Power System Stability Control Research Articles

Coordinated design of PSS and unified power flow controller using the combination of CWT and Prony methods with the help of SPEA II multi‐objective optimisation algorithm

Since the initial objective of power system stabiliser (PSS) units and flexible AC transmission system (FACTS) devices is the damping of inter-area and local oscillations, it is very substantial that the network electromechanical oscillatory modes are identified for tuning the controller of large-scale interconnected power systems. In this research, a method based on the combination of continuous wavelet transform and Prony algorithm is presented to study low-frequency electromechanical oscillations of the power system. The coordinated design of PSS and FACTS parameters become a multi-objective optimisation problem that will be solved using the SPEA II. The residue method is used to improve damping and satisfy the controller constraints of the suggested power systems. Finally, the proposed method of mode estimation and controller design is simulated on the two well-known test case systems, namely IEEE 2-area 4-generator and New England- New York 68-bus 16-generator systems using MATLAB software. The results represent accurate performance and validity of the proposed method to improve oscillation damping, dynamic stability of the power systems.

On the Rotor Angle and Voltage Dynamics Decoupling in Synchronous Generators with Nonlinear AVR

In this paper, rotor angle and voltage dynamics decoupling in a synchronous generator connected to an infinite bus using a partial feedback linearization-based nonlinear voltage regulator (FBLAVR) is described. It is well known that the fast voltage regulation using static excitation system introduces negative damping in the system. If this coupling can be eliminated then one can simultaneously achieve fast voltage regulation and desired damping performance. This paper identifies such a decoupling behavior using an FBLAVR and shows that the damping with the FBLAVR only depends on the inherent damping of the machine. The necessity of a power system stabilizer (PSS) is identified even with the FBLAVR, if the natural damping is not sufficient. Thus motivated, an FBLAVR + PSS control scheme is proposed and compared with a linear automatic voltage regulator (AVR) + PSS control scheme. It is shown that the generator-exciter-power system [GEP(s)] characteristics with FBLAVR does not change with the system operating conditions. The superiority of the proposed control scheme is validated over a wide range of operating conditions on a single machine infinite bus (SMIB) power system.

Intelligent Power System Stabilizers using Fuzzy Logic Technique and Sliding Mode Control Strategy

Each electric power grid should be equipped with a power system stabilizer (PSS) to ensure the network stability during operation and distribution. The major function of a PSS is to provide an appropriate control signal to the synchronous generator system, making its rotational speed stabilization against disturbances. This paper investigates three control strategies to design such an efficient PSS for the power network, including a PID-based PSS, a fuzzy logic – based PSS (FLC), a fuzzy logic-integrated sliding mode control – based PSS (SMC). With the rapid development of fuzzy logic technique considered to be an intelligent and successful control tool, the PSS controllers applying this control strategy are able to obtain good control performances, satisfying high requirements of the smart grids. Through a number of numerical simulations implemented in MATLAB/Simulink package for a single synchronous generator connected to an infinite bus, this work verifies the feasibility and success of the studied control strategies in designing an efficient PSS controller. Two case studies with load change and without load change will also be carried out in this paper to demonstrate the broad stability range of the proposed PSS controllers. Simulation results reveal that the FLC and the SMC are much better than the conventional PID-based PSS controllers and these two intelligent regulators can be selected for successfully solving the stabilization problem of an electric power grid in practice.

Voltage stability control of power systems using reduced network based optimisation

This study presents optimisation based strategy to successfully control voltage stability of power systems using limited number of measurements. In a multi-area power system, Ward reduction based network is used to enhance the loadability margin of the overall system, based on measurements from the internal area only. Information regarding the recent changes in the external areas is considered in the reduced network through hybrid state estimator, to enhance the estimation accuracy of the system states. Predictor-corrector primal-dual interior point technique is used to optimise the loadability margin above a given critical margin. The voltages obtained for this optimised margin are used as target values for determining the actual control parameters, by means of Gauss-Newton optimisation. The proposed methods are successfully implemented on IEEE 30-bus and 118-bus test systems.

Tuning of Controllers in Power Systems Using a Heuristic-Stochastic Approach

A method is proposed to fit parameters of Power System Stabilizer controllers in electromechanical multimachine power systems. The use of the Non-dominated Sorting Genetic Algorithm II heuristic method and Tabu search is considered to be initial search criteria. These methods give an approximation of the values that define the controllers. Then, the stochastic approach was used to evaluate the behavior of the parameters found when considering the system’s response to the presence of random and self-sustained in-time disturbances that affect the response of the system under steady state. The stochastic approach allows the evaluation of the system’s response through the calculation of the cost of energy loss under steady state. The method is applied to two systems: a three-machine nine-busbar system, and the Interconnected System of the Greater North (Sistema Interconectado del Norte Grande) in Chile. For these systems, the proposed methodology effectively optimized the controllers and Tabu search was shown to have a better performance than the Non-dominated Sorting Genetic Algorithm II.

