Transient Stability Control Research Articles

Transient Stability Improvement of Multi-machine Power System using Higher Order Sliding Mode Control

The main purpose of this paper is to design a non-linear second order sliding mode control for transient stability of two generator system (TGS). Second order sliding mode algorithms such as Twisting Algorithm (TA) and Super Twisting Algorithm (STA) have been applied and their simulation results are compared. The equilibrium point of TGS is maintained after the clearance of fault and the system is in post fault condition. Simulation results verify the proposed controller. The advantage with this type of control is that it does not require linearized model for its implementation and reduced chattering effect.

Performance Analysis of a Three Level Twelve-pulse VSC based STATCOM under Fault Condition

Recently with the progression of distributed generation, the power system needs flexible control of power transfer, better power flow control and improvement of transient stability. Additionally for improving the reliability of power system networks, using various protection strategies, power electronic switches are widely used to include new control strategies for improvement of quality of power. Cascaded multilevel inverter based STATCOM with higher bandwidth are now thus more efficient for minimizing voltage fluctuation, flicker mitigation, better reactive power compensation as well as stability enhancement. In our paper a three level twelve-pulse VSI based STATCOM is proposed in a distribution system for analyzing its effect on voltage profile as well as reactive power compensation under three phase fault condition. The proposed method for controlling the Statcom clearly shows that by proper utilization of the Statcom in our distribution system, voltage profile across the various types of load improves effectively under three phase fault condition and thus sustainability of the overall system will also improve. The output results show that the value of THD across different load voltages, e.g, FFT analysis of output voltage across STATCOM in the branch with fault (THD = 4.26%) has been shown. Additionally, FFT analysis of output voltage across Fixed Load (THD = 5.53%), Variable Load (THD = 2.76%), and Fixed Load current (THD = 2.85%) are within the acceptable limits and thus showing its well effectiveness in our proposed control strategyKeywords: STATCOM, Reactive Power Control, FFT, FACTS, THD.

IMPROVEMENT OF TRANSIENT STABILITY OF POWER SYSTEM USING SOLID STATE CIRCUIT BREAKER

The aim of this study is to use a solid state circuit breaker for the improvement of transient stability margin. Long distance AC transmission is often subject to stability problems, which limits the transmission capability. Interconnected power systems suffer from weakly damped swings between synchronous generator and sub systems. The development of modern power system has lead to an increasing complexity in the study of power system and also presents new challenges to power system stability and in particular to the aspects of transient stability and small signal stability. Transient stability control plays a significant role in ensuring the stable operation of power systems in the event of large disturbances and faults and is thus a significant area of research. This study investigates the improvement of transient stability of a two area system, using Solid State Circuit Breaker which is capable of fast switching in case of faults and thus controlling the real and reactive power flows in a faulted transmission line. Simulations are carried out in Matlab/Simulink environment for two area system model with Solid State Circuit Breaker to analyze the effects of SSCB on transient stability performance of the system. From the simulation results, swing curves of the three phase faulted power system without SSCB gets increases monotonically and thus the system can be considered as unstable whereas the swing curves of the system with an SSCB reaches to a steady state.

Optimal Comprehensive Control of Prevention and Emergency Based on DSR and Probabilistic Insecurity Measurement

Transient stability control of power system is a non-linear optimization problem which contains many constraints. Considering the cost of preventive control, emergency control and the following restorative control synthetically, a model of preventive control and emergency control based on DSR(Dynamic Security Region) and probabilistic insecurity measurement is proposed in the paper, and the optimal operating point of the system was obtained by using the improved genetic algorithm. In the end, the feasibility of the model and optimization strategy are verified by the case of the IEEE 4-generators 11-nodes system. Simulation show that the cost of comprehensive control of prevention and emergency is 13.2% less than the case that without the consideration of the random factors of the fault.

