Aanalysis of the impact of grid-forming doubly-fed induction generator parameters on transient stability and Small-signal stability

In order to utilize a Static Synchronous Series Compensator (SSSC) in the steady state condition, it is to be controlled by several modes. The most important control modes of the SSSC are constant voltage mode, constant impedance mode, and constant power control mode. Besides, this device may be furnished with supplementary controllers, such as damping controls, to enhance the dynamic performance of system. In this paper, the influence of various SSSC control modes on small signal and transient stability of a part of the Iran national grid is investigated. Next, the performance of power oscillation damping (POD) is evaluated for different input signals. The simulation results demonstrate that the utilization of the SSSC in the constant impedance mode improves both the small signal and transient stability better than other control modes.

The targeted and current development of wind energy in various countries around the world reveals that wind power is the fastest growing power generation technology. Among the several wind generation technologies, variable speed wind turbines utilizing doubly fed induction generators (DFIGs) are gaining momentum in the power industry. With the increase in penetration of these wind turbines, the power system dominated by synchronous machines will experience a change in dynamics and operational characteristics. Given this assertion, the present paper develops an approach to analyze the impact of increased penetration of DFIG based wind turbines on transient and small signal stability of a large power system. The primary basis of the method is to convert the DFIG machines into equivalent conventional round rotor synchronous machines and then evaluate the sensitivity of the eigenvalues with respect to inertia. In this regard, modes that are both detrimentally and beneficially affected by the change in inertia are identified. These modes are then excited by appropriate disturbances and the impact of reduced inertia on transient stability performance is also examined. The proposed technique is tested on a large test system representing the Midwestern portion of the U.S. interconnection. The results obtained indicate that the proposed method effectively identifies both detrimental and beneficial impacts of increased DFIG penetration both for transient stability and small signal stability related performance.

The goal of this study was to evaluate the small signal and transient stability of the Western Electric- ity Coordinating Council (WECC) under high penetrations of renewable energy, and to identify control technologies that would improve the system performance. The WECC is the regional entity responsible for coordinating and promoting bulk electric system reliability in the Western Interconnection. Transient stability is the ability of the power system to maintain synchronism after a large disturbance while small signal stability is the ability of the power system to maintain synchronism after a small disturbance. Tran- sient stability analysis usually focuses on the relative rotor angle between synchronous machines compared to some stability margin. For this study we employed generator speed relative to system speed as a metric for assessing transient stability. In addition, we evaluated the system transient response using the system frequency nadir, which provides an assessment of the adequacy of the primary frequency control reserves. Small signal stability analysis typically identi es the eigenvalues or modes of the system in response to a disturbance. For this study we developed mode shape maps for the di erent scenarios. Prony analysis was applied to generator speed after a 1.4 GW, 0.5 second,more » brake insertion at various locations. Six di erent WECC base cases were analyzed, including the 2022 light spring case which meets the renewable portfolio standards. Because of the di culty in identifying the cause and e ect relationship in large power system models with di erent scenarios, several simulations were run on a 7-bus, 5-generator system to isolate the e ects of di erent con gurations. Based on the results of the study, for a large power system like the WECC, incorporating frequency droop into wind/solar systems provides a larger bene t to system transient response than replacing the lost inertia with synthetic inertia. From a small signal stability perspective, the increase in renewable penetration results in subtle changes to the system modes. In gen- eral, mode frequencies increase slightly, and mode shapes remain similar. The system frequency nadir for the 2022 light spring case was slightly lower than the other cases, largely because of the reduced system inertia. However, the nadir is still well above the minimum load shedding frequency of 59.5 Hz. Finally, several discrepancies were identi ed between actual and reported wind penetration, and additional work on wind/solar modeling is required to increase the delity of the WECC models.« less

The improved efficiency and controllability inherent with the doubly fed induction generators (DFIGs) is bringing this technology to the forefront of power industry. However, the dynamic behavior of these machines is different from those of synchronous machines. Apparently, the large penetration of these machines entails a change in dynamics and operational characteristics of the system as a whole. Given this assertion, the present paper develops an approach to analyze the impact of increased penetration of DFIG based wind turbine generators on transient and small signal stability of a large power system. The primary basis of the method is to convert the DFIG machines into equivalent conventional round rotor synchronous machines and then evaluate the sensitivity of the eigenvalues with respect to inertia. In this regard, modes that are both detrimentally and beneficially affected by the change in inertia are identified. These modes are then excited by appropriate disturbances and the impact of reduced inertia on transient stability performance is also examined. The proposed technique is tested on a large test system representing the Midwestern portion of the U.S. interconnection. The results obtained indicate that the proposed method effectively identifies both detrimental and beneficial impacts of increased DFIG penetration both for transient stability and small signal stability related performance.

