Power System Transient Stability Enhancement Research Articles

A Barrier-Certificated Reinforcement Learning Approach for Enhancing Power System Transient Stability

Increasing integration of renewable resources brings more flexibility and poses new challenges to modern power systems, leading to highly nonlinear and complex dynamics. This paper aims to provide a general solution framework to traditional control problems, such as frequency control and voltage control, which attempt to maintain the stability of either synchronous generators-governed or inverter-governed systems when subjected to a disturbance and simultaneously guarantee operational constraints, providing a complete complement to existing works on control design. Building on reinforcement learning (RL) and control barrier functions, the framework includes two subsystems, i.e., a model-free controller and a barrier-certification system, which discover RL-based control actions and sequentially filter them using a barrier certificate to satisfy operational constraints. Calculating a barrier function is generally challenging for a complex power system. This is addressed by representing the barrier function using neural networks (NNs) and data-based approaches. An adaptive method is introduced to certify the neural barrier function that perseveres barrier conditions, which is more compatible with online implementation. The proposed framework synthesizes a stabilizing controller that satisfies predefined safety regions. The effectiveness of the proposed framework is demonstrated via several comparative case studies.

A Novel Data-Driven Self-Tuning SVC Additional Fractional-Order Sliding Mode Controller for Transient Voltage Stability With Wind Generations

This paper proposes a novel data-driven self-tuning additional sliding mode controller for power system transient voltage stability enhancement considering wind integration. We first develop a new additional fractional-order sliding mode controller (FOSMC) for the static var compensator (SVC). The tuning of FOSMC parameter settings is then reformulated as a Markov decision process (MDP) and solved by the deep reinforcement learning (DRL) algorithm. In addition, a data-driven estimation method is proposed for the identification of an equivalent transfer function that is further used to calculate reward during the training process, yielding the model-free training. After that, the well-trained agent allows us to tune the controller parameters considering system uncertainties and achieve robustness against various operating conditions. Comparative results with other state-of-art methods demonstrate that the proposed method can effectively suppress the chattering issue of the sliding mode controller and ensure transient voltage stability under different operating conditions.

A decentralized emergency control scheme for power System transient stability enhancement based on model predictive control

This paper proposes an emergency control scheme based on decentralized model predictive control (MPC) to prevent transient instabilities occurring in power systems. After an onset of transient instability due to a contingency, the control scheme acts on the intercept valves of the steam turbines and the excitation systems of the generators that are available for stabilizing the system. Using the proposed method, the system’s operational constraints as well as the turbine actuator dynamics are properly taken into account, and an objective function towards stabilization is minimized at every sampling time to generate an optimal control law. The method encompasses a decentralized control strategy allowing a straightforward implementation that does not require a communication system, nor does it suffer from its inherent delays, where each participating generator unit is equipped with an MPC controller that relies on only local measurements. Following a critical contingency, the controllers force the generators to remain in synchronism and bring the system back to a stable operating condition. The performance and efficacy of the proposed method have been evaluated and demonstrated by simulations performed on two test systems, the WSCC 9-bus and the IEEE 68-bus systems. It has been shown that the controllers, which are designed independently from the contingencies and operating conditions, are effective in restoring the system’s stability and are robust even when the system is subjected to structural changes due to integration of power electronics interfaced non-synchronous generator units.

Adaptive predictive control of flywheel storage for transient stability enhancement of a wind penetrated power system

Flywheel energy storage system (FESS) needs to be operated within its allowable speed range because it will be shut down outside this range. Furthermore, the power supplied/absorbed by FESS is constrained by the associated power electronic interface. This article proposes supervisory adaptive predictive control (APC) scheme for flywheel energy storage system to enhance power system transient stability while addressing the constraints mentioned earlier. The supervisory adaptive predictive controller gives a reference power command signal to the inner control loop of FESS while ensuring the operation of FESS within its regime of operation. The gains of the inner control loop are optimized by employing Genetic Algorithm (GA). The constraints on the state of charge of FESS and power rating of the associated converter are explicitly included in the adaptive predictive controller formulation, which is usually done in an ad hoc manner. The performance of the proposed control strategy is evaluated under four scenarios: a step wind disturbance, realistic wind profile, doubly fed induction generator (DFIG) outage, and a severe symmetrical fault condition on modified New York/New England 16 machine 68-bus power system. The validity of the adaptive predictive control based flywheel energy storage system (APC based FESS) in improving transient stability of power system is verified by the simulation studies carried out in MATLAB/Simulink environment.

