Protection Scheme For Microgrid Research Articles

A differential current based protection scheme for DC microgrid

A continuous increase in greenhouse emissions has led to more frequent use of renewable energy resources. The increased emergence of DC loads in day-to-day lives has further led to conversion to DC distribution lines. In prospect of getting more environmentally friendly, economical, and reliable power delivery a DC micro grid was developed and has become more common in recent years. The disaster management cell located at the Department of Electrical and Electronics Engineering has designed a DC micro grid which consists of sources provided from the grid, a battery bank, and an array of solar cells supplying to a set of nine loads, which are segregated into three sets of three loads each. This paper presents a protection scheme for the buses present in a micro grid that is based on the differential current principle. It is done with the help of a centralized protection controller that enables fault identification and fault isolation. This protection scheme is further extended to a DC ring-bus micro grid, where the centralized protection controller enables fault identification, fault location, and fault isolation. MATLAB/Simulink is used to obtain the simulation and verify the results.

Fault classification and localization in microgrids: Leveraging discrete wavelet transform and multi-machine learning techniques considering single point measurements

Currently, microgrids are becoming more prevalent. Therefore, it is crucial to develop robust and reliable microgrid protection schemes. Researchers have recently explored various approaches to microgrid protection, including adaptive protection and AC microgrid protection. The study offers insights into fault detection and localization in microgrid protection, utilizing precise measurements from the point of common coupling (PCC). It distinguishes between fault occurrences and overload cases, addressing various challenges. Additionally, the analysis explores the role of Linear Discriminant Analysis (LDA) within the framework of multi-machine learning techniques, shedding light on its application in microgrid protection. Ultimately, the aim is to bolster microgrid resilience and reliability for end-users and stakeholders. The system model being tested has been created using Matlab/Simulink software and is based on a real system. The training and testing of the algorithms are developed and evaluated using MATLAB tools. The accuracy of the proposed method is demonstrated in the paper, indicating that it can be used to modernize the current protection apparatus in preparation for the eventual implementation of an advanced microgrid station protection system.

A negative sequence current injection (NSCI)-based active protection scheme for islanded microgrids

The growing penetration of converter interfaced generation creates unprecedented challenges to protection strategies at all voltage levels. This paper proposes a novel Negative Sequence Current Injection (NSCI)-based active protection scheme for islanded microgrids. The faulty section identification method based on the negative sequence current increment between the pre-injection and current generation steady state conditions enables the scheme to achieve an excellent High Impedance Fault (HIF) detection capability. The proposed NSCI control algorithm maintains the phase angle of the negative sequence current fixed during injection progress, thus providing a highly discriminative feature which facilitates the correct identification of the faulty section. As no form of communication is required the proposed protection scheme can be very cost-effective and flexible in practical applications. Following the detailed description of the principle of operation and the setting procedure, a systematic simulation-based validation is undertaken considering a variety of influencing factors such as fault type, resistance and position, as well as impact of load distribution under HIFs, and possible presence of Synchronous Generators (SGs). The results show that the scheme has an excellent detection and discrimination ability, especially during unbalanced faults, and is not affected by load distribution or behaviour of other sources, including SG.

An intelligent protection scheme for DC microgrid using Hilbert–Huang transform with robustness against PV intermittency and DER outage

An intelligent protection scheme for DC microgrid using Hilbert–Huang transform with robustness against PV intermittency and DER outage

A packet-loss resilient protection scheme for hybrid microgrids based on Markov chain model and spline interpolation

A packet-loss resilient protection scheme for hybrid microgrids based on Markov chain model and spline interpolation

An Overview of DC Microgrid Protection Schemes and the Factors Involved

The development of a suitable scheme for protection of DC microgrids is still a major challenge. This is due to the shortage of practical experience in appropriate protection guidelines and standards related to the uncertainty in the network topology, absence of a natural current zero-crossing point in DC systems, and dependence of fault current shape and magnitude on various factors. These factors include network topology, type of converters used in the network, type of fault and its location, fault impedance, and type of system grounding. In this paper, these factors and their impacts on the development of a comprehensive protection plan for DC microgrids have been investigated. Various algorithms that have been proposed in previous studies for fault detection and location are reviewed, and the technical challenges associated with the use of communication links in smart protection systems are described. In addition, the advent of new technologies for development of DC circuit breakers are reported, which are different from the conventional AC circuit breakers due to the differences between the faults in DC and AC microgrids and their respective clearance times. This comprehensive review covers all aspects of the DC microgrid protection including topology, converters, configurations, and types of faults.

