Voltage Sag Research Articles

A Calculation Method Based on Analytical Formulas for Inrush Currents and Voltage Dips During Energization

ABSTRACTIf a voltage dip gets lower than a certain threshold at the moment when a transformer is energized, its mitigation is required. For this reason, when a transformer is energized, the voltage dip is calculated in advance and the need for its mitigation is considered. From the viewpoint of preventing unnecessary countermeasures, highly accurate calculations are required. However, electromagnetic transient analysis, which is known as a method with high accuracy, is not practical because its operation is rather complicated. In this paper, the analytical circuit is simplified by simulating the magnetizing inductance of the transformer with the inductance and the series connection of the ideal switch, and analytical formulas for the flux and current in the winding are derived for each switching mode. The calculated inrush currents and voltage dips during transformer energization using the derived analytical formulas agreed well with the results from electromagnetic transient analysis, which handled the nonlinear current‐flux characteristics precisely.

Comparative Analysis of PI and PR Control Strategies for Enhancing Voltage Quality in D-Statcom-Based Distribution Networks

In recent years, the rise in the number of sensitive loads in distribution networks has highlighted the importance of not only ensuring the continuity of electricity supplies but also maintaining high power quality for consumers. In the present era, one of the most prevalent power quality issues in power systems is voltage sag, which is responsible for over 80% of the observed problems. Although the duration of the disturbance is relatively brief, typically between 10 ms and 1 minute, it can have a significant impact on the production process due to a minor deviation from the rated voltage. The disturbance can occur within a second, but the restoration process can take several hours. In order to enhance the power quality of the grid, it is essential to regulate reactive power. The objective of this study is to utilise a D-STATCOM for the correction of voltage by connecting it in parallel to the bus connection point between the grid and the loads. Modelling and simulation studies have been conducted to investigate the contribution of D-STATCOM with PI (proportional-integral) or PR (proportional resonance) controllers to the system in response to various fault scenarios that cause voltage sags by commissioning various loads at low voltage (0.4 kV). The simulation of both models was conducted using the PSCAD/EMTDC program. The performance of both controllers is evaluated through a comparison with the PSCAD/EMTDC simulation program. The results demonstrate that the D-STATCOM responds to short-term voltage sags caused by a fault or other system disturbances with a high degree of efficiency, rapidly restoring the bus voltage to a level close to the nominal value. This effectively mitigates the potential disruptions associated with voltage collapse. Furthermore, the analysis reveals that D-STATCOMs employing PI and PR controllers exhibit a combination of advantages and limitations in their performance.

Enhanced Power Injection Strategies for Voltage Sag Minimization: Integrating the Maximum Apparent Power of the Converter and the Thévenin Equivalent

Enhanced Power Injection Strategies for Voltage Sag Minimization: Integrating the Maximum Apparent Power of the Converter and the Thévenin Equivalent

Gate Voltage Dip as a New Indicator for Online Health Monitoring of SiC MOSFETS

Gate Voltage Dip as a New Indicator for Online Health Monitoring of SiC MOSFETS

Induction Motor Voltage Variation and Fault Adaptation in Submarines

Induction motors are critical components in submarine systems, powering propulsion and auxiliary machinery under challenging operational conditions. These motors, however, are susceptible to faults such as voltage disturbances and mechanical anomalies that can compromise performance and operational safety. This research investigates the fault adaptation mechanisms for induction motors in submarine scenarios by integrating wavelet decomposition for fault detection and undervoltage relays for fault adaptation and mitigation. Wavelet transform analysis is employed to detect transient faults, specifically voltage disturbances occurring between 0.3 and 0.7 seconds. The system identifies fault characteristics in real-time using the high-resolution capabilities of discrete wavelet transforms, allowing precise localization and classification of anomalies. An undervoltage relay, integrated into the system, adapts to the fault condition by tripping the motor at 0.54 seconds to prevent prolonged exposure to damaging voltage dips. The study utilizes MATLAB/Simulink to model and analyze a 7.5 kW, 400 V, 1440 RPM induction motor operating under realistic submarine conditions. For fault identifications, twelve different scenarios are examined: Three phase to ground fault, three phase fault, double line to ground fault (AB-G), double line to ground fault (AC-G), double line to ground fault (BC-G), line to line fault (A-B), line to line fault (A-C), line to line (B-B) fault, single line to ground fault (A-G), single line to ground fault (B-G), single line to ground fault (C-G), and no faults. Also, for fault adaptation using under-voltage relay, two different scenarios are simulated for reference purpose: single line to ground and three phase to ground. Simulation results demonstrate the effectiveness of the wavelet-based detection in identifying faults early and the relay's timely intervention to protect the motor. These findings highlight the viability of integrating wavelet decomposition and adaptive relay mechanisms to enhance the resilience of induction motors in submarines.

