Concept and Definition of Dynamic Symmetrical Components with Time-Varying Amplitude and Frequency

This paper investigates the dynamic symmetrical component method of internal voltage vector with time-varying amplitude and frequency. With the large-scale integration of power electronic devices into the power grid, when there is an asymmetrical fault in the AC network, the voltages and currents present the characteristics of amplitude and frequency time-varying modulation. Hence, the traditional asymmetrical fault analysis method and concept based on phasor models with constant amplitude and frequency are not adaptive enough. In order to supplement the traditional symmetrical component method and concept, the phasor models and vector models with time-varying amplitude and frequency are established. Then, the asymmetrical three-phase phasors with time-varying amplitude and frequency are decomposed into three groups of symmetrical phasors with time-varying amplitude and frequency. Based on the mathematical and physical characteristics of symmetrical components, the applicable concept and definition are reestablished. Lastly, time-domain simulations corroborate the theoretical analysis.