The number of Doubly Fed Induction Generator (DFIG)-based wind power generator is increasing because of its good efficiency and controllability. Power Oscillation Damping control for power system stabilization is expected to be implemented in the DFIG, and a few works have so far discussed it. This paper proposes a control parameter optimization method considering transient response to improve not only small signal stability but also transient stability. Moreover, to improve both transient and small signal stability, a combined control method with switching control is proposed. The effectiveness of proposed method is confirmed by eigenvalue analyses and time domain simulations.

The targeted and current development of wind energy in various countries around the world reveals that wind power is the fastest growing power generation technology. Among the several wind generation technologies, variable speed wind turbines utilizing doubly fed induction generators (DFIGs) are gaining momentum in the power industry. With the increase in penetration of these wind turbines, the power system dominated by synchronous machines will experience a change in dynamics and operational characteristics. Given this assertion, the present paper develops an approach to analyze the impact of increased penetration of DFIG-based wind turbines on transient and small signal stability of a large power system. The primary basis of the method is to convert the DFIG machines into equivalent conventional round rotor synchronous machines and then evaluate the sensitivity of the eigenvalues with respect to inertia. In this regard, modes that are both detrimentally and beneficially affected by the change in inertia are identified. These modes are then excited by appropriate disturbances and the impact of reduced inertia on transient stability performance is also examined. The proposed technique is tested on a large test system representing the Midwestern portion of the U.S. interconnection. The results obtained indicate that the proposed method effectively identifies both detrimental and beneficial impacts of increased DFIG penetration both for transient stability and small signal stability related performance.

Optimization of damping controller for PSS and SSSC to improve stability of interconnected system with DFIG based wind farm

This paper proposes a novel unified prediction approach for both small-signal and transient rotor angle stability as opposed to other studies that have only addressed transient rotor angle stability. Deep learning techniques are employed in this paper to train an online prediction model for rotor angle stability (RAS) using the voltage phasor measurements which are collected across the entire system. As a result, the trained model provides a fast yet accurate prediction of the transient stability status when a power system is subjected to a disturbance. Also, if the system is transiently stable, the prediction model updates the power system operator concerning the damping of low-frequency local and inter-area modes of oscillations. Therefore, the presented approach provides information concerning the transient stability and oscillatory dynamic response of the system such that proper control actions are taken. To achieve these objectives, advanced deep learning techniques are employed to train the online prediction model using a dataset which is generated through extensive time domain simulations for wide range of operating conditions. A convolutional neural network (CNN) transient stability classifier is trained to operate on the transient response of the phasor voltages across the entire system and provide a binary stability label. In tandem, a long-short term memory (LSTM) network is trained to learn the oscillatory response of a predicted stable system to capture the step-by-step dynamic evolution of the critical poorly damped low-frequency oscillations. The superior performance of the proposed model is tested using the New-England 10-machine, 39-bus, IEEE 16-machine, 68-bus, 5-area and IEEE 50-machine, 145-bus test systems and is verified with time domain simulation.

A significant influence of a static synchronous series compensator (SSSC) on the transient and small-signal stability is demonstrated using the example of transients in a 500 kV network of a powerful hydroelectric power plant (HPP). Currently, the maximum allowable power output from a HPP is limited on the level of 75% of the installed capacity by the condition of maintaining transient stability. In order to increase the allowable power output of the plant, the installation of two SSSC on outgoing 500 kV overhead lines is considered. The proposed option of installing the SSSC in a 500 kV network increases the limits of transient stability of the HPP and increase the energy output without additional network reinforcements. The inclusion of stabilizing signals in the SSSC control law improve the quality of transient and small-signal stability.

