Single Machine Infinite Bus System Research Articles

Mitigation of power system forced oscillations based on unified power flow controller

Forced oscillations (FOs), or low-frequency oscillations (LFOs) caused by periodic, continuous, small power disturbances, threaten the security and stability of power systems. Flexible AC transmission system (FACTS) devices can effectively mitigate LFOs via stability control. We propose a novel method that mitigates FOs by shifting the resonant frequency. Based on the features of the linearized swing equation of a generator, a resonant frequency shift can be achieved by controlling the synchronous torque coefficient using a unified power flow controller (UPFC). Because of the resonance mechanism, the steady-state response of an FO can be effectively mitigated when the resonant frequency changes from the original one, which was close to the disturbance frequency. The principle is that a change in resonant frequency affects the resonance condition. Simulations are conducted in a single-machine infinite-bus (SMIB) system, and the simulation results verify that the method is straightforward to implement and can significantly mitigate FOs. The controller robustness when the resonant frequency is not accurately estimated is also analyzed in the simulations.

Dynamic stability enhancement of TCSC‐based tidal power generation using quasi‐oppositional harmony search algorithm

This study presents the dynamic and steady state stability improvement of a tidal power generation system (TPGS) assisted power system model (i.e. single machine infinite bus (SMIB) system) using a thyristor controlled series capacitor (TCSC). To achieve this objective, the TCSC used in the studied model is optimally designed using quasi-oppositional harmony search algorithm (QOHSA). The complete dynamic equation of the studied power system is realised based on d–q-axis decomposition. Eigenvalue analysis is performed using the frequency-domain approach to study the steady-state stability while the time-domain-based simulation is carried out to determine the dynamic stability of the studied system. To corroborate the effectiveness of QOHSA, results yielded by this algorithm are compared with those obtained using particle swarm optimisation technique. It may be inferred from the results obtained in this study that the QOHSA tuned TCSC outperforms the other in improving the overall stability of the TPGS-based SMIB system following disturbance. Furthermore, a similar analysis is extended to the TPGS-based multi-machine power system model to validate the efficiency of QOHSA in optimal designing of TCSC for dynamic stability improvement.

Functional observer based controller for stabilizing Takagi–Sugeno fuzzy systems with time-delays

This paper investigates the construction of a fuzzy functional observer for nonlinear systems with time-delays, and the application of the observer to estimate the state functions of the parallel distributed compensation controller for stabilizing the system. Two types of time-delays are considered: constant and time-varying delays with bounded time derivative. Stability conditions are obtained using Lyapunov–Krasovskii functional approach; and the conditions are transformed into linear matrix inequalities with equality constraints so that observer parameters can be calculated using the solution of these inequalities. Functional observer construction procedures are presented considering both constant and time-varying time-delays. Two examples, including one for obtaining a power system stabilizer for a single machine infinite bus system, are presented to illustrate effectiveness of the proposed design procedures.

A hybrid modified differential evolution-pattern search approach for SSSC based damping controller design under communication constraints

Modern power systems depend greatly on their control systems which operate over communication networks to alleviate the effects of disturbances in the power system. However, it introduces vulnerabilities such as constraints of the communication and control systems that relay precarious control signals. In power systems, damping controllers using feedback signals from remote locations are likely to be adversely affected by communication constraints in future. In this study, an approach is employed to construct the remote control input signal from locally measurable quantity so that the control system performs satisfactorily under communication failure. A hybrid of global search (i.e. differential evolution: DE) and local search (i.e. pattern search: PS) technique is employed for static synchronous series compensator-based damping controller design in Single Machine Infinite Bus and multi-machine power systems. Proposed algorithm is first tested using bench mark test functions and compared with other recent state of art algorithms as well as some other recent variants of DE to validate the efficiency of the proposed approach. It is demonstrated that the proposed methodology provides better damping performance compared to some recently published methodologies.

Design and Analysis of Gravitational Search Algorithm Based TCSC Controller in Power System

In present era, the main contact of the power segment engineers is to expand the ability and immovability of the current power segment for attractive system presentation and dependable process. This directs to the growth of FACTS technology. FACTS controllers raise power conveys ability and constancy. This article represents representing and simulation of single machine infinite bus (SMIB) system with TCSC controller. Thyristor Controlled Series Capacitor (TCSC) controller is exercised to improve transient constancy of the SMIB system. In this article propose of TCSC controller is projected. The form of SMIB with TCSC and PID controllers are expanded in MATLAB for simulation. Three phase symmetrical faults are initiated to learn its characteristics. The simulation effects confirm that the constancy of the power system is being developed by TCSC controller and it efficiently damp out the power system oscillations.

