One-machine Infinite-bus System Research Articles

Research on Power Angle Characteristics of One-Machine Infinite-Bus Power Systems of Mixed Gauss and Poisson Stochastic Excitation

Background: A high percentage of renewable energy and a high percentage of power electronic devices are connected to the power system, which leads to the diversification and complexity of stochastic excitation, and the traditional single-excitation stochastic model is no longer applicable. Objective: The study aimed to solve the problem that the high proportion of renewable energy and the high proportion of power electronic equipment are connected to the power system, which leads to the diversification and complexity of stochastic excitation and makes the traditional stochastic model of single excitation no longer applicable. Methods: Firstly, stochastic differential equations for power systems have been modelled with mixed Gaussian white noise and Poisson white noise excitation. Secondly, the Milstein-Euler predictor-corrector method has been developed to solve the stochastic differential equation model of the power system. Finally, the influence of Gauss white noise and Poisson white noise on the power system stability under different excitation intensities has been analyzed. The rationality and correctness of the model have been verified by the simulation of a one-machine infinitebus (OMIB) system. Results: The stochastic differential equation model of a power system with Gauss white noise and Poisson white noise excitation has been established and its angle stability has been analyzed. Increasing the Gaussian white noise and Poisson white noise excitation intensity can lead to an increase in the fluctuation of the power angle curve, as well as an increase in the standard deviation and expected value of the power angle mean curve, which may decrease the stability of the power system. Conclusion: This study provides a reference for stochastic power systems modeling and efficient simulation, and has important application value for power system stability assessment and safety evaluation as well as related patent applications.

Analysis of power system angle stability based on Heun algorithm under gauss and jump excitation

In the process of promoting the dual-carbon goals, the “double-high” character of the power system is gradually becoming obvious and brings a lot of random factors, such as high proportion of new energy access and cut out power system, brings gauss excitation from continuous fluctuations and jump excitation from shock fluctuations, affecting the power system safety operation. Combining the effects of gauss excitation and jump excitation, described as excitation terms acting on gauss white noise and poisson white noise. Constructing the stochastic dynamic model with jump of power system, Heun method is constructed to solve the model, and the comprehensive influence of stochastic excitation and jump excitation under different intensities on stability analysis is analyzed quantitatively. The simulation results of one-machine infinite-bus (OMIB) system shows the correctness and rationality of the method constructed, and provides ideas for the analysis of power system stability under the combined influence of multiple types of random factors.

Synchrophasor-Based Online Transient Stability Assessment Using Regression Models

An online post-fault transient stability assessment method is proposed in this study using synchrophasor or PMU measurements. Initially, a post-fault multimachine system is converted into a suitable one machine infinite bus (OMIB) system using the single machine equivalent (SIME) method. Thus, the - trajectory obtained through the OMIB system enabled a normalized transient stability index to be calculated offline. By using synchrophasor measurements before and during the fault as inputs, the regression model can be trained offline to predict the normalized stability margins. Following a fault, the synchrophasor measurements are used as input to this trained model for online stability margin prediction. If the predicted margin is negative, then the post-fault power system is indicated to be unstable. Alternatively, positive values for the predicted margin identify the system as stable. The proposed assessment method is verified using the New England (NE) 39 bus test system. The results obtained are then compared with offline simulations.

On the Initialization of Transient Stability Models of Power Systems With the Inclusion of Stochastic Processes

This letter addresses the initialization problem of power systems modeled as (SDAEs) and proposes a novel efficient initialization method. The method involves finding the co-variance matrix for the system state variables and initializing the stochastic state variables of the system randomly based on their probability distribution. Deterministic states and algebraic variables are then initialized based on the initial stochastic processes and the system co-variance matrix. The proposed method is illustrated through Monte Carlo simulations of a one-machine infinite-bus system and its numerical performance discussed through a dynamic 1479-bus model of the all-island Irish transmission system. It is shown that by utilizing the proposed method the computation time needed for the Monte Carlo simulations of the system can be reduced significantly compared to other initialization methods used in the literature.

