flow of interface lines, with compensating devices, can effectively reduce the electromechanical power oscillations. In general, interface lines in which inter-area oscillations are large are considered to be good locations for installation of compensating devices. A sensitivity analysis with respect to change in active power flow can provide an important factor in electric power system operation. This paper proposes a new methodology to calculate the damping sensitivity with respect to change in active power flow, which can be useful for accurate selection of critical lines from the viewpoint of small-signal stability. In the proposed methodology, a damping sensitivity index is used to select the critical lines to damp power system oscillations. This paper describes how to derive the damping sensitivity for the selected mode and illustrates an example applying the proposed algorithm to a simple two-area system and the New England 39-bus test system.     

Damping of inter-area and local modes by use of controllablecomponents

This paper deals with damping of inter-area and local electromechanical oscillation modes using controllable series capacitor (CSC) and controllable shunt capacitor (SVC). The impacts of SVC and CSC on the structure of the system closed loop matrix are investigated. By analyzing the sensitivities of the system inter-area and local modes to the control action of the controllable devices, some general conclusions concerning the damping of inter-area and local modes are made. A numerical example is provided to support the analytical findings. This paper provides an insight and understanding in the basic characteristics of damping effects of the studied devices. The insight is obtained by the study of a simple power system which exhibits both inter-area and local power swings. The understandings and findings could form the basis in analysis of realistic and more complex systems     

Fixed-order loop shaping robust controller design for parametric models to damp inter-area oscillations

The inter-area oscillations are common in power systems and can occur due to the changes in the load or generating power especially in long transmission lines. This paper presents the design of a robust fixed-order loop shaping controller to damp out the inter-area oscillations and to enhance the stability of the power system. The proposed loop shaping method is based on the shaping of the open-loop transfer function in the Nyquist diagram through minimizing the quadratic error between the actual and the desired open loop transfer functions in the frequency domain. The proposed method is robust with respect to multi-model uncertainty. Despite other robust controller design methods, the proposed approach deals with the entire system i.e. there is no need to reduce the system and still leads to a lower order controller. In addition, most of the robust methods are heavily dependent on selecting some weight filters which is not required in the proposed approach. This method is applied to the two-area four-machine system and 68 bus system and the effectiveness and robustness of the proposed method in damping inter-area oscillations are validated using case studies.     

利用相关分析的区间振荡振型快速估计方法

为了提高区间振荡动态特性中振型信息的有效获取速度,提出了一种利用相关分析的快速估计区间振荡振型的新方法.它首先通过一个由先验知识设计并在线校正的低通或带通滤波器,从电力系统广域测量系统(wide area measurement system,WAMS)采集的各联络线有功功率信号中提取以弱阻尼模式为主导的分最信号,然后...     

电力系统聚合理论概念及研究框架

针对分布式发电、大规模可再生能源及电动汽车等新型主动体入网引起电网运行的安全、稳定及经济性问题,将电力系统与生态学、社会学结合,提出电力系统聚合理论的分析方法.重点研究聚合体的特性建模、聚合过程与评价体系、聚合体间的管理框架及相互关系,进而构建主动体聚合化的资源系统、安全防卫系统、再建系统和智能控制系统等四大系统,实现电力系统的聚合化.进一步对基础聚合单元微电网和高级聚合单元多微电网、虚拟电厂（VPP）、超级电网等各种聚合体的结构、物理及社会特性进行研究,探讨聚合体运行过程中的演变规律和互动方式等动态特性.电力系统聚合理论是一崭新的智能电网基础理论,适应大量智能化、多元化、分布式主动体接入智能电网的发展需求.     

基于相似度同调的双馈风电场聚合研究

文章提出了一种基于相似度同调的双馈风电场聚合方法。首先利用Prony算法提取各风电场中双馈风机故障下功率响应曲线的动态特征,基于相似理论确定双馈风机间振荡模式中相似部分,应用相似振荡模式中的频率、阻尼、幅值等信息定义了双馈风机同调判别的相似度量化指标并确定同调机群。然后,根据双馈风机的外特性,提出功率聚合算法,即以双馈风机输出有功功率为权重求取等值机的暂态内电势并确定等值母线及等值机参数。该方法从同调机群识别、同调母线聚合、同调机群参数聚合等方面,系统地解决了不同双馈风电场的同调聚合问题。参数聚合方法不仅解决了聚类分群的复杂性和局限性,而且有效保留原系统中电气与结构特征。最后以实际云南电网中某地区风电场为例进行仿真验证。     

电力系统受迫振荡检测与自适应振荡抑制研究

电力系统受迫振荡的振荡频率与系统跨区域振荡模态接近,因而能够引发强烈振荡。文中首先提出了一种受迫振荡模态检测方法,其通过小信号分析方法得出系统在受迫扰动下对应受迫振荡模态的解析形式;同时提出一种不需要安装额外的功率振荡阻尼器的功率振荡阻尼控制策略用于抑制受迫振荡以及跨区域振荡。并通过改进的14机系统验证文中方法的鲁棒性和优越性。仿真算例证明本文所提方法对于外界扰动具有较强鲁棒性,且较传统方法具有明显优越性。