Identification and development of microgrids emergency control procedures

Tese de doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 200

Modeling and Evaluation of Utility-Scale Microgrid Investment for Distribution System Planning

The electrical distribution network faces two great challenges for the immediate future. First, increased affordability of distributed energy resources (DERs)—and advancing control technologies of inverters that interface them to the grid—have driven a shift from a passive to an active distribution network (ADN), which heightens the complexity of system management. Second, the increased frequency of severe weather events and increased potential for a cybersecurity attack necessitate the need for a resilient infrastructure that can respond adaptively to shutdowns within the system. Microgrids (MGs) present a promising framework both to provide hierarchal control of DERs and to increase resiliency with grid-forming and grid-restoring functionality. Though much work has been done to validate the role of MGs in the distribution system, grid owners and utilities need effective methodologies to incorporate MGs into existing system planning frameworks to ensure that this technology is quickly and wisely adopted. This thesis develops a two-stage optimization framework that models utility investment in medium-voltage microgrids (MVMGs) with consideration to normal and high-stress operating conditions. The problem is designed as a mixed-integer second-order-cone program (MISOCP) compatible with commercial solvers to obtain a global solution. The first stage models MG boundary selection as a multi-area power system splitting problem, co-optimizing network topology along with DER siting and sizing that results in optimal placement of MGs capable of prolonged self-sustainment. The second stage iterates through possible grid reconnection points for each MG to find the optimal point of common coupling (PCC) and optimizes islanding decisions for critical hours. The proposed two-stage framework was optimized and tested on the IEEE 33-Bus System for baseline, one-area, and two-area cases to analyze and compare the capabilities of the method. The results of the first case study confirm that including MGs in the planning process can lead to heightened resilience against high-stress events that lead to economic savings. The second case study analyzes the value of islanding in a system planning context and classifies scenarios that could provide additional value streams to justify microgrid investment. Finally, suggestions to foster the continued improvement of utility microgrid planning are discussed in the conclusion

Enabling digital grid for industrial revolution: self-healing cyber resilient platform

The key market objectives driving digital grid development are to provide sustainable, reliable and secure network systems that can support variety of applications against any potential cyber attacks. Therefore, there is an urgent demand to accelerate the development of intelligent Software-Defined Networking (SDN) platform that can address the tremendous challenges of data protection for digital resiliency. Modern grid technology tends to adopt distributed SDN controllers for further slicing power grid domain and protect the boundaries of electric data at network edges. To accommodate these issues, this article proposes an intelligent secure SDN controller for supporting digital grid resiliency, considering management coordination capability, to enable self-healing features and recovery of network traffic forwarding during service interruptions. A set of advanced features are employed in grid controllers to configure the network elements in response to possible disasters or link failures. In addition, various SDN topology scenarios are introduced for efficient coordination and configurations of network domains. Finally, to justify the potential advantages of intelligent secure SDN system, a case study is presented to evaluate the requirements of secure digital modern grid networks and pave the path towards the next phase of industry revolution

Protection of Active Distribution Networks and Their Cyber Physical Infrastructure

Today’s Smart Grid constitutes several smaller interconnected microgrids. However, the integration of converter-interfaced distributed generation (DG) in microgrids has raised several issues such as the fact that fault currents in these systems in islanded mode are way less than those in grid connected microgrids. Therefore, microgrid protection schemes require a fast, reliable and robust communication system, with backup, to automatically adjust relay settings for the appropriate current levels according to the microgrid’s operation mode. However, risks of communication link failures, cyber security threats and the high cost involved to avoid them are major challenges for the implementation of an economic adaptive protection scheme. This dissertation proposes an adaptive protection scheme for AC microgrids which is capable of surviving communication failures. The contribution is the use of an energy storage system as the main contributor to fault currents in the microgrid’s islanded mode when the communication link fails to detect the shift to the islanded mode. The design of an autonomous control algorithm for the energy storage’s AC/DC converter capable of operating when the microgrid is in both grid-connected and islanded mode. Utilizing a single mode of operation for the converter will eliminate the reliance on communicated control command signals to shift the controller between different modes. Also, the ability of the overall system to keep stable voltage and frequency levels during extreme cases such as the occurrence of a fault during a peak pulse load period. The results of the proposed protection scheme showed that the energy storage -inverter system is able to contribute enough fault current for a sufficient duration to cause the system protection devices to clear the fault in the event of communication loss. The proposed method was investigated under different fault types and showed excellent results of the proposed protection scheme. In addition, it was demonstrated in a case study that, whenever possible, the temporary disconnection of the pulse load during the fault period will allow the utilization of smaller energy storage device capacity to feed fault currents and thus reduce the overall expenditures. Also, in this dissertation we proposed a hybrid hardware-software co-simulation platform capable of modeling the relation between the cyber and physical parts to provide a protection scheme for the microgrid. The microgrid was simulated on MATLAB/Simulink SimPowerSystems to model the physical system dynamics, whereas all control logic was implemented on embedded microcontrollers communicating over a real network. This work suggested a protection methodology utilizing contemporary communication technologies between multi-agents to protect the microgrid

