Low Frequency Electromechanical Oscillations Research Articles

Fuzzy-PID controller based sliding-mode for suppressing low frequency oscillations of the synchronous generator

A novel intelligent stabilizer is designed to address the issue of low-frequency electromechanical oscillations in a synchronous generator in this article. This stabilizer incorporates three controllers: a three-level sliding mode controller, a fuzzy logic controller, and a proportional-integral-derivative (PID) controller enhanced through genetic algorithm optimization. The discontinuous segments of the first two levels of the sliding mode controller are substituted with fuzzy-PID links, utilizing error and its rate of change to adjust stabilizer parameters. The discontinuous portion of the third level is replaced by a saturation function to constrain current within permissible limits. The advantage of this proposed controller is that it integrates the benefits of the three constituent controllers and is capable of handling a wide range of disturbances. Additionally, thanks to the fuzzy engine, which considers error variations, there is no longer a need to calculate the error derivative, which could amplify measurement noise. The proposed stabilizer is compared to available literature results. As a result, the proposed stabilizer exhibits an undershoot of -0.003, an overshoot of 0.001, a response time of 0.01s, high robustness for parameter variations ranging from 0.5 to 4 times the nominal value, and very rapid suppression of oscillations compared to other controllers.

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

Optimal fractional SSSC auxiliary controller for power system low frequency oscillations damping improvement

This work presents a new controller design to improve inter-area low frequency electromechanical oscillations (LFEOs) damping and enhance the overall stability of the electrical network. The control strategy used the static synchronous series compensator (SSSC) based flexible AC transmission systems (FACTS) series-type device mainly performed for power flow and voltage regulation. Then, a fractional order proportional integral derivative (FOPID) is introduced as an auxiliary controller for the SSSC using the difference of rotor speed deviations of generators as input signal to improve the oscillations damping. Moreover, genetic algorithm (GA) is applied to seek for optimum controller gains. The proposed control approach is examined on two-area four-machine (2A4M) test system. The FOPID performance is compared with the integer order proportional integral derivative (PID). Obtained results show that the proposed SSSC-based FOPID controller achieves high performance for enhancement of inter-area low frequency oscillations damping.

Design and Optimal Location of Power System Stabilizer in the Multi-Machine Power Network

This paper proposes a damping torque index (DTI) to determine the optimal installation location of the power system stabilizer (PSS) in the multi-machine power network. The proposed index is based on the classical damping torque analysis (CDTA) method for power system low-frequency electro-mechanical (LFEO) analysis. The selection criteria of the PSS location is the maximum magnitude of DTI under normal operating conditions. The CDTA method is used to design PSS, and the phase compensation technique subsequently adjusts the associated parameters. Furthermore, to analyze the power system’s critical oscillation mode, a wide-area damping controller (WADC) is design for the synchronous generator where optimal location of PSS is install. The reduced-order model-based WADC includes time-varying delay in the wide-area signal. The WADC’s input signals from the phasor measurement unit (PMU) and the location of the PMU are selected using geometric measures of observability and WADC parameters design based on the residue approach. The proposed approach is validated in two separate test systems, and modal analysis is carried out on MATLAB software. The simulated results have been validated on the real-time digital simulator (RTDS) RSCAD 5.012. Results obtained on RTDS show that the proposed approach efficiently damps low-frequency electro-mechanical oscillations.

Improving the accuracy and the estimation time of inter-area modes in power system based on Tufts-Kumaresan algorithm

ABSTRACT In this paper, a new method based on the Tufts–Kumaresan (TK) algorithm is used to process nonstationary signals and extract system modes. This new algorithm for mode estimation is proposed to improve estimation accuracy under dynamic conditions. The key contribution in TK is the use of multiple orthogonal sliding windows rather than a single pair of sliding windows. Simulation results under various scenarios, such as different types of faults and load changes are used to evaluate the performance of the proposed method. The proposed method will accurately extract system modes. This method will also reduce the required memory and the calculation time of estimation in nonstationary signals. In complement to successful applications in studying the dynamic behavior of the power system, identifying and analyzing low-frequency electromechanical oscillations, and removing signal noise, this method can accurately estimate the modes of a power system. To validate the accuracy of the proposed method, the Wavelet and the Prony methods have been used for comparison. The proposed method is implemented using simulated ringdown data of standard two-area power system and real measurement data of the WSCC system breakup on 10 August 1996.

