Grid Faults Research Articles

Research on Hazard Analysis and Control Strategy of Power System Dispatching Operation Based on Information Fusion Technology

Abstract In this paper, a decision model for grid fault diagnosis based on multi-source information fusion is established, and the probability of component fault is obtained by using the change of switching quantity characteristic information and electrical quantity characteristic information during grid fault, and the static fault degree obtained by switching quantity information and the voltage and current energy distortion degree and fault degree obtained by electrical quantity information is used as independent evidence bodies, which are fused by improved D-S evidence fusion technique, and the fused The results are decided by improved fuzzy C-mean decision model to finally determine the fault components. Then, the optimal control of the grid is studied, and the corresponding self-healing control model is established according to the different operating conditions of the system so as to propose a self-healing control strategy of the microgrid based on the improved particle swarm algorithm. After analysis and verification, the accuracy of the grid fault diagnosis method proposed in this paper reaches 0.9681, and the diagnosis results are consistent with the pre-defined fault elements compared with FCM. The system network loss decreases from 0.146 kW to 0.031 kW, and the maximum power supply capacity increases from 1.574 to 2.468 after using the improved particle swarm algorithm-based microgrid self-healing control strategy. Therefore, the method in this paper can improve the reliability of grid operation and resist the risk of accidents.

Application and Comparison of a Modified Protection Scheme Utilizing a Proportional–Integral Controller with a Conventional Design to Enhance Doubly Fed Induction Generator Wind Farm Operations during a Balanced Voltage Dip

The doubly fed induction generator (DFIG) is vulnerable to grid faults due to its direct stator connection, causing issues like excess stator current during voltage dips. Consequently, sensitive inverters suffer from increased currents, and the DC-link capacitor undergoes overcharging. This document examines two protection strategies employing a proportional–integral (PI) controller to manage the transient rotor current and mitigate DC-link overcharging, thereby optimizing DFIG behavior during network faults. One option combines a classic crowbar circuit with a DC-chopper, while the other is a modified protection scheme (MPS) that includes an impedance with passive elements and a crowbar. The impedance forms a resistance Rp parallel with an inductance Lp. Both configurations, situated between the rotor coils and the rotor-side converter (RSC), augment the capacity for low-voltage ride-through (LVRT). MATLAB/SIMULINK simulations of the two schemes demonstrate successful rotor current reduction at 2.9 kA and 3.4 kA, and DC-link tension reduction below and at 1.4 KV. In addition, the conventional crowbar and MPS configurations efficiently restrict the RSC current to levels below 0.21 kA and 2.94 kA, while absorbing up to 2.52 kA and 1.52 kA, respectively. The key difference lies in the fact that fine-tuning the parameters in the MPS design prevents rotor disconnection when faced with a balanced fault. This enhancement enhances machine performance and enables full stator power control via the RSC.

Smart Sag Detection and Reactive Current Injection Control for a PV Microgrid under Voltage Faults

Low-power photovoltaic distributed generators are increasing rapidly in number by the grids of the modern era, but they also bring up the concern of grid stability. To maintain grid stability, it is essential for the network operators to update the grid codes at regular intervals due to the case of highly penetrated grid-connected photovoltaic systems (GCPVs). Integration of large-scale electrical grids with renewable energy sources, one being photovoltaic systems, faces the challenge of riding through low-voltage (LVRT) phases. As compared to the previous grid codes for power generation, recent advances require distributed generation resources to provide for such capabilities under grid faults. This work contributes to the ongoing investigation of this specified and destabilizing fault condition. Various simulations of a PV microgrid system are carried out with the ability to ride through low-voltage faults, with the help of a DC-chopper circuit to absorb DC-link over-voltage, and the current is also maintained within acceptable limits according to the required standards. The fundamental contribution of this research is a proposed neural network (NN) control framework. This framework effectively detects voltage sags, comprehends their characteristics, and provides support to the system by injecting reactive current in accordance with the demands imposed by designated grid codes. This NN control model has been systematically developed utilizing data gathered from a vast array of testing simulations conducted under different and dynamic conditions. The proposed strategy, on the other hand, is compared with the RMS fault detection method in combination with the conventional LVRT algorithm. The NN control approach showed better results as compared to the conventional methods in terms of accuracy and robustness, especially when confronted with difficult sag situations.

