Electromechanical Oscillations In Power Systems Research Articles

Grid synchronised three phase VSI-based hardware emulator to realise low frequency electromechanical oscillations in power systems and their effects on physical distance relay

Grid synchronised three phase VSI-based hardware emulator to realise low frequency electromechanical oscillations in power systems and their effects on physical distance relay

Optimizing power system stability: A hybrid approach using manta ray foraging and Salp swarm optimization algorithms for electromechanical oscillation mitigation in multi‐machine systems

AbstractThis paper emphasizes the significance of ensuring adequate damping of electromechanical oscillations in power systems to ensure stable operation. Power System Stabilizers (PSSs) are influential in enhancing system damping and refining dynamic characteristics during transient conditions. However, the efficacy of PSSs is notably contingent on parameter values, particularly in the case of lead‐lag PSSs. In response to this challenge, the paper introduces a Tilt‐Integral‐Derivative (TID)‐based PSS, optimized through a novel optimization algorithm called Hybrid Manta Ray Foraging and Salp Swarm Optimization Algorithms (MRFOSSA). The MRFOSSA algorithm demonstrates robustness and enhanced convergence, validated through benchmark function tests, and outperforms competing algorithms. These superior characteristics of MRFOSSA were employed in optimal tuning of TID‐PSSs to uphold the stability of multi‐machine power systems. The MRFOSSA algorithm demonstrates robustness and enhanced convergence, outperforms competing algorithms in the optimal tuning of TID‐PSS within the Western System Coordinating Council (WSCC)‐3‐machines 9‐bus test system. In summary, the proposed TID‐PSS, coupled with the MRFOSSA algorithm, presents a promising avenue for enhancing power system stability.

Transient stability versus damping of electromechanical oscillations in power systems with embedded multi‐terminal VSC‐HVDC systems

AbstractMulti‐terminal high‐voltage direct current technology based on voltage‐source converter stations (VSC‐MTDC) is expected to be one of the most important contributors to the future of electric power systems. In fact, among other features, it has already been shown how this technology can contribute to improve transient stability in power systems by the use of supplementary controllers. Along this line, this paper will investigate in detail how these supplementary controllers affect electromechanical oscillations, by means of small‐signal stability analysis. The paper analyses two control strategies based on the modulation of active‐power injections (P‐WAF) and reactive‐power injections (Q‐WAF) in the VSC stations which were presented in previous work. Both control strategies use global signals of the frequencies of the VSC‐MTDC system and they presented significant improvements on transient stability. The paper will provide guidelines for the design of these type of controllers to improve both large‐ and small‐disturbance angle stability. Small‐signal stability analysis (in Matlab) has been compared with non‐linear time domain simulation (in PSS/E) to confirm the results using CIGRE Nordic32A benchmark test system with a VSC‐MTDC system. The paper analyses the impact of the controller gains and communication latency on electromechanical‐oscillation damping. The main conclusion of the paper is that transient‐stability‐tailored supplementary controllers in VSC‐MTDC systems can be tuned to damp inter‐area oscillations too, maintaining their effectiveness.

Power System Stabilizer Design using Genetic Algorithms and Particle Swarm Optimization

in this paper, Meta-heuristic techniques using genetic algorithms GA and particle swarm optimization PSO to tuning optimal design of power system stabilizer PSS proposed. This latter have been used for many years to add damping to electromechanical oscillations of power system, Based on this idea we have proposed multiobjective function composed with tow function, first maximize stability margin by increasing the damping factors while minimizing the real parts of the eigenvalues. Simulation results to comparative study between genetic algorithms and particle swarm optimization obtained by our realized graphical user interface (GUI) proved the efficiency of PSS optimized by genetic algorithms in comparison with Particle Swarm Optimization, showing stable system responses almost insensitive to large parameter variations and under different operating regime (under-excited, nominal and over excited regime).