In this paper, a coordinated preventive control optimization method based on sensitivity analysis is proposed to improve both small signal and transient stability. The mathematical model based on sensitivity analysis is presented for the coordinated preventive control optimization problem of small signal and transient stability. The nonlinear optimization model is transformed into a quadratic programming model by linearization the constraints through sensitivity analysis, so as to be solved by the ordinary quadratic programming method. In this paper, the computing flow of the coordinated preventive control is presented as well as the selection principle of control generators. A State Grid Cooperation of China (SGCC) 9177-bus system is utilized to validate the proposed method. The results verify the effectiveness of the coordinated preventive control optimization strategies for both small signal and transient stability. After the control strategies are implemented, the system can meet the requirements of both small signal and transient stability.

This paper analyzes the impact of the stochastic behavior of the Electric Vehicle (EV) battery charging station on system stability. This paper examines the newly added EV power load on small-signal and transient stability, which is a major concern and significant issue. The small-signal stability is studied based on eigenvalue analysis. The transient stability is analyzed by using a large disturbance that is a three-phase fault. The stability analysis is carried out with step by step penetration of the EV battery charging station, which results in more oscillations and weekly oscillatory mode. The stability significantly reduces due to an increase in EV power load. The stability is improved with Wind Farm (WF) because the characteristics of wind and EV battery charging stations are the same. With the integration of the WF, the overall inertia of the machine is reduced and the system stability is improved. System stability is observed by considering the two-area test system.

Objectives: This work focuses on the stability analysis of grid connected microgrids. It considers the impact of load disturbance and grid voltage change on voltage and current levels, as well as reactive and active power responses, is analysed. Methods: A comprehensive small-signal state-space model is developed for an inverter-based microgrid, incorporating submodules of inverters, phase-locked loops (PLLs), and LCL filters. The model is linearized around a stable operating point, and eigenvalue analysis is performed and validated through MATLAB/Simulink simulations. A current controller operating in the d-q frame is proposed to enhance stable power conversion and maintain microgrid stability. Findings: The proposed model and control strategy demonstrate the microgrid's ability to maintain transient voltage stability under severe dynamic conditions. During a 10% grid voltage fluctuation, the microgrid exhibits stable active and reactive power responses, with currents and voltages at the point of common coupling stabilizing within 0.2 seconds. Furthermore, when a 25 kVA active load is disconnected, the microgrid effectively manages the power transition, maintaining stable operation with minimal deviations in key parameters. The current controller simplifies AC current control, integrating active power management from solar input, DC-link voltage stability, and reactive power control. Novelty: The novelty lies in the comprehensive analysis of transient voltage stability in grid-connected microgrids under grid voltage fluctuations and load disturbances, areas that have received limited attention in previous research. By developing a detailed small-signal state-space model incorporating PLL and LCL filter dynamics and proposing a robust control strategy with the current controller, this study offers new insights into enhancing the resilience and reliability of grid-connected microgrids during transient events. Keywords: Microgrid, Small Signal Stability, Voltage Source Inverter, State Space model, Eigen Values

This paper presents briefly the application results of the eigen-sensitivity theory of an augmented matrix to small signal and transient stability problems of the large Korea Electric Power Co. (KEPCO) system. First, the real parts of the eigen-sensitivity of the inter-area mode for changes in line parameters are found to be negligibly small. It may be concluded from this result that adding a new transmission line will not improve damping of the inter-area mode significantly. Second, the eigen-sensitivity of the inter-area mode for changes in line reactance is equivalent to controllability of the mode with TCSC as input. Hence, the lines having large sensitivity may be selected as the best candidates for installing TCSC for the purpose of improving damping of the inter-area oscillation. An H/sub /spl infin// controller of TCSC installed at the selected lines damps successfully the inter-area oscillation. Thirdly, critical contingencies for transient stability are identified systematically by computing the modal synchronizing torque coefficient with use of eigen-sensitivity analysis of small signal stability model.

Power System Stability Prediction Using Line Power Flow

The existing studies show that the virtual resistance scheme has positive effects on synchronous resonance (SR) suppression but negative effects on transient synchronization stability of virtual synchronous generator (VSG). To address this contradiction, this article proposes a modified VSG control scheme. The basic idea is that the virtual active power at virtual PCC, instead of real active power, is introduced as the power feedback into the control loop. Then, the effect of virtual resistance on transient stability can be equivalent to that of grid resistance, which improves transient stability. Besides, a proportion integral controller is added at the forward loop to control the real active power to track the power reference. Compared with the existing VSG control methods, the modified VSG control scheme can well solve the conflict caused by virtual resistance between small-signal stability and transient stability. The effectiveness and superiority of the proposed method are verified by CHIL experimental results.