A Variable Structured TCSC Controller for Power System Stability Enhancement

In present era, the main contact of the power segment engineers is to expand the ability and immovability of the current power segment for attractive system presentation and dependable process. This directs to the growth of FACTS technology. FACTS controllers raise power convey ability and constancy. This article represents representing and simulation of single machine infinite bus (SMIB) system with TCSC controller. Thyristor Controlled Series Capacitor (TCSC) controller is exercised to improve transient constancy of the SMIB system. In this article propose of TCSC controller is projected. The form of SMIB with TCSC and PID controllers are expanded in MATLAB for simulation. Three phase symmetrical faults are initiated to learn its characteristics. The simulation effects confirm that the constancy of the power system is being developed by TCSC controller and it efficiently damp out the power system oscillations.

An ME-SMIB Based Method for Online Transient Stability Assessment of a Multi-Area Interconnected Power System

Transient stability assessment (TSA) of the power system is essential to the safe operation of the power grid. The TSA of the multi-area interconnected power system is a challenging task due to its special multi-area power grid structure. New features, which are the time-variable instability mode and untypical two-group instability mode, emerge in the transients of the interconnected power system and affect the accuracy of conventional TSA methods. To address these problems, we propose a novel TSA method based on the modified equivalent single machine infinite bus (ME-SMIB) system. Two key technologies, namely generator groups identification and generator selection, were presented in the proposed method. Generator groups were identified at each time-step to track the time-variable instability mode. Two groups of generators that were of good coherency and closely related to the current instability mode were selected to construct the ME-SMIB system. The transient instability was finally identified by the concave-convexity-based method. The proposed method was tested in the 16-generator 68-bus power system and China interconnected power system. Results show that the proposed ME-SMIB system can avoid the misjudgments caused by new transient features of the multi-area interconnected power system, presenting superior reliability than the conventional E-SMIB system.

Nonlinear Modal Decoupling of Multi-Oscillator Systems With Applications to Power Systems

Many natural and manmade dynamical systems that are modeled as large nonlinear multi-oscillator systems like power systems are hard to analyze. For such a system, we propose a nonlinear modal decoupling (NMD) approach inversely constructing as many decoupled nonlinear oscillators as the system oscillation modes so that individual decoupled oscillators can easily be analyzed to infer dynamics and stability of the original system. The NMD follows a similar idea to the normal form except that we eliminate inter-modal terms but allow intra-modal terms of desired nonlinearities in decoupled systems, so decoupled systems can flexibly be shaped into desired forms of nonlinear oscillators. The NMD is then applied to power systems towards two types of nonlinear oscillators, i.e. the single-machine-infinite-bus (SMIB) systems and a proposed non-SMIB oscillator. Numerical studies on a 3-machine 9-bus system and New England 10-machine 39-bus system show that (i) decoupled oscillators keep a majority of the original system modal nonlinearities and the NMD provides a bigger validity region than the normal form, and (ii) decoupled non-SMIB oscillators may keep more authentic dynamics of the original system than decoupled SMIB systems.

Improving Transient Stability in Power Systems by Using Fuzzy Logic Controlled SVC

<span>This paper presents the capability of a fuzzy logic based stabilizer used for generating the supplementary control signal to voltage regulator of static VAR compensator (SVC) for improving damping oscillations in power systems. Generator speed deviation and line active power were chosen as input signals for the fuzzy logic controller (FLC). The quantity of reactive power supplied/absorbed by SVC is determined based on the two input signal and deviation of terminal voltage at each sampling time. The effectiveness and feasibility of the proposed control is demonstrated with Single Machine Infinite Bus (SMIB) system and multi machine system which show improvement over the use of a fixed parameter controller. It has been observed that a robust controller is obtained with fuzzy logic controller.</span>

PSS Based Angle Stability Improvement Using Whale Optimization Approach

This paper introduced a new swarm based optimization technique for tuning Power System Stabilizer (PSS) that attached to a synchronous generator in a single machine infinite bus (SMIB) system. PSS which is installed with Lead-Lag (LL) controller is introduced to elevate the damping capability of the generator in the low frequency mode. For tuning PSS-LL parameters, a new technique called Whale Optimization Algorithm (WOA) is proposed. This method mimics the social behavior of humpback whales which is characterized by their bubble-net hunting strategy in order to enhance the quality of the solution. Based on eigenvalues and damping ratio results, it is confirmed that the proposed technique is more efficient than Particle Swarm Optimization (PSO) and Evolutionary Programming (EP) in improving the angle stability of the system. Comparison between WOA, PSO and EP optimization techniques showed that the proposed computation approach give better solution and faster computation time.