An ultra-fast directional protection scheme for DC microgrids based on high-order synchrosqueezing transform

Protection of Direct Current (DC) microgrids is a challenging task because of large currents within a few milliseconds after the occurrence of a DC fault, which causes serious damage to converters. The present study introduces a protection algorithm based on Traveling Waves (TWs) to detect and locate faults. The proposed method implements the High-order Synchrosqueezing Transform (HOSST) to capture TWs using local measurements. Unlike conventional methods, HOSST can analyze signals in both time and frequency domains by creating a concentrated energy in the time–frequency representation. By extracting impulse features, HOSST detects TWs with high accuracy even in a noisy environment for different types of DC faults with various fault resistances. The proposed method can identify external and internal faults by determining the polarity of TWs, which makes the relays operate properly within their protection zone and prevents mal-operation. To demonstrate the efficiency of the proposed method, it is applied to a DC microgrid. The results show the high accuracy of the presented approach in the fault location with a slight error with selectivity, reliability, sensitivity, and high speed, which is independent of the voltage level and configuration. In addition, the certainty of the proposed method is higher than the previous studies due to the simultaneous use of current and voltage.

A novel differential protection scheme for AC microgrids based on discrete wavelet transform

A novel differential protection scheme for AC microgrids based on discrete wavelet transform

Overcurrent protection coordination with flexible partitioning of active distribution systems into multiple microgrids

Recently, sectionalizing active distribution systems (ADS) into partitioned microgrids has been proposed to enhance the reliability and supply-security but can have adverse effects on the performance of the protection scheme. The previous protection schemes based on overcurrent relays have been proposed for active distribution systems (ADS) with no partitioning capability. This paper analyzes the impact of microgrid partitioning on the performance of the microgrid protection schemes relying on the standard inverse time overcurrent relays (ITOCRs) and introduces a protection scheme that relies on inverse time admittance relay (ITAR) for ADS with partitioning capability. The introduced protection scheme is tested on a modified PG&E 69-bus equipped with distributed generation and partitioned into several microgrids. The protection coordination problem is formulated as a constrained nonlinear programming (NLP) problem considering grid-connected, islanded, as well as partitioned operation modes. Simulation results demonstrate that the ITAR characteristic shows promising performance in comparison to the standard ITOCR characteristic achieving minimal relay operating time and coordination failure.

Optimal Protection Coordination of Islanded Microgrids Utilizing an Adaptive Virtual Impedance Fault Current Limiter

Outages may impact power grids, e.g., lines or generation forced out of service. Thus, solving the optimal protection coordination (OPC) problem for the main network topology results in protection miscoordination under contingencies. Further, the limited fault currents of inverter-interfaced distributed generators (IIDGs) require a highly sensitive and reliable protection scheme. This paper proposes an overcurrent protection scheme for islanded microgrids powered by droop-based IIDGs. The inverter controller is modified to include a virtual impedance-fault current limiter (VI-FCL) to protect inverter switches from overcurrent and limit IIDG fault currents. The VI-FCL is designed such that it adapts to fault severity. OPC of directional overcurrent relays (DOCRs) is achieved using a two-stage optimization algorithm. The first Stage calculates the short-circuit currents involving various fault resistances. Next, constraints on the DCORs operation times are formulated for each topology resulting from an N-1 contingency and the main topology. The OPC problem is formulated as a constrained nonlinear programming problem. Finally, the second Stage is dedicated to obtaining the DOCRs optimal settings. The OPC method is tested on a radial microgrid that is part of a Canadian urban distribution system.

Empirical Wavelet Transform-Based Differential Protection Scheme for Micro-Grid

Empirical Wavelet Transform-Based Differential Protection Scheme for Micro-Grid

A novel approach for resilient protection of AC microgrid based on differential phase angle of superimposed complex power

In the last decades, the penetration rates of microgrids (MG) and distributed generations (DGs) are exponentially soared. Despite the fact that MGs can improve the reliability and resilience of distribution networks, designing a reliable protection scheme for alternating current microgrids (AC-MGs) is still a challenging task. The existence of various types of DGs and frequent changes in MGs’ operational modes, islanding, sudden increment in the value of loads, and penetration rate variation of DGs are some of the main issues which should be considered to design a reliable and resilient protection scheme for MG. In this paper, a novel adaptive resilient protection scheme employing synchronous current and voltage obtained from micro phasor measurement units (μPMU) located at both ends of the protected line, is presented. A new index is also devised to detect all types of internal and external faults based on differential phase angle of superimposed complex power (DPASCP). The threshold value of the proposed index is adaptively updated according to variations created in the network. This scheme can detect various types of faults in different locations fast and accurately in both grid connected and islanded mode of operation. The performance of the proposed protection scheme is also evaluated on IEEE 33-bus and 15-bus test networks in non-fault critical conditions such as grid-islanding switching, connection and disconnection of different DGs with changing in penetration rates of them, and load encroachment. The results demonstrate the capability and superiority of the suggested protection scheme.

