Low Frequency Power Oscillations Research Articles

Inter‐area low‐frequency power system oscillations caused by open‐loop modal resonance

This study examines a modal condition to cause inter-area, low-frequency, electromechanical power oscillations in an interconnected power system with two subsystems. The modal condition being examined is the closeness of two electromechanical oscillation modes from each subsystem on the complex plane, which is referred to as open-loop modal resonance. The analysis in this study indicates that under the condition of open-loop modal resonance, the electromechanical oscillation modes of the interconnected power system are located at approximately opposite positions on the complex plane with respect to the resonant electromechanical oscillation modes of the subsystems. Hence, when open-loop modal resonance occurs, one electromechanical oscillation mode of the interconnected power system must have reduced damping. In this study, the damping reduction in the inter-area, low-frequency power oscillations caused by open-loop modal resonance is demonstrated using example power systems. An incident of inter-area, low-frequency electromechanical power oscillations that occurred in an actual large-scale power system in China is examined. The examination results indicate that the poorly damped, inter-area, low-frequency power oscillation incident was caused by open-loop modal resonance.

HFAGC based on MOPSO technique: Optimal design, comparison, verification

Good recovery of power system’s synchronism in the affected eclectic power system caused by the loading condition changes is the main target of Automatic Generation Control (AGC). Accomplished endeavors are led to suggest Hierarchical Fuzzy AGC (HFAGC) in multi-area interconnected power system aime d at alleviating both prominent issues i.e.: the low frequency power oscillations and the tie-line power exchange deviations. In this regard, application of multi-objective optimization technique isn’t avoidable. Due to high performance of Multi Objective Particle Swarm Optimization (MOPSO) in solving non-linear objectives, it has been engaged to unravel the optimization problem and optimal tune the HFAGC. To confirm the high efficiency and robustness of suggested controller, two different multi-area interconnected power systems have been taken into account for this study. Meantime, the potency of HFAGC has been thoroughly appraised and compared with Conventional AGC (CAGC) via occurrence of the Step Load Perturbation (SLP) in both these test power systems. To sum up, the simulations results have transparently corroborated the high performance of HFAGC as compared with CAGC in both the test power systems.

Alleviation SSR and Low Frequency Power Oscillations in Series Compensated Transmission Line using SVC Supplementary Controllers

In this work, supplementary sub-synchronous damping controllers (SSDC) are proposed for damping sub-synchronous oscillations in power systems with series compensated transmission lines. Series compensation have extensively been used as effective means of increasing the power transfer capability of a transmission lines and improving transient stability limits of power systems. Series compensation with transmission lines may cause sub-synchronous resonance (SSR). The eigenvalue investigation tool is used to ascertain the existence of SSR. It is shown that the addition of supplementary controller is able to stabilize all unstable modes for T-network model. Eigenvalue investigation and time domain transient simulation of detailed nonlinear system are considered to investigate the performance of the controllers. The efficacies of the suggested supplementary controllers are compared on the IEEE first benchmark model for computer simulations of SSR by means of time domain simulation in Matlab/Simulink environment. Supplementary SSDC are considered in order to compare effectiveness of SSDC during higher loading in alleviating the small signal stability problem.

Multi objective load frequency control using hybrid bacterial foraging and particle swarm optimized PI controller

Excessive load demand with reliability in power availability, demands for interconnection of large number of generating units over existing tie lines. Due to sudden change in demand, the power transfer over existing tie lines working close to their thermal limits results in low frequency power oscillations. Thus, in modern power systems the study of mitigation of these frequency oscillations is more involved and formulates the area of Load Frequency Control (LFC). Many conventional and heuristic control techniques have been recently applied to address the issue of LFC. This paper investigates load frequency control of large interconnected power system consisting of conventional and renewable energy sources, using hybrid heuristic approach. The proposed strategy is shown to result in improved system damping resulting in faster mitigation of low frequency oscillations.

