Grid Code Compliance Testing Using Simulation

Abstract

The accelerating integration of inverter-based resources (IBRs) into power systems has fundamentally transformed grid dynamics, displacing synchronous generation and creating new demands for standardized compliance verification. As grid operators increasingly mandate technical performance requirements, including voltage and frequency ride-through, reactive power support, and fault current injection, the need for efficient, scalable, and repeatable testing methodologies has become critical. Traditional on-site and laboratory type tests are costly, time-consuming, and limited in their ability to cover the full spectrum of grid disturbances, driving the adoption of simulation-based approaches as viable pre-certifi cation alternatives. This thesis develops and validates a Software-in-the-Loop (SIL) compliance testing framework for a Danfoss inverter-based resource model against the EN 50549-2 standard for non-synchronous generating plants connected to medium-voltage distribution networks. The framework integrates the Danfoss Functional Mock-up Unit (FMU) binary into a MATLAB/Simulink co-simulation environment alongside a programmable grid emulator, implementing a black-box input-output verification methodology in which all compliance decisions are derived exclusively from externally observable signals at the point of connection. Different test categories are executed covering under-voltage and over-voltage ride-through (UVRT/OVRT), frequency ride-through across all EN 50549-2 defined bands, Rate-of-Change-of-Frequency (ROCOF) immunity, active power response to frequency deviation under both Limited Frequency Sensitive Mode over-frequency (LFSM-O) and under-frequency (LFSM-U) modes, reactive power voltage support via Q(U) volt-var characteristic including steady-state accuracy and dynamic step response, and dynamic reactive current injection during asymmetrical faults of three types. Simulation results demonstrate full EN 50549-2 compliance across all tested scenarios: UVRT and OVRT boundary tracking was accurate to within the simulation time-step resolution, LFSM droop errors remained below 0.25 percentage points, Q(U) steady-state accuracy was within ±2% Smax across all ten voltage operating points, and asymmetrical fault reactive current errors remained within the EN 50549-2 tolerance band across all five fault scenarios. The framework confirms that a SIL approach can serve as a high-fidelity, repeatable, and computationally efficient alternative to physical pre-certifi cation testing, substantially reducing the time and cost required to identify compliance issues early in the inverter development cycle.