Maintain Voltage Stability Research Articles

An enhanced consensus-based distributed secondary control for voltage regulation and proper current sharing in a DC islanded microgrid

A centralized secondary control is utilized in a DC islanded microgrid to fine-tune voltage levels following the implementation of droop control. This is done to avoid conflicts between current allocation and voltage adjustments. However, because it introduces a single point of failure, a distributed secondary control is preferred. This paper introduces a consensus-based secondary distributed control approach to restore critical bus voltages to their nominal values and properly distribute current among converters. The critical bus takes the lead in voltage adjustments, with only connected energy resources contributing to regulation. The microgrid is represented as an undirected graph to facilitate consensus building. Two adjustment terms, δv and δi, are generated to assist in returning voltage to its nominal level and correctly allocating current among energy resources. To enhance consistency and improve controller performance compared to those reported in existing literature, all buses are connected to a leader node. In the event of the failure of all converters except one, voltage can still be effectively restored. MATLAB-Simulink simulations are conducted on two medium-voltage DC (MVDC) microgrids to validate the efficiency of the proposed control method. The results confirmed that the proposed control method can effectively maintain voltage stability and enhance the precise distribution of current among agents by 8%.

Application of Delta PLC on Battery Management System in AC/DC Microgrid

To keep the energy balance and power quality in check, a proper controller must be made for all the parts of the microgrid to work together. The sizing of the microgrid is done by considering the distributed generators and their connected ACDC loads. The performance of DC will obtain according to the state of charge condition of the battery bank. So it is essential to operate the battery bank by observing the state of the charge condition. To maintain the voltage stability of the system the PLC (programmable logic controller) best switching controller is designed to operate the battery bank according to the distributed generators’ demand. The main objective of the present work is to enhance the power conversion efficiency and maintain voltage stability during essential conditions which are fulfilled by the Battery storage and its controller. It must provide effective voltage support in a fault condition.

A survey on voltage stability indices for power system transmission and distribution systems

Voltage stability is a critical aspect of power system operation, ensuring the reliable and efficient delivery of electrical energy to consumers. Recently, voltage stability in the power system has received much attention. The primary cause of voltage instability is the lack of real and reactive power generation to cope with the continuous demand increment. Maintaining voltage stability while planning, controlling, and assessing the system’s security is a difficult task for power system engineers. From knowledge of past incidents, a lack of reactive power is identified as the primary cause of voltage instability, which may further lead to the total collapse of the system. The importance of voltage stability assessment is essential to maintain the integrity of power systems. It helps prevent voltage instability, which can lead to cascading failures and widespread outages. This paper uses various parameters, including load demand, generator capacity, and system impedance, to develop voltage stability indices (VSIs). The paper mainly focuses on the idea of VSIs that have been developed in order to monitor and control the criticality of the power system. The voltage stability indices for transmission and distributed systems, as well as their subclasses, are thoroughly reviewed in this study. Furthermore, traditional voltage stability methods, as well as various software tools for monitoring the voltage stability problems, are also discussed. In addition, the development of VSIs and its related concepts are clearly described in this paper. This comprehensive survey provides a decent groundwork for future work in this area, and assists professionals in selecting the optimal VSI for various applications. Moreover, it provides a concise overview of methods and the importance of voltage stability assessment in both transmission and distribution systems.

Dispatchable Droop Control Strategy for DC Microgrid

DC(Direct Current) droop control has the advantages of plug-and-play and the convenience of parallel operation of multiple converters. However, when the power changes drastically, the DC voltage may be too low. This paper proposes a converter control method based on schedulable variable droop coefficient to maintain voltage stability when the power changes drastically. The dual-machine parallel system is simulated on MATLAB/Simulink, and compared with the traditional DC droop control, the effectiveness of the proposed method is verified.

Critical Issues of Optimal Reactive Power Compensation Based on an HVAC Transmission System for an Offshore Wind Farm