Experimental demonstration and application planning of high temperature superconducting energy storage system for renewable power grids

Since high temperature superconducting magnetic energy storage system (HT SMES) has attracted significant attention for their fast response in milliseconds, high efficiency (cyclic efficiency over 95%) and unlimited times of charging and discharging cycles, it can be used for system stabilizing – damping out low frequency power oscillations. A voltage source converter (VSC) based HTS SMES has been optimal designed for achieving a high efficiency and has been constructed by China Electric Power Research Institute (CEPRI). This SMES can store the maximum energy, while for the first time used two states of art high temperature superconductors, YBCO and BSCCO tapes. It has been tested in a 110kV transmission power system by a dynamic power fluctuation compensation experiment using three different controlling strategies in CEPRI. The experimental output powers with these three strategies are compared and the results show that the SMES can trace the power variation and provide the required power to restrain the power fluctuation in milliseconds successfully. Finally, the application planning of SMES with the equivalent capacity in a practical renewable power system at Zhangbei wind power test base is evaluated by a case study based on the PSCAD/EMTDC simulation. An optimal switch time of the SMES in wind power system is presented using the real transmission parameters of Zhangbei power grid. This study can provide a reference for the demonstration of large-scale SMES systems in renewable power system.

Robust Design of Power System Stabilizer using Harmony Search Algorithm

In this paper, a novel Harmony Search algorithm (HSA) based approach for robust and optimal design of PID controller connected to power system stabilizer (PSS) is proposed for damping low frequency power oscillations of a single machine infinite bus bar (SMIB) power system. This paper attempts to optimize the three parameters (Kp, Ki, Kd) of PID-PSS via a music-based metaheuristic optimization algorithm inspired by the observation that the aim of music is to search for a perfect state of harmony. The problem of robustly selecting the parameters of the PSS is converted to an optimization problem which is solved by a Harmony Search Algorithm with a carefully selected objective function. The eigenvalue analysis and the simulation results obtained for internal and external disturbances for a wide range of operating conditions show the effectiveness and robustness of the proposed Harmony Search Algorithm based PSS (HSAPSS). Further, the time domain simulation results when compared with those obtained using conventional PSS (CPSS) and Genetic Algorithm based PSS (GAPSS) show the superiority of the proposed design.

Robust AGC based on Fuzzy Logic Controller: Design, Comparison and Ratification

Increasing the oscillations in the affected eclectic power system caused by the growth of loading conditions and occurrence of various distributions leads to losing the synchronism in the first-swing. A maiden effort is led to attain a novel Fuzzy Logic Automatic Generation Controller (FLAGC) to provide appropriate damping low frequency power oscillations. In order to guarantee the effectiveness and robustness of the proposed FLAGC controller, it has been thoroughly compared with Proportional Integral Derivative (PID) controller considering 2% step load perturbation in thermal area of the studied power system. The Real Coded Genetic Algorithm (RCGA) optimization technique due to have high sufficiency to solve the very non-linear objective is implemented for solution of the optimization problem. The obtained results of non-linear time-domain simulation reveal the high dynamical performance of proposed FLAGC controller.

Robust design of power system stabilizer using bacterial foraging algorithm

Abstract In this paper, a novel bacterial foraging algorithm (BFA) based approach for robust and optimal design of PID controller connected to power system stabilizer (PSS) is proposed for damping low frequency power oscillations of a single machine infinite bus bar (SMIB) power system. This paper attempts to optimize three parameters (Kp, Ki, Kd) of PID-PSS based on foraging behaviour of Escherichia coli bacteria in human intestine. The problem of robustly selecting the parameters of the power system stabilizer is converted to an optimization problem which is solved by a bacterial foraging algorithm with a carefully selected objective function. The eigenvalue analysis and the simulation results obtained for internal and external disturbances for a wide range of operating conditions show the effectiveness and robustness of the proposed BFAPSS. Further, the time domain simulation results when compared with those obtained using conventional PSS and Genetic Algorithm (GA) based PSS show the superiority of the proposed design.

Survey of Ambient Excitation Based Power Oscillation Analysis Methods

In large-scale power system, low frequency power oscillation is becoming a serious threat to the power system operation. Analysis of low frequency oscillation includes model-based method and ambient-excitation-based method. Based on the investigation of the related recently-published papers, this paper presents a survey of ambient-excitation-based method. Firstly, the fundamental principle and underlying theory of ambient-excitation-based method are summarized. Furthermore, several ambient-excitation-based methods are categorized and their characteristics are introduced.

Effects of various power system stabilizers on improving power system dynamic performance

To ensure the small-signal stability of a power system, power system stabilizers (PSSs) are extensively applied for damping low frequency power oscillations through modulating the excitation supplied to synchronous machines, and increasing interest has been focused on developing different PSS schemes to tackle the threat of damping oscillations to power system stability. This paper examines four different PSS models and investigates their performances on damping power system dynamics using both small-signal eigenvalue analysis and large-signal dynamic simulations. The four kinds of PSSs examined include the Conventional PSS (CPSS), Single Neuron based PSS (SNPSS), Adaptive PSS (APSS) and Multi-band PSS (MBPSS). A steep descent parameter optimization algorithm is employed to seek the optimal PSS design parameters. To evaluate the effects of these PSSs on improving power system dynamic behaviors, case studies are carried out on an 8-unit 24-bus power system through both small-signal eigenvalue analysis and large-signal time-domain simulations.

