Reduced Order Equivalent Model Research Articles

Static analysis of corrugated lattice-core sandwich panels using VAM-based model

To investigate the mechanical properties of the composite sandwich panel with complex single- and double-layer corrugated lattice-cores (CSP-CLCs), a simplified analytical frame is developed by decoupling the original 3D model into a unit cell-based analytical model (providing equivalent plate properties) and a 2D reduced-order equivalent model (2D-REM) based on the variational asymptotic method (VAM). The validity of the equivalent plate properties and the equivalent model for CSP-CLCs is compared with the three-dimensional refined plate model (3D-RPM) under different cases, including static analysis under tension–bending coupling, global buckling analysis, second-order analysis, and local field recovery. The results of 2D-REM agreed with those of 3D-RPM, and the calculation time is greatly reduced. Subsequently, the effect of geometric parameters on the effective performance was comprehensively investigated, which helped to improve the mechanical properties of corrugated lattice-core sandwich plates. The innovation is that the present 2D-REM achieves a good balance between effectiveness and accuracy. Furthermore, the tailoring of unit cells can provide convenience for parameter analysis.

Structural analysis of composite sandwich plates with enhanced pyramid lattice core using VAM-based reduced-order equivalent model

To overcome the issues of low face sheet–core interface strength and out-of-plane bearing capacity in the traditional pyramid lattice sandwich structure, a composite sandwich plate with enhanced pyramid lattice core (CSP-EPL) is investigated. A two-dimensional reduced-order equivalent model (2D-REM) based on the variational asymptotic approach is developed to study its static and dynamic responses. The accuracy and efficiency of the proposed model are verified by comparison with three-dimensional finite element (3D-FEM) results under different boundary conditions, including global static displacement, global buckling, local field recovery, and free and forced vibration. The predicted results of 2D-REM are in good agreement with those of 3D-FEM, and the computational efficiency is improved. Finally, the influence of geometric parameters of type III reinforcements on the equivalent stiffness is thoroughly examined, which helps to further reduce the weight and improve the bearing capacity of CSP-EPL.

Harris hawks optimization for model order reduction of power system

This paper aims to investigate the application of Harris hawks optimization (HHO) optimization for the solution of model order reduction (MOR) problem of power system application. The proposed approach is implemented to determine the reduced order equivalent model of large-scale power system model. The obligations encountered by the higher-scale model like stability, calculative effort and problem into local optima can be enhanced by this propounded methodology. These yielded reduced models have been tried in addition to the existing algorithms and the obtained results are contrasted considering various technical parameters to accomplish its effectiveness, reliability and robustness of the adopted strategy. Thus, superior performance of the proposed method is demonstrated. The validation of the methodology in terms of error index, time and frequency domain outputs, convergence curves with scalability of the approach are outlined in the investigation of the system.

Analysis and Performance Enhancement of Wireless Power Transfer Systems With Intended Metallic Objects

While detection of foreign or unintended metallic objects is an important topic for wireless power transfer (WPT), operation of WPT systems with intended metallic objects is largely an unchartered territory. This article presents a methodology for analyzing the effects of intended metallic object on a WPT system through the study of the magnetic field distribution and the use of a reduced-order equivalent model of the systems for comparing the WPT system with and without the metallic object. The methodology is applied to a metallic corona ring of low resistance used with a WPT system. The analysis quantifies how an intended metallic object could change the magnetic coupling between the transmitter and receiver coils, and alter the equivalent resonant tank parameters of the WPT system. Recompensation of the resonant tank can only enhance the power transfer capability but not the energy efficiency. The theory and practical verification of a new performance-enhancement method based on a combination of recompensating the resonant tanks and maximizing the equivalent mutual inductance of the Tx and Rx coils is presented. Such methodology provides a general approach to analyze WPT systems with or without relay resonators in the presence of intended metallic objects.

