Harmonic compliance is necessary for obtaining energization (EON), interim (ION), and finale (FON), operational notifications, for grid-connection of the inverter-based resources (IBR) plants to the distribution and transmission grids. Generally, the harmonic compliance shall be proven by simulation studies using harmonic impedance envelopes.

The harmonic impedance envelopes represent operation regimes of the grid, are provided by the grid operator, and may range from tens ohms up to several thousand ohms for each relevant integer harmonic and interharmonic order. The grid operator may request the simulation results for the impedance envelopes with 1-ohm resolution. Commercially available methods will conduct load-flow (LF) followed by harmonic load-flow (HLF) simulations in each point of the impedance envelopes for each harmonic order that is an accurate but time-consuming approach.

This paper discusses accuracy of a fast simulation method introduced by AFRY Denmark A/S for assessing harmonic compliance of inverter-based resource (IBR) plants. The fast simulation method interpolates the solution for the entire impedance envelope through a couple of critical points instead of executing LF and HLF. Accuracy of the method is achieved by constructing and solving a type of optimization functions, while impedance/frequency scans and harmonic amplification calculations to establish harmonic voltage or current magnification may introduce unacceptable inaccuracies.

Accuracy of the fast simulation method is demonstrated by direct comparison to the exact solution by a commercially available method utilizing LF and HLF simulations. The fast method applies for both the IEC (balanced) and the Phase-Correct (unbalanced) harmonic assessments at high accuracy and with an execution speed that is up to hundred times faster than conventional methods. The demonstration is given by real-life, anonymized cases.