Traveling wave-based protection scheme for inverter-dominated microgrid using mathematical morphology

Inverter-dominated microgrids impose significant challenges on the distribution network, as inverters are well known for their limited contribution to fault current, undermining the performance of traditional overcurrent protection schemes. This paper introduces a new protection scheme based on the initial current traveling wave utilizing an improved mathematical morphology (MM) technology, with simplified polarity detection and new logics introduced for meshed networks and feeders with single-end measurement. The proposed protection scheme provides ultrafast response and can be adapted to varied system operational modes, topologies, fault conditions, and load conditions. Only low-bandwidth communication is required to achieve high-speed operation and adequate discrimination level in meshed networks. Simulation in PSCAD/EMTDC verifies both the sensitivity and stability of the proposed protection scheme under different microgrid operational scenarios

Protection of microgrid with high amounts of renewables : challenges and solutions

Microgrid is a small-scale network including generators, loads and storage system, which provides a friendly way for the penetration of renewables and releases the burden of transmission system arising from the increased energy demand. Moreover, since microgrid can operate in islanded mode, it can provide backup power to local consumers when the main grid is disconnected. However, the utilization of microgrid causes serious problems in the area of power system protection. The main issues comprise varied fault levels in different operating modes and fault detection in islanded microgrid particularly when the microgrid is dominated by inverter based DGs (IIDGs). In addition, to avoid non-necessary power losses raised from multi-stage power conversion of DC loads and generators, DC microgrid becomes another attractive choice, which further increases the difficult on designing protection system for the futuristic microgrid. In this paper, a comprehensive review of the existing issues and protection methods for AC and DC microgrids is presented. Furthermore, to facilitate better understanding to readers, the benefits and limitations of each method are discussed in depth. Potential protection tools for future microgrid are suggested at the end of this paper

A Review on Challenges and Solutions in Microgrid Protection

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

Recent Developments and Challenges on AC Microgrids Fault Detection and Protection Systems–A Review

The protection of AC microgrids (MGs) is an issue of paramount importance to ensure their reliable and safe operation. Designing reliable protection mechanism, however, is not a trivial task, as many practical issues need to be considered. The operation mode of MGs, which can be grid-connected or islanded, employed control strategy and practical limitations of the power electronic converters that are utilized to interface renewable energy sources and the grid, are some of the practical constraints that make fault detection, classification, and coordination in MGs different from legacy grid protection. This article aims to present the state-of-the-art of the latest research and developments, including the challenges and issues in the field of AC MG protection. A broad overview of the available fault detection, fault classification, and fault location techniques for AC MG protection and coordination are presented. Moreover, the available methods are classified, and their advantages and disadvantages are discussed

Challenges, advances and future directions in protection of hybrid AC/DC microgrids

Hybrid microgrids which consist of AC and DC subgrids interconnected by power electronic interfaces have attracted much attention in recent years. They not only can integrate the main benefits of both AC and DC configurations, but also can reduce the number of converters in connection of Distributed Generation (DG) sources, Energy Storage Systems (ESSs) and loads to AC or DC buses. In this paper, the structure of hybrid microgrids is discussed, and then a broad overview of the available protection devices and approaches for AC and DC subgrids is presented. After description, analysis and classification of the existing schemes, some research directions including communication infrastructures, combined control and protection schemes, and promising devices for the realisation of future hybrid AC/DC microgrids are pointed out

Real time adaptive relay settings for Microgrid protection verified using Hardware in Loop

Microgrids with penetration of renewables is imposing new challenges for system protection. Renewables are characterized with high source impedance which limit the short circuit current. The value of short-circuit current is limited due to converters used which limit the current to a maximum of 1.1 to 1.5 times maximum rated load current. This can result in faults during the islanded mode of microgrid to go unnoticed if the relay settings are not adapted to account for it. The presence of such uncleared faults in the microgrid can result in exposing it to overcurrent for a long time which can damage the equipment. One solution is to have different protection element pickup settings for different modes of operation. This report discusses the development of an algorithm to switch these settings upon microgrid state changes and test the algorithm using OPAL-RT hardware in loop real-time testing with SEL-351S relay as the hardware