A time-variant power distribution network voltage sag identification method based on the concept of inheritance

The present paper introduces a novel method for identifying voltage sags in time-variant power distribution networks, effectively addressing the challenges arising from the temporal variability of network topology and data. The proposed method is founded on the concept of inheritance, which is bifurcated into breadth and depth inheritance strategies. The breadth inheritance strategy employs transfer learning to manage topological temporality, utilizing the Euclidean distance between samples to ascertain the sequence of sample migration, and implements multitask learning to share feature representations across different tasks. The depth inheritance strategy, on the other hand, utilizes incremental learning to handle data temporality, building upon the initial model parameters to learn new sample features, which in turn reduces the time required for model updates and enhances the accuracy of target tasks. Case study findings validate the suitability of the proposed methods for reconstructing fault identification models in scenarios characterized by topological temporal variability and for rapidly updating fault identification models in scenarios with data temporal variability. The approach presented herein holds significant implications for the enhancement of power supply reliability and the adaptability of electrical grids.

Artificial intelligent fuzzy control and LAPO algorithm for enhancement LVRT and power quality of grid connected PV/wind hybrid systems

Low Voltage Ride Through (LVRT) is considered one of the main and serious problems facing the electrical grid. It occurs due to three-phase symmetric faults and asymmetric faults such as a double line to ground fault that applies in this system. This paper applies Static Synchronous Compensators (STATCOM) to improve the LVRT capability and dynamic performance of an electrical grid linked to a Photovoltaic (PV)/Wind hybrid system through grid disturbances. A hybrid power system containing a PV station that produces 1 MW and a wind farm from type Doubly Fed Induction Generator (DFIG) that produces 9 MW is connected to STATCOM with 48 pulses at PCC bus and energized load. It compensates reactive power to improve LVRT that occurred due to fault. The applied STATCOM controller adjusts the voltage of the PCC bus during an occuring fault on the grid by compensating reactive power. STATCOM is controlled by a Proportional–Integral–Derivative (PID) and is compared with STATCOM controlled by Artificial Intelligence Control (AIC)-based on Proportional—Integral Fuzzy Logic Control (PI FLC). The Lightning Attachment Procedure Optimization Algorithm (LAPO) optimization method is used to adjust the parameters of the PI controller to reduce error signals. A simulation model of the suggested hybrid power system has been performed using Matlab/Simulink. The simulation results of STATCOM proved powerful and the effectiveness of STATCOM with PI FLC in reducing voltage dip, compensating active power of wind and PV farm, protecting DC-link voltage of PV and wind from overvoltage and oscillation that happens at three-phase fault and double line to ground fault as compared with PID STATCOM in enhancement LVRT capability, and power quality.

Series Active Power Filter for Power Quality Improvement

The paper discusses the theoretical framework and operating principles of the SAPF, including its control strategies based on instantaneous reactive power theory and synchronous reference frame theory. The design criteria for the SAPF components, such as the voltage source inverter, DC link capacitor, and coupling transformer, are also elaborated to ensure optimal performance. Simulation studies using MATLAB/Simulink are conducted to evaluate the effectiveness of the proposed SAPF under various power quality disturbance scenarios. The results demonstrate that the SAPF effectively compensates for voltage sags, swells, and harmonics, maintaining voltage stability and reducing total harmonic distortion (THD) to within acceptable standards. Additionally, a prototype of the SAPF is developed and tested in a laboratory environment, confirming the simulation results and showcasing the practical feasibility of the solution. The study concludes that the Series Active Power Filter is a robust and versatile solution for power quality improvement in modern electrical distribution systems. Future work may involve exploring hybrid configurations combining series and parallel active filters for comprehensive power quality management and the development of advanced control algorithms for enhanced performance under dynamic load conditions.