The reactive power (RP) control of the high voltage alternating current transmission system (HVAC TS) for offshore wind farms (OWFs) is a crucial task to assure the consistent and efficient operation of the system. The importance of RP compensation (RPC) in power system operation is to maintain voltage stability and reduce power losses. Offshore wind farms present unique challenges for power system operation due to their distance from the onshore grid, variable wind conditions, and complex electrical infrastructure. The HVAC TS is common for OWFs as it is well-suited for transmitting large amounts of power over long distances. In this paper, a literature-based analysis helps in improving the operation and reliability of OWFs, ultimately leading to greater renewable energy utilization. This paper concludes that optimal RPC is a critical task for ensuring the stable and efficient operation of HVAC TSs for OWFs. Advanced control and optimization techniques can help achieve an optimal RPC, thereby minimizing TLS and improving the overall system efficiency. Furthermore, the study investigates the possible benefits of incorporating novel technologies and approaches, such as RESs, into the power compensation process. By offering insightful information on how to optimize HVAC TSs for OWFs, for example, subsea power cables with multiple layers must be used to carry electricity from large offshore wind farms, the development of more sustainable and effective energy solutions is possible. The research concludes by stating that ensuring the steady and effective operation of HVAC TSs for OWFs is a crucial responsibility. Advanced optimization and control solutions can reduce TLS and increase system efficiency by assisting in achieving the optimal RPC.

Load Shedding Technique for Power System Using Neural Network Improved by Cuckoo Search Algorithm

The present paper introduces a load shedding methodology that leverages an upgraded neural network that relies on the Cuckoo search (CS) optimization algorithm to compare the efficiency and applicability with other methods in terms of speed and feasibility. The proposed method will be tested on the IEEE-37 bus system. The results of the method are compared with other optimization methods. Thereby, this method gives good results and feasibility in application. The criteria of voltage are considered, specifically the sensitivity index dV/dQ is proposed to find weak buses in the system that need to be relieved of the active power burden. Then, the shedding priority bus ranking is created to ensure the most favorable load shedding plan for the system to maintain voltage stability. Besides, the frequency parameter is also considered to calculate the optimal amount of shed load. The model system was tested by using POWERWORLD software. After comparing the results with other methods outlined in the paper, it has been determined that the proposed approach is highly effective for optimizing grid shedding in the system.

ANALISA PERUBAHAN PEMBEBANAN TERHADAP ARUS EXITASI UNIT 1 PADA PT PLN (PERSERO) SEKTOR PEMBANGKITAN TELUK SIRIH

Changes in the load of a generator are always changing according to the needs of community demand. On the generator side of the Teluk Sirih PLTU using charcoal brush media as a reinforcing field. Where excitation plays an important role providing DC current to the generator rotor to create an intersection of electromotive forces. Changes in generator load that are always changing can have an impact on damage to equipment such as generators, and excitation. Where on December 6, 2017 the excitation current reads low at 473.7 amperes directly proportional to the armature current of 1404.2 amperes, the resulting power will also be low at 13200000 watts and a frequency of 49.9 Hz, creating a magnetic flux of 0.125 Weber that is larger or feels heavy so that the generator rotation is low at 2999 rpm and vice versa. Therefore the role of excitation takes over in order to provide greater current so that the field strength is maintained stable. Increasing the excitation current (If) results in a greater induced electromotive force (Ea). This increase in Ea also impacts the terminal voltage (Vt), causing it to vary. This relationship demonstrates that higher excitation current leads to an increase in terminal voltage, which is essential for maintaining voltage stability. To stabilize the low terminal voltage resulting from load changes, it is necessary to amplify the field gain current. This can be achieved by increasing the excitation current on the synchronous generator rotor. Understanding the characteristics of the excitation system allows for minimizing and avoiding damage to the generator caused by both overexcitation and underexcitation, ensuring the maintenance of a stable terminal voltage.

Two‐stage self‐adaption security and low‐carbon dispatch strategy of energy storage systems in distribution networks with high proportion of photovoltaics

AbstractWith the goal of achieving carbon neutrality, active distribution networks (DNs) with a high proportion of photovoltaics (PVs) are facing challenges in maintaining voltage stability and low‐carbon operation. Energy storage systems (ESSs), which have the ability to store and transfer energy temporarily, can be used as effective measures to enhance the capacity of consuming PVs and reduce carbon emissions in DNs. However, existing low‐carbon dispatch strategies for multiple sources, storages and loads fail to consider voltage violations, while the temporal carbon emission intensity of the upper‐level power grid is also often overlooked, which is an important factor that affects the dispatch strategy. Therefore, a two‐stage self‐adaptive dispatch strategy of ESSs that considers the temporal characteristics of slack nodal carbon emission intensity to minimise carbon emissions while maintaining voltage stability in DNs with high access to PVs is proposed. First, the framework of the proposed two‐stage self‐adaptive dispatch strategy of ESSs is established by taking into account the effects of ESSs on adjusting voltages and reducing carbon emissions, respectively, with the two‐stage switch principle of two operation modes being determined. On this basis, an optimization dispatch model is established to improve voltages and carbon emissions, and the optimal day‐ahead dispatch strategy of ESSs can be obtained by solving the model using genetic algorithm. Case studies of the modified 10 kV IEEE 33‐node DN and IEEE 123‐node DN verify the feasibility and superiority of the proposed two‐stage self‐adaptive security and low‐carbon day‐ahead dispatch strategy for ESSs, showing that the voltage stabilisation and lower carbon emissions of DNs are both improved.