Quantitative transient stability assessment in microgrids combining both time-domain simulations and energy function analysis

Hybrid microgrids of the future comprise synchronous generators and inverter-based photovoltaics, battery storage systems etc. Interconnection of off-grid hybrid microgrids can provide economic benefits and increase security of supply. Both in the short-term and long-term planning phase as well as during operation, transient stability assessment (TSA) of such clustered hybrid microgrids is essential at different operating points. Quantitative TSA helps in, for example, optimal generation dispatching, adjusting clearing times in the protection systems, optimal clustering of microgrids etc. However, the existing five hybrid methods developed for transmission systems with certain assumptions and limitations, taking the advantages of both time-domain simulations and transient energy function (TEF), cannot be directly applied for microgrids. Although there could be less than ten synchronous generators in clustered hybrid microgrids, a detailed TSA in such systems is too complex to begin with. Hence, two basic power system models – one-machine infinite-bus system (OMIBS) and two-machine system (TMS) – with classical 2nd order and detailed 5th order modelling of diesel generators (DG) with and without controllers are studied in this paper. One of the aims is to get a better knowledge of the dynamic behaviour and analyse kinetic energy (KE) and potential energy (PE) profiles. The main goal is to develop a new hybrid method to define a stability margin (SM) and a stability degree (SD) for both the types of generator modelling. The stability analyses in the OMIBS show that, the influence of the generator modelling on the end results, i.e., SM and SD, is significant. The duration of the sub-transient state in DG might be of just several tens of milliseconds after the fault incident, but the indirect effect of the sub-transient short-circuit currents especially on speed governors until the end of the forward swing is substantial. In the TMS, the synchronous operation of the DG is strongly dependent on each other. The TEF and its components like KE and PE, which are applied individually to each DG, are inversely proportional to the inertia constants of the DG. It was shown not only graphically, but also by postulating and proving two propositions. Therefore, an important foundation regarding the TEF has been laid for the quantitative TSA in multi-machine clustered hybrid microgrids.

Improvement of Power System Stability by Using New Switching Technique in Bridge-type Fault Current Limiter

The bridge-type fault current limiter has the capability of controlling the fault current by controlling the DC reactor current. This fault current limiter is mainly composed of a diode bridge rectifier and a DC reactor. To achieve this capability, a resistor parallel with a semiconductor switch has been used in series with a DC reactor. For this fault current limiter, a control scheme is proposed that uses the DC reactor current as a control variable to improve transient stability of the model power system without measuring any parameters of system. In this article, an analytical and simulation study was conducted on a one-machine infinite-bus system including a bridge-type fault current limiter and the proposed control scheme. Simulation results show that by controlling the turn-on and turn-off times of the switch, i.e., the switching technique, the proposed fault current limiter can not only limit the fault current but also absorb the accelerating energy of the generator, thereby improving power system transient stability. The rotor velocity, maximum output power of the generator, and critical fault clearing time are studied in this article to evaluate the effects of the proposed fault current limiter on power system transient stability.

Applications of Nonlinear Control for Fault Ride-Through Enhancement of Doubly Fed Induction Generators

Applications of several nonlinear control laws, including differential geometric approach and the robust variable structure system (VSS) approach, will be investigated for the fault ride-through (FRT) enhancement of the doubly fed induction generator wind power system. In differential geometric approach, both input-output feedback linearization and state feedback linearization will be studied for rotor-side converter and stator-side converter control. In robust VSS approach, supplementary control generated by the complete models is achieved for FRT enhancement. Two objectives, maximizing the active power output as well as regulating the terminal voltage, will be utilized for designing the sliding manifold. Since the proposed methods are based on the general nonlinear system theory, the FRT capability can be indeed improved even under severe fault conditions. Simulations on a one-machine infinite bus system and a two-area four-machine system are presented to validate this result. Performance comparisons among several existing FRT enhanced control will also be examined to show the effectiveness of these nonlinear control schemes.

Basin stability of the Kuramoto-like model in small networks

Power system stability is quantified as the ability to regain an equilibrium state after being subjected to perturbations. We start by investigating the global basin stability of a single machine bus-bar system and then extend it to two and four oscillators. We calculate the basin stability of the stable fixed point over the whole parameter space, in which different parameter combinations give rise to a stable fixed point and/or a stable limit cycle depending crucially on initial conditions. A governing equation for the limit cycle of the one-machine infinite bus system is derived analytically and these results are found to be in good agreement with numerical simulations.

