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This paper presents a detailed model of low-frequency oscillations and their damping within the Electric Power System (EPS) of Bosnia and Herzegovina (B&H). The system is modeled using MATLAB software, analysing the steady state and dynamic responses. This research highlights the challenges and impacts of integrating renewable energy sources, such as wind farms, on grid stability and oscillation damping. The paper utilizes eigenvalue analysis to investigate the dynamic characteristics of the system, emphasizing the need for efficient damping strategies to maintain system stability. The methodology includes a comprehensive review of existing literature, the creation of a detailed EPS model of B&H, and the application of eigenvalue and oscillation amplitude analysis to determine damping ratios. The dynamic responses of hydro power plants, HPP Mostar and HPP Jablanica, to transient disturbances are analysed to validate the model and refine damping strategies. The results indicate that the B&H EPS is well-damped, with all eigenvalues possessing negative real parts, and demonstrate the system's resilience to small disturbances. The results are compared with the technical report on the integration of the wind power plant WPP Podveležje. This comparative analysis shows consistent patterns between the modeled calculations and empirical data, confirming the robustness of the EPS model. This alignment underscores the effectiveness of current damping mechanisms and provides a foundational strategy for enhancing system stability with increasing renewable energy penetration. The findings highlight the importance of developing advanced control strategies to sustain system stability as the integration of variable renewable energy sources continues to grow. [ABSTRACT FROM AUTHOR]

In this paper, a holistic nonlinear state-space model of a system with multiple converters is developed, where the converters correspond to the wind turbines in a wind farm and are equipped with grid-following control. A novel generalized methodology is developed, based on the number of the system's converters, to compute the equilibrium points around which the model is linearized. This is a more solid approach compared with selecting operating points for linearizing the model or utilizing EMT simulation tools to estimate the system's steady state. The dynamics of both the inner and outer control loops of the power converters are included, as well as the dynamics of the electrical elements of the system and the digital time delay, in order to study the dynamic issues in both high- and low-frequency ranges. The system's stability is assessed through an eigenvalue-based stability analysis. A participation factor analysis is also used to give an insight into the interactions caused by the control topology of the converters. Time domain simulations and the corresponding frequency analysis are performed in order to validate the model for all the control interactions under study. [ABSTRACT FROM AUTHOR]

In the static stability analysis of the grid-connected photovoltaic (PV) generation and energy storage (ES) system, the grid-side is often simplified using an infinite busbar equivalent, which streamlines the analysis but neglects the dynamic characteristics of the grid, leading to certain inaccuracies in the results. Furthermore, the control parameter design does not consider the coupling relationships among parameters, resulting in arbitrary values and the inability to achieve overall optimality. To address these issues, this paper presents a comprehensive parameter optimization method for the oscillation characteristics of grid-connected PV generation and ES systems in various frequency ranges. Firstly, a detailed modeling of the grid-connected PV generation and ES system is conducted, resulting in the derivation of the system's small-signal model. This study investigates the impact of parameters related to PV arrays, ES units, and the virtual synchronous generator (VSG) on the system's characteristic roots using participation factors, sensitivity analysis, and eigenvalue root trajectories. Subsequently, based on the analysis of system root trajectories and the Particle Swarm Optimization (PSO) algorithm, a holistic parameter optimization design method for the system's oscillation modes is proposed, and the parameter optimization results are obtained. Finally, the accuracy of the theoretical analysis is validated through perturbation testing using both Matlab/Simulink models and the small-signal model. [ABSTRACT FROM AUTHOR]

The accurate prediction of rotating stall inception is critical for determining the stable operating regime of a compressor. Among the two widely accepted pathways to stall, namely, modal and spike, the former is plausibly believed to originate from a global linear instability, and experiments have partially confirmed it. As for the latter, recent computational and experimental findings have shown it to exhibit itself as a rapidly amplified flow perturbation. However, rigorous analysis has yet to be performed to prove that this is due to global linear instability. In this work, an eigenanalysis approach is used to investigate the rotating stall inception of a transonic annular cascade. Steady analyses were performed to compute the performance characteristics at a given rotational speed. A numerical stall boundary was first estimated based on the residual convergence behavior of the steady solver. Eigenanalyses were then performed for flow solutions at a few near-stall points to determine their global linear stability. Once the relevant unstable modes were identified according to the signs of real parts of eigenvalues, they were examined in detail to understand the flow destabilizing mechanism. Furthermore, time-accurate unsteady simulations were performed to verify the obtained eigenvalues and eigenvectors. The eigenanalysis results reveal that at the rotating stall inception condition, multiple unstable modes appear almost simultaneously with a leading mode that grows most rapidly. In addition, it was found that the unstable modes are continuous in their nodal diameters, and are members of a particular family of modes typical of a dynamic system with cyclic symmetries. This is the first time such an interesting structure of the unstable modes is found numerically, which to some extent explains the rich and complex results constantly observed from experiments but have never been consistently explained. The verified eigenanalysis method can be used to predict the onset of a rotating stall with a CPU time cost orders of magnitude lower than time-accurate simulations, thus making compressor stall onset prediction based on the global linear instability approach feasible in engineering practice. [ABSTRACT FROM AUTHOR]

This work deals with doubly fed induction generator (DFIG) modeling and stability when connected to weak AC grids. A detailed state-space model that includes the phase-locked loop (PLL) is developed. This work aims to determine the influence of the network's strength on DFIG stability through the short-circuit ratio (SCR). The critical values of the proportional control parameters of the grid-side and rotor-side converters (RSC and GSC), as well as PLL, which make the system unstable, are calculated for different SCR values. Finally, PSCAD/EMTDC dynamic simulations are used to validate the critical control parameters obtained by studying the eigenvalues of the DFIG state-space model regarding system stability. [ABSTRACT FROM AUTHOR]