Technology for Power Outage Research and Judgment-dependent Data Feature Noise Analysis

INTRODUCTION: Power grid blackouts occur frequently, which significantly impacts social impact. Because these accidents are dynamic and random, predicting and evaluating them is challenging. OBJECTIVES: To explore the complexity of the power grid itself, analyzes the critical changes of the self-organizing model during power grid fault, extracts the data characteristics related to the steady-state maintenance of abnormal systems, and puts forward an effective outage prediction model. METHODS: Starting with cluster analysis, The authors can reduce data fluctuation and eliminate noise interference to optimize data. The evaluation indexes of initial fault occurrence possibility and fault propagation speed in the power grid are constructed. RESULTS: The validation of the outage forecasting model has produced promising results, achieving 96.4% forecasting accuracy and a meager error rate. In addition, the evaluation index developed in this study accurately reflects the possibility and spread speed of power outage accidents. CONCLUSION: The research proves the feasibility of establishing an outage prediction model based on the power grid system data characteristics. The model has high accuracy and reliability and is a valuable tool for power outage research and judgment.

Frequency and voltage regulation control strategy of Wind Turbine based on supercapacitors under power grid fault

As the penetration rate of wind turbines gradually increases, the fluctuation of system voltage and frequency significantly increases under power grid fault. In severe cases, wind turbines will disconnect from the grid, leading to large-scale power outages. In order to improve the stability of wind turbine grid connection, a large number of literature has studied the frequency and voltage regulation strategies. However, the existing fault ride through control methods mainly solve the problem of reactive power support during faults, while frequency regulation schemes focus on the frequency changes caused by load fluctuations. There is little research on methods that simultaneously consider voltage ride through and frequency regulation under power grid fault. This paper proposes a voltage and frequency regulation control strategy of wind turbines based on supercapacitors to address the above issues. By switching the functional modes of the energy storage device at different stages, wind turbines achieve the fault through and frequency recovery, thereby enhancing the fault tolerance ability. In the strategy, control process is divided into power grid fault period and fault recovery stage, and it adjusts the auxiliary priority level of energy storage devices based on the electrical response degree of different stages. During the fault, energy storage device is in voltage regulation stage because the voltage drop degree is greater than the frequency fluctuation, and it can ensure the wind turbine does not run off the grid by providing dynamic reactive power support to power grid. In the fault recovery stage, energy storage device is in the frequency regulation stage because of the large frequency deviation, it output active power to accelerate the system frequency recovery rating. Finally, the effectiveness of the control strategy proposed in this paper is verified through simulation.

Over-current low voltage ride-through operation of grid-connected converters based on thermal analysis

The grid-connected converters are becoming an important role in modern power grid. The grid codes have been proposed for the operation of grid-connected converters. The low voltage ride-through, namely one of the grid codes, is the operation of grid-connected converters under grid fault. The reactive power is generated by gird-connected converters to support grid under low voltage ride-through operation. However, the maximum reactive power is restricted by the capacity of converter, which is designed for long-term operation. Since the low voltage ride-through is a short-term operation, the maximum output reactive power can be enhanced. An over-current low voltage ride-through operation is proposed, and it is designed based on the maximum short-term capacity. The maximum short-term capacity is designed to ensure the junction temperature of semiconductor devices in the converter under the reliable operation, which is calculated based on thermal analysis. Furthermore, the different approaches to enhancing the maximum short-term capacity is analyzed.

A novel low voltage ride-through scheme for DFIG based on the cooperation of hybrid energy storage system and crowbar circuit

To improve the low voltage ride-through (LVRT) capability of DFIG, a novel LVRT scheme based on the cooperation of hybrid energy storage system (HESS) and crowbar circuit is proposed. The HESS composed of superconducting magnetic energy storage (SMES) and batteries is connected in the DC-link bus of DFIG. During grid faults, the HESS is switched to stabilize the DC-link bus voltage of DFIG, the grid-side converter (GSC) of DFIG is switched to inject reactive power to the grid for improving the grid fault voltage and the crowbar circuit is activated in real-time to avoid RSC from being damaging according to the rotor current. During normal operation, the HESS is controlled to deal with power difference between the turbine generation power and power dispatching command, and the GSC of DFIG is controlled to manage the output power of the DFIG with HESS. Finally, the simulations of the DFIG with HESS system is conducted in RTDS platform, and the simulation results show that the proposed scheme can effectively achieve the LVRT of DFIG during gird faults and flexibly manage the DFIG output power with HESS during normal operation.