FLC based on static var compensator for power system transient stability enhancement

Transient Stability is the capability of a system to be able to return to its normal state after experiencing large disturbances. The static var compensator (SVC) is a shunt device of the flexible AC transmission systems (FACTS) family using power electronics to improve transient stability in power system. For the SVC control, it is usually used a PI controller, although PI controller is simpler and cheaper but not suitable when power system is subjected to transient stability since power system become non-linear system. In order to overcome this problem, the PI controller combined with Fuzzy controller is designed. Two types of faults were considered for this study to examine the effect of the fuzzy-SVC controller on system transient stability, the proposed fault types are single line to ground fault and three lines to ground fault. The performance and behavior of the designed fuzzy controller compared with that of the conventional PI controller in term of terminal voltage, rotor angle, and transmission line active power.

SFCL-SMES Control for Power System Transient Stability Enhancement Including SCIG-based Wind Generators

SFCL-SMES Control for Power System Transient Stability Enhancement Including SCIG-based Wind Generators

SFCL-SMES Control for Power System Transient Stability Enhancement Including SCIG-based Wind Generators

The resolution of the environment pollution depends on renewable energy sources, such as wind energy systems. These systems face transient and voltage stability issues with wind energy employing fixed-speed induction generators to be augmented with resistive type Superconducting Fault Current Limiter (SFCL) and Superconducting Magnetic Energy Storage (SMES) devices. The use of a combined model based on SFCL and SMES for promoting transient and voltage stability of a multi-machine power system considering the fixed-speed induction generators is the primary focus of this study. Our contribution is the development of a new model that combines the advantages of SFCL and SMES. The proposed model functions assure flexible control of reactive power using SMES controller while reducing fault current using superconducting technology-based SFCL. The effectiveness of the proposed combined model is tested on the IEEE11-bus test system applied to the case of a three-phase short circuit fault in one transmission line.

A Distributed Model-Free Controller for Enhancing Power System Transient Frequency Stability

The transient stability control of power systems with growing penetration of renewable energy resources is challenging due to inherent small damping of generators and complicated operating conditions. To address the drawbacks of existing control approaches which need accurate systemwide network parameters, a model-free fuzzy controller is proposed to enhance the transient and frequency stability of power systems. Also, an adaptive parameter estimation scheme is developed to eliminate the fuzzy approximation errors and compensate the external disturbances. The proposed strategy is implemented based on the multiagent framework, which enables the sharing of communication and computation burdens among local controllers for fast and coordinated response. The convergence of the proposed distributed control approach is rigorously proved using the Graph theory and Lyapunov stability theory. Simulation studies validate the effectiveness of the proposed distributed control approach.

Influence of solid oxide fuel cell on power system transient stability

Due to its modular, efficient and non-polluting characteristics, solid oxide fuel cell (SOFC) is promising to be widely utilised in the area of distributed generation. Previous studies mainly focused on dynamic modelling of SOFC to analyse its load following behaviour, however, the influence of SOFC on power system transient stability is not yet clear and needs further discussion. In this study, a system-level electromechanical transient mathematical model for SOFC is proposed, based on the circuit structure of SOFC, DC/DC step-up converter and DC/AC converter. Then, a double closed-loop control scheme is designed for the control of SOFC. Finally, the effect of SOFC on the power system's transient stability is discussed through simulations based on IEEE 3-machine 9-bus standard system. Results show that, under real and reactive power coordinated control strategy, cell current can be adjusted. Therefore, the output power of SOFC can be modulated to help with voltage recovery and power angle stability. The authors’ work reveals the feasibility of using SOFC to enhance power system transient stability.