A new series‐parallel active compensator for DC microgrids based on three‐leg voltage source converter

AbstractDC microgrids are gaining increasing attention due to their advantages such as high reliability, high efficiency, ease of renewable energy sources integration, and the absence of frequency and reactive power regulation problems. Connection of AC energy sources and loads to the DC microgrids through AC/DC converters can distort the DC microgrids voltage and current. In addition, the fault occurrence in the DC or upstairs AC microgrids can cause voltage sag and swell. Compensating and reducing these voltage and current distortions requires efficient and cost‐effective solutions. This article proposes two new topologies of DC series‐parallel active compensators for voltage and current compensation in DC microgrids. In the first topology, the back‐to‐back connection of an isolated bidirectional DC/DC converter with a full‐bridge converter is used to compensate voltage and current. In the second one, to eliminate the transformer, simplify the converter structure and reduce its cost, an active compensator based on a three‐leg voltage source converter is proposed which can compensate both the microgrid voltage harmonics, sag and swell, and the load current harmonics. The proposed topologies performances are confirmed through their simulation in the MATLAB/SIMULINK environment. A simple experimental setup is also provided to validate the simulation results.

An induction machine‐based drive system and supervisory control for application to smart water‐pumped storage and networks

AbstractThe authors present an effective induction machine (IM) drive system and intelligent supervisory control for application to smart water‐pumped storage and networks. The main IM drive unit comprises reduced voltage starter, regenerative clutch/variable speed mode fluid coupling and reversible pump to allow bidirectional power flow. Under the wide umbrella of supervisory control, the following objectives are achieved: (1) Recurrent neural network (RNN) and RNN‐aided Kalman filter are proposed for wired and wireless sensor fault‐tolerant control of the plant based on Wald's likelihood ratio test. (2) Cheap fuzzy logic‐based availability assessment scheme is presented and deployed on cloud to arrange for preventive maintenance of the starter. (3) Robust energy saving mode decision‐making algorithm is developed for best energetic cost reduction. (4) Remote synchronisation method of multi‐motor starting with a mechanically switched capacitor is introduced to minimise voltage dip. Further, an auxiliary inverter fed pump unit is adopted to improve system availability and revenue. The validity and superiority of the proposed drive system and control are confirmed through theoretical analysis, computer simulations, cost study, efficiency evaluation and application example to a single‐pump water network during motor and generator operational modes using preliminary test results.

Stochastic assessment of voltage sags and techno-economic optimization

Power quality has become an essential concern for industries and domestic energy consumption with the development of sophisticated equipment like micro-electronic devices. When a power quality event happens, such as voltage sag, financial losses for industries increase tremendously. Therefore, voltage sag evaluation becomes crucial for predicting the number of events and severity of voltage sag events of the electrical network. Industries can determine the mitigation investment needed for optimal operation using the knowledge obtained through voltage sag analysis method. Thus, the first part of the study addressed the development of a stochastic assessment method for voltage sag at an interested bus in the power system network, which was an initial objective of the study. The second part of the research investigates dynamic voltage restorer (DVR) control techniques, as well as the necessary capacitance and energy storage dimensions. The studies also recommend a technique for economic evaluation that emphasizes the expense of voltage sag events as well as the cost of investment in DVR with and without voltage sag events. The size of DVR and economic assessment model established in these studies enables industries to rate the cost of voltage sag and the total investment in mitigation devices.

Transient stability enhancement of virtual synchronous generators with virtual resistance

Abstract Virtual synchronous generators (VSGs) incorporate virtual resistance (VR) in inverter control as a damping mechanism for oscillations that appear around the synchronous frequency due to interactions between the inverter impedance and the line impedance while operating in low inertia grids. Damping is critical for synchronization stability in the small-signal and large-signal disturbance scenarios to suppress oscillations that threaten system stability. While VR enhances stability in the steady state, it is shown that its conventional application affects the transient stability of VSGs by reducing the angle overshoot range in the dynamic behaviour of the power angle δ, illustrated using the power-angle (P − δ) and frequency-angle (δ̇− δ) curves. In this article, a novel damping mechanism to improve the transient stability of VSGs using VR to enhance the power angle dynamics is proposed. By using the concept of virtual point of common coupling, the virtual power of the internal VSG is introduced in the active power feedback during a voltage sag, providing an equivalent damping effect proportional to the VR applied. In this way, the negative effects of VR on transient stability are averted while VR is used to improve the power angle dynamics of conventional VSG. Simulations of different transient stability scenarios are carried out in MATLAB/Simulink to verify the proposed method.

