Mode-based Damping Torque Analysis in Power System Low-frequency Oscillations

The mode-based damping torque analysis (M-DTA) method for studying the effect of an external controller on power system low-frequency oscillations is proposed in this paper. First, based on the interconnection model between the system and the controller in the frequency domain, the oscillation loop corresponding to the electromechanical oscillation mode is built, and then the mode-based damping torque of the controller can be calculated. Then, the application of the M-DTA method in the power system is illustrated. The derivation shows that in the single-machine infinite-bus power system, the M-DTA method is completely equivalent to the classical damping torque analysis (C-DTA) method. In the multi-machine power system, the mode-based damping torque directily reflects the effect of the controller on the oscillation mode, overcoming the shortcomings of the C-DTA method in which there is no direct correspondence between the damping torque and the oscillation mode. By deriving the relationship with the residue index, the M-DTA method shows higher accuracy than the residue method in applications, such as controller parameter adjustment. Finally, two example power systems are presented to demonstrate the application of the proposed M-DTA method.