The power system and microgrid protection-a review

In recent years, power grid infrastructures have been changing from a centralized power generation model to a paradigm where the generation capability is spread over an increasing number of small power stations relying on renewable energy sources. A microgrid is a local network including renewable and non-renewable energy sources as well as distributed loads. Microgrids can be operated in both grid-connected and islanded modes to fill the gap between the significant increase in demand and storage of electricity and transmission issues. Power electronics play an important role in microgrids due to the penetration of renewable energy sources. While microgrids have many benefits for power systems, they cause many challenges, especially in protection systems. This paper presents a comprehensive review of protection systems with the penetration of microgrids in the distribution network. The expansion of a microgrid affects the coordination and protection by a change in the current direction in the distribution network. Various solutions have been suggested in the literature to resolve the microgrid protection issues. The conventional coordination of the protection system is based on the time delays between relays as the primary and backup protection. The system protection scheme has to be changed in the presence of a microgrid, so several protection schemes have been proposed to improve the protection system. Microgrids are classified into different types based on the DC/AC system, communication infrastructure, rotating synchronous machine or inverter-based distributed generation (DG), etc. Finally, we discuss the trend of future protection schemes and compare the conventional power systems

Protection of converter dominated MV microgrid using changes in current\u27s phase angle

Converter interfaced distributed generations in a microgrid feed the modulated current of limited magnitude during fault conditions. The protection design and its operation are thus challenging due to limited fault current which is further reduced by Petersen coil grounding in medium-voltage (MV) level. This paper aims to address this challenge by developing a current-only directional relay algorithm for the protection of converter dominated MVmicrogrid with Petersen coil grounding. The relay’s operating principle is based on the sign of the change in phase angle of the fault current with respect to the prefault which indicates the direction of fault. The negative and positive changes in current’s phase angle determine the fault in forward and reverse direction, respectively. The tripping decision is derived by comparing the binary output of the relay at both ends of the line segment under protection. This requires a simple, flexible and low bandwidth communication channel. Both theoretical analyses and simulation studies have been performed on a typical distribution grid intended to be operated as microgrid. The proposed protection method is suitable for microgrid having the converters with and without reactive power support. Various operating conditions are evaluated, including bidirectional power flow, high resistance fault,different fault types, loading conditions and signals with noise

A communication-free active unit protection scheme for inverter dominated islanded microgrids

Large-scale integration of different renewable energy resources introduces significant challenges to the protection of microgrids (particularly those that may operate in islanded mode), including variable and low fault levels, difficulty in operation of main and backup protection with their coordination, and bidirectional power flow during faults. As a solution to such challenges, this paper presents a novel active protection strategy for the inverter dominated islanded microgrids that coordinates protection actions with the inverter control strategy. The proposed scheme dictates specific actions from the inverter interfaced distributed generator (IIDG) controller to inject specific harmonic components into the microgrid during the fault. Relays throughout the network detect and analyse the injected harmonic components to identify the faulted section, and take appropriate isolating actions, without any requirement for relay-to-relay communication. The scheme achieves selectivity and coordination using definite time delay settings. To verify the performance of the scheme, a realistic microgrid model incorporating the proposed protection strategy has been developed in MATLAB Simulink, where a wide range of fault scenarios have been simulated with variations in fault location, type, fault resistance, line impedance, and different combinations of IIDGs (including with and without connection of a synchronous generator). Additionally, case studies using a real-time digital simulator (RTDS) platform have also been conducted to validate the performance of the proposed solution in real-time, with multiple relays implemented as hardware prototypes running on the OPAL-RT platform – thereby demonstrating the system operation in a hardware-in-the-loop (HiL) configuration. It is shown that the scheme is highly effective in detecting and isolating faults, with proper discrimination, stability and provision of backup, under all investigated scenarios

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

There is a large difference in fault current level between the GC and IS mode for a microgrid (MG) with inverter-based distributed generators (IBDGs). The fault currents are minimal in the IS mode owing to the low current-carrying capacity of power electronics devices. 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. This paper proposes a positive sequence differential current protection scheme as the main protection. The envisioned concept can overcome the protective device coordination problems, and all fault types can be detected during both operation modes of MG, grid-connected (GC), and islanded (IS) for radial and loop configuration. The validation of the proposed design is performed using PSCAD/EMTDC software. The results show that the maximum fault clearing time for the main protection in GC mode and IS mode of 31.5 ms and 34 ms respectively. Compared with other schemes, the proposed scheme has a faster clearing time and is less expensive