Performance Evaluation of Solar PV Integrated with Custom Power Device under Various Load Conditions

The non-linear properties and rapid switching of power electronic equipment are the primary causes of power quality issues in power systems, particularly in the power distribution systems. The widespread use of delicate equipment, which continuously pollutes the environment, is making power quality problems worse. The increasing integration of renewable energy sources into the generation mix and the decarburization of the economy have created new challenges for smart grid technology, requiring creative solutions such as energy storage systems and smart transformers. This article describes a solar photovoltaic integrated unified power quality conditioner (UPQC) that uses a deep learning method based on neural networks and a novel compensating technique. Here, two Deep Neural Network algorithms are used, one in the solar PV system to obtain the maximum power under various irradiance situations, and the other to manage the UPQC under various load conditions. When compared to the conventional UPQC based on PQ Theory, DNN-UPQC produces superior results in terms of reducing total harmonic distortion. This iterative strategy, which is focused on soft computing, provides faster convergence to the target condition while maintaining the updating weight within a predetermined limit. PV-based UPQC has been connected individually to reduce voltage sag, swell, and unbalance in variable load conditions. The system's dynamic and steady state performance are assessed by modelling it with a MATLAB-Simulink in different load condition.

A Novel Semisupervised Classification Method for Voltage Sag Based on Virtual Adversarial Mean Teacher Model

A Novel Semisupervised Classification Method for Voltage Sag Based on Virtual Adversarial Mean Teacher Model

Enhancing Grid-Connected Photovoltaic Systems' Power Quality through a Dynamic Voltage Restorer Equipped with an Innovative Sliding Mode and PR Control System.

This study focuses on enhancing power quality in on-grid photovoltaic (PV) schemes through an innovative dynamic voltage restorer (DVR) that integrates two control strategies with a multi-level inverter. The DVR, a power electronic compensator, corrects voltage disturbances such as sag and swell by adjusting the voltage at the point of common coupling (PCC). It utilizes sliding mode control (SMC) for normal operations and proportional resonance (PR) during voltage disruptions, ensuring accurate voltage correction. The system's multi-level inverter offers a distinct advantage over traditional high-frequency inverters, which typically suffer from significant switching losses in high-power applications. The multi-level inverter effectively detects and mitigates voltage issues while minimizing harmonic distortion. The study evaluates the DVR's performance under various conditions, including voltage swell, disruption, mild sag, and severe sag. Simulation results using the Simulink tool demonstrate that the proposed DVR significantly reduces voltage disturbances and enhances power quality in the PV panel's output, the PCC, and the injected voltage. The findings suggest that this dual-control DVR designe, with its efficient use of a multi-level inverter, is a promising solution for improving power quality and stability in on-grid PV arrangements.

A Soft Start Method for Doubly Fed Induction Machines Based on Synchronization with the Power System at Standstill Conditions

Due to their exceptional operational versatility, doubly fed induction machines (DFIM) are widely employed in power systems comprising variable renewable energy-based electrical generation sources, such as wind farms and pumped-storage hydropower plants. However, their starting and grid synchronization methods require numerous maneuvers or additional components, making the process challenging. In this paper, a soft start method for DFIM, inspired by the traditional synchronization method of synchronous machines, is proposed. This method involves matching the frequencies, voltages, and phase angles on both sides of the main circuit breaker, by adjusting the excitation through the controlled power converter at standstill conditions. Once synchronization is achieved, the frequency is gradually reduced to the rated operational levels. This straightforward starting method effectively suppresses large inrush currents and voltage sags. The proposed method has been validated through computer simulations and experimental tests, yielding satisfactory results.

An Efficient Archerfish Hunting Optimizer (AHO)-Based Power Quality Improvement in Distribution System Connected UPQC

These days, because power quality (PQ) issues are costing industrial customers a lot of money, both electrical utilities and end-users are paying a lot of attention to them. The most significant and frequent PQ concerns for sensitive loads are voltage sag and swell. This manuscript proposes an optimization technique for enhancing the control system of a unified power quality conditioner (UPQC) connected solar photovoltaic system in the distributed generation system. The proposed strategy is the archerfish hunting optimizer (AHO). The objective of the AHO approach is to optimizing UPQC operation in distribution systems, focusing on targeted power quality enhancement. The optimal control pulses are produced by the series active power filter and the shunt active power filter, depending on the load-side and source circumstances. During the load variation states the AHO technique manages the power loss, total harmonic distortion (THD), and voltage instability issue respectively. The performance of the AHO methodology is carried out on the MATLAB platform and compared with existing methods, like particle swarm optimization (PSO), latent semantic analysis (LSA), and ant-lion optimizer (ALO). The existing methods THD are 6.35%, 7.85%, and 9.19%. The proposed method of THD is 4.22%. From the outcome, it concluded that the proposed method based on the THD is low contracted to present techniques.

