Small signal stability analysis of PMSG based WECS with coordinated controller tuning

Summary form only given. Small signal stability analysis in a power system is typically concerned with electromechanical oscillations. For this purpose, it is adequate to model the transmission system using a constant admittance matrix. For torsional oscillations and HVDC interactions, the frequency of interest is much higher and the constant admittance representation is not sufficient. This paper proposes a hybrid model, which allows the parts of the transmission network in the vicinity of HVDC converters or any other dynamic devices to be modeled with their dynamics and the remaining parts to be modeled as constant admittances. The proposed hybrid methodology for small signal stability assessment is the main contribution of this paper. The proposed methodology is validated against an electromagnetic transient simulation program (PSCAD/EMTDC) using time responses. The proposed model and two other small signal models are compared against each other in the frequency domain using modal analysis.

As an effective solution for managing the access of distributed generations, medium-voltage AC/DC distribution networks are emerging as prospective forms of future distribution systems under the circumstances of increasing energy crisis and environmental pollution. Compared with the transmission systems, the medium-voltage distribution network has a lower voltage level, and the two-level voltage source converter (VSC) has become the preferred topologies for the interconnected converter. This paper proposes a comprehensive small-signal model for two-level-VSC-based medium-voltage AC/DC distribution systems, considering AC and DC distribution networks, AC filters, and all the controllers in the VSCs. The complex transformation between two dq coordinate systems in current studies is avoided based on the characteristics of dq transformation and discipline of the linearization. The impact of various control parameters on the small signal stability of the AC/DC distribution system is analyzed, and the feasible region of each parameter is obtained based on the small signal model proposed. Numerical calculations by MATLAB programming and electromagnetic transient simulations on PSCAD are compared. The results indicate that the small-signal mathematical model proposed in this paper can accurately represent the dynamic process of corresponding AC/DC distribution system, and the analysis of impact of parameters on small-signal stability can also be proved.

The paper studies the impact of realistic WideArea
\nMeasurement System (WAMS) time-varying delays on the
\ndynamic behaviour of power systems. A detailed model of
\nWAMS delays including pseudo-periodic, stochastic and constant
\ncomponents is presented. Then, the paper discusses numerical
\nmethods to evaluate the small-signal stability as well as the timedomain
\nsimulation of power systems with inclusion of such delays.
\nThe small-signal stability analysis is shown to be able to capture
\nthe dominant modes through the combination of a characteristic
\nmatrix approximation and a Newton correction technique. A case
\nstudy based on the IEEE 14-bus system compares the accuracy of
\nthe small-signal stability analysis with Monte-Carlo time-domain
\nsimulations. Finally, the numerical efficiency of the proposed
\ntechnique is tested through a real-world dynamic model of the
\nall-island Irish system.

With the rapid growth in the size of Henan grid, in the context of UHV networking, Henan power grid operation is facing a more complex mechanism and operating characteristics. Risks affecting the security and stability will be more subtle. There are more and more problems in frequency oscillation. The power system has much more generators and dimension after interconnection. Small signal stability analyzing eigenvalue complex and longer, which greatly reduces the work efficiency. This paper which based on Henan power system stability diagnostic platform developed technology based on multi-band parallel algorithm for small signal stability analysis. The analysis of the small signal stability eigenvalue calculation is assigned to a different platform computing nodes simultaneously. Then this method is applied to Henan grid in the year of 2012. The results show that the small signal stability algorithm which based on the multi-band can ensure the correctness of calculations. Simultaneously, calculation time is greatly reduced and the work efficiency is improved. The practice has a strong role in the promotion.

Small signal stability analysis and control of the wind turbine with the direct-drive permanent magnet generator integrated to the grid

Small signal stability constrained optimal power flow model based on trajectory optimization

This paper provides a small-signal model and stability analysis of interconnected AC microgrids (MGs) connected through back-to-back converters (BTBCs). The proposed modeling method of the networked microgrids (NMGs) is derived and it is generalized for any number of NMGs through BTBCs. Different BTBC control parts are analyzed to study their impact on the NMG stability. The eigenvalue analysis and participation matrix are employed to identify dynamic modes of BTBC DC voltage controller. For two NMGs, main participating state variables and corresponding parameters in the dominant low-frequency modes (LFMs) are recognized, then acceptable ranges of the parameters are calculated using the sensitivity analysis (SA). The contribution of the control BTBC parameters including PLL and DC voltage controller parameters in the small-signal stability margin are shown. In addition, to show the BTBC control impact on the NMGs stability in the time domain, simulation results are provided for the two NMGs in SimPowerSystems/Matlab environment.

With the integration of large-scale wind farm of direct-driven permanent magnet synchronous generator (PMSG) type into power systems, the impacts on the existing power system have to be evaluated elaborately and systematically. This paper will discuss the impact of grid-connected wind farm of PMSG type on power system small signal stability. First, a simplified practical model of wind farm of PMSG type is derived for analyzing small signal stability in this paper. The rotor-flux-oriented control strategy is applied in the modelling of PMSG. Second, the simulation scenario involving replacing synchronous generator with wind farm of PMSG type based on the IEEE 3-generator-9-bus test system as benchmark is carried out to conduct the eigenvalue analysis and to assess the effect of wind farm of PMSG type on power system small signal stability. Finally, some preliminary conclusions and comments are drawn according to the simulation results.