An Equivalent Model of Wind Farms for Torsional Vibration Analysis

Torsional vibration of wind turbines can be excited by the small electrical disturbance from the power system, which can cause damage to the shaft. In this paper, based on the established model of fixed speed induction generator (FSIG), the small signal model of the FSIG-based wind farm is developed according to the step by step transfer of the state variables of the differential equations. Then through similarity transformation of the state matrix, a novel equivalent model of the multi-machine infinite-bus system is derived. In this model, the original N–FSIG wind farm is decomposed into N-1 identical independent single-machine infinite-bus subsystems and one modified single-machine infinite-bus subsystem. Finally, simulations are performed in Matlab/Simulink and results comparison between the small signal model without equivalence and the proposed equivalent model is conducted extensively. The results show that the torsional vibration modes are reserved completely in the reduced order equivalent model. In addition, the obtained torsional vibration frequencies match well with those from the small signal model without equivalence, indicating the effectiveness and robustness of the equivalent model. Through modal analysis, it is also found that the torsional vibration is excited in both the disturbed FSIGs and the undisturbed ones. Besides, the obtained results are also verified through time-domain simulation.

Reduced-order equivalent model to large power networks derived from its spectral dispersion

This paper describes a general methodology for identification of a reduced-order dynamic equivalent with modal frequency distribution to large power networks, derived from its frequency-varying response. The method is used to define a state space model with modal frequency dispersion established from both, the application of the empirical orthogonal functions (EOFs) analysis and vector fitting (VF) procedure for rational functions approximation from frequency-domain data sets. Initially, our approach uses orthogonal modes of major contributions of spectral dispersion derived from the EOFs analysis to construct a reduced-order approximation with applications to multiple-input, multiple-output (MIMO) linear-time invariant (LTI) systems. This approximation defines an optimal distributed solution to the frequency-varying data set, where their fundamental properties are based on the interpretation of pre-selected frequencies contained into the eigenvectors of a cross-spectrum matrix. Once the reduced-order empirical modal decomposition is derived, its coefficients are used in the VF procedure in order to generate a rational function approximation into a frequency band with particular level of kinetic energy with applications to MIMO systems. Additionally, the reduced-order equivalent network in a state space model is derived from a VF, which can be efficiently incorporated in a power network simulator to electromechanical studies of multimachine dynamics with modal frequency splitting. Finally, an example for large power networks is examined to both demonstrate the effectiveness for fitting reduced-order dynamic equivalents and to capture its modal coherence and frequency distribution.

Coordinated application of FACTS controllers to damp out inter-area oscillations

Abstract This paper proposes a systematic analysis and design procedure for simultaneously determining the best locations and input signals of flexible AC transmission system (FACTS) devices in order to damp out inter-area oscillations. First, a modified modal power flow oscillation flow method is developed to determine the nature of the energy exchange over the transmission network in the presence of FACTS devices. With this method, the modal distribution along critical system paths is identified, and the contribution of each machine and network device is computed. Controllability and observability studies are then used to assess the effect of existing FACTS controllers on system damping as well as to identify optimal locations for new devices. The proposed procedure is demonstrated on a 46-machine, 190-bus reduced-order equivalent model of the Mexican interconnected system that includes several static VAR compensators.

Reduced Order Equivalent Models for Transient Stability Studies: Application to the Power System of Egypt

In this paper, the dynamic equivalent models of the Unified Power System of Egypt (UPS) are obtained based on the RMS coherency approach. The validity of these reduced order models is checked by calculating the time response of the system variables under different disturbances. Analysis of the effect of system topology on the dynamic equivalent models is made. The results obtained show the significant reduction in computation efforts required for transient stability studies, while keeping a reasonable accuracy of simulation.

Derivation of equivalents for dynamic security assessment

A method is described by which the order of interconnected power systems is reduced. When the system under study is composed of a main system and several subsystems connected to the main system, the method gives an equivalent model to each subsystem with far fewer generators, even when each subsystem is connected to the main system at more than one point. The paper also discusses the data that needs to be sent from each subsystem when it is expressed by a reduced-order equivalent model. A numerical example of a 250-bus and 61-machine system shows that the method is effective and causes no loss of accuracy. Although the proposed method provides an accurate reduced-order model, it is rather time-consuming, because it is based on the linearized dynamic equations of the system, and their eigenvectors are needed. This problem must be solved before practical use of the method can proceed.

Derivation of dynamic equivalents for stability analysis

A method of deriving a reduced-order equivalent model for stability studies of interconnected power systems is presented. Where the system under study is composed of a main system and interconnected subsystems, this method gives an equivalent model to each subsystem with fewer generators, so that, as far as the transient behaviour of the main system is concerned, the computing cost is greatly reduced by using these equivalents instead of the original subsystems. A numerical example applied to a 930 bus and 369 machine system shows that the reduction obtained by this method is quite effective with no loss of response accuracy.