In order to achieve the above-mentioned aims of this research, a step by step approach has been implemented in this research. These steps can be summarized with the following research methodologies and techniques:
Literature review for new concepts such as microgrids and smartgrids
A thorough literature review has been performed to get the full grasp of these newly introduced concepts. Since these concepts have emerged recently, they are evolving very fast and special attention shall be paid to stay up-to-date. Moreover, the interpretation and implementation of these new concepts may differ in different parts of the world. Therefore, various microgrid test cases from different countries have been examined. In addition to management and stability issues, special attention has been paid to protection considerations due to relatively less research work done in this particular field.
Investigation of the effects of DGs and other equipment such as FCLs
Following the wide-scoped literature review explained above, research work has been
dedicated to investigate the effects of DG deployments and use of other devices such as FCLs on microgrids. This step was particularly important to analyze the behavior and effects of such equipment on the microgrid operation since the protection system modeling has to account for them. The design of the new protection scheme was heavily based on these findings.
Investigation of the impact of EVs and V2G technology
Although this item is very close to the one above, some differences ask for a separate analysis. Firstly, most of the devices considered in the above item are large establishments such as diesel generators or wind farms. It is not likely that every household would have a
diesel generator or a wind turbine on its own. However, the vehicle predictions show that almost all households could own an EV in the future. Furthermore, most of these devices have single operating mode, either generator or load, whereas EVs can freely alter between charging (G2V) and generating (V2G) modes of operation. Due to these major differences, EVs and their modes of operation have been investigated as a separate item in this research.
Design of a novel protection system based on extensive communication
Once the necessary investigations were done and the knowledge gap regarding the microgrid protection systems were identified and understood, a novel protection system has been designed. This new protection system considers the smartgrid vision where extensive communication lines will be utilized between the grid components. Therefore, the proposed protection system does not require new communication line installation for protection purposes, rather it uses the lines which will be present in future smartgrids. Although the use of communication in protection lines might seem a tedious task, it makes it possible to monitor the changes occurring in the microgrid and take necessary actions immediately. These changes might be short-term changes such as disconnection of a relay or long-term changes such as a new DG deployment.
Modeling of the proposed protection system with IEC 61850 Standard and its recent extension IEC 61850-7-420
In order to make the developed protection system universal, the research focused on modeling of this conceptual design using the international substation communication standard IEC 61850 and its recent extension for DGs, IEC 6180-7-420. This step is very crucial to have a universal protection system which can be implemented in different microgrids. When the standard modeling stipulated by IEC standards has been implemented, the developed protection system can be used in all microgrids regardless of the manufacturer or the model
of the grid components. Instead of having a localized, custom-made protection system for a particular microgrid, this approach ensures that the proposed protection system can be utilized as a generic system.
Extending IEC 61850-7-420 for new equipment
Although a recent extension of IEC 61850 was recently published for DGs, i.e. IEC 61850-7- 420, there are still some devices which are not defined in this standard. These include FCLs and EVs. Since they are bound to be used very often in future power networks, they need to be incorporated to IEC communication standards. In this research, these missing links have been connected by proposing IEC models for these devices.
Automated microgrid structure detection for plug-and-play purposes
After designing a new protection scheme and modeling it within the IEC communication framework, it was required to automate the microgrid structure detection. This has particular importance in microgrids, since several connections/disconnections may happen in a very short period of time and some new deployments are always bound to occur. These deployments need not be very high cost projects. For instance, whenever a new EV is purchased by a household, this will appear as a new deployment from network operator‟s
point of view. Therefore, a new approach has been taken to enable the microgrid protection system monitor the changes and extract the resulting structure. Thanks to this automated approach, network structure is not required to be known by the protection system beforehand.
Adaptation of the proposed system for other protection systems
Finally, the developed protection system was implemented with other protection schemes seen in microgrids. This adaptation was designed in two aspects. The first one envisages that the proposed protection system would support others wherever they are insufficient. For
instance, multi-terminal protection with long distance between the terminals in a differential protection set-up would be very meticulous and tedious task. Furthermore, any new deployment would require the multi-terminal connections to be updated. The proposed protection system is utilized to support differential protection in this aspect. Secondly, some protection schemes such as differential protection require the communication link to be active continuously. Should there be a communication failure the protection scheme becomes ineffective. Thanks to the local decision making of the proposed scheme, it is implemented as a roll-back strategy in case of a failure. This is also important to depict the interaction between different protection schemes.