Controllable Grid Interface for Testing Ancillary Service Controls and Fault Performance of Utility-Scale Wind Power Generation: Preprint

The rapid expansion of wind power has led many transmission system operators (TSOs) to demand modern wind power plants (WPPs) to comply with strict grid interconnection requirements. Such requirements involve various aspects of wind power plant operation, including fault ride-through and power quality performance as well as the provision of ancillary services to enhance grid reliability. During recent years, the National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy has developed a new, ground-breaking testing apparatus and methodology to test and demonstrate many existing and future advanced controls for wind power generation (and other renewable generation technologies) on the multi-MW scale and medium-voltage (MV) levels. This paper describes the capabilities and control features of NREL’s 7MVA power electronic grid simulator (also called a controllable grid interface, or CGI) that enables testing many active and reactive power control features of modern wind turbine generators—including inertial response, primary and secondary frequency responses, and voltage regulation under a controlled medium-voltage grid environment. In particular, this paper focuses on the specifics of testing the balanced and unbalanced fault ride-through characteristics of wind turbine generators under simulated strong and weak MV grid conditions. This paper also describes the test results for some advanced control features, such as wind generation’s participation in power system oscillation damping. In addition, the paper provides insights on the power hardware-in-the-loop (PHIL) feature implemented in the CGI to emulate (in real time) the conditions that might exist in various types of power systems under normal operations and/or contingency scenarios. Using actual test examples and simulation results, this paper describes the value of CGI as an ultimate modeling validation tool for all types of “grid-friendly” controls by wind generation. Keywordselectric grids; power system faults; power quality; wind energy integration; wind turbine test facilities