A coherency based generator rescheduling for preventive control of transient stability in power systems

This paper proposes a preventive control of transient stability with generation rescheduling based on coherency obtained using time domain simulations. The transient security dispatch finds a generation configuration with better transient stability behavior. One of the most practiced and an obvious technique of preventive control is rescheduling the power outputs of generators in the system. However, all generators in the system need not take part in rescheduling process. Selection of participating generators has been introduced using generator coherency for given contingency. The effectiveness of the proposed methodology is demonstrated on IEEE 145-bus 50-generator system for a three phase fault at different loading conditions with single and multiple line outage cases.

A New Nonlinear Excitation Control Strategy with Terminal Voltage Feedback

This paper presents a new nonlinear excitation controller for transient stability with voltage feedback of a synchronous power generator connected to a single machine infinite bus. In this design terminal voltage is introduced as a feedback. The proposed controller based on voltage feedback technique which enhance the transient stability of power system and stabilizes the terminal voltage about the given operating point when the fault occurs closer to the infinite bus bar. Simulation results show that, compared with the controller without voltage feedback, the proposed controller has better control effect on power system and which remarkably improves the deficiencies in the control of generator terminal voltage of the traditional control.

Transient stability analysis and control of power systems with considering flux decay by energy function approach

Transient stability analysis and control of power systems with considering flux decay by energy function approach In this paper, transient stability of power systems with structure preserving models is considered. A Hamiltonian function which can be regarded as a Lyapunov function for the system is proposed. Based on this, the influence of flux decay dynamics, especially during a fault, on transient stability is analyzed. With the increase of load power, the variation of stability boundary in the rotor angle/E'q plane is shown. The Energy-based excitation control, aiming at injecting additional damping into the post-fault system may reduce the critical clearing time (CCT). This can be demonstrated by the comparison of different flux decay dynamics in the fault-on condition, and the reason is illustrated by the relationship between rotor angle/E'q and the stability boundary. An improved control strategy is proposed and applied to increase the CCT. Simulation results verify that improvement is obtained both in transient stability and dynamic performance.

A Particle Swarm Optimization based Approach for Power System Transient Stability Enhancement with TCSC

Power system engineers are currently facing challenges to increase the power transfer capabilities of existing transmission system. This led to the evolution of FACTS technology. FACTS controller helps in raising dynamic stability limit, provide better power flow control also provides improvement in asset utilization, system flexibility and system performance. Thyristor controlled series compensator (TCSC) is a series FACTS controller which can control the line impedance, improve network stability and damp the power system oscillations. This paper presents a procedure for modelling and optimal tuning the parameters of Thyristor controlled series compensator (TCSC) controller for the power system transient stability. For the simulation purpose, the model of Single Machine Infinite Bus (SMIB) power system with TCSC controller is developed in MATLAB. The design problem of TCSC controller is formulated as an optimization problem and particle swarm optimization (PSO) is applied to search for the optimal TCSC control parameters. The results obtained shows that the proposed TCSC controller is effective in damping small disturbance condition in the power system.

Area‐Based COI‐Referred Rotor Angle Index for Transient Stability Assessment and Control of Power Systems

This paper describes an index for judging the severity of transient events of power systems in simulation. The proposed transient stability index, known as the area‐based COI‐referred rotor angle index, is developed by considering the fact that a large‐sized power system is divided into several areas according to the coherency of generators in a particular area. It can be assumed that an equivalent single large machine can represent all the generators in that area. Thus, the assessment of rotor angles for all generators can be simplified by only assessing the index of areas in a power system. The effectiveness of the proposed index in assessing the stability of power systems and its ability in pinpointing the weakest area in the power system is analyzed. Furthermore, this paper developed an emergency control scheme known as the combined UFLS and generator tripping in order to stabilize the system when unstable faults occurred in a power system. The proposed index is used to identify the generator to be tripped when the developed emergency control scheme operates. The performance of the proposed index and the combined UFLS and generator tripping scheme are evaluated on the IEEE 39‐bus test system.