A two-stage business model for voltage sag sensitive industrial users employing energy storage systems

Integration of a behind-the-meter (BTM) energy storage system (ESS) is a dependable method of reducing electricity costs and improving power quality for industrial users susceptible to voltage sags. However, at present, barriers such as substantial initial investment costs, extended investment return periods, and limited service strategy flexibility are impeding the widespread implementation of BTM ESSs in industrial contexts. Integrated energy service providers (IESPs) supply innovative BTM ESS solutions and have emerged as viable options for navigating these challenges. This study proposes a new two-stage business model designed to advance ESS deployment while considering the needs of both the IESP and users. Herein, the framework of the proposed business model is outlined to delineate the participant roles and responsibilities at different stages. A detailed cost–benefit analysis is conducted to support a scenario analysis based on prospect theory. Then, a Stackelberg game model is constructed to describe the interactive relationship between the participants; using this model, an optimal ESS service strategy can be determined by resolving a simplified Stackelberg game problem. Our findings reveal that this model effectively mitigates long-term income risks for IESPs and substantially lowers initial investment costs for users by 21.93 % to 89.23 %, along with a reduction in lifecycle costs by 2.35 % to 17.12 % for users. A comprehensive analysis of six critical parameters indicates that the ESS lifetime, the disparity between peak and off-peak electricity prices, and power quality management performance exert the most significant influence on the total net benefits for all participants. The proposed model is expected to further the adoption of ESSs among industrial users.

A Comprehensive Study of Voltage Swell and Sag in Power Distribution Systems: Characteristics, Causes, Effects, and Mitigation Strategies

Voltage variations, such as swells and sags, are prevalent disturbances in power distribution systems, posing significant challenges to system reliability and equipment performance. This research paper provides a comprehensive study of voltage swell and sag phenomena, encompassing their characteristics, causes, effects, mitigation strategies, and case studies. The study explores the magnitude, duration, and frequency of voltage variations, delving into the underlying factors contributing to their occurrence, including switching operations, faults, and load variations. Moreover, the paper examines the detrimental effects of voltage variations on electrical equipment and industrial processes, highlighting the importance of understanding and mitigating these disturbances. Various mitigation techniques, such as voltage regulation, uninterruptible power supplies (UPS), and dynamic voltage restorers (DVRs), are evaluated for their effectiveness in minimizing the impact of voltage variations. Additionally, the paper explores the use of PWM-based Distribution Static Synchronous Compensator (DSTATCOM) as a promising solution for mitigating voltage swell and sag issues, discussing principles, design considerations, control strategies, and performance evaluation. Through case studies, simulation results, and modeling approaches using MATLAB/Simulink, the research paper offers valuable insights into the complex landscape of voltage swell and sag in power distribution systems, equipping researchers and practitioners with knowledge to address these challenges effectively.

An identical bipolar buck‐boost AC‐AC converter based on a coupled‐inductor with safe‐commutation, high gain, and high efficiency

AbstractThis article proposes a new identical bipolar buck‐boost AC‐AC converter with integrated coupled inductors. It possesses all the critical features of a bipolar buck‐boost topology, providing both in‐phase and anti‐phase output voltages. Compared to its counterparts, a high boost factor is achieved without large duty ratios due to using magnetic coupling. Also, a high efficiency is obtained. A unipolar half‐cycle modulation is employed in which only half of the switches of a phase‐leg are modulated per half‐cycle. Therefore, only two out of eight power switches operate at high frequency at any instant, ensuring high‐efficiency operation. The safe‐commutation operation is achieved by completely turning on the auxiliary switches of the main phase leg for a half‐cycle, ensuring a continuous inductor current path during dead times. This results in voltage‐spike‐free operation. Additionally, this converter benefits from continuous input current and performs well with inductive and non‐linear loads. The proposed topology can mitigate both voltage sags and swells due to bipolar operation when employed as a dynamic voltage restorer (DVR). Its high boost factor helps compensate for deep voltage sags (above 50%). This article presents the detailed theoretical aspects of the proposed topology, followed by experimental verifications on laboratory‐built hardware.