Distributed Power Generation in Europe: Technical Issues for Further Integration

The electric power sector in Europe is currently facing different changes and evolutions mainly in response to the three issues at EU level - environmental sustainability, security of supply, and competitiveness. These issues, against a background of growing electricity demand, may represent drivers for facilitating the further deployment of Distributed Power Generation technologies in Europe. The present Report focuses on the potential role of Distributed Power Generation (or simply Distributed Generation, DG) in a European perspective. More specifically, this work aims to assess the technical issues and developments related to DG technologies and their integration into the European power systems. As a starting point the concept of Distributed Generation is characterised for the purpose of the study. Distributed Generation, defined as an electric power source connected to the distribution network, serving a customer on-site or providing network support, may offer various benefits to the European electric power systems. DG technologies may consist of small/medium size, modular energy conversion units, which are generally located close to end users and transform primary energy resources into electricity and eventually heat. There are, however, major issues concerning the integration of DG technology into the distribution networks. In fact, the existing distribution networks were not generally designed to operate in presence of DG technologies. Consequently, a sustained increase in the deployment of DG resources may imply several changes in the electric power system architecture in the near future. The present Report on Distributed Generation in Europe, after an overview of the basic elements of electric power systems, introduces the proposed definition and main features of DG. Then, it reviews the state-of-the-art of DG technologies as well as focuses on current DG grid integration issues. Technical solutions towards DG integration in Europe and developments concerning the future distribution systems are also addressed in the study.JRC.F.7-Energy systems evaluatio

ICT-Enabled Control and Energy Management of Community Microgrids for Resilient Smart Grid Operation

Our research has focused on developing novel controllers and algorithms to enhance the resilience of the power grid and increase its readiness level against major disturbances. The U.S. power grid currently encounters two main challenges: (1) the massive and extended blackouts caused by natural disasters, such as hurricane Sandy. These blackouts have raised a national call to explore innovative approaches for enhanced grid resiliency. Scrutinizing how previous blackouts initiated and propagated throughout the power grid, the major reasons are lack of situational awareness, lack of real-time monitoring and control, underdeveloped controllers at both the transmission and distribution levels, and lack of preparation for major emergencies; and (2) the projected high penetration of renewable energy resources (RES) into the electric grid, which is mainly driven by federal and state regulatory actions to reduce GHG emissions from new and existing power plants, and to encourage Non Wire Solutions (NWS). RESs are intermittent by nature imposing a challenge to forecast load and maintain generation/demand balance. The conceived vision of the smart grid is a cyber-physical system that amalgamates high processing power and increased dependence on communication networks to enable real-time monitoring and control. This will allow for, among other objectives, the realization of increased resilience and self-healing capabilities. This vision entails a hierarchical control architecture in which a myriad of microgrids, each locally controlled at the prosumer level, coordinates within the distribution level with their correspondent distribution system operator (i.e. area controllers). The various area controllers are managed by a Wide Area Monitoring, Protection and Control operator. The smart grid has been devised to address the grid main challenges; however, some technical barriers are yet to be overcome. These barriers include the need to develop new control techniques and algorithms that enable flexible transitions between operational modes of a single controller, and effective coordination between hierarchical control layers. In addition, there is a need to understand the reliability impacts of increased dependence on communication networks. In an attempt to tackle the aforementioned barriers, in my work, novel controllers to manage the prosumer and distribution networks were developed and analyzed. Specifically, the following has been accomplished at the prosumer level, we: 1) designed and implemented a DC MG testbed with minimal off-the-shelf components to enable testing new control techniques with significant flexibility and reconfiguration capability; 2) developed a communication-based hybrid state/event driven control scheme that aims at reducing the communication load and complexity, processor computations, and consequently system cost while maintaining resilient autonomous operation during all possible scenarios including major emergencies; and 3) analyzed the effect of communication latency on the performance of centralized ICT-based DC microgrids, and developed mathematical models to describe the behavior of microgrids during latency. In addition, we proposed a practical solution to mitigate severe impacts of latency. At the distribution level, we: 1) developed a model for an IEEE distribution test network with multiple MGs integrated[AM1] [PL2] ; 2) developed a control scheme to manage community MGs to mitigate RES intermittency and enhance the grid resiliency, deferring the need for infrastructure upgrade; and 3) investigated the optimal placement and operation of community MGs in distribution networks using complex network analysis, to increase distribution networks resilience. At the transmission level (T.L), New York State T.L was modeled. A case study was conducted on Long Island City to study the impact of high penetration of renewable energy resources on the grid resilience in the transmission level. These research accomplishments should pave the way and help facilitate a smooth transition towards the future smart grid.