Comparison of FACTS Devices for Power System Stability Enhancement

development of the modern power system has led to an increasing complexity in the study of power systems, and also presents new challenges to power system stability, and in particular, to the aspects of transient stability and small-signal stability. Transient stability control plays a significant role in ensuring the stable operation of power systems in the event of large disturbances and faults, and is thus a significant area of research. This paper investigates the improvement of transient stability of a two-area power system, using UPFC (Unified Power Flow Controller) which is an effective FACTS (Flexible AC Transmission System) device capable of controlling the active and reactive power flows in a transmission line by controlling appropriately its series and shunt parameters. Simulations are carried out in Matlab/Simulink environment for the two-area power system model with UPFC to analyze the effects of UPFC on transient stability performance of the system. The performance of UPFC is compared with other FACTS devices such as Static Synchronous Series Compensator (SSSC), Thyristor Controlled Series Capacitor (TCSC), and Static Var Compensator (SVC) respectively. The simulation results demonstrate the effectiveness and robustness of the proposed UPFC on transient stability improvement of the system.

Coordinated preventive control of transient stability with multi-contingency in power systems using trajectory sensitivities

In this paper, the challenging multi-contingency transient stability constrained optimal power flow problem is partitioned into two sub-problems, namely optimal power flow (OPF) and transient stability control, solved in turn with conventional well trusted power system analysis tools instead of tackling it directly using a complicated integrated approach. Preventive multi-contingency transient stability control is carried out with generation rescheduling based on trajectory sensitivities using results obtained from a conventional transient stability simulation. A new iterative approach is proposed to optimally redistribute the generation from the critical machines to noncritical machines with the help of conventional OPF. Results on the New England 10-machine 39-bus systems demonstrate that the proposed method is capable of handling multiple contingencies and complex power system models effectively with solution quantity and time comparable with conventional integrated approaches.

The Transient Stability Preventive Control of Power System Based on RBF Neural Network

The transient stability preventive estimation and control is one of the most important tasks of the power system. The traditional time domain simulation method cannot meet the standard of on-line estimation because of its heavy computation burden. In this paper, we realize the on-line estimation of transient stability limits on critical lines of a power system using the favorable approximation ability of RBF network. We choose right samples by off-line count to train the RBF network in order to make the error satisfy demand. Preventive control direction and amount are determined based on first-order sensitivities of transient stability limits to generator outputs. The sensitivities are derived from partial derivatives of RBF network outputs to inputs. In the end, we take a practical power system for an example to demonstrate the efficiency of RBF network in estimation of the transient stability limit on critical lines and ability to provide preventive control strategy.

Global Transient Stability-Constrained Optimal Power Flow Using an OMIB Reference Trajectory

This paper presents a new approach to transient stability control using global transient stability-constrained optimal power flow (TSC-OPF) methods. Its novelty consists in using the single machine equivalent (SIME) method to perform (and improve) two main important functions of global TSC-OPF approaches: first, SIME is used to efficiently perform the power system transient stability analysis; second, SIME determines a stable one machine infinite bus equivalent rotor angular trajectory that is used as the reference stability constraint, at one specific integration step. In this way, the stability constraint is adjusted by SIME, at each iteration of the TSC-OPF method, in order to accurately reflect power system dynamic behavior. The prowess and main characteristics of the proposed approach are shown by numerical examples.