Comprehensive Evaluation Index System and Application of Low-Carbon Resilience of Power Grid Containing Phase-Shifting Transformer under Ice Disaster

In view of the high impact of extreme disasters, this paper comprehensively evaluates power grid performance from a new low-carbon toughness perspective. First, considering the increase in carbon emissions and the recovery time of carbon emissions, low-carbon resilience indicators are proposed. At the same time, considering the power-regulation effect of the phase-shifter transformer, the fault and response model of a power grid under an ice disaster is established, and then, a comprehensive evaluation index system of low-carbon toughness of the power grid is constructed. The weight determination is carried out using the fuzzy analytic hierarchy process-entropy-based weight method, while the fuzzy comprehensive evaluation center of gravity method is used to evaluate the power grid comprehensively. Finally, examples are presented to verify the feasibility of the proposed method, emphasizing its potential for evaluating the comprehensive performance of low-carbon and toughness of the power grid in the future.

Current Reference Control Scheme of Voltage Source Converters to Ensure the Existence of Stable Equilibrium Points During Grid Fault

Current Reference Control Scheme of Voltage Source Converters to Ensure the Existence of Stable Equilibrium Points During Grid Fault

The role of hydrogen electrolysers in frequency related ancillary services: A case study in the Iberian Peninsula up to 2040

This paper investigates the contribution of hydrogen electrolysers (HEs) for frequency related Ancillary Services (AS), namely Frequency Containment Reserve (FCR), Synthetic Inertia (SI) and Fast Frequency Response (FFR) in future operation scenarios in the Iberian Peninsula (IP) considering low system inertia. The proposed framework for analysis consists of a dynamic model developed in MATLAB/Simulink. Simulations show that an instantaneous inverter based resource (IBR) trip induced by a grid fault may lead to the occurrence of values of Rate of Change of Frequency (RoCoF) close to undesirable thresholds if the FCR is provided solely by the conventional generators. The obtained results illustrate that HEs can outperform conventional generators on the provision of FCR. Furthermore, the FCR is unable to unlock the full potential of fast responding HEs. This suggests the advantage of providing additional AS such as SI or FFR in critical periods. Simulations also show that the benefit of additional AS can be limited in specific conditions, especially depending on the evolution of HEs’ ramping capabilities, but are still a relevant complement to other solutions designed to deal with low inertia in power systems such as synchronous compensators.

Phaselet Transform-Based Digital Ground Fault Protection of Grid-Connected Photovoltaic Systems

The growing interests in utilizing Photovoltaic (PV) systems are usually faced with challenges of accurate and reliable protection of these distributed generation units. A desired protection of PV systems has to effectively and accurately detect and respond to internal faults (within the PV system) and external faults (in the host grid and/or fed loads). This paper presents and tests the performance of a digital ground fault protection (DGFP) for grid-connected PV systems. The presented DGFP detects faults based on the energy contents of high frequency sub-bands of the ground current. These energy contents are extracted using the phaselet transform that can process signals with non-stationary variations in their phases. Energy contents of the high frequency sub-bands can provide accurate, fast, and reliable detection and identification of faults experienced by a PV system operated. The phaselet transform (PHT)-based DGFP is implemented for performance testing using PV systems that are operated in the grid-connected mode, and subjected to various fault and non-fault events. Performance results demonstrate accurate, fast, and reliable detection and response to different types of fault and non-fault events. Response features of the PHT-based DGFP are complimented with minor sensitivity to the level of power production and/or type and location of faults.

