Voltage Stability Improvement Research Articles

Slime Mold Algorithm for Optimal Reactive Power Dispatch Combining with Renewable Energy Sources

The optimal reactive power dispatch (ORPD) is a complex, nonlinear, and constrained optimization problem. This paper presents the application of a new metaheuristic optimization technique called the slime mold algorithm (SMA) for solving the developed objective function of ORPD combining with renewable energy sources. The presented objective function is to minimize the total operating cost of the system through the minimization of all reactive power costs, total real power loss, voltage deviation of load buses, the system overload and improve voltage stability. The formulation of the ORPD problem combining with renewable energy sources with five different objective functions is then converted to a coefficient single objective function achieving various operating constraints. The SMA technique has been tested and proven on the IEEE 30-bus system and IEEE-118 bus system using different scenarios. Five different scenarios, with and without renewable energy sources, are presented on the two-test system and the simulation results of the SMA is compared to some optimization techniques from the literature under the same test system data, optimal control variables, and operational constraints. The superiority and effectiveness of the SMA are proven through comparison with the other obtained results from recently published optimization techniques.

Voltage profile improvement using demand side management in distribution networks under frequency linked pricing regime

Voltage stability improvement and load profile management remain the major concerns of the power system load serving entities. The evolution in demand side management technology with automatic control enables a large number of appliances including energy storage devices to provide efficient ancillary services for the distribution utilities. In this paper, a novel methodology is developed for residential consumers using battery energy storage systems as a key vehicle for centralized incentive based demand side management. The aim is to employ energy storage at end-users’ premises to provide both active and reactive power support to the distribution utility so as to achieve the desired voltage stability margin at various network nodes while optimizing the deviation settlement charges under frequency linked pricing environment. The results indicate that the centrally controlled active and reactive power dispatch from the energy storage minimizes the load shedding required to bring the network node voltages within the operating limits and optimizes the costs involved. The demonstration is carried out on the IEEE-33 bus radial distribution system using the realistic loading data of a distribution utility in India. The proposed strategy could be of immense importance to the distribution utilities to optimize load curtailment and maximize their social welfare while operating under real time pricing environment.

Real Power Loss Reduction by Billfish and Red Mullet Optimization Algorithms

In this paper Billfish Optimization Algorithm (BOA) and Red Mullet Optimization (RMO) Algorithm has been designed for voltage stability enhancement and power loss reduction. Electrical Power is one among vital need in the society and also it plays lead role in formation of smart cities. Continuous power supply is essential and mainly quality of the power should be maintained in good mode. In this work real power loss reduction is key objective. Natural hunting actions of Billfish over pilchards are utilized to model the algorithm. Candidate solutions in the projected algorithm are Billfish and population in the exploration space is arbitrarily engendered. Movement of Billfish is high, it will attack the pilchards vigorously and it can’t escape from the attack done by the group of Billfish. Then in this paper Red Mullet Optimization (RMO) Algorithm is proposed to solve optimal reactive power problem. Projected RMO algorithm modeled based on the behavior and characteristics of red mullet. As a group they hunt for the prey and in each group there will be chaser and blocker. When the prey approaches any one of the blocker red mullet then automatically it will turn as new chaser. So roles will interchangeable and very much flexible. At any time chaser will become blocker and any of the blocker will become a chaser with respect to prey position and conditions. Then in that particular area when all the preys are hunted completed then red mullet group will change the area. So there will be flexibility and changing the role quickly with respect to prey position. Alike to that with reference to the fitness function the particle will be chosen as chaser. By means of considering L (voltage stability) - index BOA, and RMO algorithms verified in IEEE 30- bus system. Then without L-index BOA and RMO algorithms is appraised in 30 bus test systems. Both BOA and RMO algorithms condensed the power loss proficiently with improvement in voltage stability and minimization of voltage deviation.

Optimal feeder reconfiguration in distributed generation environment under time-varying loading condition

The development and planning of optimal network reconfiguration strategies for electrical networks is greatly improved with proper application of graph theory techniques. This paper investigates the application of Kruskal's maximal spanning tree algorithm in finding the optimal radial networks for different loading scenarios from an interconnected meshed electrical network integrated with distributed generation (DG). The work is done with an objective to assess the prowess of Kruskal's algorithm to compute, obtain or derive an optimal radial network (optimal maximal spanning tree) that gives improved voltage stability and highest loss minimization from among all the possible radial networks obtainable from the DG-integrated mesh network for different time-varying loading scenarios. The proposed technique has been demonstrated on a multiple test systems considering time-varying load levels to investigate the performance and effectiveness of the suggested method. For interconnected electrical networks with the presence of distributed generation, it was found that application of Kruskal's algorithm quickly computes optimal radial configurations that gives the least amount of power losses and better voltage stability even under varying load conditions.Article HighlightsInvestigated network reconfiguration strategies for electrical networks with the presence of Distributed Generation for time-varying loading conditions.Investigated the application of graph theory techniques in electrical networks for developing and planning reconfiguration strategies.Applied Kruskal’s maximal spanning tree algorithm to obtain the optimal radial electrical networks for different loading scenarios from DG-integrated meshed electrical network.