Decentralized Model-Reference Adaptive Control Based Algorithm for Power Systems Inter-Area Oscillation Damping

Being the primary cause of inter-area oscillations and due to the fact that they limit the generation’s output, Low-Frequency Electromechanical Oscillations (LFEOs) represent a real threat to power system networks. Mitigating their effects is therefore crucial as it may lead to system collapse if not properly damped. As rotor angle instability is the primary cause of LFEOs, this paper presents a novel Model-Reference Adaptive Control (MRAC) scheme that enhances its stability. The proposed scheme is tested using the Single-Machine Infinite Bus (SMIB) network. The results obtained validate the proposed decentralized control architecture. The robustness of this oscillation damping controller is verified through simulations in MATLAB/SIMULINK. With Gaussian noise added to the structure of the generator to emulate small load variations responsible for the rotor angle instability, the results of the simulations show that the rotor angle remains stable. Furthermore, when subjected to faults, the recovery time is less than 500 ms.

Power System Rotor Angle Stability Enhancement Using Lyapunov-Based Trajectory Tracking Controller and Model Reference Adaptive Control

It is vital that the synchronous generator rotor angle be kept stable to avoid disastrous consequences such as the loss of synchronism amongst generators within a power system network. Once it is unstable, the time that is taken to remedy this is advised to be 5–10 s for smaller power systems and 15–20 s for larger ones. The instability that is caused by poorly damped Low-Frequency Electromechanical Oscillations (LFEOs) may result in inter-area oscillations, where a group of generators in one area oscillates against those in another area, thus affecting the stability of the entire network. This paper explores two control architectures, namely, a nonlinear Lyapunov-based trajectory tracking controller and a Model Reference Adaptive Controller (MRAC) as options to enhance the stability of the rotor angle. The performance of each of these controllers was assessed under steady-state conditions, and then, the synchronous generator was subjected to Gaussian noise and an impulse. While the first one is aimed at emulating small variations in the system loads that are responsible for inter-area oscillations, the latter one is an attempt to explore their performance for transient stability.

Linear quadratic regulator design via metaheuristics applied to the damping of low-frequency oscillations in power systems

This paper proposes the application of control by state feedback using the linear quadratic regulator (LQR) optimized by metaheuristics to damp low-frequency electromechanical oscillations in electrical power systems. The current sensitivity model was used to represent the single machine infinite bus (SMIB) system in the time domain. The weighting matrices of the LQR were adjusted using four different algorithms: (i) the genetic algorithm, (ii) the differential evolution algorithm, (iii) the particle swarm optimization algorithm, and (iv) the gray wolf optimization (GWO) algorithm. In the cases considered, disturbances were applied to the electrical power system and, then, performances comparisons associated with each metaheuristic were statistically analyzed, in which the number of iterations, error, and time to achieve convergence of each algorithm were compared. From the results, it was possible to conclude that the algorithms were efficient in adjusting the weighting matrices of the LQR, providing additional damping to the poles of interest of the system. It was also possible to conclude that the GWO algorithm presented the best performance, accrediting it as a powerful tool in the study of small-signal stability for the analyzed case.

Small‐disturbance stability of a concentrating solar power collecting system with multiple synchronous generators

This paper examines the small-disturbance stability in planning a concentrating solar power collecting system (CSPCS) with multiple concentrating solar power (CSP) generation plants, which are modelled as synchronous generators (SGs). The examination indicates that an oscillation mode of the CSPCS gradually moves to the right half of complex plane when the planned number of the CSP generation plants increases. Such oscillatory instability is different with the low-frequency electromechanical power oscillations (LEPOs) in a conventional multi-machine power system, because the unstable oscillation mode is associated with the excitation systems, rather than the electromechanical dynamics of the SGs. Analysis is carried out in the paper to explain why the instability risk found in the planning is associated with the excitation systems instead of electromechanical dynamics of the SGs. The analysis helps to understand the finding made in the planning. Furthermore, rules are proposed to adjust the gain of feedback loop of the excitation systems to eliminate the risk of oscillatory instability. This suggests that the parameters’ setting of excitation systems recommended by the IEEE standard may need to be modified to accommodate the planning of CSPCS. Tests are presented to demonstrate and evaluate the analysis and conclusions made.

