Testing a communication assisted protection scheme for AC microgrid in a laboratory setup

Protection of microgrid has become challenging due to the hosting of various actors such as distributed generation, energy storage systems, information and communication technologies, etc. The main protection challenges in the microgrid are the bi-directional power flow, protection blinding, sympathetic tripping, change in short-circuit level due to different modes of operation, and limited fault current contribution by converter-interfaced sources. This paper presents a comprehensive review of the available microgrid protection schemes which are based on traditional protection principles and emerging techniques such as machine learning, data-mining, wavelet transform, etc. A categorical assessment of the reviewed protection schemes is also presented. The key findings of the paper suggest that the time-domain and communication-assisted protection schemes could be suitable solutions to address the identified protection challenges in the microgrid.

This paper focuses on the development of a protection scheme for a smart distribution system containing DERs (Distributed Energy Resources) and Solid State Transformers (SSTs). First, the paper describes the fault analysis that needs to be conducted on such systems. Then, a communication assisted protection scheme is proposed, in order to overcome the shortcomings observed in the conventional protection schemes.

Implementation of micro grid concept creates several issues to the existing protection scheme in the radial distribution network. Depending on the location and capacity of the distributed generators, the short-circuit current from the main grid and distributed generations causes variations in the fault current levels inside the micro grid. The changes cause effect of sympathetic tripping, blinding of protection, relay over-reaching, relay under-reaching and loss of selectivity of the overcurrent protection scheme. Such issues must be managed carefully to ensure full benefit from micro grid adaptation. Conventional protection schemes are unable to detect fault current levels common in micro grid. Several methods have been proposed in various research paper. Micro grid protection is substantial to provide reliable and continuous power supply to the customers. The main aim of proposed work is to detect the fault for fast restoration of the system back to the normal operation. The proposed protection scheme for micro grid uses intelligent electronics device for detecting the fault

This paper proposes a pattern recognition based differential spectral energy protection scheme for ac microgrids using a Fourier kernel based fast sparse time-frequency representation (SST or simply the sparse S-Transform). The average and differential current components are passed through a change detection filter, which senses the instant of fault inception and registers a change detection point (CDP). Subsequently, if CDP is registered for one or more phases, then half cycle data samples of the average and differential currents on either side of the CDP are passed through the proposed SST technique, which generates their respective spectral energies and a simple comparison between them detects the occurrence and type of the fault. The SST technique is also used to provide voltage and current phasors and the frequency during faults which is further utilized to estimate the fault location. The proposed technique as compared to conventional differential current protection scheme is quicker in fault detection and classification, which is least effected from bias setting, has a faster relay trip response (less than one cycle from fault incipient) and a better accuracy in fault location. The significance and accuracy of the proposed scheme have been verified extensively for faults in a standard microgrid system, subjected to a large number of operating conditions and the outputs vindicate it to be a potential candidate for real time applications.

Microgrid protection schemes play a vital role in ensuring the reliability and efficiency of power distribution in urban and rural areas, especially as renewable distributed energy resources are increasingly integrated. This paper aims to provide a comprehensive analysis of existing microgrid protection schemes, discussing their advantages and limitations and highlighting key challenges and opportunities for future research. As microgrid systems become increasingly common, the management of power flow in small-community networks equipped with intelligent electronic devices, non-linear loads, and multiple distributed generation sources becomes more complicated. In order to address these challenges, coordination of protective schemes is required to prevent overload and damage to equipment. Firstly, the study discusses microgrid definitions and functional categories, highlighting their benefits and drawbacks. An analysis of microgrid protection literature includes adaptive protection systems as intelligent methods to address coordination challenges. Secondly, this review classifies microgrid protection techniques as modified, new knowledge-based and conventional schemes and provides a systematic analysis of optimization approaches. The study also examines the essential problems associated with the coordination of protective relays within microgrids. Finally, examining the current state of microgrid protection to identify the key research directions and opportunities for future development in this rapidly advancing field. The findings of this comprehensive analysis highlight the importance of effective microgrid protection in ensuring a stable and sustainable energy future.