Stability Enhancement of a Power System With a PMSG-Based and a DFIG-Based Offshore Wind Farm Using a SVC With an Adaptive-Network-Based Fuzzy Inference System

This paper presents the stability-improvement results of a synchronous generator (SG)-based one-machine infinite-bus system with a permanent-magnet SG (PMSG)-based offshore wind farm (OWF) and a doubly fed induction generator (DFIG)-based OWF using a static VAR compensator (SVC). The operating characteristics of the studied two OWFs are simulated by an equivalent aggregated PMSG driven by an equivalent wind turbine (WT) and an equivalent aggregated DFIG driven by an equivalent WT through an equivalent gearbox, respectively. A damping controller of the SVC is designed by using adaptive-network-based fuzzy inference system (ANFIS) to contribute adequate damping characteristics to the dominant modes of the studied SG under various operating conditions. A frequency-domain approach based on a linearized system model using root-loci technique and a time-domain scheme based on a nonlinear system model subject to various disturbances are both utilized to examine the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed SVC joined with the ANFIS damping controller is capable of improving the stability of the studied SG system subject to different disturbances.

Performance Assessment of Fuzzy Logic Power System Stabilizer on North Benghazi Power Plant

Fuzzy logic design has been implemented online to tune the power system stabilizer gain (KPSS). To assess the performance of the proposed technique, Benghazi North Power Plant (BNPP), at eastern Libyan network, has been utilized as a power system stabilizer (PSS) benchmark. The design considers different operating conditions and large disturbance. A selection of fuzzy rules is derived by means of system output power to tune KPSS, whereas Particle Swarm Optimization technique (PSO) is exploited to calculate the PSS parameters offline according to real-time measurements of the considered plant. Several simulation scenarios have been conducted to show the effectiveness of the proposed PSS in damping of local and interarea modes of oscillation of one-machine infinite-bus system. The study also contains comparison between the proposed technique and conventional PSS (CPSS).

Comparisons of Damping Controllers for Stability Enhancement of an Offshore Wind Farm Fed to an OMIB System Through an LCC-HVDC Link

This paper presents an effective control scheme to simultaneously perform power-fluctuation mitigation and damping improvement of a permanent-magnet synchronous generator (PMSG)-based offshore wind farm (OWF) fed to a one-machine infinite-bus (OMIB) system using a high-voltage direct-current (HVDC) link based on line-commutated converter (LCC). The rectifier current regulator (RCR) and the inverter current regulator (ICR) of the HVDC link are individually designed using modal control theory to render adequate damping to the dominant modes of the synchronous generator (SG) of the studied OMIB system under different operating conditions. A frequency-domain scheme based on eigenvalue analysis and a time-domain method based on nonlinear model simulations are both carried out to compare the damping characteristics of the two damping controllers. It can be concluded from the simulation results that the proposed LCC-HVDC link combined with the designed ICR can render better damping performance to the qualities of the LCC-HVDC and the OWF than the designed RCR.

Power Flow Control and Stability Improvement of Connecting an Offshore Wind Farm to a One-Machine Infinite-Bus System Using a Static Synchronous Series Compensator

This paper presents the stability improvement and power-flow control results of a DFIG-based offshore wind farm (OWF) connected to a one-machine infinite-bus (OMIB) system using a static synchronous series compensator (SSSC). An oscillation damping controller (ODC) of the proposed SSSC is designed by using modal control theory to render proper damping to the dominant mode of the studied synchronous generator (SG). A frequency-domain approach based on a linearized system model using eigenvalue analysis is accomplished. A time-domain scheme based on a nonlinear system model subject to a disturbance is also performed. It can be concluded from the simulation results that the proposed SSSC joined with the designed ODC can effectively improve the stability of the studied OMIB system with an OWF under various disturbances. The inherent low-frequency oscillations of the OMIB system can also be effectively suppressed by the proposed control scheme.

Stability Improvement of a Hybrid DFIG-Based and PMSG-Based Offshore Wind Farm fed to a SG-Based Power System Using a STATCOM

This paper presents the stability-improvement results of a synchronous generator (SG)-based one-machine infinite-bus (OMIB) system with a hybrid doubly-fed induction generator (DFIG)-based and permanent-magnet synchronous generator (PMSG)-based offshore wind farm (OWF) using a static synchronous compensator (STATCOM). The operating performance of the studied PMSG-based OWF is simulated by an equivalent PMSG driven by an equivalent wind turbine (WT) while an equivalent DFIG driven by an equivalent WT through an equivalent gearbox is used to simulate the operating characteristics of the DFIG-based OWF. The hybrid OWF is connected to the point of common coupling (PCC) of the SG-based OMIB system through an undersea cable and an underground cable. The proposed STATCOM is connected to the PCC to supply the required reactive power to the SG-based power system. A frequency-domain approach based on a linearized system model using eigenvalue technique and a time-domain scheme based on a nonlinear system model subject to various disturbance conditions are both utilized to examine the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed STATCOM is capable of offering adequate damping characteristics to stabilize the studied OMIB system under various operating conditions.

