Power System Stability Control Research Articles

Damping of Low-Frequency Oscillations via Active Disturbance Rejection Control

Linear active disturbance rejection control (LADRC) is applied as power system stabilizer (PSS) in power systems to damp the low-frequency oscillations. A tuning method for second-order LADRC is proposed specifically for damping the low-frequency oscillations. The tuning method is based on its own structure (zeros and poles) and the oscillation frequencies that need to be damped, thus it is independent of system models and not restricted to single-machine-infinite-bus (SMIB) systems. Moreover, a method to analyze the robustness is proposed for SMIB systems using the structured singular value method. Simulation studies on a SMIB system and two multi-machine power systems show that LADRC is easy to tune and can achieve good performance in damping both the local modes and the inter-area modes, thus it has great potential in power system stability control.

An optimal placement of phasor measurement unit using new sensitivity indices

This paper presents an alternative approach to solve an optimal phasor measurement unit (PMU) placement by introducing two new sensitivity indices. The indices are constructed from the information measured from PMUs such as voltage magnitude and angle. These two parameters are essential for power system stability assessment and control. Therefore, fault analysis is carried out to obtain the voltage magnitude and angle deviations at all buses in order to construct the indices. An exhaustive search method is used to solve the linear integer programming problem where all possible combinations of PMU placement are evaluated to obtain the optimal solution. Unfortunately, the traditional objective function to minimize the total number of PMU placement leads to multiple solutions. The indices can be used to assess multiple solutions of PMU placement from the exhaustive method. In this work, an optimal solution is selected based on the performance of PMU placement in according to the indices. The proposed method is tested on the IEEE 14 bus test system. Only four PMUs are required to monitor the whole test system. However, the number of PMUs can be reduced to three PMUs after applying zero injection bus elimination.

Bi-Level Dispatch and Control Architecture for Power System in China Based on Grid-Friendly Virtual Power Plant

Non-synchronous renewable energy sources (RESs) have strong volatility and low inertia, which brings about great challenges on the accommodation of RESs and the security and stability of power systems. This paper proposes a bi-level power system dispatch and control architecture based on the grid-friendly virtual power plant (GVPP), so as to accommodate RESs flexibly and securely. The typical dispatch and control system of the power system in China is presented, and the particular challenges stemming from non-synchronous RESs are analyzed. The functional requirements, concept, and fundamental design of the GVPP are provided, which is distinguished from traditional virtual power plants (VPPs) for its active participation in power system stability control. Based on the cloud platform, a bi-level dispatch and control architecture considering two objectives is established. First, in the inner level, the GVPP operates to promote the accommodation of RESs under normal condition. Then, from the perspective of out-level power systems, GVPPs serve as spinning reserves for power support under contingencies. Besides, the key problems to be solved in the development of the GVPP-based architecture are summarized. Although the architecture is proposed for the power system in China, it can be applied to any power systems with similar challenges.

A distributed deep reinforcement learning-based approach for fast preventive control considering transient stability constraints

Preventive transient stability control is an effective measure for the power system to withstand high-probability severe contingencies. It is mathematically an optimal power flow problem with transient stability constraints. Due to the constraints involved the differential algebraic equations of transient stability, it is difficult and time-consuming to solve this problem. To address these issues, this paper presents a novel deep reinforcement learning (DRL) framework for preventive transient stability control of power systems. Distributed deep deterministic policy gradient is utilized to train a DRL agent that can learn its control policy through massive interactions with a grid simulator. Once properly trained, the DRL agent can instantaneously provide effective strategies to adjust the system to a safe operating point with a near-optimal operation cost. The effectiveness of the proposed method is verified through numerical experiments conducted on New England 39-bus system and NPCC 140-bus system.

