Time Domain Implementation of Rational Models of Power System Components With Calculation of Instantaneous Power Dissipation and Absorption

Frequency-dependent modeling of components and subsystems using rational functions allows fast and accurate representation of the component's terminal behaviors in electromagnetic transient simulation studies. One shortcoming with general state-space model formulations of the rational model is that it is not possible to directly simulate the component's active losses during transient excitations, for instance when the losses are to be used as input for thermal calculations. In this work we propose applying an add-on secondary model for calculation of the losses. The secondary model is based on a circuit equivalent formulation which takes the component terminal voltages as input. Precise calculation of instantaneous power dissipation (active losses) is achieved by using currents/voltages through/over resistors as state variables. The power absorption in dynamic elements is also calculated. The proposed approach is verified via theoretical examples and applied to a cable system within a motor drive.