State of art fractional order controller for power system stabilizer

State of art fractional order controller for power system stabilizer

Coordination of Power-System Stabilizers and Battery Energy-Storage System Controllers to Improve Probabilistic Small-Signal Stability Considering Integration of Renewable-Energy Resources

This paper proposes a probabilistic method to obtain optimized parameter values for different power-system controllers, such as power-system stabilizers (PSSs) and battery energy-storage systems (BESSs) to improve probabilistic small-signal stability (PSSS) considering stochastic output power due to wind- and solar-power integration. The proposed tuning method is based on a combination of an analytical method that assesses the small-signal-stability margin, and an optimization technique that utilizes this statistical information to optimally tune power-system controllers. The optimization problem is solved using a metaheuristic technique known as the firefly algorithm. Power-system stabilizers, as well as sodium–sulfur (NaS)-based BESS controllers with power-oscillation dampers (termed as BESS controllers) are modeled in detail for this purpose in DIGSILENT. The results show that the sole use of PSSs and BESS controllers is insufficient to improve dynamic stability under fluctuating input power due to the integration of renewable-energy resources. However, the proposed strategy of using BESS and PSS controllers in a coordinated manner is highly successful in enhancing PSSS under renewable-energy-resource integration and under different critical conditions.

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.

A preventive transient stability control method based on support vector machine

This paper presents a support vector machine (SVM)-based method for preventive transient stability control (TSC) of power systems. The features of the SVM model used in TSC are the same as in transient stability assessment (TSA). The features include non-control variables so as to improve the accuracy of TSA and sensitivities. A hybrid method combining SVM and time-domain simulation is also proposed to increase the TSA accuracy. First, this paper defines a transient stability assessment index based on SVM model. Second, the sensitivities of the SVM-based transient stability assessment index with respect to control variables (generator active power) are calculated and ranked to select control generators from them. Then, the power shifting amount of all the control generators and balance generators is calculated and the corresponding control scheme is verified by the hybrid TSA method. If generation redispatching measures are invalid, then load shedding measures are used at the same time. Finally, comprehensive studies are conducted on the WECC 9-bus system and a certain provincial 2036-bus system in China. The results reveal that the proposed hybrid TSA method increases the classification accuracy rates from 99.0%, 99.3% to 100% for the certain provincial 2036-bus system, and effective control measures are obtained with the proposed SVM-based TSC method for both systems.

Optimization of damping controller for PSS and SSSC to improve stability of interconnected system with DFIG based wind farm

This paper studies the stability issues of the Double Fed Induction Generator (DFIG) based wind farm in the power system with variable wind speed in strong and weak grid. With the intermittent generation of the wind power, it experiences instability and malfunction. The nature of Electromechanical Modes of Oscillations (EMOs) for DFIG incorporated into the multi-machine system under various conditions is explored considering system uncertainties. In this paper, the impact of Power System Stabilizer (PSS) and Static Series Synchronous Compensator (SSSC) on the stability of wind power system is analyzed by utilizing modified IEEE 14-bus test system. The rotor speed deviation is the objective function for particle swarm optimization and is formulated based on the transient and small signal stability. The transient and small signal stability investigations are performed by using time domain simulation and eigenvalue analysis respectively. The sensitivity analysis is carried out with degree of compensation of SSSC and coefficient of damping gain of PSS as sensitivity parameter. The performance of the modified test system is examined for transient and small signal stability for DFIG based wind farm for variable wind speed and grid strength considering different combinations of PSS and SSSC. From the results, it is noticed that oscillations in the system are minimized, damping, transient and small signal stability are enhanced and also the capability of synchronous generator and DFIG under extreme disturbance is intensified by optimization the coordinated controllers’ parameters. The analyses also show that damping ratio is improved for most of the EMOs. Sensitivity analysis identifies EMOs that have detrimental and beneficial impacts on the system.

Influence of moment of inertia on electric power system security and stability control

The moment of inertia is the basic parameter of the generator and also the basic data of PSS parameter tuning. The parameter setting of PSS will increase the damping of the unit and improve the small disturbance stability of the system. When the rotational inertia parameter is not consistent with the real rotational inertia of the unit, the PSS parameter setting will not increase the damping of the unit, but sometimes it will cause the oscillation of the unit. Here, the correlation analysis is carried out with the small signal stability analysis program, and the field test is carried out in Qinghai Kang Yang power plant. The influence of moment of inertia on PSS is analysed by small disturbance analysis and field test.