Optimization of Battery Energy Storage to Improve Power System Oscillation Damping

A placement problem for multiple Battery Energy Storage System (BESS) units is formulated towards power system transient voltage stability enhancement in this paper. The problem is solved by the Cross-Entropy (CE) optimization method. A simulation-based approach is adopted to incorporate higher-order dynamics and nonlinearities of generators and loads. The objective is to maximize the voltage stability index, which is setup based on certain grid-codes. Formulations of the optimization problem are then discussed. Finally, the proposed approach is implemented in MATLAB/DIgSILENT and tested on the New England 39-Bus system. Results indicate that installing BESS units at the optimized location can alleviate transient voltage instability issue compared with the original system with no BESS. The CE placement algorithm is also compared with the classic PSO (Particle Swarm Optimization) method, and its superiority is demonstrated in terms of a faster convergence rate with matched solution qualities.

Power System Transient Stability Enhancement by Tuning of SSSC and PSS Parameters Using PSO Technique

In this paper, the tuning design of SSSC and PSS was examined in increasing the damping of system oscillations and improve the stability of the power system during disturbances. The design problem of the SSSC controller and PSS is designed as problem of optimization and the technique uses (PSO) technique to find for optimal control parameters. By minimizing the objective function based on the speed deviation and time domain, which deliberately deviates at the oscillation angle of the alternator rotor to improve performance of transient stability of the system. The proposed controllers are tested on the system of weak bonding ability exposed to severe disturbance. Nonlinear simulation results are presented to demonstrate the proposed controller's effectiveness and its ability to give efficient damping. It is also noted that the proposed controllers of SSSC and PSS greatly improves the power system stability.

PV-based virtual synchronous generator with variable inertia to enhance power system transient stability utilizing the energy storage system

The Photovoltaic (PV) plants are significantly different from the conventional synchronous generators in terms of physical and electrical characteristics, as it connects to the power grid through the voltage-source converters. High penetration PV in power system will bring several critical challenges to the safe operation of power grid including transient stability. To address this problem, the paper proposes a control strategy to help the PVs work like a synchronous generator with variable inertia by energy storage system (ESS). First, the overall control strategy of the PV-based virtual synchronous generator (PV-VSG) is illustrated. Then the control strategies for the variable inertia of the PV-VSG are designed to attenuate the transient energy of the power system after the fault. Simulation results of a simple power system show that the PV-VSG could utilize the energy preserved in the ESS to balance the transient energy variation of power grid after fault and improve the transient stability of the power system.

Wave Aspect of Power System Transient Stability—Part I: Finite Approximation

Electromechanical wave propagation is present in power systems as a transient spatial delay of generator rotor angle variations when a disturbance occurs. The control and mitigation of the this wave phenomenon, which spreads out to different locations at a comparably slow speed, is important for enhancing power system transient stability, as shown in part two of this two-paper series. In an idealized power system consisting of infinitesimal generators and line impedances, this traveling wave can exist to infinite frequencies, its speed can be derived from a wave equation and its reflection can be eliminated by a characteristic termination. Part one of this paper series examines realistic power systems with finite size generators and line impedances. It shows that there is a finite approximation of the traveling wave in real power systems as the wave can exist only within a finite frequency range. This paper also examines aspects such as reflections due to discrete elements, controller design based on the load modulation effect, and the existence of traveling wave and its attenuation in the Australian power system.

Wave Aspect of Power System Transient Stability—Part II: Control Implications

This second part of a two-paper series gives an overview of key insights and control implications arising from the wave characteristics of power system transient stability. These insights, which are unique to traveling wave interpretation, are obtained through time-domain analysis of artificial and real test systems: “ critical region for a stressed link near the end of a longitudinal system ,” “ dispersed control in a path ,” “ placement of controllers considering structure and load distribution in a system ,” and “ localized transient stability enhancement .” Good transient stability enhancement is successfully achieved by controllers in all test systems in terms of larger critical clearing time, which directly translates to increased maximum safe power transfer. The controller design is based on the transmission line analogy of traveling waves and load modulation effect. The concepts in this paper series can assist in improving the design of control strategies to enhance power system transient stability by considering the wave aspects.

