“…A severe winter storm has passed through your area. A couple of minutes into the storm your lights have turned off and you wonder how long before the power comes back on. As you contemplate leaving to an emergency shelter, someone knocks on your door. It is your neighbour who has hot coffee and heat and invites you over to wait for the power to be restored. Your neighbour’s lights are on due to an installed diesel and solar-storage backup power system. Your neighbour now runs a microgrid providing a warm shelter close to home as utility personnel restore power to your area…”
Grid resiliency and reliability
In conventional power systems, electrical energy is generated from large centralized power plants such as hydro, coal or nuclear. The generated energy is transmitted over long distances at high voltages to substations which then supply consumers at reduced voltages. Consumers include residential buildings, critical centres like hospitals and airports, large industrial factories and the local dairy farm.
During emergencies such as severe weather storms or grid system faults [1, 2], the supply of electrical energy from the utility to consumers can be interrupted for periods ranging from minutes, hours or days. Prolonged and/or frequent power outages have adverse impact on the economy and critical infrastructure such as water supply, transportation, security, food and healthcare [3, 4]. The deployment of technology to increase grid resiliency and reliability remains a critical factor for both consumers and producers of electrical energy.
The Microgrid Concept
Microgrids are small, localized groups of electric power resources and loads. Microgrids can be operated in parallel with the centralized grid and also independently when the centralized grid is disconnected. The microgrid concept is gaining rapid attention worldwide as an enabling technology to increase grid resiliency and reliability during severe weather conditions and emergency events. Additional benefits of microgrids include integration of renewable energy sources such as wind and solar, providing power to remote communities with limited or no access to transmission infrastructure, peak load management and voltage support functions to distribution networks .
How Microgrids Work – Challenges in Control and Protection
A significant challenge to microgrid implementation is the stable control and operation of the microgrid when operated in parallel with the centralized grid or independently as a power island. As shown in Figure 2, microgrids are operated by a hierarchy of control systems. The central controller coordinates the overall control and protection functions and sends commands to the distributed resources and load control systems in the microgrid . The microgrid central control can include several optimization algorithms to send operating commands to the loads and distributed energy resources based on cost pricing, fuel use, grid availability, load forecasting and climate models for renewable energy sources.
Applying conventional protection concepts based on unidirectional power flow becomes challenging with microgrids due to the bidirectional power flow from multiple distributed energy resources. Microgrid islands during grid outages have to be properly detected and isolated to avoid power instability, equipment damage and injury/death to utility personnel working on lines energized by the microgrid. The voltage, frequency and phase of an islanded microgrid have to be synchronized within specified limits before reconnection to the centralized grid can occur [6, 7].
Understanding and solving the technical challenges related to the deployment of microgrid technology has generated a demand for detailed study tools and sophisticated hardware in the loop test facilities. Electromagnetic Transient based Real Time Digital Simulators (EMT – RTDS) allow detailed modeling of power and control system components required for microgrid dynamic studies. The hardware in the loop capability of the RTDS provides a realistic environment to perform a large number of contingency tests to validate the operation of physical control and power devices in microgrid applications .
The demand for fast, reliable and efficient operation of distribution networks with distributed energy resources has driven the use of information and communication technologies (ICT) enabled devices. The RTDS provides the capability to interface microgrid controllers with industry standard protocols such as distributed network protocol (DNP) for supervisory control and data acquisition (SCADA); IEC 61850 GOOSE and Sampled Values for automation, control and protection, MODBUS and TCP/IP Sockets for microgrid control communication .
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Author: Onyi Nzimako
 R. H. Lasseter, “Microgrids [distributed power generation],” in Power Engineering Society Winter Meeting, 2001. IEEE (Volume:1 ), Columbus, OH, 28 Jan 2001-01 Feb 2001.
 S. Chowdhury , S. Chowdhury and P. Crossley, Microgrids and Active Distribution Networks, London: The Institution of Energy and Technology, 2009.
 IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems,” IEEE Std 1547-2003, pp. 1,28, July 28 2003.