The prominence of incorporating the renewable energy resources in a power system via microgrids has increased in the recent years, which impose a caution on conventional protection schemes. Protection schemes proposed earlier use local measurements, but fault classification for selective phase tripping using wide area measurements for microgrid has not been reported so far. This paper presents a wide area monitoring and protection of microgrid with distributed generations (DGs) using modular artificial neural networks (MANNs) for the fault detection and classification without affecting the relays in non-faulty or healthy sections of the microgrid. The distinct characteristics of the microgrid sort the proposed methodology into two stages. In stage 1, ANN 1 is developed to identify the operating mode of microgrid, whether it is operating in grid-connected mode (GCM) or islanded mode (IM). In stage 2, there are two MANNs corresponding to GCM and IM. Each MANNs consists of three separate ANNs for fault detection, classification, and section identification. A standard IEC 61850-7-420 microgrid with DGs (wind and photovoltaic) penetration is modeled in MATLAB/Simulink. The three-phase voltages and currents are measured with time synchronization considering the microphasor measurement units located at each bus. The extensive study includes different simulation scenarios such as shunt faults, high impedance fault, and dynamic situations like connection/disconnection of DGs/distribution lines. The results confirm the efficacy of the proposed methodology.

The dependence of modern societies on electric energy is ever increasing by the emergence of smart cities and electric vehicles. This is while unprecedented number of cyber-physical hazards are threatening the integrity and availability of the power grid on a daily basis. On one hand, physical integrity of power systems is under threat by more frequent natural disasters and intentional attacks. On the other hand, the cyber vulnerability of power grids is on the rise by the emergence of smart grid technologies. This underlines an imminent need for the modeling and examination of power grid vulnerabilities to cyber-physical attacks. This paper examines the vulnerability of the communication-assisted protection schemes like permissive overreaching transfer trip to cyberattacks using a co-simulation platform. The simulation results show that the transient angle stability of power systems can be jeopardized by cyberattacks on the communication-assisted protection schemes. To address this vulnerability, two physical solutions including the deployment of communication channel redundancy, and a more advanced communicated-assisted protection scheme, i.e., directional comparison unblocking scheme (DCUB), are considered and tested. The proposed solutions address the vulnerability of the communication-assisted protection schemes to distributed denial of service attack to some extent. Yet, the simulation results show the vulnerability of the proposed solutions to sophisticated cyberattacks like false data injection attacks. This highlights the need for the development of cyber-based solutions for communication channel monitoring.

To design a perfect protection scheme is a big challenge for microgrid (MG) network implementation because it can operate either grid connected mode neither islanding mode. Due to distributed generation (DGs) resources the fault current always varied steadily hence the system parameters. This research focus on two vital properties of microgrid: peer-to-peer and plug-and-play to avoid sophisticated communication network for microgrid adaptive protection schemes. A microgrid model has been proposed by conventional protection scheme and addressing all possible drawbacks along with distributed energy resources. Whole microgrid is divided into different protection zone to identify perfect fault detection techniques by analyzing corresponding system parameters. Moreover, transformer protection also considered in new proposed protection scheme.

Microgrid protection schemes are different from those used in conventional distribution networks. With the incorporation of distributed generation (DG), and the ability for bi-directional power flow and island operation; the fault current and delay parameters of protective relays need to be recalculated and updated in response to the dynamic operation of microgrid. Performance evaluation (e.g. fault clearance time and recovery time) and parameter estimation (fault current and trip delay) for such a protection scheme have been difficult because they require comprehensive modeling of electrical network, IED behaviors, and IEC61850-based communication. In this paper, we present a centralized scheme with detailed modeling and co-simulation of all these aspects. We also demonstrate how the analysis of the simulation results helps overcoming the forth-mentioned difficulties.