Improvement of Static Voltage Stability of 16-Bus Bali System by Optimal Placement of SVC

In a power system, the reactive power imbalance is related to the stability of the static voltage because the injection of reactive power that the bus receives from the system determines the bus's capability in the system. Rapid increases in real and reactive power losses occur as the system approaches the voltage drop point or the maximum load point. It is necessary to support local and adequate reactive power to avoid system leading to be voltage collapse. This study analyzes the improvement of the margin of static voltage stability using one type of modern control equipment of shunt flexible AC transmission system (FACTS), namely the static var compensator (SVC). The controller's representations are used in the continuation power flow (CPF) process to study static voltage stability. The proposed method's effectiveness has been investigated using a practical test system, namely the Bali 16-bus system, to increase the system loading capacity. The simulation was carried out by installing a modern controller in the best location, namely on bus 07 ASARI; an increase in system margin loading closed to 2% compared to the base case condition, namely λmax = 1,879 p.u with the voltage profile not changing significantly.

Single-Delta Bridge-Cell Converter With Single Single-Phase Medium-Frequency Transformer Capable of Active Power Control

A modular multilevel cascade converter based on single-delta bridge cells, hereinafter referred to as the single-delta bridge-cell (SDBC) converter, is a prospective power converter for a static synchronous compensator intended for voltage regulation and stability improvement of electric power systems. However, the SDBC converter cannot exchange nonzero active power with the three-phase ac mains unless energy storage elements such as batteries are connected to the dc side of each bridge cell. This article presents a dc/1φ/3φ power converter that combines the SDBC converter with a single-phase converter via a single-phase medium-frequency transformer with an operating frequency of 150 Hz. It can control the active power of 37% of the rated reactive power between the dc source and three-phase ac mains, thus enhancing voltage regulation and stability improvement. The operating principles and control method are first discussed, followed by a description of experiments using a downscaled 110-V, 5-kVA model.

Multi-objective optimization of optimal placement and sizing of multiple DG placements in radial distribution system using stud krill herd algorithm

This paper presents the Stud krill herd algorithm (SKHA) implementation to find the optimal location and sizing of DG units in a radial distribution system. In recent years, distributed generation (DG) plays an important role in the electric power industry. DG units are connected to the system mainly for improving voltage stability, real power loss reduction, reliability, grid strengthening, and reduction of SO2, CO2 gas emission. The problem formulation is based on the multi-objective function. This work focuses on real power loss reduction, cost minimization, and improvement of voltage stability and formulates a single objective function with suitable weightage preference subject to various constraints like voltage limit, DG real power limit, power balance constraint, and DG location limit. The algorithm has been tested on IEEE 33 bus, 69 bus, and 94 bus radial systems at different load levels with DG placement. The obtained simulation results are compared with other methods. The comparison reveals that the proposed algorithm offers a better solution for the optimal placement of DG in the radial distribution system with faster convergence.

Voltage Stability Improvement with finest position of UPFC using GA &PSO

Power system is a largely inter connected network, due to this interconnection some of the lines may get over loaded and voltage collapse will occur , hence these lines are called weak lines, this causes serious voltage instability at the particular lines of the power system. The improvement of stability will achieve by controlling the reactive power flow. The Flexible Alternating Current Transmission Systems (FACTS) devices have been proposed to effectively controlling the power flow in the lines and to regulate the bus voltages in electrical power systems, resulting in an increased power transfer capability, low system losses and improved stability. In FACTS devices the Unified Power Flow Controller (UPFC) is one of the most promising device for power flow control. It can either simultaneously or selectively control both real and reactive flow and bus voltage. UPFC is a combination of shunt and series compensating devices. Optimal location of UPFC is determined based on Voltage Stability Index (VSI). GA and PSO techniques are used to set the parameters of UPFC [6]. The objective function formulated here is fitness function, which has to be maximized for net saving. The results obtained using PSO on IEEE 14 Bus is compared with that of results obtained using GA, to show the validity of the proposed techniques and for comparison purposes

Assessment and Integration of Renewable Energy Resources Installations with Reactive Power Compensator in Indian Utility Power System Network

