motulator-impedance: Mechanical Impedance and Output Admittance for motulator

motulator-impedance: Mechanical Impedance and Output Admittance for motulator#

This package measures small-signal frequency responses of systems built in motulator by frequency sweeps: the system is simulated to its operating point, a small-signal excitation is injected one frequency at a time, and the response is computed with the discrete Fourier transform. Two responses are provided:

  • The mechanical impedance \(Z_\mathrm{M}(s) = -\Delta\tau_\mathrm{M}(s)/\Delta\omega_\mathrm{M}(s)\) of a machine drive describes the dynamics of the machine and its control system as seen from the shaft [Hartikainen et al., 2023]. The rotor speed is imposed, and speed excitations are superimposed on it. A drive whose mechanical impedance is passive, i.e., its phase is within ±90°, is stable with any passive mechanical system.

  • The output admittance of a grid converter at the point of common coupling [Määttä et al., 2026] is a 2×2 matrix in synchronous coordinates. The PCC voltage is imposed by a stiff source, and voltage excitations are injected in the d- and q-axes. The admittance is the basis of impedance-based stability analysis, e.g., through its passivity index.

This documentation covers only the measurements. The system models and control methods are described in the documentation of motulator.

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