Voltage Stability Improvement Using Intelligence Technique

Numerous Artificial Intelligence procedures have been anticipated for reactive power dispatch to maintain voltage stability of the power system. This paper presents particle swarm optimization (PSO) approach for framework boundaries improvement and ideal reactive power dispatch. The transformers tap transformers, Generator exciters, switchable VAR sources/Static VAR compensators (SVC) are utilized as control factors for progression of framework boundaries and voltage stability. The recommended procedure depends on the minimization of total of the squares of L-index value at all load bus. The PSO Algorithm is tested on an IEEE 30 bus test system. The presentation of PSO is compared with conventional technique and results are introduced for illustration purpose. The margin of voltage stability is estimated in terms of system parameters.

Off-policy deep reinforcement learning with automatic entropy adjustment for adaptive online grid emergency control

Electric overloading conditions and contingencies put modern power systems at risk of voltage collapse and blackouts. Load shedding is crucial to maintain voltage stability for grid emergency control. However, the rule- or model-based schemes rely on accurate dynamic system models and face considerable challenges in adapting to various operating conditions and uncertain event occurrences. To address these issues, this paper proposes a novel deep reinforcement learning (DRL)-based voltage stability control algorithm with automatic entropy adjustment (AEA) for grid emergency control. Various dynamic network components for complex system operations are modeled to construct the DRL environment. An off-policy soft actor-critic architecture is developed to maximize the expected reward and policy entropy simultaneously. The AEA mechanism is proposed to facilitate the policy maximum entropy procedure, and the proposed method can automatically provide effective discrete and continuous actions against various fault scenarios. Our approach accomplishes high sampling efficiency, scalability, and auto-adaptivity of the control policies under high uncertainties. Comparative studies with the existing DRL-based control methods in IEEE benchmarks indicate salient performance improvement of the proposed method for dynamic system emergency control.

Optimal Placement and Size of SVC with Cost-Effective Function Using Genetic Algorithm for Voltage Profile Improvement in Renewable Integrated Power Systems

Given the concern for maintaining voltage stability in power systems integrated with renewable power systems due to a mismatch in generation and demand, there remains a need to invoke flexible alternating current transmission system (FACTS) devices in the distribution network. The present paper deals with identifying the locations of placement of a static var compensator in an experimental IEEE 14-bus system; the voltage drop in different buses in an IEEE 14-bus system is calculated by the standard formula. The total voltage drop in the network (TVDN) is also calculated as a reference. The ranking of buses in order of decreasing voltage drop is made, and the weak buses are identified as those showing the maximum or near-maximum voltage drop for the installation of a Static Var Compensator (SVC). The optimum usable size is calculated using a Genetic Algorithm approach to optimize the installation cost. After size optimization, installing a 2 MW solar generator is considered for the weak and most potential bus, which suffers from voltage drops or power loss. Based on the generator at the weakest bus, the total power loss in the network is calculated and compared with a similar method to assess the efficiency of the proposed model. Thus, the voltage stability enhancement problem is solved by applying a Genetic algorithm (GA) to optimize SVC size and using the Total Voltage Drop in Network (TVDN) method to identify weak buses in the systems. It is found that the performance of the proposed system is comparable with another existing system. It is further observed that a gain in power loss to 6.56% is achievable by adopting the proposed strategy, and the gain is better than the other system.

IC Pattern Based Power Factor Maximization Model for Improved Power Stabilization

The voltage fluctuation in electric circuits has been identified as key issue in different electric systems. As the usage of electricity growing in rapid way, there exist higher fluctuations in power flow. To maintain the flow or stability of power in any electric circuit, there are many circuit models are discussed in literature. However, they suffer to maintain the output voltage and not capable of maintaining power stability. To improve the performance in power stabilization, an efficient IC pattern based power factor maximization model (ICPFMM) in this article. The model is focused on improving the power stability with the use of IC (Inductor and Conductor) towards identifying most efficient circuit for the current duty cycle according to the input voltage, voltage in capacitor and output voltage required. The model with boost converter diverts the incoming voltage through number of conductors and inductors. By triggering specific inductor, a specific capacitor gets charged and a particular circuit gets on. The model maintains number of IC (Inductor and Conductor) patterns through which the power flow occurs. According to that, the pattern available, the mofset controls the level of power to be regulated through any circuit. From the pattern, the model computes the Circuits Switching Loss and Circuits Conduction Loss for various circuits. According to the input voltage, the model estimates Circuit Power Stabilization Support (CPSS) according to the voltage available in any capacitor and input voltage. Using the value of CPSS, the model trigger optimal number of circuits to maintain voltage stability. In this approach, more than one circuit has been triggered to maintain output voltage and to get charged. The proposed model not only maintains power stability but also reduces the wastage in voltage which is not utilized. The proposed model improves the performance in voltage stability with less switching loss.