Real-Time Hardware-in-The-Loop Implementation of Protection and Self-Healing of Microgrids

The design of a reliable protection scheme for microgrids often requires communication between protective devices and microgrid controllers. The authors have developed such a communication assisted scalable protection scheme with a self healing feature to protect a microgrid with 100% Inverter Based Resources (IBRs). The communication assisted scheme must be validated in real time with cyber physical co-simulation for successful demonstration. In this regard, the paper presents a co-simulation platform between a simulated power system model using RTDS and physical protective devices. The primary protection of the scheme is programmed in SEL 421-7 relay and backup protection is programmed in MATLAB on a generic computer acting as a microgrid controller. The IEC 61850 models are used to communicate between SEL-421-7 relay and RTDS, whereas TCP/IP communication connects the microgrid controller to RTDS. The paper's focus is to demonstrate the co-simulation platform with communication links established using both protocols and validate the proposed scheme in real-time on the IEEE 123 node distribution feeder. The paper explains the configuration of the IEC 61850 and TCP/IP communications as the interface requires proper hardware and software setup. The real time performance indicates the Hardware In the Loop (HIL) framework as a competent testing environment for the developed protection scheme for microgrids.

Rate of Change of Direct-Axis Current Component Protection Scheme for Inverter-Based Islanded Microgrids

Rate of Change of Direct-Axis Current Component Protection Scheme for Inverter-Based Islanded Microgrids

Harmonic Dual-Setting Directional Overcurrent Protection for Inverter-Based Islanded Microgrids

Limited fault currents in inverter-interfaced islanded microgrids impose immense challenges on conventional overcurrent protection schemes. This paper proposes a sensitive and selective protection scheme for islanded microgrids using a third harmonic voltage generated by inverter-interfaced distributed generators (IIDGs). The generated harmonic voltage results in a harmonic layer formed during short-circuit faults and is decoupled from the fundamental fault current, i.e., limited by IIDGs. Further, the generated harmonic voltage is adaptively adjusted based on fault severity to enhance protection sensitivity and obtain a universal set of relays’ settings. The proposed protection scheme utilizes harmonic directional overcurrent relays (HDOCRs) equipped with a dual-setting time-current-voltage setting that sense the generated harmonic voltages and currents at the relay location to ensure optimal protection coordination (OPC) of islanded microgrids. The OPC with the proposed dual-setting is formulated as a constrained nonlinear program to determine the optimal forward and reverse relays’ settings. The proposed scheme is tested on the Canadian benchmark urban distribution system and compared to the conventional protection scheme, which relies only on a single time-current-voltage trip characteristic. The results ensure the ability of the proposed scheme to protect islanded microgrids without communication and its capability to reduce relays’ operation times.

Time-Domain Protection Scheme for Microgrids With Aggregated Inverter-Based Distributed Energy Resources

This paper proposes a time-domain-based protection scheme for radial and loop microgrid systems with inverter-based resources (IBRs), such as solar photovoltaic (PV) and type-4 wind turbines. The protection scheme is designed to function during both grid-interconnected and grid-isolated modes. The proposed scheme provides an ultra-high-speed sub-cycle directional element aided with low bandwidth communication between relays. Like directional comparison schemes, relays identify whether faults are in-zone or out-zone. The directional element is based on time-domain superimposed quantities and Park’s transformation algorithms. More specifically, the element calculates the superimposed positive-sequence direct component of transient energy during faults. Superimposed voltage and current quantities are calculated using delta filters and decoupled double synchronous reference frame (DDSRF) filters. The proposed filtering method improves the reliability of the superimposed directional element when IBRs are present. The protection scheme is evaluated on a modified IEEE 34-bus distribution system simulated using an electromagnetic transients program.