Enhancing power system transient stability using optimal unified power flow controller based on Lyapunov control strategy

This paper presents a new control strategy for an Optimal Uni ed Power Flow Controller (OUPFC) through a Lyapunov energy function in terms of local parameters to improve the transient stability of a power system. The OUPFC is a hybrid con guration of Flexible AC Transmission System (FACTS) devices, i.e. an arrangement of small-sized Uni ed Power Flow Controller (UPFC) and a full-scale Phase Shifting Transformer (PST).In this study, a new term of OUPFC's energy function and its injection model in a simpli ed structure preserving model is developed and implemented in a two-machine power system using MATLAB/Simpower. The ability of the OUPFC controller to enhance the transient stability is compared to that of UPFC. The results show that using the proposed control strategy for OUPFC leads to more abatement of the rst swing oscillations and enlargement of stability margin. It is concluded that compensation of UPFC's angle displacement maycome true using OUPFC with appropriate angles in proper locations. So, compared to UPFC, OUPFC enjoys another degree of freedom.

可変速揚水発電機を利用した潮流フリンジの抑制による過渡安定度の向上

可変速揚水発電機を利用した潮流フリンジの抑制による過渡安定度の向上

A unified control scheme for power system transient stability enhancement through preventive and emergency control

Summary In this paper, a unified approach for transient stability enhancement following large disturbance is proposed through preventive or/and emergency control measures. Transient stability-constrained generation rescheduling is proposed as a preventive control strategy with participation of only few generators on the basis of the rotor angle swings. However, if generator rescheduling fails to regain the transient stability of the power system, heuristic real-time transient stability assessment scheme is proposed through synchrophasor measurements. If the system is predicted to be unstable in real-time, emergency control actions like generator tripping and load shedding are proposed with information about their initiation, location, type, and the magnitude. These emergency actions are purely based on the voltage magnitudes and phase angles obtained through phasor measurement units in real-time. The effectiveness of the proposed scheme is demonstrated on IEEE-39 New England test system, and the results obtained are promising. Copyright © 2015 John Wiley & Sons, Ltd.

Enhance Power System Transient Voltage Stability by Difference Coefficient of Generator Excitation System Optimization

Lack of dynamic reactive power compensation result in power system transient voltage instability. To improve the transient voltage stability, an optimization strategy for setting the excitation system difference coefficient of the generator is presented in this paper. The concept of the excitation system difference coefficient is introduced. Then the impacts of difference coefficients of generator excitation system on generator stability are analyzed and adjustment range is proposed. The calculation results of Guangdong province system show that the transient voltage stability level is enhanced effectively after optimizing the excitation system difference coefficient.

Controllable resistive type fault current limiter (CR-FCL) with frequency and pulse duty-cycle

In this paper a controllable resistive type fault current limiter (CR-FCL) is introduced. The CR-FCL inserts a pre-specified value of resistance based on a pre-defined function, by using a simple switching method, in series with the fault current path. When a fault occurs, a self turn off switch starts switching with a pre-specified frequency and duty cycle. By this switching pattern, the controlled value of resistance enters to the fault current path. So, the CR-FCL limits the fault current to the desired values. In addition, from transient stability point of view, by inserting the optimal resistance value, the CR-FCL is capable to enhance power system transient stability in a good manner. In fact, generation of the controllable resistance that depends on the duty cycle of the self turn off switch is the main idea of the CR-FCL. The variable duty cycle results the variable resistance and the fixed duty cycle results the fixed resistance. Analytical analyses of the proposed FCL are presented in details. Simulation results by power system computer-aided design/electromagnetic transients, including dc (PSCAD/EMTDC) software and corresponding experimental results are studied to validate the effectiveness of the CR-FCL. Considering error analyses, there is the good agreement between the simulation results and the experimental results.

Combined Operation of SVC, PSS and Increasing Inertia of Machine for Power System Transient Stability Enhancement

In this paper improvement of transient stability by coordination of PSS (Power System Stabilizer) and SVC (Static var Compensator) and increasing inertia of synchronous machine has been observed. Because single method is not sufficient for improving stability. For this purpose a 9 bus multi machine system has been considered. Transient stability improvement has been tested subjected to three phase fault at bus 3 after 0.5 second and fault has been cleared after 1 second. By the use of PSS, SVC and by increasing inertia method for the test system the electromechanical oscillation for generator electrical power has been reduced and the steady state power transfer has been enhanced. In this paper the Inertia of the machine is not so much increased. Because after increasing inertia of the machine rotor will be havier.so that it is kept always within limit as considering its reliability and economy. And field voltage is also kept limited.