Synchrophasor Data Based Q-V Droop Control of Wind Farm Integrated Power Systems

With increasing scalability of grid-integrated wind farms (WFs), reactive power ancillary service through Q-V droop control of doubly-fed inducton generators (DFIGs) is one of the prime interests of power system operators. However, variable and uncertain availability of wind-resource at the wind turbines creates challenge against allocating reactive power reserve at the WFs for maintaining voltage stability of the grid. This issue can be resolved through online coordination among the WFs. This paper proposes a synchrophasor data based Q-V droop (SQVD) control technique for the WFs integrated to the grid through different point of common couplings (PCCs) in the power system transmission network. The data from the phasor measurement units (PMUs) at the WF-connected PCCs are used to obtain synchronized Q-V droop gain for each WF. Further, distributed coordination among DFIGs within each WF is performed to allocate optimum reactive power share at the converters. The total reserve of each WF is employed by their synchronized droop, in improving voltage stability at both the local PCC and neighboring PCCs. Performance of SQVD is verified at 418-bus practical Indian power system, in different dynamic situations of the grid, and found to be more effective as compared to the constant Q-V droop and variable Q-V droop control methods.

Strategic Integration of DG and ESS by using Hybrid Multi Objective Optimization with Wind Dissemination in Distribution Network

The importance of distributed generation (DG) has increased recently as a result of the growth in commercial and industrial loads, which has put more pressure on conventional energy sources and utilities. Alternative power generation methods that can handle the massive load without endangering the environment are therefore urgently needed. The installation of Energy Storage Systems (ESSs) may give a substantial opportunity to enhance the aesthetic appeal of the distribution system. DG is a practical substitute for conventional energy sources, which have drawbacks for both the economics and the environment. It goes without saying that there are situations in which a large amount of land and money are required. However, improper DG location or sizing increases safety issues because to the increasing power loss caused by larger reverse flow from the load to the supply. In order to reduce power losses and maintain voltage stability, the ideal location and dimensions for the DG and ESS in IEEE Radial Distribution systems are evaluated. To accomplish these objectives, a hybrid Shuffled Frog Leap Algorithm (SFLA) and Improved Firefly Algorithm (SFLA-IFFA) is suggested. The SFLA-IFFA produced better results in terms of the ideal location and DG size when compared to other existing algorithms.

Analysis of Voltage Stability of the Slovak Republic’s Power System

This paper studies the voltage stability of the Slovak Republic’s power system (PS) based on an assessment of the PV curves. The PV curve is a tool for assessing voltage stability, and based on its shape, it is possible to determine weak and strong voltage nodes with the possibility of voltage stability reserve quantification. We present an analysis of the influence of transformers with an automatic voltage regulator (AVR) on the shape of the PV curves and on the magnitude of voltage in the PS. In general, the 400 kV/110 kV transformers equipped with AVRs are critical assets for the PS as they address voltage control in the DS. However, in the case of voltage problems in the TS, the AVR function may worsen the voltage situation across the entire PS. Therefore, we closely analyze the negative effects of the AVR on the PS operation. This impact is clearly proved, and recommendations are given for the transmission system operator (TSO) in order to maintain voltage stability. In addition, the PV curves of the pilot nodes are analyzed very accurately, thereby confirming their importance in the TS in terms of a sufficient reserve of reactive power. The study was conducted in cooperation with the TSO, Slovenská elektrizačná prenosová sústava, a.s.

Hybrid Micro-Grid: a Review on Operational Stability Aspects

With the significantly rising demand for alternate energy resources like renewable sources, the power demands are fulfilled at reduced expenses, and increased efficiency. Despite these alternate generation techniques, there are still considerable challenges in controlling and working Microgrids (MG’s) configured in DC and AC. Hybrid Micro-Grids (HMGs) are developed particularly for overcoming the effective power regulation difficulties encountered in standalone MGs by combining the advantages of individual AC and DC configurations. Since microgrids are equipped with power electronic interfaces, unlike the conventional system, maintaining voltage stability, frequency stability, and optimal power management is challenging and requires a different approach. This paper attempts to analyze various stability issues in existing systems and the control methods employed in prior works for a better understanding and management of HMG systems. It also presents a comparative study of related works in terms of their control techniques and achieved performance. The paper further discusses various research challenges prevailing in this field thereby providing an insight into the development of better control methods and techniques for resolving various stability issues in HMG for better management and supporting future applications.

