Microgrid Protection and Control Strategies at Duke Energy
In the past few years, numerous weather events have caused significant outages to the electrical power grid, resulting in billions of dollars of damage. In order to increase the resiliency to the customers, the topic of microgrids has gained a lot of traction among different stakeholders. Recent advances in Distributed Energy Resources (DER) technology have resulted in creation of microgrid test beds. Equipped with photovoltaic (PV) farms, diesel or natural gas generators, batteries, flywheels, wind farms, fuel cells, combined heat and power (CHP), and other DERs these microgrid testbeds provide research and development areas for testing, integration and operation. In 2015, Duke Energy’s Emerging Technologies Office (ETO) designed, built, commissioned and started operating its Mount Holly microgrid, located on the northwest side of Charlotte, North Carolina. The microgrid, which has been expanded couple of times, consists of 650kW/326kWh battery, 150kW PV farm connected to 100kVA inverter, DC coupled battery rated at 240kW/122kWh along with 250kW DC-DC converter. Currently, 250kW/500kWh battery and 360kW natural gas generator are also being added to the microgrid. The main objective of initiating the Mount Holly microgrid project was to try to get better understanding of engineering challenges associated with design, building, commissioning, implementation, control and integration of numerous DERs, investigate the challenges with different protection and control schemes during the grid connected operation, islanded operation and transitions between the two, and determine the delays associated with different communication protocols, and their effect on the microgrid operating algorithms. This paper describes the lessons learned from all of the challenges described above.