An Investigative Study on Impact of Frequency Dynamics in Load Modeling

Load modeling plays a significant impact in assessing power system stability margin, control, and protection. Frequency in the power system is desired to be kept constant, but in a real sense, it is not constant as loads continually change with time. In much literature, frequency dynamics are ignored in the formulation of load models for the basic assumption that it does not affect the models. In this paper, the composite load model was formulated with Voltage-Frequency Dependency (V-FD) on real and reactive powers and applied to estimate the load model. 2- Area network 4- machines Kundur test network was used for testing the developed model. The model was trained with measurements from a low voltage distribution network supplying the Electrical Engineering department at Ahmadu Bello University, Zaria. Both training and testing data were captured under normal system operation (dynamics). To evaluate the V-FD model performance, Voltage-Dependent (VD) model was examined on the same measured data. The work makes use of the Feed Forward Neural Network (FFNN) as a nonlinear estimator. Results obtained indicate that including frequency dynamics in modeling active power reduces the accuracy of the model. While in modeling reactive power the model performance improves. Hence, it can be said that including frequency dynamics in load modeling depends on the intended application of the model.

Optimal coordinated design of PSS and UPFC-POD using DEO algorithm to enhance damping performance

Low-frequency oscillations (LFO) are an inevitable problem of power systems and they have a great effect on the capability of transfer and power system stability. The power system stabilizers (PSSs) as well as flexible AC transmission system (FACTS) devices can help to damp LFO. The target of this study is to tackle the problem of a dual-coordinated design between PSS and unified power flow controller (UPFC) implementing the task of power oscillation damping (POD) controller in a single machine infinite bus (SMIB) system. So, dolphin echolocation optimization (DEO) technique is utilized as an optimization tool to search for optimal parameter tunings based on objective function for enhancing the dynamic stability performance for a SMIB. DEO an algorithm has a few parameters, simple rules, provides the optimum result and is applicable to a wide range of problems like other meta-heuristic algorithms. Use DEO gave the best results in damping LFO compared to particle swarm optimization (PSO) algorithm. From the comparison results between PSO and DEO, it was shown that DEO provides faster settling time, less overshoot, higher damping oscillations and greatly improves system stability. Also, the comparison results prove that the multiple stabilizers show supremacy over independent controllers in mitigationg LFO of a SMIB.

A Novel Nature-Inspired Improved Grasshopper Optimization-Tuned Dual-Input Controller for Enhancing Stability of Interconnected Systems

Power system often experiences the problem of low-frequency electromechanical oscillations which leads the system to unstable condition. The problem can be corrected by implementing power system stabilizers (PSSs) in the excitation control system of alternator. This paper provides a novel and efficient approach to design an Improved Grasshopper Optimization Algorithm (IGOA)-based dual-input controller to damp the inter-area-mode power system oscillations. A three-fold optimization criterion has been formulated to calculate the optimum values of the controllers required for power system stability. The damping performance of the proposed controller is compared with conventional PSS and genetic algorithm-based controllers to validate the better performance of the proposed IGOA-based controller under various system loading conditions and disturbances.

A DC Power System Stabilizer Based on Passivity-Oriented DC bus Impedance Shaping

High penetration of Power Electronic (PE) converters in DC power grids has caused new stability challenges due to dynamic interactions among a network’s subsystems. Dynamic interactions can be avoided by the impedance coordination between the subsystems through the modification of control loops or passive elements inside a grid. Impedance coordination is a very complex and time-consuming task with no adaptations to dynamic changes in a power grid. In this paper, the concepts of dynamic interaction and passivity are explained and combined together to provide an online stability measure in terms of the DC bus impedance characteristics. A novel DC Power System Stabilizer (PSS) is proposed which is connected to a DC bus as a separate module passivizing the bus impedance at non-passive interaction frequencies. The interaction frequencies are detected through a broadband online identification process. The PSS working principle, topology, modeling, and control designs are explained in detail. Finally, the functionality and performance of the proposed stabilizer are validated by simulation results.

