Ensure Voltage Stability Research Articles

Justification of the need to improve emergency control systems for preventing disturbances of voltage stability in power systems

This article is aimed at justifying the need to modernize the existing systems that ensure voltage stability in the Unified Power System of Russia under the conditions of its permanent development, structural complication and active implementation of distributed generation. To this end, an analysis of the existing systems of emergency control used in the Unified Power System of Russia was conducted by considering their efficiency during major system accidents, including those in 2005 and 2017. In addition, specific features of operating power system facilities in the northern part of the Irkutsk Oblast were investigated from the standpoint of voltage stability. The conducted analysis of the operation of emergency control systems in the context of system accidents, including possible incorrect actions, identified their following disadvantages: insufficient fault tolerance, weak adaptability to emergency disturbances (including abnormal situations), as well as a lack of coordination between local devices and the discreteness of regulation. These shortcomings can be eliminated by introducing intelligent automation systems based on artificial neural networks and machine learning, as well as high-performance multi-agent systems into the structure of the emergency management of the Unified Power System of Russia. The results obtained indicate the need to modernize the existing voltage stability systems operated in the Unified Power System of Russia, both their software and hardware components. The proposed implementation of intelligent systems is expected to improve the existing systems at the same time as maintaining the current effective hierarchical principles of emergency management.

Optimal Secondary Control to Suppress Voltage Fluctuations in an HVDC-Linked Wind Farm Grid

High-voltage direct-current (HVDC) systems using voltage source converters (VSCs) have been developed to suppress voltage fluctuations in offshore grids due to the intermittent power generation of offshore wind farms (OWFs). This paper proposes a new strategy for the optimal secondary voltage control of HVDC-linked OWFs. In the proposed strategy, optimal coordinated control of an HVDC system and OWFs is achieved to minimize real-time voltage fluctuations throughout an offshore grid. A full-order dynamic model of HVDC-linked OWFs is implemented, and its unobservable and uncontrollable state variables are then eliminated using a model reduction algorithm. Given the dynamic model, a linear quadratic Gaussian regulator is designed for optimal coordinated control, and an eigenvalue analysis is conducted focusing on the effects of communication time delays on the stability of the proposed strategy. Simulation case studies are also carried out to verify that the proposed strategy more effectively improves real-time regulation of offshore grid voltages, compared to conventional strategies, while ensuring voltage stability even for relatively large delays in communications systems.

A novel load shedding methodology to mitigate voltage instability in power system

Aim. A novel technique for detecting imminent voltage instability is proposed in this paper, accompanied by a novel load shedding approach to protect the system from voltage instability. Methodology. The proposed methodology utilizes the computation of nodal reactive power loss to voltage sensitivities with load increments in the system. Originality. The nodal reactive power loss to voltage sensitivity is a novel computation and is explored to detect the likelihood of voltage instability in this work. Results. If the system is experiencing an unprecedented load growth and if all the measures reach their limits, then load shedding is the last resort to safeguard the system against instability. The sudden change in nodal reactive power loss to voltage sensitivities is utilized to devise the quantity of load to be cut in the system. Practical value. The time-based simulations performed in New England 39 bus test system (NE-39 bus), the simulated results show that nodal reactive power loss to voltage sensitivities can be used as a trusted indicator for early diagnosing of menacing voltage instability and the timely implementation of load shedding developed from nodal reactive power loss to voltage sensitivities on the system ensures voltage stability.

Enhanced nutrient removal from mixed black water by a microbial ultra-low weak electrical stimulated anaerobic-two stage anoxic/aerobic process