Robust Power Designing of Supplementary Damping Controller in VSC HVDC System to Improve Energy Conversion Efficiency of Wind Turbine and Power System Stability

Because of low losses and voltage drop, fast control of power, limitless connection distance, and isolation issues, using high-voltage direct-current (HVDC) transmission system is recommended to transfer power in the power systems, including wind farms. This paper aims to propose a supplementary damping controller (SDC) based on the HVDC to improve not only power system dynamic stability but also energy conversion efficiency and torsional vibration damping in the wind power plants (WPPs). When the WPPs are working in power control mode, the active power is set to its reference value, which is extracted from power-speed curve. This paper shows that torsional oscillations associated with the poorly torsional modes can be affected by different operating regions of the power-speed curve of WPP. Therefore, it is essential to employ an SDC to have the optimum energy conversion efficiency in the wind turbine and the most dynamic stability margin in the power system. The SDC is designed using a fractional-order PID controller (FOPID) based on the multiobjective bat-genetic algorithm (MOBGA). The simulation results show that the proposed control strategy effectively works in minimizing the torsional and electromechanical oscillations in power system and optimizing the energy conversion efficiency in the wind turbine.

Connection Between Damping Torque Analysis and Energy Flow Analysis in Damping Performance Evaluation for Electromechanical Oscillations in Power Systems

The damping performance evaluation for electro-mechanical oscillations in power systems is crucial for the stable operation of modern power systems. In this paper, the connection between two commonly-used damping performance evaluation methods, i.e., the damping torque analysis (DTA) and energy flow analysis (EFA), are systematically examined and revealed for the better understanding of the oscillatory damping mechanism. First, a concept of the aggregated damping torque coefficient is proposed and derived based on DTA of multi-machine power systems, which can characterize the integration effect of the damping contribution from the whole power system. Then, the pre-processing of measurements at the terminal of a local generator is conducted for EFA, and a concept of the frequency-decomposed energy attenuation coefficient is defined to screen the damping contribution with respect to the interested frequency. On this basis, the frequency spectrum analysis of the energy attenuation coefficient is employed to rigorously prove that the results of DTA and EFA are essentially equivalent, which is valid for arbitrary types of synchronous generator models in multi-machine power systems. Additionally, the consistency between the aggregated damping torque coefficient and frequency-decomposed energy attenuation coefficient is further verified by the numerical calculation in case studies. The relationship between the proposed coefficients and the eigenvalue (or damping ratio) is finally revealed, which consolidates the application of the proposed concepts in the damping performance evaluation.

An analytic methodology to determine generators redispatch for proactive damping of critical electromechanical oscillations

This paper presents a model-based method for applying online proactive generators redispatch to improve damping of the critical electromechanical oscillations of power system. The proposed method comprises two stages: 1) monitoring modal characteristics of oscillatory modes in ambient condition, and 2) applying generators redispatch based on sensitivities of the critical mode to the generators active power changes using a new analytic method. An online identification method such as error feedback lattice recursive least square adaptive filter is applied for online estimation of the oscillatory modes. Then, whenever the damping ratio of an identified mode is less than a preset threshold, its sensitivities to the generators active power changes are calculated in terms of power system model parameters and power flow variables, which can be obtained via state estimation or measured directly by phasor measurement units. The formulae for calculating these sensitivity factors are developed considering 3rd order dynamic model of synchronous generators along with excitation system and power system stabilizer, and ZIP model of loads. The resultant equations are organized as a quadratic eigenvalue problem and the sensitivity factors are calculated in a systematic manner. Nextly, the candidate generators are ranked online by a new index based on sensitivity factors. Finally, using the proposed index, the most effective generators are proactively redispatched to improve the critical mode damping before occurrence of any fault that jeopardizes the system stability. Applicability and accuracy of the proposed formulae are investigated in the IEEE 39-bus New England power system. Effectiveness of the proposed method is also confirmed with time-domain simulation and state space analysis.