Low-frequency power oscillation damping enhancement and voltage improvement using unified power flow controller (UPFC) in multi-machine power system

The problem of low-frequency power swings is a matter of concern for power systems engineers in the operation and planning of power systems. Therefore, this paper is an investigation of the use of unified power flow controller (UPFC) that is suitably tuned to improve the damping of low frequency power oscillations present in Nigerian grid system. A large disturbance is initiated, during simulation in PSAT, in the network to induce nonlinear oscillations of the power system in order to ascertain the damping effect of UPFC. The dynamic responses of the system simulated show that the system is well damped and is stabilized at minimal time which confirms the robustness of the UPFC. Finally, a comparative study in a typical transient stability problem on IEEE 14-bus system using a UPFC model and the Nigerian high voltage interconnected system is used to illustrate the concepts presented in this paper. Key words: Power oscillation damping, power systems, unified power flow controller (UPFC), flexible AC transmission system (FACTS) devices, low frequency oscillation

Low Frequency Power Oscillation Damping Enhancement and Voltage Improvement Using Unified Power Flow Controller (UPFC) in Multi-Machine Power System

The problem of low-frequency power swings is a matter of concern for power systems engineers in the operation and planning of power systems. Therefore, this paper is an investigation of the use of unified power flow controller (UPFC) that is suitably tuned to improve the damping of low frequency power oscillations present in Nigerian grid system. A large disturbance is initiated, during simulation in PSAT, in the network to induce nonlinear oscillations of the power system in order to ascertain the damping effect of UPFC. The dynamic responses of the system simulated show that the system is well damped and is stabilized at minimal time which confirms the robustness of the UPFC. Finally, a comparative study in a typical transient stability problem on IEEE 14-bus system using a UPFC model and the Nigerian high voltage interconnected system is used to illustrate the concepts presented in this paper. Key words: Power oscillation damping, power systems, unified power flow controller (UPFC), flexible AC transmission system (FACTS) devices, low frequency oscillation

Damping of sub-synchronous resonance and low-frequency power oscillation in a series-compensated transmission line using gate-controlled series capacitor

In this paper, the impact of different gate-controlled series capacitor (GCSC) control methodologies on sub-synchronous resonance (SSR) problems of series capacitive compensated transmission lines is analyzed. The low-frequency power oscillation (LFPO) damping using GCSC also is studied. In these studies, the effect of the rating of the GCSC is also considered. Three different control methodologies are proposed: open loop, constant power, and Takagi-Sugeno (TS) fuzzy control. It is shown that the GCSC can damp both the SSR and LFPO using the constant power control (CPC) methodology. It is also shown that when the parameters of the CPC is optimized by the TS fuzzy controller, the third methodology can present a cost-effective solution for both the SSR and LFPO damping. In this work, the IEEE First Benchmark Model is employed, including a GCSC device, and the study is performed using MATLAB program.

Simplified models of a single-phase power electronic inverter for railway power system stability analysis—Development and evaluation

Use of power electronic equipment has increased and introduced new dynamical phenomena in power systems. For example, new electric rail vehicles (locomotives) equipped with modern power electronic traction chains have caused situations of low-frequency power oscillations and instability in single-phase railway power supply systems. This paper presents the development and implementation of an instantaneous value model and simplified fundamental frequency (RMS) models of such an advanced electric rail vehicle in order to investigate their representation of low-frequency dynamics. The dynamical behaviour is studied by use of both time-domain simulations and linear analysis (eigenvalues) and the degree of simplifications regarding controller dynamics and power system dynamics are presented and discussed. An enhanced RMS model is tested in order to account for the impact of fast current dynamics on the low-frequency behaviour. The results show that this enhanced model is corresponding more closely to the instantaneous value model than what can be obtained by the traditional RMS simplifications and indicate that current dynamics should be included in stability studies involving power electronic inverters.