Efficient nutrient removal from mixed black water is under challenge in the context of global pollution control and circular economy. The anaerobic-anorexic-aerobic process is a widely used biological nutrient removal technology for wastewater treatment, yet its denitrification capacity is limited by the low biodegradable organics to nitrogen (C/N) ratio due to prior degradation of mixed black water. We have previously proved that weak electrical of 0.2 V could stimulate microbial denitrification of black water using an external electrical supply to ensure voltage stability. To reduce the dependence on additional electrical and to ensure a stable voltage output, we built a microbial fuel cell (MFC) and a microbial electrolytic cell (MEC) embedded in the anaerobic-two stage anoxic/aerobic (A-(A/O)2) system in this study, where the MFC degrades organic matter and generates electricity first. Then, the electroactive bacteria in the MEC catalyze denitrification at low carbon levels, which is affected by microbial ultra-low weak electrical stimulation (MUlWES) generated by MFC. Results showed that the removal rates of total nitrogen (TN) and total phosphorus (TP) were up to 91.3% and 98.3% respectively at a stimulation voltage of 0.1 V. Fluorescence spectroscopy revealed the formation of aromatic proteins and an increase in tightly bound-extracellular polymeric substances (TB-EPS), suggesting the involvement of these compounds in electron transfer. Community analysis disclosed the activation of autotrophic denitrifying bacteria and the inhibition of most heterotrophic denitrifying bacteria.

PI Controller for Hybrid Biomass- Solar Photovoltaic- Wind in Microgrid: A Case Study of Mersing, Malaysia

Renewable energy has become an alternative energy to replace fossil fuels in electric power generation systems to alleviate environmental problems in the future. Alongside the shift to renewable energy, microgrid technology has also evolved to integrate renewable energy into the power generation and distribution system. In addition, the issue of voltage stability is also a vital factor in sustaining microgrids with renewable energy integration to ensure system stability. Reports in earlier studies have included three voltage control methods such as Model Predictive Control (MPC), PI controller, and negative feed-forward voltage control, implemented to ensure voltage stability of hybrid renewable energy microgrids. However, very a few research reports apply voltage control in hybrid biomass (BM)-solar photovoltaic (PV)-wind microgrid, choosing only to focus on energy management, economic analysis, and best sizing. For this reason, this main objective of this paper is integration of hybrid Biomass-Solar Photovoltaic-Wind off-grid microgrid comprising a PI controller as the voltage control of the system based on an actual input database at a location in a small rural town named Mersing in Malaysia. Additionally, this paper also intends to illustrate the implemented efforts to support the voltage stability of the system for the Mersing case study. A PI controller with harmonic filter voltage controller is implemented in this study to reduce the Total Harmonic Distortion (THD) percentage. The average power output for solar, wind, and biomass energy sources were 60kW, 20kW, and 750kW, respectively. Concurrently the measured THD voltage and current at each renewable energy and distribution line show a percentage below 10%. It is thus shown that a hybrid BM-Solar PV-wind microgrid is stable, especially for distribution lines, according to harmonic standards in the electricity supply application book by the local electricity provider Tenaga Nasional Berhad (TNB). Indeed, a PI controller with a harmonic filter has proven as an effective method for controlling the voltage instability in this study.

Computationally efficient method for placing reactive power sources against contingencies

This paper presents a computationally efficient algorithm to find the locations and required reactive power injections for a minimum number of reactive power compensators under a set of considered contingencies. The problem is formulated and solved in two stages. The first stage solves the security-constrained DC optimal power flow problem to find the active power generation dispatch. Then, the second stage determines the best locations for a minimum number of reactive power compensators to assist the reactive power generation dispatch in order to maintain bus voltages within limits and to ensure voltage stability under the considered set of contingencies. Effectiveness and computational performance of the proposed method are illustrated by extensive simulations carried out on PEGASE 2869-bus system.

Design of Cost-Effective Compensators to Enhance Voltage Stability and Harmonics Contamination of High-Power More Electric Marine Vessels