Optimal design of probabilistically robust PIλDμ controller to improve small signal stability of PV integrated power system

With the rapidly increasing penetration level of power generated by large scale photovoltaic (PV) units into the power systems, the effect of the variable output power of the PV unit on the stability of the system cannot be ignored. This paper presents a mathematical approach to study the effect of high infiltration of PV power plant on the small signal stability of a power network and design of optimal fractional order PID (PIλDμ) controller for improving the probabilistic small signal stability of the power systems, taking into consideration the uncertainty of system operating conditions. Due to the probabilistic characteristics of large scale PV power generation, deterministic analysis approaches are not able to fully reveal the impact of high-level PV penetration. At first, this work introduces the main module and mathematical modeling of the large scale PV generation jointly with the single-machine infinite-bus power system. In the following, the paper proposes an efficient method that tunes power system stabilizer (PSS) to have the robustness for damping electro-mechanical oscillations in power systems with incorporated random PV power. For this reason, a robust PSS based on hybridization of PIλDμ controller and Non-dominated Sorting Genetic Algorithm (NSGAII) is designed. This paper targets at finding the optimal gain scheduling of the PIλDμ through the use of the advanced heuristic optimization technique with two objective functions in PV-grid connected systems. The performance of the proposed NSGAII-based PIλDμ controller (NSGAII- PIλDμ) under different solar irradiation, temperature conditions and disturbances is tested. Simulation results illustrate that the model presented can be used in designing of essential controllers for large scale PV power plant.

A Computationally Efficient Method to Design Probabilistically Robust Wide-Area PSSs for Damping Inter-Area Oscillations in Wind-Integrated Power Systems

This paper proposes an efficient method that tunes wide-area power system stabilizers (WPSSs) to have probabilistic robustness for damping inter-area electromechanical oscillations in power systems with incorporated random wind power. Specifically, the efficiency of this method benefits from unique consideration and deduction of the analytic forms of cumulative distribution functions (cdfs) of two types of random variables and their derivatives with respect to tunable parameters of the conventionally structured WPSSs, based on approximations of wind power probability density functions by Gaussian mixtures. These cdfs then compose the objective function of an optimization that can rapidly solve for optimal parameters of WPSSs by a sequential quadratic programming algorithm. The optimized WPSSs are probabilistically robust because they enhance the probability of two commonly desired control effects. Simulation studies on a modified IEEE 10-machine and 39-bus system validate the superior efficiency of the proposed tuning method and the excellent performance of the derived WPSSs.

Sparse and Resilient Hierarchical Direct Load Control for Primary Frequency Response Improvement and Inter-Area Oscillations Damping

The aim of this paper is to define and develop an optimal hierarchical demand-side power-system primary-frequency control structure in order to provide a reliable complement to generator inertia and governor response while improving inter-area oscillation damping. This resilient optimal load control strategy utilizes both wide-area and local signals to guarantee that the system remains stable in the case of communication failures. In the device layer, we deal with demand-response and frequency regulation by minimizing the total disutility of consumers subject to power balance and frequency regulation over the network. In the supervisory layer, we handle the power system's electromechanical oscillations using an linear-quadratic regulator (LQR)-based state feedback scheme with sparsity promotion to achieve the necessary tradeoff between complexity and performance. Since the wide-area feedback loops are built on top of an existing decentralized load control strategy, this design approach creates a decentralized/hierarchical demand-side load-control structure with significant advantages in terms of reliability and operational flexibility. Our study clearly shows by simulation that a demand-side hierarchical load-control strategy has a significant potential for improving the dynamic performance of power systems, even when implemented with a limited number of measurement units and controlling less than $1\%$ of the total base load.

Investigation of UPFC Based Damping Controller Parameter for Power Oscillation Damping by Grey-Wolf Optimizer with Time Delay for Multi Machine System

Selection of a proper control action for UPFC based damping controller so as to deem fit to a specific operating condition is a challenging task to design the controller. In this work Grey Wolf Optimization technique is proposed for investigation of proper control action and optimizing the parameters of UPFC based lead-lag controller to enhance dynamic stability pertaining to damping of electromechanical oscillations in power system. There are two main contributions of this work. The first one is an elaborate investigation of proper damping controller to meet a specific operating condition and it has been considered by a recent algorithm known as GWO algorithm in contrast to PSO and DE algorithm by applying all controllers to the single machine system. Also the versatility of this optimized controller is judged by considering different disturbances like change in input prime mover power, wide range of loading conditions, and change in line reactance. To provide a real time approach for multi machine system, additional time delay is considered, to meet the requirement of a wide area network. The efficacy of GWO optimized controller is also compared with PSO and DE optimized controllers for same disturbances. Eigen value analysis is performed for each case and it has been found that the performance of proposed controller is much better as compared to others.