A Control-Oriented Energy Function for Generation Shedding Determination for Transient Stability Control

This paper proposes a control-oriented energy function (COEF) based on passivity for transient stability control (TSC) of power systems and investigates the feasibility of an iterative process using the COEF for determining generation shedding (GS) requirements for real-time TSC, in particular, for severe cases when autoreclosing fails due to permanent faults. The COEF for TSC set up in this paper gives directly the GS requirement without calculations of stability region and Critical Clearing Time, and exempts all modeling assumptions except for nonnegative damping the generator models. The simulation with the full planning model of Western Electricity Coordinating Council system shows that the passivity-based COEF for TSC offers a concise, practical, and effective index for GS determination for transient stability control of power systems, which is particularly suitable for the Remedial Action Schemes that BC Hydro has been using.

Robust Online Estimation of Power System Center of Inertia Frequency

The real-time center of inertia frequency plays an important role in power system stability analysis and control. This letter proposes a robust approach to identify power system center of inertia frequency with consideration of system uncertainties and synchrophasor measurement quality. A model decoupling strategy is first presented by taking measured generator active power as the swing equation input, whereas remaining the bus frequency as output. This allows deriving the linear discrete-time state-space form, which will be used by the robust Kalman filter for generator rotor speed, angle, and inertia estimation. The robust Kalman filter is mandatory as the measured frequency can change abruptly due to impulsive noise or system sudden changes. Simulations carried out on the IEEE 39-bus system validate the effectiveness and robustness of the proposed approach in the presence of various sources of uncertainties.

A New Technology Applied to Power System Stability Control: Phase Sequence Exchange Technology

AC transmission systems are often affected by stability issues. During the design phase of such systems, their ability to cope with the various kinds of disturbance is taken into consideration, however, sudden large disturbances may still result in power angle instability, which can greatly increase the risk of an overarching power system break down. Therefore, the development of a safety protection system is a priority in the field of power system construction. In response to this problem, we propose a new exploratory solution strategy - Phase Sequence Exchange Technology (PSET). The PSET can be summarized as follows: when the power angle of an equivalent dual power supply system swings to a suitable angle between 90° and 180°, disconnect the primary side phase of the communication line by power electronic equipment and causing the swift misalignment of the connection. The A, B, C three-phase sequence then, connects to the three-phase C, A, B sequence. The PSET instantaneously realizes this change and reduces the power angle by 120°, pulling the formerly increasing power angle back to a smaller angle and preventing the system from becoming imbalanced. In this paper, the mechanism which improves the stability of the PSET is explained by using the equal area rule. The threshold of the PSET work angle is determined by the energy function and the unbalanced potential energy in the system that can be effectively reduced by the PSET. Based on these findings, the phase trajectory method is used to determine the evaluation criteria for the PSET. This allows us to establish whether the PSET is effective by examining the state of the system after the fault is removed. Finally, an example is given in order to verify the effectiveness of the PSET and to prove that PSET is able to prevent the system from becoming imbalanced while still maintaining its structural integrity.

PSS AND IPFC POD controllers coordinated tuning by an Adaptive Genetic Algorithm with Hyper-mutation

Flexible AC transmission systems (FACTS) are a modern technology to increase controllability in power systems. This work presents an analysis of Interline Power Flow Controller (IPFC) which is a FACTS device. This device control and manage power flow in transmission lines. Supplementary damping controller is installed on IPFC Proportional Integral (PI) control. Power Oscillation Damping (POD) and Power System Stabilizers (PSS) contribute to power system stability. This works represents the electric power system and Interline Power Flow Controller FACTS device by a current sensitivity model (CSM). This work focuses on small-signal stability studies using an Adaptive Genetic Algorithm and Hyper-mutation (AGAH) to design simultaneously controller parameters. Adaptive Genetic Algorithm aims to find optimal controller parameters to enhance greatly stability of the power system. This paper considers two areas 14 bus symmetrical system in order to assess proposed algorithm. Simulations are carried out in MatLab platform in order to compare genetic algorithm with proposed algorithm performance. Results show AGAH outweighed AG by time convergence and accuracy.

Design of wide‐area POD with resiliency using modified DEA for power systems with high penetration of renewable energy

Recently, the electromechanical oscillations are becoming the primary concerns in power grids due to the integration of renewable energy generations (REGs). The inherent characteristics of REGs, e.g. low or no inertia, stochastic generation, could lead to the lower damping margin in power systems. A supplemental control such as power system stabiliser or power oscillation damping (POD) controller is widely applied to augment the damping margin in power systems. However, the PSS or POD using local signal is not adequate to damp the oscillation contributed from different sources. Hence, a wide-area damping controller can be employed in this context. Nonetheless, the wide-area controller suffers from communication failure. Therefore, the wide-area controller with resilient to communication failures is inevitable. This study proposed a wide-area POD design method considering resiliency. A modified differential evolution algorithm is employed to synthesise the wide-area damping control. The two-area and Java-Indonesian (three-area) power systems are used to evaluate the performance of the proposed controller for oscillation damping. From the results, it is evident that the critical mode(s) of the system successfully damped by employing the proposed controller. It is also found that the proposed controller is robust against communication failures.