Renewable energy (RE) resource assessment is essential for planners and investors to increase its penetration capacity, and improve social and economic security. Integration of renewable power generations (RPGs) and reactive power compensators (RPCs) offer potential benefits to the existing power system network by providing a prospect for voltage control, reduction in power losses, sustainability, and reliability improvement. There are proven outcomes with these RPGs and RPCs placement in distribution systems. This work proposes a candidature location and sizing of RPGs and RPCs optimally in the Indian utility transmission power system network. The foremost purpose of this integrated operation at multiple nodes is to increase the performance of the power system concerning power loss and voltage deviation reductions, and voltage stability improvement. The loss sensitivity factor (LSF) based particle swarm optimization (PSO) technique is adapted for finding the candidature locations and sizing the RPGs and RPCs under five different configurations. Simulation outcomes display the proposed methodology can lead to extensive performance enhancement in the power system towards the sustainable development of electric energy transactions. Further, renewable resource assessment is carried out to find the viability of the candidature locations. The potential of wind and solar energy resources is assessed widely and suitable tools are used to evaluate the power extraction through RE at these selected locations. The results show that the candidature locations have great potential to evacuate the energy, which can effectively improve the existing power system technically and economically. Additionally, it is attested that the RPGs can also be utilized for power system enhancement.

Improving Voltage Stability of Electrical Power System by Optimal Location of FACTS Devices Using an Evolutionary Method

In the present work, a new approach for improving voltage stability by optimal location of the Flexible AC Transmission Systems (FACTS) devices has been discussed. We used Genetic Algorithm (GA) as an optimization technique to search the good placements of different FACTS systems in great electrical networks and its contribution to enhance voltage stability. Various FACTS devices were used in our study such as SVC, TCSC, SSSC, STATCOM, TCVR, TCPST and UPFC. The search of optimal parameters of those devices has been also investigated. The method presented in the paper was tested by using Matlab/environment. In addition, the proposed method has been implemented and tested on various IEEE power systems; 14Bus, 57Bus, and 118Bus. The obtained results show the validity of the proposed method.

Hybrid power plant bidding strategy for voltage stability improvement, electricity market profit maximization, and congestion management

This article models a hybrid power plant (HPP), including a compressed air energy storage (CAES) aggregator with a wind power aggregator (WPA) considering network constraints. Three objective functions are considered including electricity market profit maximization, congestion management, and voltage stability improvement. In order to accurately model the WPA, pitch control curtailment wind power levels are also added to the wind power generator models. To optimize all the mentioned objective functions, a multi-objective Pareto front solution strategy is used. Finally, a fuzzy method is used to find the best compromise solution. The proposed approach is tested on a realistic case study based on an electricity market and wind farm located in Spain, and IEEE 57-bus test system is used to evaluate the network constraint effects on the HPP scheduling for different objective functions.

Static Voltage Stability Assessment of the Kenyan Power Network

In recent years, the Kenyan Power Network has witnessed large growths in load demand. Although the increased load demand has somewhat been matched with an increase in transmission and generation capacity, the rate of expansion has not been matched with the rate of increase in load demand due to economic, environmental, and geographical constraints. This has led to the system being prone to instability since it is being operated under stressed conditions. In the recent past, several studies have been carried out on voltage stability analysis and improvement using various conventional methods. However, conventional methods have various limitations in their utilization for voltage stability analysis. One solution to overcome these limitations is to employ a combination of one or more methods so as to get more information and greater degree of accuracy in voltage stability studies. In this paper, a methodology is proposed involving the combination of QV modal analysis, sensitivity analysis (VQ) and power-voltage curves in assessing the static voltage stability analysis taking a case study of the Kenyan Power Network. V-Q sensitivity analysis and QV modal analysis have been used to identify the load regions most susceptible to voltage instability and the corresponding weak buses in the network for various V-Q responses. Reactive power loss sensitivities for branches in the network have been used to determine the critical (weak) lines in the network. Loading margins (LM) and voltage stability margins (VSM) have then been used to determine the proximity to voltage collapse of the voltage weak buses identified by QV modal analysis. The effect of tripping one the critical lines on the voltage weak buses is also investigated. The current high voltage power network under the average peak loading conditions during the year 2019 is considered for the study. The paper also reviews existing voltage stability analysis methods and their limitations.

