Ward Equivalent Method Research Articles

Online Equivalent Method of External Network Based on Measurement Information

How to acquire the accurate equivalent network of external system in the interconnected power grid has always been a challenging issue in the fields of both academic and engineering. This paper proposes a new method for online equivalence of the external network based on the measurement information of the internal network. Firstly, it builds an equivalent network of the external system, including the coupled branches between each of the boundary node, the equivalent generators and the equivalent lines from corresponding boundary nodes to them. Then, based on the SCADA (Supervisory Control and Data Acquisition) measurement information, an optimization model to estimate the parameters of the equivalent network is constructed, with the minimization of the mismatch between the boundary’s measurement and the calculation value of the equivalent network being the objective and the parameters of each line of the equivalent network within the reasonable range being the constraints. In order to reduce the calculation scale, measure is adopted to remove the coupled lines whose electrical distances (or impedances) are larger than a relative big threshold. The impedance range of each line in the equivalent network is determined by ward equivalent method under the condition of maximum and minimum operation mode. The model is solved by interior point method, which owns the satisfactory convergency performance. The solution of the model makes each of the calculated value of the equivalent network at the boundary node closest to the measured value, while all the parameters of the equivalent network within a practical range. The results of an example demonstrate the validity and effectiveness of the model and method proposed in the paper.

A modified Ward equivalent based on sensitivity matrices for static security analysis

This letter proposes a modified Ward equivalent method (M‐Ward) for the static security analysis of electric network. The M‐Ward develops the external to boundary sensitivity matrices to track the change of the operation condition in the external network. Hence, the M‐Ward can guarantee the accuracy of the equivalent network along with the condition change of the external network. Simulation studies of static security analysis conducted on the IEEE 39‐bus system demonstrate that the results of M‐Ward are more accurate than those of the classic Ward and the extended Ward method. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Research on Method of Power System Electromagnetic Transient External System Equivalence Based on Fault Current Distribution

随着电力系统的重要性越来越高，仿真作为预防事故的重要手段也显得尤为必要，为提高仿真效率一般将仿真区域外的系统做一个等值，而目前常见的两种等值方法Ward等值法和网络等值法各有优缺点且无法满足大系统多节点的要求。针对以上问题，本文提出了一种基于动态分区的电力系统电磁暂态仿真外部系统等值方法，用来满足大系统多节点情况下的仿真需求，并提出了存在的问题及未来的发展趋势。 Due to fact that the importance of electric power system is higher and higher, the simulation as an important means of accident prevention is very necessary. In order to improve the simulation efficiency, an equivalent area is generally used for simulation system. Two common equivalent methods, Ward equivalent method and network equivalent method, have its advantages and disadvantages and cannot satisfy the requirement of large system more nodes. This paper, to solve above problems, according to a research unit based on the research and development of dynamic partitioning of power system electromagnetic transient simulation software, studies the use of two kinds of common external system equivalence method and dynamic partitioning method, and puts forward the existing problems and future development trend.

Sufficient and necessary condition of sensitivity consistency in static equivalent methods

Both power flow states and sensitivities between variables are important information in power system analysis and should be kept consistent before and after equivalence. The general sufficient and necessary condition for sensitivity consistency in equivalent methods is derived. Based on the proposed general condition, it is further derived that Thevenin equivalent method can keep sensitivity consistent before and after equivalence, whereas the specific preconditions for sensitivity consistency are required for the traditional Ward equivalent method and extended Ward equivalent method. These two Ward equivalent methods cannot meet the preconditions in general cases and may lead to significant errors. This conclusion is confirmed by simulation results of the IEEE 39-bus system and an actual power system with 661 buses.

Zonal Dynamic Equivalents Based on the Concept of Relative Electrical Distance

Abstract: This article presents a systematic approach to construct the zonal dynamic equivalents of a large-power system based on the concept of relative electrical distance (RED). The task of dynamic equivalencing is to eliminate the full model of the external system and replace it with an equivalent model, which has dynamic characteristics close enough to the full model. The dynamic equivalent models are used for large-scale power system offline transient stability analysis with large disturbance. Dynamic equivalencing also helps in reducing the computation burden and memory requirements in wide area monitoring system (WAMS) for online stability assessment. The procedure is illustrated on IEEE 39 bus system and on a practical 205 bus system consisting of three zones of Indian Southern grid, where an equivalent of a zone has been constructed. The simulation results of the original system and equivalent system are compared. The proposed approach is also compared with the existing Ward equivalent method and the results are found to be similar. The simulation results show that the developed equivalent system has close accuracy in representing the dynamic characteristics of the original system.

An ANN-Based Ward Equivalent Approach for Power System Security Assessment

This paper presents a novel hybrid Artificial Neural Network (ANN) and extended Ward-type equivalent approach for fast on-line voltage security assessment of power systems. The proposed approach maintains the desirable properties of the Ward equivalent method and can update online the parameters of the equivalent model when the topology of the external system changes. Moreover, fast boundary matching is achieved by using ANN. Test results demonstrate that the new approach is efficient and has good accuracy.

A hybrid artificial neural network (ANN) and Ward equivalent approach for on-line power system voltage security assessment

Abstract This paper presents a novel hybrid artificial neural network (ANN) and Ward-type equivalent approach for fast, on-line voltage security assessment of power systems. The proposed approach possesses the good properties of Ward equivalent method and can update the parameters of the equivalent model for representing real-time topology change of the external system. Moreover, the boundary equivalent power injection can be quickly matched using hybrid ANN. Test results demonstrate that the new equivalent model is efficient and has accurate response.