Application of a neuro-fuzzy controller for single machine infinite bus power system to damp low-frequency oscillations

Generally, power systems experience a variety of disturbances that can result in low frequency electromechanical oscillations. These low frequency oscillations (LFOs) take place among the rotors of synchronous generators connected to the power system. These oscillations may sustain and grow to cause system separation if no adequate damping is provided. Power system stabilizers (PSSs) are one of the alternative devices used to solve this rotor oscillation problem. The major limitation of using PSSs at the excitation system of synchronous machine is that the conventional PSS is a permanent parameter type operating under a particular system operating condition, and its parameters are acquired through trial and error. An efficient way of operating the PSS has been by designing the PSS parameters using a powerful optimization procedure. However, designing PSS damping controller is a cumbersome task as it needs a comprehensive test system modeling and a heavy computational burden on the system. In this research, a novel, model-free neuro-fuzzy controller (NFC) is designed as the LFOs’ damping controller to substitute the traditional PSS system making the power system simple without complications in PSS design and parameter optimization. The proposed controller application implements the LFOs’ control without a linearized mathematical model of the system, as such it makes the system less complex and bulky. Single machine infinite bus (SMIB) test system was simulated in SIMULINK domain with the PSSs and with the proposed controller to compare the NFC effectiveness. The simulation outcome for the eigenvalue study with NFC stabilizer yields steady eigenvalues that enhanced the damping status of the system greater than 0.1 with decreased overshoots and time to rise via the proposed NFC process than with the conventional FFA-PSS. Similarly, the generator transient reaction also presents the ω and δ based on the time to settle was improved by 64.66% and 28.78%, respectively, via the proposed NFC process than with the conventional FFA-PSS. Finally, the conventional PSS was found to be complicated in its design, parameter optimization and less effective than the proposed controller for the LFOs’ control.

Optimization based power system stabilizer tuning

Abstract The most cost-effective method to improve the damping of low frequency electromechanical oscillations in interconnected power systems is the use of Power System Stabilizers (PSS), which act as supplementary controllers in the generator excitation system. In general, the performance of a power system stabilizer depends on the proper tuning of its parameters, to ensure a positive contribution to the small signal stability of the power system, without negatively impacting its transient stability. This paper will discuss the different roles of the excitation system automatic voltage regulator and the power system stabilizer in improving the transient stability and the oscillatory stability of the power system. The focus of the paper will be on the tuning methodology for power system stabilizers, which can ensure a robust performance of the PSS over a wide range of frequencies and operating conditions. In addition, mathematical optimization techniques will be introduced into the tuning process to improve the efficiency and accuracy of the tuning process.

A Hybrid Coordinated Design Method for Power System Stabilizer and FACTS Device Based on Synchrosqueezed Wavelet Transform and Stochastic Subspace Identification

The occurrence of low-frequency electromechanical oscillations is a major problem in the effective operation of power systems. The scrutiny of these oscillations provides substantial information about power system stability and security. In this paper, a new method is introduced based on a combination of synchrosqueezed wavelet transform and the stochastic subspace identification (SSI) algorithm to investigate the low-frequency electromechanical oscillations of large-scale power systems. Then, the estimated modes of the power system are used for the design of the power system stabilizer and the flexible alternating current transmission system (FACTS) device. In this optimization problem, the control parameters are set using a hybrid approach composed of the Prony and residual methods and the modified fruit fly optimization algorithm. The proposed mode estimation method and the controller design are simulated in MATLAB using two test case systems, namely IEEE 2-ar-ea 4-generator and New England-New York 68-bus 16-genera-tor systems. The simulation results demonstrate the high performance of the proposed method in estimation of local and interarea modes, and indicate the improvements in oscillation damping and power system stability.