Coordinated Wide-Area Control of Multiple Controllers in a Power System Embedded With HVDC Lines

This paper develops a coordinated wide-area control of power system stabilizers (PSSs), static VAr compensators (SVCs), and supplementary damping controllers (SDCs) for damping low frequency oscillations (LFOs) in a power system embedded with multiple high voltage DC (HVDC) lines. The improved damping is achieved by designing a coordinated wide-area damping controller (CWADC) that employs partial state feedback. The design methodology uses a linear matrix inequality (LMI)-based mixed H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> robust control for multiple operating scenarios. To reduce the high computational burden, an enhanced version of selective modal analysis (SMA) is employed that not only reduces the number of required wide-area feedback signals, but also identifies alternate feedback signals, in case of failure of the primary signals. Additionally, the impact of delays on the performance of the control design is investigated. The studies are performed on a 29 machine, 127 bus equivalent model of the Western Electricity Coordinating Council (WECC) system-embedded with three HVDC lines and two wind farms.

Analysis of the Effects of PSS and Renewable Integration to an Inter-Area Power Network to Improve Small Signal Stability

Power system often suffers from low frequency oscillations (LFOs) which might result in instability in the long run, if allowed to sustain in the system for a long time. In order to mitigate these oscillations, power system stabilizers (PSS) are used through excitation control. Three recently developed meta-heuristic algorithms namely: Collective Decision Optimization (CDO), Grasshopper Optimization Algorithm (GOA) and Salp Swarm Algorithm (SSA) have been applied for the optimal tuning of PSS parameters for small signal stability analysis of a renewable integrated power network. This was done by designing a conventional speed-based lead-lag PSS in a multi-machine interconnected power system, whose parameters have been tuned using CDO, GOA and SSA in a way to shift all the eigenvalues associated to electromechanical modes to the left half of S plane. Comparison of the results obtained by the algorithms demonstrates the superiority of SSA over GOA and CDO to boost the overall system stability over a wide range of operating conditions. The PSS controller designed using SSA is observed to be more robust and efficient in damping out oscillations under different operating conditions.

The Small-Signal Stability of Offshore Wind Power Transmission Inspired by Particle Swarm Optimization

Voltage source converter-high-voltage direct current (VSC-HVDC) is the mainstream technology of the offshore wind power transmission, which has been rapidly developed in recent years. The small-signal stability problem is closely related to offshore wind power grid-connected safety, but the present study is relatively small. This paper established a mathematical model of the doubly fed induction generator (DFIG) integrated into the IEEE9 system via VSC-HVDC in detail, and small-signal stability analysis of offshore wind farm (OWF) grid connection is specially studied under different positions and capacities. By selecting two load nodes and two generator nodes in the system for experiments, the optimal location and capacity of offshore wind power connection are obtained by comparing the four schemes. In order to improve the weak damping of the power system, this paper presents a method to determine the parameters of the power system stabilizer (PSS) based on the particle swarm optimization (PSO) algorithm combined with different inertia weight functions. The optimal position of the controller connected to the grid is obtained from the analysis of modal control theory. The results show that, after joining the PSS control, the system damping ratio significantly increases. Finally, the proposed measures are verified by MATLAB/Simulink simulation. The results show that the system oscillation can be significantly reduced by adding PSS, and the small-signal stability of offshore wind power grid connection can be improved.

Identification of coherent generators based on clustering methods

The identification of coherent generators is very important for the stability analysis and control of power system. So far, there are three main identification methods of coherent generators which have cetain disadvantages. In this paper, two new algorithms based on clustering are proposed for the identification of coherent generators. Algorithm 1 is the optimal classification of generators based on given swing curves. By introducing the validity index into the algorithm, the optimal classification of the given generator swing curves can be obtained. Algorithm 2 is identification of coherent generators under specific faults. This algorithm firstly calculates the critical clear time of the system. Since the swing curves obtained at the critical clear time(critical curves) contain the complete information reflecting the swing and oscillation between generators, they can be used as reliable samples for clustering. Examples show that the two algorithms are effective.