Research on Power Grid Fault Diagnosis Based on a Quantitative Representation of Alarm Information

Power grid operation is trending toward digitalization and intelligence, and data-driven power grid fault diagnosis has become a realistic demand for smart grid dispatching. At present, power grid fault diagnosis is based on text content analysis and alarm information feature extraction. With a lack of models and methods for alarm information quantitative representation, current models cannot adapt to complex and changeable engineering field practices. Based on quantity and time series distribution characteristics of alarm information during faults, this paper proposes a quantitative representation method for alarm information and uses the quantified alarm information as classification features. The classification algorithm is used to obtain the classification results based on a power grid fault diagnosis framework. A fault diagnosis strategy is designed to integrate fault classification and faulty device discrimination model results, and fault types and faulty devices are determined. Finally, the simulation system-generated fault cases and actual fault cases collected by a power grid are used to verify the calculation example. The experiments and model comparisons show that the method, with advantages of simple modeling, stronger practicability and better diagnosis accuracy than previous methods, can handle different forms of alarm information and perform power grid fault diagnosis based on the data.

Reduced Order DFIG Models for PLL-Based Grid Synchronization Stability Assessment

This paper presents a reduced-order modeling approach to study the grid synchronization stability of type-3 wind turbine generator (WTG) by considering the dynamics of the phase-locked loop (PLL) alone. The proposed model is validated by comparing its time-domain response and small-signal results with the full-order dynamical model of a type-3 WTG system. Extension of the proposed reduced-order model is shown in a wind farm with N numbers of the WTGs, and time-domain simulations are performed under stable and unstable scenarios. The developed model is further utilized for directly assessing the transient stability of a doubly-fed induction generator-based wind turbine generator (DFIG-WTG) system leveraging Lyapunov's direct method. From the direct transient stability assessment methodology, an approximate estimate of the critical clearing time (CCT) is obtained for the DFIG-WTG system to ensure large-signal stability following severe grid fault. Finally, the parametric conditions are derived theoretically, which can determine the stable and unstable region of operation of the DFIG-WTG system with respect to the PLL parameters, grid impedance, and input wind speed.

Impact of Grid Unbalances on Electric Vehicle Chargers

There is a global trend to reduce emissions from cars through the adoption of other alternatives, such as electric vehicles (EVs). The increasing popularity of EVs has led to a growing demand for electric vehicle chargers. EV chargers are essential for charging the batteries of EVs. Since the EV charger stays connected to the grid for long periods of time to charge the EV battery, it must be able to handle disturbances in the power grid. The goal of this paper is to present an overview of the impact of grid events on EV battery chargers. As well as the impact of grid unbalances on EV chargers, this paper also provides an overview of the impact of grid faults on other, similar power electronics interfaced resources such as PV and energy storage systems.

Cognitive knowledge graph generation for grid fault handling based on attention mechanism combined with multi-modal factor fusion

With the rapid development of artificial intelligence, reinforcement learning frameworks combined with knowledge graph have been widely applied in power grid fault detection and handling. However, the existing algorithms lack the consideration of multi-modal factors, which makes it difficult to improve the accuracy of prediction. To solve the above problems, we propose the cognitive knowledge graph generation algorithm for grid fault handling based on the attention mechanism combined with multi-modal factors fusion. It uses the variational auto-encoder to initialize the embedding of power equipment nodes with different modal factor constraints and dynamically fuses the embeddings of nodes based on attention mechanism, then we train the representation of nodes and relations based on TransR and construct a cognitive knowledge graph of power grid fault handling. Our algorithm is validated on the power grid fault handling data set, and the accuracy is improved.

Fault protection scheme of flexible DC grid based on transient power instantaneous energy difference

The DC line protection is the key to the stable operation of the multi-terminal flexible DC grid, and the current limiting reactor (CLR) as the boundary condition provides great convenience for the design of the flexible DC grid fault protection scheme. Using the boundary condition characteristics of the CLR, the paper proposes a fault protection method for flexible DC grid based on transient power instantaneous energy (IE) difference. First, the equivalent circuit of the DC line of the flexible DC grid under different faults is established. On this basis, the conclusion that the transient power amplitude of internal fault is much larger than the external is deduced from the full-power in the time-domain. The Teager energy operator is used to calculate the maximum IE of the transient power, and then the internal and external faults are identified. Secondly, according to the difference of the transient power amplitude of the CLR on the fault pole and the healthy pole, the ratio of the IE of the positive and negative CLR transient power is used to construct the fault pole selection. The scheme is simple and easy to implement, and does not need to consider the synchronization problem of data at both sides. Finally, the simulation results show that the proposed method can better satisfy the speediness and selectivity requirements of DC grid protection. The scheme can accurately detect faults under different working conditions, and has strong fault resistances capability.