Синтез системного стабилизатора с применением методов нечеткой логики и нейронной сети

Power systems are large non-linear systems that are often subject to low frequency electromechanical oscillations with a frequency of 0.5–2.5 Hz. Power system stabilizers (PSS) are commonly used as effective and economically efficient means to dampen electromechanical oscillations of generators and increase the stability of power systems. PSS can increase the power transmission stability limits by adding a stabilizing signal through the channels of the automatic excitation control system. The article presents the results of training a neural network based on which a fuzzy logic PSS is obtained for increasing the stability of electric power systems. The synchronous generator rotor speed deviation and acceleration were taken as input data for the fuzzy logic controller. These variables have a significant effect on damping the rotor's electromechanical oscillations. The characteristics of the power system equipped with the proposed fuzzy logic based PSS are compared with its characteristics with a PSS with non-optimized parameters and without a PSS.

A Novel Hybrid Technique of Frequency Control for Distributed Energy Resources

The rapid increase in the population and fastest development in the industrial sector has increased the energy demand throughout the world. Frequent outages and load shedding has seriously deteriorated the efficiency of the electrical power distribution system. Under such circumstances, the implementation of Distributed Generation (DG) is increasing. Small hydel generators are considered as the most-clean and economical for generating electrical energy. These are very complex nonlinear generators which usually exhibits low frequency electromechanical oscillations due to insufficient damping caused by severe operating conditions. These DGs are not connected to the utility in many cases because, under varying load, they cannot maintain the frequency to the permissible value. This work presents detailed analysis of operating characteristics and proposes a hybrid frequency control strategy of the small hydel systems. The simulation and testing is performed in MATLAB, the results verified the improved performance with the recommended method. The proposed method conserves half of the power consumption. The control scheme regulates the dump load by connecting and disconnecting it affectively. The application of presented methodology is convenient in the deregulated environment, especially under the severe shortage of energy. The proposed model keeps the frequency of system at desired level. It reduces the noise, thereby improving the response time of the designed controller as compared to conventional controllers. The innovative scheme also provides power for small scale industrial, agricultural and other domestic application of far-off areas where the supply of utility main grid is difficult to provide. The recommended scheme is environmental friendly and easy to implement wherever small hydel resources are available.

WITHDRAWN: Analysis, design and implementation of hardware neural network based rotor oscillations compensator

In this paper, an Artificial Neural Network (ANN) based Rotor Oscillations Compensator (ROC) is proposed and its equivalent Hardware Realizable Neural Network (HARNN) has been developed on the Field Programmable Gate Array (FPGA) board. The basic function of a ROC is to minimize the low frequency electro mechanical oscillations created in the Electric power network. Whenever the fault is occurred outside the operating range of a fixed gain ROC, the system damping is insufficient and the machine is still under unstable mode. Hence a hardware having sufficient “intelligence” that is capable of producing necessary and sufficient damping to the system is proposed in this paper. A detailed study has been done with the plant response without any controller, with a fixed gain controller and a FPGA based ANN controller. The studies revealed that when an intelligent controller has been included in the Exciter loop, the oscillations have been eliminated more effectively. But it is also observed that the realization of an ANN absolutely on an FPGA is having its own design limitations. The ARTIX 7 FPGA development board has been used for the complete analysis and the results and outcomes discussed at the end.