In recent years, due to the large spread of power electronics converters onboard shipboard power systems (SPSs), harmonic contamination became an inherent problem. Moreover, as the SPSs are mostly operating in an islanded mode with a limited rating of the generators that feed heavy variable loads, voltage stability issues became a challenge as well. To address these issues, implementing PWM-based FACTS devices using IGBTs such as the active power filters may not be very practical for high-power SPSs due to their limited rated powers, high implementation cost, and high losses. The passive power filters (PPFs) and fixed capacitor-thyristor controlled reactors (FC-TCR) can be effective alternatives due to their capability to operate in high-power applications, smaller losses and, lower cost. The aim of this article is to provide more in-depth analytical investigations to evaluate and compare the behavior of the PPFs and the FC-TCR compensator in reducing the harmonics and enhancing the voltage stability concurrently of high-power SPSs. In addition, details of the voltage stability concept are addressed to visualize the potential risk of the voltage collapse. Besides, the modeling of the FC-TCR and design of the closed-loop control algorithm to ensure voltage stability is conducted. Via intensive simulation studies of a practical ship, which are carried out in MATLAB/Simulink environment, it has been demonstrated that the FC-TCR based on the proposed design can enhance the power quality and voltage stability of SPSs better than traditional PPFs filters.

Distributed Event-Triggered Voltage Control with Limited Re-Active Power in Low Voltage Distribution Networks

A high proportion of photovoltaic (PV) connections to a low-voltage distribution network (LVDN) causes serious voltage problems. In order to ensure voltage stability for renewable energy networks, we propose a distributed reactive voltage control strategy that is event-triggered. The voltage information of the PV nodes is transmitted to the upper layer of the communication network, where the agent calculates the output set value of the PV inverter. The underlying control strategy is based on the voltage sensitivity matrix, and the upper-level control strategy is based on an event-triggered consensus protocol. This strategy can accommodate the requirements for multi-time modeling and control. We verified the convergence of the event-triggered control algorithm using numerical analysis and proved the reduction of the communication times. We conducted case studies and simulation experiments to verify the effectiveness of our proposed voltage control strategies.

Micro-Grid Stability Improvement Using Static Synchronous Compensator Assisted with Battery Energy Storage System

Integration of distributed generation (DG) with a distribution network is essential for the best utilization of renewable resources in better economics and clean environmental aspect. Micro-grid (MG) is an aggregation of electrical loads and DGs. Intermittencies of load variation has adverse effect on the voltage at the point of a common couple (PCC). It also prevents the restoring of MG power back to a stable state. In this article, the placement of static synchronous compensator (STATCOM) Assisted with Battery Energy Storage System (BESS) at PCC scheme is developed. STATCOM assisted with battery energy storage system (BESS) provides instant power support for coupled MG with the power grid to ensure voltage stability margin at PCC and it is effective in restoring power stability.  Proposed scheme is implemented on a test system that is simulated in MATLAB-SIMULINK. The obtained results verify the effectiveness of placing STATCOM assisted with BESS at PCC.

Voltage stability based placement of distributed generation against extreme events

This paper is concerned about improving the resilience of power grids against extreme events which may lead to the line and generator outages and subsequent voltage stability problems and blackouts. The reported study investigates ways of eliminating or substantially reducing the chances of having such voltage stability problems during expected extreme events, by strategically placing a few distributed generators in the system. The problem is addressed in two stages, where a reasonably inclusive list of credible contingencies are individually considered first. A minimum number of distributed generators are selected and placed in order to maintain voltage stability under each considered contingency. In the second stage, the number of generators is minimized by the strategic selection of locations to reach a solution that ensures voltage stability under all considered contingencies in the system. Effectiveness and computational performance of the developed strategy are illustrated by simulating several outage scenarios using the IEEE 118-bus system.

A Review of Fault Diagnosis Research on On-Load Tap-Changers

As the core component of transformer voltage regulation, on-load tap changer plays an important role in ensuring voltage stability of power system. With the increase of times of voltage regulation, the failure rate also increases correspondingly. In view of the common faults of on-load tap changer, this paper introduces several existing fault diagnosis methods and summarizes their advantages and disadvantages. Finally, the problems in fault diagnosis of on-load tap-changer and the future research focus are analysed.