Retransmission Methods to Improve Voltage Control of Distributed Generation System

In smart grid, voltage control feeds back state information from sensors to controllers via wired or wireless channels to stabilize the electricity distribution. When wireless channel is applied, because of the interference among wireless sensors, scheduling is necessary for efficient and reliable data aggregations. Previous work proved that delay-tolerant Kalman filter (DTKF)-based dynamic state-aware scheduling can improve voltage stability of distributed generation system. However, in practice, the transmission of sensor data over fading channels suffers losses, and lost packets would miss the opportunity of providing state information for voltage controllers. In this work, we use retransmission to combat losses, and study the impact of retransmission on voltage control. Network-coding-based retransmission is also used to increase retransmission efficiency and reduce delays. Simulation results show that the scheduling strategies with retransmission are indeed effective in certain scenarios.

Multi-Objective Energy Management of a Micro-Grid Considering Stochastic Nature of Load and Renewable Energy Resources

Optimal inclusion of a photovoltaic system and wind energy resources in electrical grids is a strenuous task due to the continuous variation of their output powers and stochastic nature. Thus, it is mandatory to consider the variations of the Renewable energy resources (RERs) for efficient energy management in the electric system. The aim of the paper is to solve the energy management of a micro-grid (MG) connected to the main power system considering the variations of load demand, photovoltaic (PV), and wind turbine (WT) under deterministic and probabilistic conditions. The energy management problem is solved using an efficient algorithm, namely equilibrium optimizer (EO), for a multi-objective function which includes cost minimization, voltage profile improvement, and voltage stability improvement. The simulation results reveal that the optimal installation of a grid-connected PV unit and WT can considerably reduce the total cost and enhance system performance. In addition to that, EO is superior to both whale optimization algorithm (WOA) and sine cosine algorithm (SCA) in terms of the reported objective function.

Impact of integrating large-scale DFIG-based wind energy conversion system on the voltage stability of weak national grids: A case study of the Nigerian power grid

This paper investigates the impact of integrating large-scale Doubly-Fed Induction Generator (DFIG)-based wind energy conversion system (WECS) on the voltage stability of the 52-bus, 330 kV Nigerian power grid. Indices derived from Active Power–Voltage (PV) and Reactive Power–Voltage (QV) analyses have been utilized to determine the voltage stability limits in terms of the maximum active power margin (APM) and minimum reactive power margin (RPM) of the system with the associated critical voltage-reactive power ratio (CVQR) of the system buses. Simulations have been done in DIgSILENT PowerFactory and the results analysed using MATLAB. This work also demonstrates the effectiveness of DFIG-based WECS in mitigating the overvoltage issues in the Northern region by ensuring that all bus voltages are within the acceptable limits of 1.0 ± 0.05 p.u. The results show that the optimal DFIG-based WECS penetration level (PL) that satisfies a bus voltage criterion of 1.0 ± 0.05p.u with the APM and CVQR not falling below their respective base case values and the loading of all critical power system equipment not exceeding 80% is 35%. Therefore, this work has demonstrated the possibilities of large-scale DFIG-based WECS as a viable solution for voltage stability improvement of a weak National grid while meeting the increasing energy demand.

Congestion management with improved real power transfer using TCSC in 30 bus system

Secure operation and reliable utilisation of transmission lines is a challenging issue in deregulated power system. The scheduled power transactions are difficult due to the overloading of transmission lines in restructured power system as the electricity market has become more competitive. Due to congestion of transmission lines, the transfer of real power and the power system voltage profile are greatly affected in the power system. The aim of this research work is to increase the real power and the reactive power flowing in the lines of multibus system using thyristor controlled series compensator (TCSC). Real power transfer with reduced losses and improved voltage stability is an important factor in the present global scenario. This paper deals with the improvement of power flow in power transmission lines by series compensation device in 30 bus system with reduced congestion. The 30 bus system without and with thyristor controlled series compensation device (TCSC) is modelled and simulated and the results are presented. The simulation studies indicate a significant improvement in the real and the reactive power flow with the introduction of TCSC. The advantages of the proposed system include the smooth variations of the real and the reactive powers.

Improving Voltage Stability in Nigerian 330kv Transmission Network Using Intelligent Solid State Var Compensator (SSVC)