Coordinated Setting of Multiple PSSs for Actual Size Power Network

SUMMARY The power system stabilizer (PSS) is a low-cost method of stabilizing the intertie and local oscillations of a power network. The PSS parameters are usually adjusted based on the one-machine infinite-bus system model. In contrast, a real power system consists of multimachine systems. Thus, coordinated setting of the PSS parameters, with the real characteristics of the power system network taken into consideration, is expected to improve stability. For this purpose, the modal performance measure (MPM) method is used to adjust the PSS parameters. The power network mathematical model that is required for this calculation is given by the system identification method. Utilizing the MPM method characteristics, restrictions such as the damping coefficient and maximum gain, which constitute practical design specifications used for conventional controllers, are naturally introduced. Furthermore, radial basis function (RBF) frequency weighing is introduced in order to adjust the frequency responses. The expected favorable results were found in large-scale power system simulations.

PSS協調整定のための詳細系統モデルのシステム同定

The PSS is a reasonable controller to stabilize the intertie and local oscillations of power networks. PSSs are usually set with the one-machine infinite-bus system model. The coordinated setting of the multiple PSSs considering the characteristics of the network is expected to improve stability. For this purpose, the Modal Performance Measure method is used to adjust the PSS parameters. The model is identified by the N4SID identification method. In this paper, the conditions of identification and validation of identification are presented. Identified models are validated by comparison of vector diagrams, impulse response, and so on. Identification of a power network that consists of many generators is successful. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(2): 10–19, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22287

Influence of a voltage compensation type active superconducting fault current limiter on the transient stability of power system

We have proposed a voltage compensation type active superconducting fault current limiter (SFCL). In this paper, the influence of the SFCL on the transient stability of power system is investigated. For the typical one-machine infinite-bus system, the power-angle characteristics of generator with SFCL are studied in different working conditions, and the transient physical process is analyzed. Using MATLAB SIMULINK, the power-angle swing curves are simulated under different current-limiting modes, fault types and fault clearance times. The results show that the proposed SFCL can effectively reduce the transient swing amplitude of rotor and extend the critical clearance time under mode 1, compared with mode 2 and mode 3 having few effects on enhancing the transient stability.

System time-varying controller design via E.A. method

The new concepts of time-varying stabilizer via dynamic pole assignment and eigenstructure assignment method (E.A. method) are introduced in this paper. The theorem of dynamic pole assignment is obtained by employing the piecewise constant concept. By specifying the final eigenstructure, the parameters of the time-varying stabilizer can be determined via output controller is evaluated, and examples of a one-machine infinite-bussystem and a multimachine system in power system, are given to illustrate the advantages and effectiveness of the proposed technique.

Generator Control Based on Equilibrium Point Analysis of Standard One-Machine Infinite-Bus System Model-Comparison with PSS-

We have recently proposed a new controller based on equilibrium point analysis for power system models. In this paper, first the Japanese standard one-machine infinite-bus system model is formulated, and the equilibrium points are analyzed. Next, complementary control inputs for AVR and GOV with limiters of the system model are determined on the basis of the analysis. Finally, it is shown that the unstable equilibrium point is eliminated by adding the proposed inputs, and then the critical clearing time can be improved in comparison with PSS of the standard model. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(3): 16–23, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20359

Dynamic and Transient Analysis of Power Distribution Systems With Fuel Cells—Part II: Control and Stability Enhancement

The objective of this paper is to analyze the dynamics of distribution systems that contain fuel cells and to enhance the stability of these systems by controlling the fuel cells. The models used in this second part of the two-part paper are the solid-oxide fuel cell (SOFC) models developed in part one. The fuel-cell control loops through the power conditioning units are first explained using a one-machine infinite bus system. Then, fuel cells are integrated into a power distribution test system, which initially contains gas turbines only. Simulation results show how a combination of fuel cells and gas turbines can help control frequency fluctuations, and supply power after islanding of the distribution system.

A Study on Reclosing Operation Considering Fault Current Limiter

This paper proposes the effective reclosing operation method in the current lirniter introduction power system. From a angular velocity, a field system voltage, a phase of the generator, the proposed method calculates the optimum reclosing time domain. The current lirniter used reactance type and resistive type. The examination was carried out using the Inst. of Electrical Engineers of Japan one-machine infinite bus system model in order to demonstrate the effectiveness of the proposal method. In the simulation, Impact ver2.3 was used.