A hybrid PSO-ABC algorithm for optimal load shedding and improving voltage stability

In this paper, a hybrid method is proposed for reducing the amount of load shedding and voltage collapse. The hybrid method is the combination of particle swarm optimisation (PSO) algorithm and artificial bee colony (ABC) algorithm. Both algorithms equally contribute in the paper to determine the optimal load shed values for improving the voltage stability of the power system. Here, PSO is used to determine the weak buses in the system whereas ABC computes the optimal amount of load shed value to be cut for voltage stability purpose. They work on different fitness functions as per the requirements of their purpose. The appropriate buses for load shedding are selected based on the sensitivity of minimum eigenvalue of load flow Jacobian with respect to the load shed. The proposed method based on PSO and ABC is implemented in MATLAB working platform and its performance is tested with six bus and IEEE 14 bus bench mark test systems. From the simulations, the performance of the proposed method is analysed and compared with various techniques in terms of sensitivity of minimum eigenvalues, voltage profile and load power. Through comparison performance, it is showed that the proposed method ensures voltage stability with minimum load shedding.

Optimal Value Capacitor Selection and Power Control Using Continuous Time Ant Colony Algorithm in Nonlinear Loads

The necessity of consumption and energy that emerged in our world with the ever-developing industry and urbanization has become an important problem. This problem has made it necessary to conduct research on how to use existing energy resources in the most efficient way while constantly directing new energy sources. Although legal regulations have been made to remedy these problems in part, they are often seen to be inadequate. One of the most effective and efficient ways to relieve operation in electrical energy systems, increase system and energy efficiency, reduce costs and ensure voltage stability is to make reactive power compensation. In this study, in a linear welded power system, it is ensured that the capacity value of the capacitor required for compensation is reduced to a minimum by reducing the effects of the harmonics in the nonlinear loads affecting the system and reducing the voltage drop which may occur even by minimizing the effect of reactive power and optimizing the minimum apparent power, the maximum power factor is obtained and the voltage drop in the line is minimized.

Integration of distributed generation in electrical grid: Optimal placement and sizing under different load conditions

This paper proposes a novel approach for the placement and sizing of distributed generation (DG) ensuring voltage stability and reducing total power losses in electrical grid. The main concern of the proposed method is to guarantee voltage stability along with load fluctuations, while selecting optimal DG sites and power capacities. First, vulnerable buses are determined using Voltage Stability Margin Index (VSMI). Optimum size of DG unit is computed using Matlab curve-fitting approximation. For each load level, optimal DG size and its corresponding site are recomputed. General expressions for DG power capacity are established. For different load scenarios, the determined DG locations and size are always valid. The proposed method is implemented on the 33-bus and the 69-bus distribution systems using PSAT MATLAB toolbox and results are compared to other techniques published in the literature. The obtained results prove the effectiveness, the robustness and the good performances of the proposed method.

Undisruptive load curtailment scheme to ensure voltage stability margin

Curtailable loads (CLs) are regarded as one of the last lines of defence to maintain the security and stability of power systems. Nevertheless, if organised carefully, they can also be exploited as preventive security procurement measures for power systems. This is especially true for heavily loaded power systems in which the normal control schemes are already exhausted. In this study, a new power market approach is proposed to utilise CLs’ potential in ensuring voltage stability margin (VSM) for heavily-loaded power systems. The proposed method aims to provide a mechanism to engage CLs as active players in the power market, and hence, minimise the disruptive effect of the load curtailment. Next, CLs participation in the power market is utilised to minimise the cost of achieving a desired level of VSM, at normal and N − 1 contingency conditions, in a preventive manner. The most efficient load curtailment and power generation pattern are determined, using a modified particle swarm optimisation algorithm, to minimise the system's total cost, while meeting grid's VSM requirements. The simulation results verify that the desired level of VSM can be effectively obtained using the proposed approach, with much less operational cost compared to the established methods.