Stabilizing Controller Design for Nonlinear Power System Using Particle Swarm Optimization

Major problem of power system is to maintain transient stability and voltage regulation on inception of a severe fault or large change of load. It is required to maintain both the synchronism and post fault voltage regulation for satisfactory operation. In general the transient stability is improved by increasing the excitation rapidly, by this method either the voltage regulation will be achieved or the transient stability could be improved. To improve both the transient stability and voltage regulation of power system simultaneously a composite controller (excitation and governor control) based on direct feedback linearization (DFL) technique is considered in this paper. It is proposed to compute the controller parameters by particle swarm optimization (PSO) technique, a heuristic optimization method. The complete procedure has been explained by an example of a single machine infinite bus system. By simulation it has been shown that both the transient stability and good voltage regulation is achieved by implementing this controller. For simulation MATLAB 7 software is used.

Dynamic Performance Enhancement of Synchronous Generator Excitation via Nonlinear Backstepping Control

Abstract This paper addresses the transient stability problem in power systems of nonlinear character. A recursive nonlinear backstepping controller for improving the single machine infinite bus system’s dynamic behavior is proposed for the system global stabilization considering the network transfer conductances. Despite parameters uncertainties, nonlinear dynamics and/or disturbances, the feedback laws based on the backstepping approach are explicitly derived and the conservatism of the stability property is guaranteed for both lossy and lossless power system representations. Simulation results, via MATLAB™-Simulink, reveal that the proposed backstepping technique can be feasibly designed to ensure significant dynamic performance enhancements.

Comparison of Dynamic Stability Response of A SMIB with PI and Fuzzy Controlled DPFC

Consumer utilities are non –linear in nature. This injects increased flow of current and reduced voltage with distortions which cause adverse effect on the stability of consumer utilities. To overcome this problem we are using a modern Flexible Alternating Current Transmission System controller i.e. distributed power flow controller (DPFC). This controller is similar to UPFC, which can be installed in a transmission line between the two electrical areas. In DPFC, instead of the common Dc link capacitor three single phase converters are used. In this paper we are concentrating on system stability (oscillation damping). For analyzing the stability of a single machine infinite bus system (SMIB) we have used PI controlled Distributed Power Flow Controller (DPFC) and Fuzzy controlled DPFC. All these models are simulated using MATLAB/SIMULINK. Simulation results shows Fuzzy controlled DPFC are better than PI controlled DPFC. The significance of the results are better stability and constant power supply.

Comparison of Dynamic Stability Response of A SMIB with PI and Fuzzy Controlled DPFC

Consumer utilities are non –linear in nature. This injects increased flow of current and reduced voltage with distortions which cause adverse effect on the stability of consumer utilities. To overcome this problem we are using a modern Flexible Alternating Current Transmission System controller i.e. distributed power flow controller (DPFC). This controller is similar to UPFC, which can be installed in a transmission line between the two electrical areas. In DPFC, instead of the common Dc link capacitor three single phase converters are used. In this paper we are concentrating on system stability (oscillation damping). For analyzing the stability of a single machine infinite bus system (SMIB) we have used PI controlled Distributed Power Flow Controller (DPFC) and Fuzzy controlled DPFC. All these models are simulated using MATLAB/SIMULINK. Simulation results shows Fuzzy controlled DPFC are better than PI controlled DPFC. The significance of the results are better stability and constant power supply.

Phillips-Heffron model for current-controlled power electronic generation unit

This paper presents a Phillips-Heffron model for the generation unit with current-controlled (CC) voltage source converter (VSC) as the interface. A concept of current angle is put forward for the CC-VSC, and the relationship between the current angle and the power angle is also quantified. Based on the current angle, a Phillips-Heffron model is established for the generation unit with CC-VSC, considering the dynamic of phase-locked-loop (PLL) in the weak grid. The model demonstrates that small-signal dynamics of the generation unit is similar to that of the traditional synchronous generator (SG) which is characterized by the electromechanical swing equations. Then the dynamics can be depicted by the famous inertia, synchronizing and damping coefficients. Small-signal stability of a CC-VSC-based single machine infinite bus system is analyzed by means of the traditional theory of power system. Based on the relationship between the current angle and the power angle, the Phillips-Heffron model of the CC-VSC is also used in stability analysis of multi-machine power system, and parameter optimizations of the CC-VSC are also studied for stability improvement.