Robust PSS Parameters Design Using a Trajectory Sensitivity Approach

A new model for coordinated optimal design of power system stabilizers (PSSs) is proposed for damping low frequency power oscillation of interconnected power systems and enhancing overall performance of both transient and small-signal stability. In this model, a novel objective function is constructed using rotor speeds of generators in a post disturbed period. Trajectory sensitivity mapping technique is proposed to evaluate the approximate gradients of the objective function relative to the PSS parameters. With the gradients, conjugate gradient method is employed to assess the PSS parameters for minimizing the objective function. Two schemes of gradient formulation and optimization procedure are suggested and compared. The model and effectiveness of the method are verified by eigenvalue assessments and time domain nonlinear simulations on the IEEE four-generator and the ten-generator New England test systems.

Active and reactive power control of a VSC-HVdc

Voltage source converter-based HVdc (VSC-HVdc) systems have the ability to rapidly control the transmitted active power, and also to independently exchange reactive power with transmissions systems. Due to these characteristics, VSC-HVdcs with a suitable control scheme can offer an alternative means to enhance transient stability, to improve power oscillations damping, and to provide voltage support. In this paper, a VSC-HVdc is represented by a simple model, referred to as the injection model. Based on this model, an energy function is developed for a multi-machine power system including VSC-HVdcs. Furthermore, based on Lyapunov theory (control Lyapunov function) and small signal analysis (modal analysis), various control strategies for transient stability and damping of low-frequency power oscillations are derived.

Controller Design for SVC and TCSC to Enhance Damping of Power System Oscillations

This article describes a systematic approach for the design of a supplementary controller for static VAR compensators (SVC) and thyristor-controlled series capacitors (TCSC) to improve the damping of power system oscillatory modes. The problem is analyzed from the control point of view. The reduced order model of the power system is obtained using the Prony identification method; the residue and root locus methods are then used for controller design. It is noticed that by adjusting the controller gain according to the operating condition, better damping effects could be achieved. Dynamic simulations were performed to investigate the effect of the damping controller in increasing system dynamic stability. Simulation results show that with the designed controller installed, low frequency power oscillations are effectively damped.

Indirect Adaptive External Neuro-Control for a Series Capacitive Reactance Compensator Based on a Voltage Source PWM Converter in Damping Power Oscillations

A series capacitive reactance compensator (SCRC), using a voltage source converter to inject a controllable voltage in quadrature with the line current of a power network, is capable of rapidly providing a specified and controllable magnitude of capacitive reactance compensation independent of the line current. Moreover, with a suitably designed external controller, the SCRC can also be used to damp low-frequency power oscillations in a power network. Conventionally, linear control techniques are used to design the SCRC external controller around a specific operating point, where the nonlinear system equations are linearized. However, at other operating points its performance degrades. Nonlinear adaptive neuro-controllers offer an attractive approach to overcome this degradation problem. In this paper, an indirect adaptive external neuro-controller (INDAEC) using two radial basis function neural networks (RBFNNs) is proposed to improve the damping performance of an SCRC connected to a power network. This nonlinear INDAEC needs no mathematical model of the SCRC or the power network. It provides the SCRC with improved damping performance over a wide range of system operating conditions. This is shown by results on a single machine infinite bus power system, as well as a multimachine power system

Damping of Low Frequency Power Oscillations Using Improved Pole-Assignment Controller

This article presents a methodology for modelling and control of low frequency oscillations existing in a single and in two-area power systems. The proposed controller is based on shifting the eigenvalues of the system to optimum locations that provide an improved dynamic performance as compared with a previously reported work. The implemented pole-assignment algorithm has a simplified formulation procedure and requires less computation time as compared with equivalent algorithms. Computer simulations that assess the effectiveness and performance of the proposed controller are presented.

A fuzzy logic-based adaptive damping controller for static VAR compensator

This paper presents an approach for designing a fuzzy logic-based adaptive SVC damping controller for damping low frequency power oscillations. The proposed approach uses linear optimal controllers and, in addition, a fuzzy signal tuner is introduced to achieve adaptiveness. Two linear damping controllers are designed to accommodate two extreme operating conditions and a fuzzy logic mechanism is used to generate one single control signal by properly combining the outputs of the linear controllers. The fuzzy controller is optimized using a least squares error criterion and, as a result, a higher-order adaptive controller is achieved. Simulation studies of the proposed fuzzy adaptive damping controller show that it provides satisfactory damping against low frequency oscillations under different operating conditions. Results are given for a one-machine infinite-bus and a four-machine two-area test system, which show improvement over the use of a fixed parameter controller.