Compatible Decentralized Control of AVR and PSS for Improving Power System Stability

Automatic voltage regulator (AVR) and power system stabilizer (PSS) as the most common excitation controllers have implemented incompatible decentralized control (IDC) due to the asynchronous sampling by the voltage&#x002F;current transformer. However, IDC results in the incompatibility of decentralized AVR and PSS in regulating generator dynamics, which seriously reduces the capability of AVR and PSS in improving the power system stability. In this article, the concept of compatible decentralized control (CDC) based on synchronous local measurements is first proposed for the decentralized AVR and PSS to improve the power system stability. The mathematical models on IDC and CDC are, respectively, modeled to represent the compatible characteristics of CDC. The distinguishing feature of the proposed CDC is that the decentralized AVR and PSS can be compatible with one another in regulating generator dynamics. Simulation results on four IEEE benchmark systems show the advantages of CDC in improving power system stability compared with IDC.

New Chaotic Sunflower Optimization Algorithm for Optimal Tuning of Power System Stabilizers

The problem of stability is generally caused by insufficient damping of electromechanical oscillations (EMOs). Power system stabilizers (PSSs) are the most advised and efficient devices to increase the system damping and enhance the dynamic characteristics of power networks during abnormal conditions. Unfortunately, the performance of the PSS controller is mostly dependent on the parameters of the lead-lag compensator. Within this context, this study presents a new chaotic-based sunflower optimization algorithm with local search (CSFO-LS) for optimum design of PSS controllers. In the proposed algorithm symbolized by CSFO-LS, the random parameters of the original SFO are substituted by chaotic sequences to avoid premature convergence at local optima and improve the accuracy of the optimum solution. Firstly, the CSFO-LS is tested and evaluated on various benchmark functions with different characteristics such as multimodality, separability and regularity. Then, it is applied for selecting the optimum parameters of the PSS controllers. These parameters are tuned in order to shift all electromechanical modes in a pre-specified zone in the left side of the s-plan. Simulation results based on eight benchmark functions show that CSFO-LS outperforms all the algorithms used for comparison. Moreover, to demonstrate the applicability and performance of the proposed method for providing good damping of low frequency oscillations, a standard power system test under various operating conditions and severe fault is used. Obtained results are compared with those obtained using the original SFO and other recent optimization techniques. In this study, an improved version of the SFO is proposed for providing optimum EMOs damping. All EMOs have to be shifted as much as possible to the left side of the s-plan instead of shifting them to a fixed zone. To our best knowledge, this technique is not suggested or used for any power system problem.

Decentralized constrained optimal control of the multimachine power system stability improvement

&lt;p&gt;The paper proposes, a decentralized constrained optimal control of the multimachine power system stability. Today’s power network conditions, operating closer to their limits. Alternative Current power grids are more vulnerable and subject to instability than ever before. A three machine power system and four machines, power system connected with a transmission line lossy. Nonlinear controllers are more complex structure and inflexible to be used in practice paralleled with a linear controller. The linearized dynamical equations of the multimachine power system are near to an equilibrium point and it can be stabilized by using a decentralized constrained controller based on optimal control. The feedback controller, which comprises independent control stations receives the measurement data and influences the control input of the machine is only attached to the subsystems. State feedback controller guarantees the closed-loop system is asymptotically stable can guarantee the performance index. It bases designed controlled systems on the algebraic Riccati equations and all its poles are in the closed left half-plane. Decentralized constrained optimal control of the multimachine power system is achieved through simulation of the results. This achievement of results is proposed by improves power system stability.&lt;/p&gt;

Wide Area Control of Governors and Power System Stabilizers With an Adaptive Tuning of Coordination Signals

This paper presents the formulation of Wide Area Control (WAC) signals for either coordinating all the governors of the system or coordinating simultaneously both the governor and the Power System Stabilizer (PSS) of each generator. This is achieved through the development of suitable WAC signals intended for the coordination of their common input signal (rotor speed deviation) having as objective the compensation of all the local and inter-area oscillations. Furthermore, an adaptive tuning method to estimate weights for each inter-generator interaction is also presented. This is required to regulate adaptively the level of the WAC contribution to all the local controllers. The weights are computed according to the electric connectivity between the generators. For the evaluation of the proposed methods, both offline and real-time simulations are performed on the IEEE 39-bus test system. The results indicate the substantial improvement of the system’s stability when the proposed governor/PSS coordination is considered. The performance of the WAC scheme is further increased when the adaptive tuning procedure is applied. Finally, the requirement of having PMUs at each generator bus is relaxed by utilizing the coherency concept.