Comparison of Stabilization Methods for Fixed-Speed Wind Generator Systems

Static synchronous compensator (STATCOM), pitch control system, braking resistor (br), and superconducting magnetic energy storage (SMES) have recently been reported as stabilization methods for fixed-speed wind generator systems. Although the individual technologies are well documented, a comparative study of these systems has not been reported so far. This paper aims to fill in the gap, and provides a comprehensive analysis of these stabilization methods for fixed-speed wind generator systems. The analysis is performed in terms of transient stability enhancement, controller complexity, and cost. A novel feature of this work is that the transient stability analysis of wind generator system is carried out considering unsuccessful reclosing of circuit breakers. Simulation results demonstrate that the SMES is the most effective means of transient stability enhancement and minimization of both power and voltage fluctuations, but it is the most expensive device. The STATCOM is a cost-effective solution for transient stability enhancement and minimization of voltage fluctuations. The BR is the simplest in structure and a cost-effective solution for transient stability enhancement. The pitch controller is the cheapest one, but its response is much slower than that of other devices.

Nonlinear Excitation Control for Transient Stability of Multi–Machine Power Systems using Structure–Preserving Models

Abstract The approach adopted in this paper for the problem of transient stability of multi-machine power systems sees the entire network as the (structure-preserving) interconnection of the network components, described by well known models. These structure-preserving models preserve the identity of the network components and allow for a more realistic treatment of the loads. Our main contribution is the explicit computation of a control law which provides transient stabilization, i.e , prevents the system from loss of synchronism after a large perturbation. The theory is illustrated by means of simulation on a 3-machine power system.

Transient Stability Control of Wind Farm

Transient Stability Control of Wind Farm

Transient stability and emergency control

Comparability of emergency control strategies with different instability modes is the key issue to decide which control strategy to be implemented. This paper considers that the essential factor causing instability should be used to form a unified standard to assess the effectiveness of control strategies with different instability modes. Thus a switching control stabilization principle was proposed based on elimination of the unbalanced energy between mechanical and electrical energies of generator sets. Along this way, the difficulty of seeking a Lyapunov function was circumvented. According to the principle, an emergency control algorithm framework was established to handle transient stability assessment, control location selection and control amount evaluation. Within the framework, this paper studied instability mode transition, then proposed an algorithm based on prediction function and a new approach to normalized stability margin stemmed from static EEAC method, which can increase comparability of various control locations. The simulations on the New-England System verified the proposed emergency control method for stabilizing transient stability.

Efficient and robust model predictive control for first swing transient stability of power systems using flexible AC transmission systems devices

A wide area measurement, nonlinear, model predictive control (MPC) approach is introduced to provide first swing stability protection of vulnerable power system transmission lines. The authors consider large disturbance events and focus on the avoidance of first swing angular separation using flexible AC transmission systems (FACTS) devices. The presented control strategy for FACTS devices is designed to be numerically efficient (due to the short MPC horizons) and robust (against complicated separation mechanisms). Simulation studies conducted on a three-machine system illustrate that the proposed MPC approach achieves first swing large disturbance performance that is near optimal and superior to existing transient stability controllers. Moreover, the proposed control approach is demonstrated to improve critical clearance times and to improve transfer capacity in simulation studies on the 39 bus New England system.

Transient Stability Ranking Technique based on System Parameter Estimation and Extended Equal-Area Criterion

The on-line TSC (Transient Stability Control) system is the world's first online-type stabilization system for electric power systems, which realizes optimum stabilized control of moment-by-moment power system conditions by obtaining power system information online and carrying out stability calculations at certain intervals.This paper discusses the new transient stability ranking method for severity of each contingency, which will be introduced to the new on-line TSC system of Chubu Electric Power Company. The ranking method is based on system parameter estimation and the Extended Equal Area Criterion. The method can be applied to unbalanced fault.

Transient Stability Ranking Technique based on Simplified Transient Stability Calculation

Over ten years have passed since the start of operation of on-line TSC (Transient Stability Control) system, which is the world's first online-type stabilization system for electric power systems. This paper discusses the challenges this on-line TSC system has so far faced in its actual operations and our development of new technologies and functions to overcome these challenges. Using transient stability ranking technique based on simplified transient stability calculation, new TSC system expect two advantages; (1) Accurate response to changes in power system conditions. (2) Using differentiation of severity of stability for each contingency contribute cost reduction.