The low performance of power supply in the transmission network is as a result of voltage instability, this is overcome by improving voltage stability in Nigerian 330kv transmission network using intelligent solid state var compensator (SSVC). It is achieved in this procedure by running the load flow from the characterized data thereby locating the faulty buses that their per unit volts do not fall within the ranges of 0.95 through 1.05, designing a conventional model for voltage stability in Nigerian 330KV transmission network, designing SIMULINK model for SSVC, designing a rule base that will enhance the faulty buses to attain voltage stability. Integrating the designed SIMULINK model for SSVC to designed rule base and designing a SIMULINK model for improving voltage stability in Nigerian 330KV transmission network using intelligent solid state var compensator. The results obtained were as follows: In bus1 the conventional per unit volts is 0.92P.U.volts which did not reach the range of voltage stability of 0.95 through 1.05 P.U.volts. On the other hand, when intelligent solid state var compensator (ssvc) is incorporated in the system the per unit volts becomes 0.9779P.U.volts thereby attaining voltage stability that enhances power supply. In bus 9 the conventional per unit volts is 0.922P.U.volts which did not attain the voltage stability range of 0.95 through 1.05 P.U.volts. On the other hand, when intelligent solid state var compensator (ssvc) is incorporated in the system the per unit volts becomes 0.9801P.U.volts thereby attaining voltage stability that enhances power supply.

D-STATCOM d-q Axis Current Reference Control Applying DDPG Algorithm in the Distribution System

The high penetration level of renewable energy in large-scale power systems could adversely affect power quality, such as voltage stability and harmonic pollution. This paper assesses the impacts of Distribution Static Compensator (D-STATCOM), one of the Flexible AC Transmission System (FACTS) devices, on power quality of 4.16kV-level distribution systems via transient and steady-state analysis. Carrier-based Pulse Width Modulation (PWM) control in D-STATCOM generates d-q axis current reference via the PID (Proportional-Integral-Differential) controller to control d-q axis current and voltage. A new control method, via the Deep Deterministic Policy Gradient (DDPG) algorithm-based reinforcement learning (RL), is studied to create a new d-q axis current reference applying to the voltage control, which can improve voltage stability and transient response and derive fast convergence of current and voltage at the D-STATCOM bus. The real-time simulations on an IEEE 13-bus system show that the proposed approach can better control the D-STATCOM than the conventional control methods for enhancing voltage stability and transient performance.

Voltage Stability Improvement in Optimal Placement of Voltage Regulators and Capacitor Banks Based on FSM and MMOPSO Approach

Installation of Shunt Capacitor Banks (SCBs) and Voltage Regulators (VRs) within distribution system is one of the most effective solutions in reactive power control for improving the voltage profile and reducing power losses along the feeder. However, the presence of the VRs can deteriorate the Voltage Stability Margin (VSM) in distribution feeders. To address this issue, this paper proposes a multi-objective programming model for the simultaneous optimal allocation of VRs and SCBs in the distribution network to improve the voltage profile and to minimize power losses and installation costs. In the proposed model, a Voltage Stability Index (VSI) is considered to prevent voltage instability during SCBs/VRs allocation. A new Modified Multi-Objective Particle Swarm Optimization (MMOPSO) algorithm which includes a dynamic inertia weight and mutation operator is proposed to obtain the optimal solutions as a Pareto set. Thereinafter, a Fuzzy Satisfaction Method (FSM) determines the optimal solution. A practical long radial distribution feeder has been employed to demonstrate the efficiency and efficacy of the proposed model along with a comparison between the proposed MMOPSO and the original MOPSO.

Growth of 4H-SiC recombination-enhancing buffer layer with Ti and N co-doping and improvement of forward voltage stability of PiN diodes

“Bipolar degradation” phenomenon has severely impeded the development of 4H-SiC bipolar devices. Their defect mechanism is the expansion of Shockley-type stacking faults from basal plane dislocations under the condition of electron-hole recombination. To suppress the “bipolar degradation” phenomenon, not only do the basal plane dislocations in the 4H-SiC drift layer need eliminating, but also a recombination-enhancing buffer layer is required to prevent the minority carriers of holes from reaching the epilayer/substrate interface where high-density basal plane dislocation segments exist. In this paper, Ti and N co-doped 4H-SiC buffer layers are grown to further shorten the minority carrier lifetime. Firstly, the dependence of Ti doping concentration on TiCl<sub>4</sub> flow rate in 4H-SiC epilayers is determined by using single-dilution gas line and double-dilution gas line. Then the p<sup>+</sup> layer and p<sup>++</sup> layer in PiN diode are obtained by aluminum ion implantation at room temperature and 500 ℃ followed by high temperature activation annealing. Finally, 4H-SiC PiN diodes with a Ti, N co-doped buffer layer are fabricated and tested with a forward current density of 100 A/cm<sup>2</sup> for 10 min. Comparing with the PiN diodes without a buffer layer and with a buffer layer only doped with high concentration of nitrogen, the forward voltage drop stability of those diodes with a 2 μm-thick Ti, N co-doped buffer layer (Ti: 3.70 × 10<sup>15</sup> cm<sup>–3</sup> and N: 1.01 × 10<sup>19</sup> cm<sup>–3</sup>) is greatly improved.