A Method to Design Power System Stabilizers in a Multi-Machine Power System Based on Single-Machine Infinite-Bus System Model

This paper proposes a method to design power system stabilizers (PSSs) based on single-machine infinite-bus system models to mitigate the risk of low-frequency electro- mechanical power oscillations in an N-machine power system. First, models of N fabricated identical-machine power systems are established for the N-machine power system. Analysis in the paper indicates that the electromechanical oscillation mode of fabricated identical-machine power systems with the least damping is of less damping than the electromechanical oscillation modes of N-machine power system. Second, it is proved that models of fabricated identical-machine power systems are dynamically equivalent to the single-machine infinite-bus system models. Finally, it is suggested that the PSSs are designed using single-machine infinite-bus system models to enhance the least damped electromechanical oscillation mode of fabricated identical-machine power systems. This eventually improves the damping of electromechanical oscillation modes of N-machine power system, thus mitigating the risk of low-frequency electromechanical power oscillations. In the paper, the proposed method is demonstrated and evaluated by using three well-known example multi-machine power systems. Effectiveness of PSSs is confirmed by the results of modal computation and simulation.

A Novel Nature-Inspired Improved Grasshopper Optimization-Tuned Dual-Input Controller for Enhancing Stability of Interconnected Systems

Power system often experiences the problem of low-frequency electromechanical oscillations which leads the system to unstable condition. The problem can be corrected by implementing power system stabilizers (PSSs) in the excitation control system of alternator. This paper provides a novel and efficient approach to design an Improved Grasshopper Optimization Algorithm (IGOA)-based dual-input controller to damp the inter-area-mode power system oscillations. A three-fold optimization criterion has been formulated to calculate the optimum values of the controllers required for power system stability. The damping performance of the proposed controller is compared with conventional PSS and genetic algorithm-based controllers to validate the better performance of the proposed IGOA-based controller under various system loading conditions and disturbances.

Robust Linear Parameter Varying Scalar Control Applied in High Performance Induction Motor Drives

This article presents a robust stabilizer designed to damp low-frequency electromechanical oscillations which occurs in induction machines controlled by scalar control when operating at low speed and light load. The robust stabilizer design is based on the linear parameter varying (LPV) approach. A discrete LPV model is identified to allow the design of the robust LPV controller. Experimental tests are performed on a 7.5-kW induction motor dynamometer using an industrial inverter driver. The results show satisfactory improvement of the motor performance with the damping controller activated.

Comparing strategies to damp electromechanical oscillations through STATCOM with multi-band controller

This paper aims to compare two strategies for damping low-frequency electromechanical oscillations in multi-machine power systems through Static Synchronous Compensators (STATCOM) with a multi-band controller. STATCOM is represented by a controllable voltage source behind an impedance and the multi-band controller acts as a power oscillation damper that modulates parameters of the voltage source in the transient period. In the first strategy, the multi-band controller acts on the voltage-control loop through the voltage modulation. In the second one, the controller acts on the real power-control loop to modulate the phase angle of the voltage source. The coordinated design of multi-band controllers and power systems stabilizers is performed through an optimization approach taking into account several operation conditions.

Novel Analytical Method for Dynamic Design of Renewable SSG SPC Unit to Mitigate Low-Frequency Electromechanical Oscillations

Grid operators require grid-connected renewable generation units (RGUs) to provide specific dynamic features. Among those features, the RGUs must support the dynamic performance of the power grid as well as operate in such a way to ward off new issues in the power system. Recently, unfavorable oscillatory modes have appeared through the grid connection of RGUs due to their dynamic interaction with other classical components of the grid. Therefore, it is essential to develop a novel technique for the dynamic design of RGUs to mitigate such risky oscillations. In this article, a novel analytical method is proposed for dynamic tuning of a renewable static synchronous generation unit controlled by synchronous power controller (RSSG-SPC). The proposed method is based on the mathematical analysis of the derivative function of general damping ratio formula. The analytical results establish generalized solutions that cover all operation mode of the RSSG-SPC. Further on, the solutions are implemented into the dynamic model of the RSSG-SPC to obtain clear, accurate, and trustable criteria for tuning of the virtual damping and virtual inertia. The dynamic tuning aims toward avoiding new oscillations in the system as well as to mitigate the natural oscillations of the power grid. The proposed approach was used for stability enhancement in high penetrated generation area as well as to support synchronization between interconnected areas in a two-area Kundur system. The proposed method was validated through modal analysis, time domain simulations as well as real-time evaluations which ensured that the proposed approach is a reliable technique for dynamic design of RSSG-SPCs.