Modern Power systems are designed for the fine tuning of frequency and less tolerance for system frequency deviation from nominal value. The Power System is dynamically subjected to the small perturbations of load leading to non-oscillatory Instability due to insufficient damping. The article entente the single area and two area load frequency control and small signal stability analysis. It dispenses the simulation of single area and two area systems with small perturbations of load, with three cases for both kinds of power systems. Case1 without any controller, case2 with PI controller and case3 with Fuzzy Controllers. The simulation is carried out for both single area and two area power systems with all three cases. In the first part of the case study, the simulation results of single area power system for all three cases have been presented. In the second part, the simulation results of two area power system for all three cases have been presented. The simulation results demonstrate the effectiveness of Fuzzy Control perpetuates the frequency with in the endurable range of frequency and subsequently it ensures the small signal stability of both the Power systems against load disturbances.

Research on Power Transmission Capability of VSC-HVDC Based on Second Order LADRC

Regular load generation imbalances aka power system small disturbances in a network is always a matter of great concern which lead a major task of stability improvement to the technicians. Moreover when in place of single area network, there comes multi-area multi-machine power system, the overall dynamics becomes very integrated and complex to analyze. To suppress the oscillations of the system state variables i.e. to keep their deviation within some limit for a long period during small disturbances caused by load swinging or others , small signal analysis is needed first in place. Till date extensive researches has been done developing many toolboxes to analyze small signal stability like PSAT, SSST, PST, PAT, PSS/E, DigSILENT, EUROSTAG, SimPow and others. Among all PSAT is the most recommended and used software for the purpose. In this work a new algorithm has been developed to analyze the classical two-area four- machine system which is compared with PSAT's ( Power system analysis toolbox) result and literature's result. It came out that there's a significant amount of inaccuracy in PSAT's outcome and inter-area oscillation mode is found to be the most critical zone for analysis rather than local modes of oscillations in power system network.

This paper presents a method to find the dynamic stability margin of power system using genetic algorithm. Power systems are subjected to wide range of operating conditions. Modern power systems are equipped with fast-acting protective devices for transient stability problems. Hence, power systems are operated above the transient stability limit. The dynamic behaviour of system can be evaluated using small signal stability analysis. The maximum loading to which the system can be subjected can be obtained by observing the eigenvalue variations of the system under different loading conditions. The loading for which system exhibits a pair of imaginary eigenvalues is the maximum loading limit. Beyond this limit, the system will become unstable. The loading for which the power system exhibits imaginary eigenvalues is evaluated by using genetic algorithm. The dynamic stability margin is evaluated for a 3-machine 9-bus system. The efficacy of the proposed method is tested for the power system including conventional power system stabilizers (CPSS).

This paper reports a new technique for achieving optimized design for power system stabilizers. In any large scale interconnected systems, disturbances of small magnitudes are very common and low frequency oscillations pose a major problem. Hence small signal stability analysis is very important for analyzing system stability and performance. Power System Stabilizers (PSS) are used in these large interconnected systems for damping out low-frequency oscillations by providing auxiliary control signals to the generator excitation input. In this paper, collective decision optimization (CDO) algorithm, a meta-heuristic approach based on the decision making approach of human beings, has been applied for the optimal design of PSS. PSS parameters are tuned for the objective function, involving eigenvalues and damping ratios of the lightly damped electromechanical modes over a wide range of operating conditions. Also, optimal locations for PSS placement have been derived. Comparative study of the results obtained using CDO with those of grey wolf optimizer (GWO), differential Evolution (DE), Whale Optimization Algorithm (WOA) and crow search algorithm (CSA) methods, established the robustness of the algorithm in designing PSS under different operating conditions.

The focus of documented research in this paper is the Low Voltage Ride Through (LVRT) capability of electric grid connected Wind Energy Conversion System (WECS) using Takagie-Sugeon (TS) type fuzzy controller. The increased deployment of Wind Turbine technology in modern power systems makes the LVRT capability of WECS one of the important research topics. Consequently, to avoid power network instability, power utilities defined technical specifications for modern WECS. These specifications are known as Grid Codes and are further categorized as static and dynamic requirements. The LVRT capability falls under the category of dynamic requirements of Gird Codes. The most frequently and extensively used generator for wind turbines is the Doubly Fed Induction Generator (DFIG) due to its lower cost, less power loss, variable speed, and four-quadrant operation. However, DFIG based WECS are highly sensitive to electric network disturbances because the stator of the DFIG is directly connected to the power system. Therefore, in this research study, the main attention is drawn towards the control of power electronic interface i.e., grid side converter of DFIG based WECS. The simulation results of symmetrical and asymmetrical faults, with different fault injection locations, are analyzed in order to provide a comprehensive understanding of the impact of electric grid disturbances on WECS. The results of the TS-type fuzzy controller are compared with the PI controller to illustrate the effectiveness of the fuzzy controlled DFIG based WECS. The aforementioned comparison of simulation results demonstrated that the transient stability of WECS is considerably improved by using TS type fuzzy controller. Thus, it is concluded that the TS-type fuzzy controller can be an efficient and promising solution for modern DFIG based WECS.

The power system small signal stability analysis considering wind generation intermittence is studied comprehensively in this paper. The modelling of doubly‐fed induction generator (DFIG) involving the converters with application of stator flux‐oriented vector control strategy is addressed briefly. In order to reveal how the intermittent nature of wind power affects the operating behaviour of an existing power system, a probabilistic small signal stability analysis method based on Monte Carlo simulation technique is proposed to explore and exploit the impact of intermittent grid‐connected wind power on small signal stability. The IEEE New England test system is applied as benchmark to verify the proposed model and approach. Total 3 scenarios are elaborately designed to figure out the potential relationship between the small signal stability indices and the wind generation intermittence. Finally, some preliminary conclusions and comments were drawn based on the numerical simulation results. Copyright © 2010 John Wiley & Sons, Ltd.