Improved robust adaptive backstepping control approach on STATCOM for non‐linear power systems

The problem of large disturbance attenuation in the single-machine infinite-bus system with a static synchronous compensator (STATCOM) is proposed to be alleviated by an improved robust backstepping algorithm, which utilises error compensation and sliding mode variable structure control methods to achieve stability. For STATCOM systems with internal and external disturbances, the adaptive backstepping method is used to construct the storage function, and a non-linear L 2 gain interference rejection controller and parameter substitution law are applied simultaneously. The improved method differs from the traditional adaptive backstepping design in terms of error-compensation design methodology, in order to ensure robustness and insensitivity to large disturbances of the STATCOM system, and furthermore, preserving useful non-linearities and the real-time estimation of uncertain parameters. Finally, a simulation demonstrates that the improved method is more efficient than traditional adaptive backstepping with respect to the speed of adaptation and the response of the STATCOM system. Hence, the effectiveness and practicality of the proposed control method is demonstrated by engineers in applications.

Virtual Synchronous Generator Based Auxiliary Damping Control Design for the Power System with Renewable Generation

Aiming for large-scale renewable energy sources (RES) integrated to power systems with power electronic devices, the technology of virtual synchronous generator (VSG) has been developed and studied in recent years. It is necessary to analyze the damping characteristics of the power system with RES generation based on VSG and develop its corresponding damping controller to suppress the possible low frequency oscillation. Firstly, the mathematical model of VSG in a per unit (p.u) system is presented. Based on the single-machine infinite bus system integrated with an RES power plant, the influence of VSG on the damping characteristics of the power system is studied qualitatively by damping torque analysis. Furthermore, the small-signal model of the considered system is established and the damping ratio of the system is studied quantitatively by eigenvalue analysis, which concluded that adjusting the key control parameters has limited impacts on the damping ratio of the system. Consequently, referring to the configuration of traditional power system stabilizer (PSS), an auxiliary damping controller (ADC) for VSG is designed to suppress the low frequency oscillation of the power system. Finally, simulations were performed to verify the validity of theoretical analysis and the effectiveness of designed ADC.

A Novel Approach for Improvement of Power Swing Blocking and Deblocking Functions in Distance Relays

Power swing conditions in power systems make distance relays take the wrong breaker action in some cases. In this context, power swing blocking and power swing deblocking are two important functions in distance relays so as to distinguish power swing from a fault, which maintains stability of system and continuity of the power supply. In this paper, a sample estimation and error calculation method based on Taylor Series expansion is proposed for improving power swing detection performance of the relay. Performance of the method is compared with four conventional methods and a novel method in literature. Analyses are carried out in two systems: single machine-infinite bus system with parallel lines and 68-bus New England test—New York power system for fault, power swing, and fault during power swing scenarios. Simulations and performance analyses are carried out by using EMTDC/PSCAD and MATLAB, respectively. According to the results, when performances in correct operation, algorithm response times, clarity of outputs, and time passed for program execution on processor are considered, the proposed method has the best performance overall. It is found that by using the proposed method, distance relay performance in correct operation and speed for taking power swing blocking and deblocking actions are improved.

Optimization of Active Current for Large-Scale Wind Turbines Integrated into Weak Grids for Power System Transient Stability Improvement

Power system transient stability is a challenge when integrating large-scale wind turbines into weak grids. This paper addresses the issue of transient stability in such situations by optimizing a wind turbine’s active current behavior. A wind turbine’s active current reference controller and its setting optimization method are proposed based on analyses of two associated problems: the mechanism for improving transient stability of a single (synchronous) machine infinite bus (SMIB) system, as well as the various physical factor dependencies dictating how active and reactive wind turbine currents affect the swing dynamics of synchronous machines. Analysis of the first problem guided the design of the controller’s main structure. Analysis of the second problem guided selection of the control object within a wind turbine’s active and reactive currents, as well as helped recognition of the influential physical factors that must be considered in the parameter setting process. The efficiency of the controller and the validity of the analyses were verified by case studies using Kundur’s two-area system.

Nonlinear Synergetic Governor Controllers for Steam Turbine Generators to Enhance Power System Stability

This paper proposes a decentralized nonlinear synergetic governor controller (NSGC) for turbine generators to enhance power system stability by using synergetic control theory and the feedback linearization technique. The precise feedback linearization model of a turbine-generator with a steam valve control is obtained, at first, by using a feedback linearization technique. Then based on this model, a manifold is defined as a linear combination of the deviation of the rotor angle, speed deviation, and speed derivative. The control law of the proposed NSGC is deduced and the stability condition of the whole closed-loop system is subsequently analyzed. According to the requirement of the primary frequency regulation, an additional proportional integral (PI) controller is designed to dynamically track the steady-state value of the rotor angle. Case studies are undertaken based on a single-machine infinite-bus system and the New England system, respectively. Simulation results show that the proposed NSGC can suppress the power oscillations and improve transient stability more effectively in comparison with the conventional proportional-integral-derivative (PID) governor controller. Moreover, the proposed NSGC is robust to the variations of the system operating conditions.