Risk-Based Stochastic Allocation of ESS to Ensure Voltage Stability Margin for Distribution Systems

High intermittency in today's renewable-rich distribution systems, and the prohibitive cost of upgrading the system infrastructure, has rendered voltage instability a real concern for heavily loaded systems. The voltage instability of distribution systems can spread to the corresponding transmission grid, as proven by real-life incidents. Recent advances in energy storage systems (ESSs), however, have offered a viable means of enhancing the reliability and robustness of power systems. In this paper, the optimal placement, sizing, and operation of ESS devices in wind-intensive distribution power systems are studied. The objectives of this paper are to minimize the ESS size (power and energy), required to ensure a desired voltage stability margin (VSM), and to minimize the reactive power loss and reactive power import from the upstream network. Wind uncertainty has been accounted for through a risk-based stochastic optimization framework. Besides, active network management (ANM) tools, such as the tap position of on-load tap changers, modelled by using a new method, and reactive power capabilities of both ESS devices and wind farms, are used as additional means to reduce the required ESS size. The results show that the required ESS significantly increases with increase in the desired VSM. Nevertheless, the increase can be considerably curtailed by using risk-based VS constraints and ANM tools.

Techniques for the Identification of Critical Nodes Leading to Voltage Collapse in a Power System

AbstractThis paper proposes two techniques for the identification of critical buses in a power system. The technique of Network Structural Theory Participation Factor (NSTPF) depends on the network structural interconnection of buses as captured by the admittance matrix of the system and is formulated based on the fundamental circuit theory law using eigenvalue decomposition method. Another power flow based technique which depends on the system maximum loadability, the system step size among other factors is also proposed. Traditional power flow based techniques are used as benchmarks to determine the significance of the proposed methods. To ensure voltage stability enhancement, STATCOM FACTS device is installed at the selected weak load buses of the practical Nigerian 24 bus and IEEE 30 bus test systems. The results of the simulation obtained show that, the suggested approach of NSTPF is more suitable in the identification of weak buses that are liable to voltage instability in power systems as it requires less computational burden and also saves time compared to techniques based on power flow solutions.

Optimal Location of SVC using Particle Swarm Optimization and Voltage Stability Indexes

<p>Flexible AC transmission system are widley used in power sytems to ensure voltage stability, in virtue of their high cost the choise of the best location in electrical network is essential. The porpose of this paper is to present a new method for finding the optimal location, size and number of Static Var Compensator in order to enhace the voltage stability of electrical network. The optimal solution has been found by using the evolutionary programming algorithm, particle swarm optimization, combined with voltage stability indexes used for the estimation of the voltage collapse in power systems.The proposed algorithm has been validated by application on both simulation network model IEEE 30-Buses under different load cases and the electric network model of Casablanca region in Morocco.The results of the application have been analysed and compared in each case in order to get the optimal number of Static Var Compensator to be used.</p>

Optimal Location of SVC using Particle Swarm Optimization and Voltage Stability Indexes

<p>Flexible AC transmission system are widley used in power sytems to ensure voltage stability, in virtue of their high cost the choise of the best location in electrical network is essential. The porpose of this paper is to present a new method for finding the optimal location, size and number of Static Var Compensator in order to enhace the voltage stability of electrical network. The optimal solution has been found by using the evolutionary programming algorithm, particle swarm optimization, combined with voltage stability indexes used for the estimation of the voltage collapse in power systems.The proposed algorithm has been validated by application on both simulation network model IEEE 30-Buses under different load cases and the electric network model of Casablanca region in Morocco.The results of the application have been analysed and compared in each case in order to get the optimal number of Static Var Compensator to be used.</p>

A hybrid method for optimal load shedding and improving voltage stability

Abstract In this paper, a hybrid method is proposed for reducing the amount of load shedding and voltage collapse. The hybrid method is the combination of Genetic Algorithm (GA) and Neural Network (NN). The GA is used by two stages, one is to frame the optimization model and other stage is to generate data set for developing the NN based intelligent load shedding model. The appropriate buses for load shedding are selected based on the sensitivity of minimum eigenvalue of load flow Jacobian with respect to the load shed. The proposed method is implemented in MATLAB working platform and the performance is tested with 6 bus and IEEE 14 bus bench mark system. The result of the proposed hybrid method is compared with the GA based optimization algorithm. The comparison shows that, the proposed method ensures voltage stability with minimum loading shedding.