#### SIMPOW - Frequency domain analysis

Simpow employs Eigenvalue calculation and frequency response techniques in the frequency domain. These include linearization of the power system equations at the actual operating point and consider only incremental changes of the state variables around the operating point.

The frequency domain analysis allows e.g.:

- Calculation of sensitivity of an Eigenvalue with respect to parameters.
- Displaying Eigenvalues in locus diagram in the complex plane. Useful when manipulating a parameter and observing its influence of the Eigenvalue.
- Single-line diagram of the power system with "vector" visualization of the generator speed components of the Eigenvectors related to a selected pair of complex Eigenvalues corresponding to a particular mode of generator electromechanical oscillations.
- Calculation of participation factors.
- The Eigenvalue technique can be applied at any time during a simulation.
- Frequency scanning technique which calculates the response of selected variables to a sinusoidal perturbation, either in the form of a current injected to a selected node or by adding a signal to a selected variable. Frequency scanning is performed for a specified range of frequencies.
- Calculating of the frequency dependant impedance of the network at any perturbed bus.

These techniques are excellent means for the study of the small signal stability of generators and automatic control systems.