Abstract: A method for testing a plant control system of an inverter-based resource (“IBR”) coupled to an electric power grid, the method comprising: using a power systems modeling environment implemented in an information system, generating an IBR model, the IBR model including an inverter control model, a generator model, a network solution model, and a model power meter; using a hardware-in-the-loop (“HIL”) simulation environment including the IBR model, a phasor data concentrator (“PDC”), a test automation server, and the plant control system, performing a test of the plant control system by iteratively: receiving measurements from the PDC and setpoints from the test automation server and sending the measurements and the setpoints to the plant control system; generating and sending an active power command and a reactive power command from the plant control system to the inverter control model; generating and sending desired active current and desired reactive current from the inverter control model to the generator