Machine Learning Based Protection Scheme for Low Voltage AC Microgrids

The microgrid (MG) is a popular concept to handle the high penetration of distributed energy resources, such as renewable and energy storage systems, into electric grids. However, the integration of inverter-interfaced distributed generation units (IIDGs) imposes control and protection challenges. Fault identification, classification and isolation are major concerns with IIDGs-based active MGs where IIDGs reveal arbitrary impedance and thus different fault characteristics. Moreover, bidirectional complex power flow creates extra difficulties for fault analysis. This makes the conventional methods inefficient, and a new paradigm in protection schemes is needed for IIDGs-dominated MGs. In this paper, a machine-learning (ML)-based protection technique is developed for IIDG-based AC MGs by extracting unique and novel features for detecting and classifying symmetrical and unsymmetrical faults. Different signals, namely, 400 samples, for wide variations in operating conditions of an MG are obtained through electromagnetic transient simulations in DIgSILENT PowerFactory. After retrieving and pre-processing the signals, 10 different feature extraction techniques, including new peaks metric and max factor, are applied to obtain 100 features. They are ranked using the Kruskal–Wallis H-Test to identify the best performing features, apart from estimating predictor importance for ensemble ML classification. The top 18 features are used as input to train 35 classification learners. Random Forest (RF) outperformed all other ML classifiers for fault detection and fault type classification with faulted phase identification. Compared to previous methods, the results show better performance of the proposed method.

Differential Protection Scheme for A Micro Grid with Inverter-Type Sources Based On Positive Sequence Fault Currents

The microgrid (MG) is a coordinated collection of different distributed generation (DG) typesthatsupply local demandthrough a distribution network. MG may operate in two different modes: grid-connected (GC), and islanded (IS)modes.The fault current valuevaries significantly between the GC and IS mode for a MG with inverter-based distributed generators(IBDGs). The fault currents are minimal in the IS mode owing to the power electronics equipment have a limited current carrying capacity. Therefore, the coordination of traditional overcurrent (OC) protection is difficult for these two operation modes. Therefore, a comprehensive MG protection scheme should be established to safeguard MG against all kinds of faults. The main protection strategy proposed in this paperis a positive sequence differential current protection scheme. The envisioned concept can overcome the protective device coordination problems, and all fault types can be detected during both operation modes of MG for radial andloop configurations. The validation of the proposed design is performed using PSCAD/EMTDC software. The results indicate that the maximum fault clearing time for the main protection in GC mode and IS modeisof 31.5 ms and 34 ms respectively. Compared with other schemes, the proposed scheme has a faster clearing time and is less expensive.

A State-Observer-Based Protection Scheme for AC Microgrids with Recurrent Neural Network Assistance

The microgrids operate in tie-up (TU) mode with the main grid normally, and operate in isolation (IN) mode without the main grid during faults. In a dynamic operational regime, protecting the microgrids is highly challenging. This article proposes a new microgrid protection scheme based on a state observer (SO) aided by a recurrent neural network (RNN). Initially, the particle filter (PF) serves as a SO to estimate the measured current/voltage signals from the corresponding bus. Then, a natural log of the difference between the estimated and measured current signal is taken to estimate the per-phase particle filter deviation (PFD). If the PFD of any single phase exceeds the preset threshold limit, the proposed scheme successfully detects and classifies the faults. Finally, the RNN is implemented on the SO-estimated voltage and current signals to retrieve the non-fundamental harmonic features, which are then utilized to compute RNN-based state observation energy (SOE). The directional attributes of the RNN-based SOE are employed for the localization of faults in a microgrid. The scheme is tested using Matlab® Simulink 2022b on an International Electrotechnical Commission (IEC) microgrid test bed. The results indicate the efficacy of the proposed method in the TU and IN operation regimes on radial, loop, and meshed networks. Furthermore, the scheme can detect both high-impedance (HI) and low-impedance (LI) faults with 99.6% of accuracy.

A signed correlation index-based differential protection scheme for inverter-based islanded microgrids

The different fault characteristics of the inverter-based distributed generation (IBDG) units make the protection of the inverter-based islanded microgrids (IBIMGs) a formidable task. According to IEEE Std 1547.4, the limited fault current levels associated with the IBIMGs may result in misleading decisions of the traditional protective relays during fault occurrence. In this paper, a new differential protection scheme for the IBIMGs is introduced based on the signed correlation technique. The proposed scheme is formulated based on the signs of the instantaneous phase currents at both line ends instead of the current magnitudes. In addition, a signed correlation index is defined to measure the similarity between the signs of the instantaneous phase currents at both line ends employing only a time window of half-cycle. Moreover, a fault detection index is introduced to discriminate the internal faults from other events. In order to validate the proposed scheme, the 9-bus IBIMG and the modified IEEE 33-bus system are simulated on the PSCAD/EMTDC platform, and several scenarios are conducted, including load switching, outage of IBDG units, external bus faults, and internal faults. The obtained results emphasize that the proposed scheme operates correctly considering all types of faults, different fault resistances and inception angles, as well as measurement and synchronization errors.