The high-voltage voltage-source converter (VSC)-based multi-terminal dc (MTDC) grid is a key technology for integrating offshore wind energy and enabling bulk power transmission across nations and continents. This paper addresses the small-signal stability of an MTDC grid equipped with a power flow controller (PFC) under extremely weak ac system interconnections. Using a comprehensive linearized state-space model, eigenvalue analysis uncovers that beyond the well-documented low-frequency oscillations (LFO), an MTDC grid may experience unstable medium-frequency oscillations (MFO) under rectifier operation of droop voltage-controlled VSCs when interfaced to an extremely weak ac system. Moreover, it was shown that the most challenging scenario is when multiple droop voltage-controlled VSCs are interfaced to very weak ac systems, with unstable LFO and MFO observed at short-circuit ratio values of 1.4 and 1.8, respectively. Sensitivity analysis is conducted to assess the impact of the droop voltage control gains, PFC control parameters, and dc breaker reactor on the system dominant eigenmodes in such critical weak conditions. Simple yet efficient LFO and MFO compensators are proposed to stabilize the system, and their parameters design was detailed. Extensive simulation studies and real-time validation tests verify the analytical analysis and demonstrate the effectiveness of the proposed compensators and their feasibility for real-time implementation.

The significant increase of converter interfaced generation, consumption, storage, and transmission in power systems, results in the need to consider converter-driven stability in detail, as well as to study modelling and analysis methods with which such stability effects can be represented and investigated. Due to the multiple causes of converter-driven stability effects, a classification into further categories of fast and slow converter-driven stability is necessary, which is systematically presented in this paper. We further provide a detailed overview on appropriate modelling methods including static, quasi-dynamic and dynamic modelling and their respective applications. Typical analysis methods such as eigenvalue and impedance based analysis are explained and related to the previous modelling approaches. Based on that, a guide to which modelling and analysis method is appropriate for which type of converter-driven stability, is provided. In addition, open and recent research questions with regard to studies on nonlinear analyses of large systems with acceptable computational costs are pointed out.

Power converters and their interfacing networks are often treated as modular state-space blocks for small-signal stability studies in microgrids; they are interconnected by matching the input and output states of the network and converters. Virtual resistors have been widely used in existing models to generate a voltage for state-space models of the network that require voltage inputs. This paper accurately quantifies the adverse impacts of adding the virtual resistance and proposes an alternative method for network modelling that eliminates the requirement of the virtual resistor when interfacing converters with microgrids. The proposed nonlinear method allows initialization, time-domain simulations of the nonlinear model, and linearization and eigenvalue generation. A numerically linearized small-signal model is used to generate eigenvalues and is compared with the eigenvalues generated using the existing modelling method with virtual resistances. Deficiencies of the existing method and improvements offered by the proposed modelling method are clearly quantified. Electromagnetic transient (EMT) simulations using detailed switching models are used for validation of the proposed modelling method.

Back-to-Back (B2B) HVDC systems can enhance cross-regional transmission capacity and overall power system stability. However, their use in interconnecting two extremely weak grids can compromise system stability. This paper presents a comprehensive stability analysis of a B2B HVDC system to distinguish the root causes of instability mechanisms and identify the critical short circuit ratio (CSCR) of each converter station under inverter and rectifier operations considering the impact of power feedforward compensation of the dc-bus voltage controller. The study also investigates the stability implications and CSCR changes when a dc transmission line connects the converter stations, creating a point-to-point (P2P) HVDC system. Eigenvalue analysis, based on detailed small-signal modeling, showed that three distinct instability mechanisms, high-, low-, and medium-frequency instabilities, can compromise the operation of VSC stations under extremely weak grid conditions. Notably, the medium-frequency instability observed in the P2P HVDC system during inverter operation is predominantly caused by the power feedforward compensation of the dc-bus voltage controller. Furthermore, the analysis reveals that the CSCRs for dc-bus voltage-controlled VSC stations are higher in comparison to power-controlled ones. This suggests that a dc-bus voltage-controlled VSC is more susceptible to instability in weak grid scenarios than its power-controlled counterpart. Active compensators are designed based on participation factor analysis to mitigate the identified instabilities. The findings are validated with extensive simulations and real-time hardware-in-the-loop tests, demonstrating the analysis's accuracy and the proposed compensators' efficacy.

This study examines the influence of a direct-power control technique for a DFIG (Doubly-Fed Induction Generator)-based wind generator on sub-synchronous resonance (SSR). A series capacitor of a transmission line will exchange power with the synchronous generator when it runs via an SSR. DFIG includes power converters built into its rotor circuit, allowing for quick control of both the active and reactive power of the device. This is made possible by the rotor converter circuit's fast IGBT switching. Examining the ability of the LQR (Linear Quadratic Regulator) on the DFIG to provide the required active power and reactive power during SSR is the primary goal of this work. Additional DFIG is added to the test system in addition to the original test system, and during SSR its performance is evaluated using an additional control signal that is obtained from the synchronous generator and supplied to DFIG through LQR. The analysis of SSR was completed based on eigenvalue analysis utilizing the D-Q model test system and transient simulation using MATLAB Simulink. Independent model control is used to control the DFIG rotor converter that dampens multimodal SSR oscillations. The test system was developed using the IEEE first benchmark model's adopted system. [ABSTRACT FROM AUTHOR]