Designing SSSC, TCSC, and STATCOM controllers using AVURPSO, GSA, and GA for transient stability improvement of a multi-machine power system with PV and wind farms

In this paper, the effects of three FACTS controllers, static synchronous series compensator (SSSC), thyristor-controlled series compensator (TCSC), and static synchronous compensator (STATCOM), on the transient stability of a multi-machine power system in the presence of two 200 MW wind farms based on a doubly fed induction generator (DFIG) and a 120 MW photovoltaic (PV) solar plant are studied. Also, power system stabilizers (PSSs) are installed on four synchronous machines. It is generally accepted that there is a threat to the stability of power systems with the penetration of wind farm and PV plant. Therefore, in order to improve transient stability in the power system, this paper proposes the application of PI controllers in PV and wind farm controllers and a combination of PSS and FACTS controllers, whose coordination is very important. The design problems of the PSS, FACTS, and PI controllers are formulated as an optimization problem, and the adaptive velocity update relaxation particle swarm optimization (AVURPSO) algorithm, gravitational search algorithm (GSA), and genetic algorithm (GA) are employed to search for the optimal controller parameters. These three approaches identify the solution to a given objective function, but they employ different strategies and computational efforts. Therefore, a comparison of their performance is required.

New Design of a Fractional Order Controller Based on Padé Approximation to Enhance a Stable Power System Load Frequency

This paper introduces a design technique of a novel fractional order (FO) proportional-integral-Derivative (PID) controller. The new control technique is a strategy to design a power system stabilizer (PSS) based on Pade approximation (PA). This control strategy is to enhance power system load frequency stability. Load frequency oscillations always follow disturbances that may occur at any point and at any time in power systems, and can affect its performance. This type of PSS controllers is designed specially for the damping of load frequency state variations in power systems. The simple single synchronous machine connected to an infinite bus (SMIB) power system model is taken under study in this paper. Design, analysis and stability tests of the proposed FO-PID controller and its effectiveness are performed for different cases in the proposed power system. MATLAB package is used to carry out the different simulations of power system model with its control strategy. Simulation results in different situations are presented, compared and discussed between two main cases; with system classical control, and with the proposed control strategy. These results present and show the important effects of FO-PID-PSS-PA controllers on the reduction of load frequency oscillations in the proposed power system.

A Hybrid Complementary Optimization Scheme of Wind- Solar- Pumped Storage Integrated by Voltage Source Converter Multi-terminal DC

A hybrid complementary optimization scheme of wind-solar-pumped storage integrated by voltage source converter multi-terminal DC(VSC-MTDC) is proposed, which considered power system stability control and actual generation schedule of pumped storage units. The goal anticipation is based on the minimum power flow and minimum frequency difference on tie line between voltage source converter multi-terminal DC(VSC-MTDC) and AC power system, improves the stability of voltage source converter multi-terminal DC(VSC-MTDC) and decrease renewable energy fluctuation’s impact on AC power system. Simulation example shows that this method can reduce power flow on tie line effectively and improve system stability.

Coordinated Supplementary Damping Control of DFIG and PSS to Suppress Inter-Area Oscillations With Optimally Controlled Plant Dynamics

This paper proposes a design method to coordinate dual-channel supplementary damping controllers (SDCs) of doubly-fed induction generators (DFIGs) and power system stabilizers (PSSs) for suppression of inter-area power oscillations. A dynamic performance index is introduced to measure the dynamics of the conventional synchronous generator and DFIG during the damping control process. Hence, the proposed method designing the PSS and SDC is formulated as an optimization problem with the objective function being the sum of weighted performance indexes and the constraints indicating the requirements on the damping of the inter-area modes. Solving the optimization problem can obtain the optimal SDC and PSS, which can meet the required damping results as well as optimize dynamics of the controlled plants. Moreover, by adjusting weights in the objective function, the damping control burden can be flexibly and feasibly allocated between active and reactive power channels of DFIGs or among the damping controllers. Simulations with the modified New England and New York interconnected system prove that the proposed optimization based tuning method can not only robustly coordinate the PSS and SDC to effectively damp inter-area oscillations but also improve the dynamics of controlled plants during the damping control process over different operating conditions.