Reinforcement Learning Based Distributed Control of Dissipative Networked Systems

We consider the problem of designing distributed controllers to stabilize a class of networked systems, where each subsystem is dissipative and designs a reinforcement learning based local controller to maximize an individual cumulative reward function. We develop an approach that enforces dissipativity conditions on these local controllers at each subsystem to guarantee stability of the entire networked system. The proposed approach is illustrated on a DC microgrid example, where the objective is maintain voltage stability of the network using local distributed controllers at each generation unit.

Topology of a Three-Port Converter for High-Altitude Platforms

Three-port converter (TPC) with non-regulated bus cannot meet the voltage stability demands of high-altitude platforms (HAPs) during daytime operations. In contrast, full-regulated bus TPC is complex in topology and inferior in power density, although it can maintain voltage stability across whole day operations. Therefore, semi-regulated bus TPCs are more suitable for this scenario, which can not only maintain voltage stability during daytime operations, but also have simple topology. However, conventional semi-regulated bus structure converts the power twice, leading to lower efficiency and power density. In order to overcome this problem, the paper proposes a novel semi-regulated bus TPC that can be used on high-altitude platforms. The topology only has one conversion between the ports. It regulates the bus voltage during the day and prevents the loss of diode during the night by directly discharging through the MOSFET and achieving high efficiency. The paper adopts GaN devices to elevate the working frequency to further improve the power density, and conduct a theoretical analysis for all working modes and provide key equations. The closed-loop transfer function of the system is deduced for stability analysis. The results show that the proposed topology has high efficiency and power density.

Improving performance of transmission networks using facts through continuation power flow method

Over the past 50 years, modern electrical systems have become more complex, as they overrun the geographical boundaries of neighboring countries. The problem is that the power system faces many challenges, because it is exposed to difficult operating conditions. The phenomenon of voltage instability is the most frequent phenomenon, and this can lead to the collapse of the power system. To avoid power outages in the system (especially in blackout situations), the power system must be analyzed in order to maintain voltage stability in the expected difficult operating conditions. The main objective is to determine the maximum load capacity of the system and the causes of voltage instability. The voltage instability problem is related to the nature of nonlinear loads, so different load characteristics must be taken into consideration when analyzing voltage stability. This study aims to discover the maximum load capacity required by using the continuous power flow method (CPF) in the studied network. Then, the performance of this network using a Flexible Alternating Current Transmission System (FACTS) will be utilized. FACTS systems present a promising solution in improving the voltage stability by improving the power transmission capacity and controllability of the parameters of the existing power networks. This study will be conducted on a reference network platform under normal working conditions, then installation of one of the FACTS systems will show its effect on improving voltage stability. The continuous power flow method will be used to find PV curves, which in turn will help to determine the conditions of maximum loading while maintaining stability, and identify the bus bar with the smallest voltage, on which the flexible AC systems will be installed. The software environment MATLAB/PSAT will be used for modeling and simulation.

A Comparison of Inverter Control Modes for Maintaining Voltage Stability During System Contingencies

Inverter-based power sources are increasingly being connected to the power system due to the global drive towards renewable generation. This paper investigates the voltage stability of a power system where a load center is supplied by the grid through a transmission system along with an inverter-based generation located close to the load center. It is also assumed that there is no additional reactive power compensation at the load center and voltage control at Point of Common Coupling (PCC) is done by the inverter. This is challenging as the inverter has an added duty. If the inverter controllers are not designed properly, the inverter could reach its current limit following to contingencies rendering it unable to support the voltage at the PCC. This is due to the fact that once the current limit is reached, the inverter ceases to function as a voltage source. When the voltage at the PCC is not supported, the active power transfer capability of both the inverter and the grid will be reduced. An effective control method is required under such circumstances to handle the active and reactive components of the inverter current. Various strategies exist for controlling the active and reactive components of the inverter current while preserving the current magnitude at the rated value. The necessity of an adequate control strategy to sustain long-term voltage stability following a system contingency is emphasized in this research. This paper further discusses three candidate control strategies and the effectiveness of the reactive current prioritizing approach as a solution for operation upon system contingencies.