Optimal Scheme of Remote Backup Automatic Switch Applied to Renewable Energy Grids

The support of renewable energy to the bus voltage during the grid fault period will cause the failure action of the backup automatic switch (BPAS). Moreover, the improper coordination of renewable energy and source supply lines in the process of BPAS operation will lead to the asynchronous close of a circuit breaker, which seriously threatens the stable operation of the power system. To solve the above problems, an optimal operation strategy applied to the remote BPAS is proposed in this paper. Firstly, the operation logic and characteristics of internal BPAS and remote BPAS are analyzed. Secondly, the mechanism of failure action and asynchronous close of a circuit breaker in regional power grids with renewable energy sources are analyzed. Then, to improve the speed and reliability of the BPAS, a strategy of remote BPAS operation suitable is proposed. To avoid the problem of failure action, by monitoring the low-frequency condition of the regional power grid, the strategy accelerates the bus voltage loss to shorten the operation time of the BPAS. Moreover, the operation conditions of BPAS are optimized to avoid the asynchronous close of the circuit breaker between renewable energy and source supply lines. Finally, the experimental results in the 110 kV transformer substation verify that the improved remote BPAS strategy can effectively improve the reliability and quickness of the grid connecting to renewable energy.

Transient synchronous stability analysis and enhancement control strategy of a PLL-based VSC system during asymmetric grid faults

The stability of a voltage source converters (VSC) system based on phase-locked loop (PLL) is very important issue during asymmetric grid faults. This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of synchronous generators. Based on the model, the synchronization characteristics of the VSC system under asymmetric grid faults are described, and the interaction mechanisms, as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained. Using the equal area criterion, the influences of sequence control switching action, detection delay, and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed, respectively. In addition, a transient stability assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed. Finally, the analytical results are validated through simulation and experiments.

Operating Voltage and Frequency Regime Validation of Grid Code Requirements in South Africa

South Africa first implemented rolling blackouts known as load shedding to protect the integrity and maintain stability of their ailing electrical grid over a decade ago. Since then, load shedding has become a daily occurrence, which South Africa plans to alleviate through the addition of grid-connected renewable generation. Significant renewable energy (RE) additions can however negatively affect a grid, prompting South Africa to develop RE-specific grid code requirements as mitigation. Given this strategy to address the country’s supply challenges using RE, and the still unknown effects of the country’s aggressive RE integration planned, South Africa must perform the necessary simulations tailored to the country’s unique grid conditions, and local RE-specific grid code requirements to ensure a RE-driven solution are indeed viable. Prompted by the lack of a suitably tailorable simulation platform, this paper proceeds to discuss the development of a tailorable grid code-guided renewable power plant (RPP) behavioral studies testbed. The testing methodology involves feeding grid disturbance event data to an RPP modeled after Eskom’s Sere wind farm in South Africa, which is operated in line with local RPP-specific grid code voltage and frequency requirements to assess the testbed’s grid code-guided RPP operating approach. Results show the testbed to effectively distinguish between grid code-specified no-fault, fault ride-through, and trip conditions, operating the simulated RPP accordingly. Consequently, as compared to comparable RE integration simulation platforms, the reviewed testbed has the potential of producing individualized results, owing to its tailorable grid, RPP, and incorporated grid code guiding specifications.

Technical Assessment of the Key LVRT Techniques for Grid-Connected DFIG Wind Turbines

As a key portion of renewable energy resources (RESs), wind energy penetration is rapidly deployed. The effects of grid faults on grid-connected wind turbines (WTs) are causing problems for wind energy producers. To meet the necessary requirements, additional resources and technical interventions are needed. One of these requirements is low voltage ride-through (LVRT) of doubly fed induction generator (DFIG)-based WTs. This means that DFIG-WTs must stay connected to the grid during transient grid faults and supply active and reactive power after the fault is cleared. Many techniques for improving the LVRT capability of DFIG-WTs have been developed and this paper examines them. The paper also evaluates how well they align with grid codes, and offers case studies and simulations of the selected key techniques. Lastly, this paper provides guidelines and suggested designs for the LVRT techniques for DFIG-WTs to ensure they meet local grid codes.