An Alternative Way to Locate Disturbance Source for Low Frequency Oscillation Considering Control Devices of Generator

Fast and accurate location of the power oscillation disturbance source is of great significance for the implementation of power system safety and stability control measures. This paper focuses on the applicability study of the oscillation energy flow. Aiming at the evaluation of the oscillation energy flow in disturbance source location of low frequency power oscillation, the effects of different methods are compared. After that, a fast Fourier transform (FFT)-based oscillation energy flow method considering control devices of generator is proposed. Taking a low frequency oscillation case caused by the abnormal governor system as an example, the effectiveness and accuracy of the proposed method is verified.

A New Protection Strategy Based on Negative Sequence Current Coordinated Control on the Generator Extremity

When the single-phase reclosing of the high-voltage circuit, there will be tremendous negative sequence current generation. The connection of inverter-type new energy sources may increase the negative sequence current of the power system. The risks will be greatly increased if a large negative sequence current invades the generator, and it will cause the general stator damaged and offline. Based on the chain STATCOM compensation, a new strategy of negative sequence current coordinated control protection on the generator extremity is put forward. This strategy can predict the operation time of inverse time negative sequence current protection by monitoring the negative sequence current on the generator extremity. Once it is determined that the negative sequence current has an effect on the power system, according to the relationship between the STATCOM capacity and the magnitude of negative sequence current, two schemes of full compensation and incomplete compensation are proposed. The negative sequence current output by STATCOM suppresses the magnitude of the negative sequence current invading the generator. It eliminates or prolongs the operation time of the negative sequence current protection and gets more time for power system security and stability control. Finally, the simulation results verify the correctness and feasibility of the proposed strategy.

Investigating the steady state stability of the Nigerian 48- bus systems using facts devices

With the ongoing expansions and growth of the electric utility industry, including deregulation in Nigeria, numerous changes characterized by additional generating stations, increase in transmission lines and loads are experienced thereby pushing the transmission systems closer to their stability and thermal limits and hence, causing the transfer of reactive power during steady state operating conditions to constitute a major problem of voltage instability. Flexible ac transmission systems (FACTS) controllers have been utilized for finding solutions to various power system stability control issues such as voltage instability. This paper uses Static Synchronous Series Compensator (SSSC) and Thyristor Controlled Series Compensator (TCSC) to investigate the voltage magnitude profile, active and reactive power losses of the Nigerian 48-bus power system network for steady state stability enhancement using power system analysis toolbox (PSAT) in MATLAB environment. Optimal location of the FACTS devices was achieved through the computation of the voltage stability sensitivity factors (VSSF) for all the buses after continuation power flow (CPF) was carried out. Simulation results obtained without and with the FACTS devices revealed that the two FACTS devices especially TCSC has the capability to raise voltage profile of the buses and mitigate against power losses. http://dx.doi.org/10.4314/njt.v38i3.27

Trajectory sensitivity based preventive transient stability control of power systems against wind power variation

The penetration of high-level wind power has significantly made the power system’s operation complicated. The random power variation of the wind farms may deteriorate the power system’s transient stability degree since it alters the operating state of the power system. In this paper, based on trajectory sensitivity and Extended Equal Area Criterion (EEAC) method, a new preventive control approach is proposed to optimally balance the wind power variation by rescheduling synchronous generators while maintaining the transient stability for credible contingencies. The whole problem is formulated to a programming problem with linear stabilization constraints. The proposed method is validated on the New-England 10-machine 39-bus system by using commercial simulation software Transient Security Assessment Tool (TSAT), and both single- and multiple-contingency cases are tested. Simulation results verify its satisfactory performance on control effectiveness, computational efficiency, transparency, and accuracy.