Damping wide-area oscillations in power systems: a model predictive control design

Electromechanical oscillations in power systems have been observed ever since synchronous generators were interconnected to provide reliability and higher generation capacity, and they have become a severe threat for the safe and economic operation of modern interconnected power grids. To dampen these oscillations, wide-area damping controllers (WADCs) have been introduced by utilizing wide-area measurement systems and synchronized phasor measurement units. In this paper, we present a systematic approach for designing WADCs using a model predictive control (MPC) technique to damp interarea oscillations in the power system. The MPC controller computes optimal control signals for the excitation system of a remote generator where it will supplement the local power system stabilizers that are used as damping controllers. The performance of the proposed approach has been assessed on the IEEE 16-generator 68-bus test system, and it is shown that the interarea oscillations can be effectively and robustly damped under varying operation conditions.

LPV-based power system stabilizer: Identification, control and field tests

This paper shows the design and tests of an LPV power system stabilizer aimed at improving the damping of electromechanical oscillations in power systems. In order to capture the dynamic model for control design, LPV models were estimated from experimental data. The generator active and reactive powers were used as scheduling parameters. The control problem is formulated as a parameterized linear matrix inequality, which the positivity condition is relaxed through a sum-of-squares decomposition. The controller ensures stability and H∞ performance for a set of operating conditions. Field tests were carried out on a 10-kVA machine and on a 350-MVA hydroelectric generator.

Impact of Dynamic Interactions Introduced by the DFIGs on Power System Electromechanical Oscillation Modes

This paper derives the index of dynamic interactions (IDI), which is the sensitivity of a power system electromechanical oscillation mode (EOM) of concern to the dynamic interactions introduced by a grid-connected double-fed induction generator (DFIG). Based on the IDI, analysis is carried out with the following generally-applicable conclusions obtained: 1) Impact of dynamic interactions introduced by the DFIG increases when wind power penetration increases; 2) as long as the frequency response of an equivalent single DFIG model approximately matches the frequency response of a wind farm around the frequency of electromechanical oscillations of concern, this equivalent dynamic model of single DFIG can be used to represent the wind farm to examine the impact of wind farm on EOMs. Furthermore, an indicator of DFIG control (IDC) is derived for comparing the impact of terminal voltage control and reactive power control implemented by the DFIG. Main merit of the IDC is the computational simplicity without need to know dynamic model of the DFIG to indicate that either the terminal voltage control or the reactive power control is more beneficial to power system stability. An example multi-machine power system with grid-connected DFIGs is presented to demonstrate and validate the analysis and conclusions made in the paper.

PLL-Induced Modal Resonance of Grid-Connected PMSGs With the Power System Electromechanical Oscillation Modes

This study investigates the impact of a grid-connected permanent magnet synchronous generator (PMSG) for wind power generation on the power system electromechanical oscillation modes (EOMs) caused by a phase-locked loop (PLL). A closed-loop interconnected model of a power system with the PMSG is established, where the PLL and rest of the power system are modeled as two separate open-loop interconnected subsystems. Analysis based on the established model indicates that, when an open-loop PLL oscillation mode (POM) is close to an open-loop EOM of concern on the complex plane, the dynamic interactions between the PMSG and the power system may become strong. It is very likely that the modal resonance due to the closeness of the open-loop POM and EOM may degrade the small-signal stability of the power system. In this paper, case studies of an example power system with PMSGs are presented. It is demonstrated that open-loop modal resonance occurs when power system operating conditions change and the PLL parameters are tuned. Strong dynamic interactions between the PMSGs and power system are caused by the open-loop modal resonance, resulting in considerable damping degradation of the low-frequency electromechanical oscillations.

