Vulnerability assessment is one of the main tasks in a Self-Healing Grid structure, since it has the function of detecting the necessity of performing global control actions in real time. Due to the short-time requirements of real time applications, the eligible vulnerability assessment methods have to consider the improvement of calculation time. Although there are several methods capable of performing quick assessment, these techniques are not fast enough to analyze real large power systems in real time. Based on the fact that vulnerability begins to develop in specific regions of the system exhibiting coherent dynamics, large interconnected power systems can be reduced through dynamic equivalence in order to reduce the calculation time. A dynamic equivalent should provide simplicity and accuracy sufficient for system dynamic simulation studies. Since the parameters of the dynamic equivalent cannot be easily derived from the mathematical models of generators and their control systems, numerical identification methods are needed. Such an identification task can be tackled as an optimization problem. This paper introduces a novel heuristic optimization algorithm, namely, the Mean-Variance Mapping Optimization (MVMO), which provides excellent performance in terms of convergence behavior and accuracy of the identified parameters. The identification procedure and the level of accuracy that can be reached are demonstrated using the Ecuadorian-Colombian interconnected system in order to obtain a dynamic equivalent representing the Colombian grid.

Identification of dynamic equivalents based on heuristic optimization for smart grid applications

A strategy to simultaneously tune power system stabilizers

Dynamic equivalence by an optimal strategy

This paper presents a new method for detecting the early stages of unstable conditions in large-scale power systems. A reduced order dynamic model is introduced for each control area that includes an aggregated generator and associated controllers. An innovative nonlinear observer proposed that can simultaneously estimate the parameters and states of the model benefiting from available online measurements. A sensitivity analysis is used to improve the efficacy and performance of the proposed estimator. The estimated states of the proposed equivalent generator model are then used to define a Real-Time Transient Stability (RTSA) index. The recommended RTSA index demonstrates to be a clear measure of the distance to instability and prevents economic losses due to blackouts and cascading system trips. The PSS/E simulation results on two case studies using show the excellent performance of the proposed index.

Real-Time Transient Stability Assessment Using Dynamic Equivalents and Nonlinear Observers

Heuristic optimization based approach for identification of power system dynamic equivalents

Dynamic equivalent has been a basic approach for analysis and computation of large scale-increasing interconnected power systems in China. Security defense of power systems and real-time monitoring of system states require more rapid and effective computation of large power grids. This paper introduces a solution for real-time dynamic equivalent of large multi-area power systems. It is based on real-time measurement data from Wide Area Measurement System and parameter identification. A parallel dynamic equivalent model composed of an equivalent generator and an equivalent synthesis load was put forward, in which the equivalent generator uses a 3rd order electromechanical transient model with damping while the equivalent synthesis load uses a static characteristic model considering both voltage and frequency. Identifiability analysis was carried out for this nonlinear dynamic equivalent model. In order to apply Laplace transformation-transfer function method, the model was firstly linearized. Particle Swarm Optimization algorithm was utilized for parameter identification of the dynamic equivalent model. For AC power systems, this model is verified on CEPRI 8-machine 36-bus example system. Load model and the style of disturbance are two remarkable factors that relate to the stability of the whole power system, which are fully considered in this paper. The simulation results show that the dynamic equivalent model can reflect the dynamic responses and the transient stability of the original system, no matter which is transient stable or unstable, angle unstable or voltage stable. When we change the load model in the original system, the static characteristic model with both voltage and frequency factors can throughout represents the dynamic behavior of the original system, which confirms its robustness of this dynamic equivalent model. All the simulation work was performed on PSASP.

A real-time dynamic equivalent solution for large interconnected power systems

In order to reduce the calculation amount of numerical simulation in transient analysis for large-scale power system, the network can be simplified by dynamic equivalence. This paper presents the coherency-based equivalent technique for power system with HVDC. Both frequency-domain method and weighting method are comprehensively used in parameter aggregation section in this paper. The adaptability of ac system equivalence to dc system is concerned, and the accuracy of dynamic equivalence of ac system is estimated using dc system disturbance. In numerical simulator PSASP, a dynamic equivalence of EPRI 8-machine 36-bus ac/dc hybrid power system can be derived, in which the specific model of HVDC system is considered. The comparisons of steady-state and dynamic response of original and equivalent system show that the dynamic equivalent model is feasible and available.

Zhou Yang

Papers

A real-time dynamic equivalent solution for large interconnected power systems

Study of Coherency-based Dynamic Equivalent Method for Power System with HVDC

Study of Power System Online Dynamic Equivalent Based on Wide Area Measurement System