Communication-less protection scheme for AC microgrids using hybrid tripping characteristic

This article proposes a localized protection scheme for dc microgrids with radial configuration under the impact of constant power loads (CPLs) to determine the location of faults accurately. The proposed fault location scheme is primarily designed for fault location of CPLs in dc microgrids. First, a local protection relay for CPL is designed based on the transient behavior of the current and voltage in the main distribution line. Then, the estimation of the fault resistance is formulated based on the power sharing in the system to improve the accuracy of the protection system. To realize a robust protection scheme considering the variation of fault resistance, a fault resistance estimation procedure is employed to design a system that locates both low- and high-impedance faults. Finally, the effectiveness of the proposed strategy is evaluated based on offline digital time-domain simulations in Digsilent PowerFactory software environment and experimentally verified by implementing on a laboratory scale hardware setup. The obtained simulation and experimental test results, and comparison with other methods prove that the proposed scheme is immune against these disturbances and can efficiently and reliably estimate the location and resistance of faults with high accuracy and acceptable error margin.

The behavior of anomalous dielectrics : H. Jordan. ( Deutsch. Phys. Gesell. Verh., xiv, 9, 451)

When the grid voltage is imbalance, the current decoupling control strategy in d‐q frame designed for the balanced system still let STATCOM output balanced voltage. In this case, the negative sequence component in the grid voltage may cause the device overcurrent. Here, the positive and negative sequence of grid voltage are separated first and that of the STATCOM output voltage is also controlled independently. However, how to determine and coordinate the positive and negative sequence voltage have not been effectively investigated yet. From the perspective of power balance, this paper gets the quantitative relationship between the phase shift angles of the positive and the negative sequence voltages. It also gets the quantitative relationship between the modulation ratios of the positive and the negative sequence voltages, and hence the effective coordination control strategy of positive and negative voltages of cascaded STATCOM operating under imbalanced grid voltage was developed. In addition, the phase of the positive and negative voltages, which is critical for the proposed coordination control strategy, can be obtained by the advanced open‐loop phase synchronisation scheme. Finally, its detailed implementation was also provided. Simulation results show that the proposed method is correct and effective.

A differential protection scheme for the ring microgrids based on the power change rate of the bus is proposed. By setting the power change rate on both sides of the bus as the differential amount, the power change rate is maximized at the moment of short-circuit, which can immediately indicate whether a fault has occurred. Compared to the protection scheme that uses the current for fault identification, the proposed scheme reduces the time for the fault current to increase to the action threshold, saves the time required for fault detection. Moreover, it is proportional to the square of the current, and the higher orders increase the speed of the change rate, meanwhile, it is proportional to the short-circuit impedance which broadens the fault identification range and improves the protection sensitivity. Finally, the results of simulations prove that the proposed protection scheme has improved speed, sensitivity, and interference resistance while maintaining good selectivity for differential protection.

The low-voltage dc (LVDC) microgrid possesses numerous benefits and their penetration in the power system has increased rapidly in recent years. However, the detection of faults in the LVDC microgrid is a challenging issue due to the large magnitude of fault currents and fault-level variation in the microgrid. The performance of the recent current and its derivative-based protection scheme is limited in case of faults in the islanding mode of operation, different microgrid topologies, varying distributed generations (DGs) penetration, and against the measurement noise. This article presents an enhanced differential protection scheme for LVDC microgrid integrated with multiple DGs and storage. The differential current and its first derivative are processed through the decision tree (DT) algorithm for fault detection and the K-nearest neighbor (KNN) technique is utilized for fault classification. The robustness of the proposed protection scheme is tested for different fault types and fault conditions with variation in microgrid topology and operating conditions. The impact of the intermittent and volatile nature of the DGs, the presence of measurement noise, and assessment during external faults and critical no-fault cases have been investigated. The proposed scheme is tested on the MATLAB/ SIMULINK and validated on the Typhoon HIL platform for the assessment of real-time performance. The test results show that the proposed scheme can detect and classify faults with high accuracy and faster response time and, thus, can be a potential candidate for providing dependable protection measures for LVDC microgrids.