Power System Electromechanical Oscillation Modes as Affected by Dynamic Interactions From Grid-Connected PMSGs for Wind Power Generation

Dynamic interactions between a grid-connected permanent magnet synchronous generator (PMSG) and power system are normally weak. This paper reports a special condition of modal resonance, under which the grid-connected PMSG may dynamically interact with power system strongly to affect power system electromechanical oscillation modes (EOMs). The special condition of modal resonance reported in this paper is that an open-loop converter oscillation mode (COM) of PMSG is close to an open-loop EOM of a power system on the complex plane. Damping torque analysis is carried out to explain why strong dynamic interactions between PMSG and power system may occur under the condition of modal resonance. Results of theoretical analysis in this paper indicate that occurrence of modal resonance may possibly cause the damping of either closed-loop COM or EOM to decrease such that power system small-signal angular stability is affected negatively by grid connection of PMSG. Responsible COMs for modal resonance are found to be related with active/reactive power control systems of a grid-side converter of PMSG. In the paper, an example multimachine power system with PMSGs is presented to demonstrate and validate analysis and conclusions made.

Optimal placement method of multi UPFCs to damp power system oscillations

Summary This paper proposed the placement of multi unified power flow controllers (UPFCs) using the system critical modes and residue factor to increase damping of the electromechanical oscillations in power system. For this purpose, the critical modes are used to determine the number of UPFCs and their optimal locations are determined using residue factor. Also, the dynamic model of UPFC, which is consists of a voltage source and a current source is used for small signal stability analysis. To control the parameters of this model, supplementary controller is designed and applied. Detection of the input signal for this controller is based on the participation factor, which is a simple and effective method. Finally, the proposed method is investigated on IEEE 39-bus system and the results are presented.

Distributed oscillation damping estimation to large scale power systems: A multi-area online empirical approach

Online extraction and characterization algorithms to the distributed damping factor that can accurately monitoring the transient response in large interconnected power systems has attracted much attention, principally to maximize the multi-area functions in energy control centers. In this paper we present an online estimation algorithm to the distributed damping factor of inter-area electromechanical oscillations in power systems. The method is based on a statistical analysis of multi-area matching patterns (MPs) modes from spatially coupled empirical coefficients, and derived with a network partitioning method by coherent signal blocks into data clusters from the phase domain. This provides a distributed global picture on the modal behavior, which is derived using synchronized-time multi-area signals simultaneously recording from wide-area monitoring schemes (WAMS). For purposes as our multi-area online approach, a sliding data window frame for estimating the distributed damping factor of low-frequency electromechanical oscillations based on Prony and Fourier methods with multiple empirical orthogonal functions (EOFs) analysis is presented. In order to demonstrate the usefulness and adaptivity to obtain an online damping factor estimation and global picture of inter-area electromechanical modes from dynamic oscillations in distributed power systems, the proposed algorithm is applied in detail to the 16 machine-68 bus New England test system.

Benchmark Models for the Analysis and Control of Small-Signal Oscillatory Dynamics in Power Systems

This paper summarizes a set of six benchmark systems for the analysis and control of electromechanical oscillations in power systems, recommended by the IEEE Task Force on Benchmark Systems for Stability Controls of the Power System Dynamic Performance Committee. The benchmark systems were chosen for their tutorial value and particular characteristics leading to control the system design problems relevant to the research community. For each benchmark, the modeling guidelines are provided, along with eigenvalues and time-domain results produced with at least two simulation softwares, and one possible control approach is provided for each system as well. Researchers and practicing engineers are encouraged to use these benchmark systems when assessing new oscillation damping control strategies.

Formulation and Characterization of Power System Electromechanical Oscillations

When generators of a power system are subject to a large disturbance, their electromechanical oscillations (EOs) are essentially nonlinear as observed from their rotor angle waveforms due to the nonlinear power network. However, traditional modal analysis has not given enough considerations to nonlinearities in EOs. This paper analytically formulates the accurate oscillation frequency (OF) of an EO mode addressing nonlinearities. It is revealed that when the system model and condition are fixed, the OF of any EO mode is energy-dependent as a function of the oscillation amplitude (OA). That is characterized by a new tool named Frequency-Amplitude (F-A) curve regarding each mode, from which the frequency decreases from the natural frequency toward zero when the amplitude grows to a critical threshold. The paper proves that an F-A curve is actually a projection of the system trajectory between the stable equilibrium and the stability boundary onto the OF-OA plane regarding one mode. Based on the concept of F-A curve, a stability index is defined and estimated from measurements for online angle stability analysis. The proposed methodology is presented in detail using an SMIB system and then demonstrated on the IEEE 9-bus system and WECC 179-bus system having multiple EO modes.