A research for time-varying power in power electric power system

Traditional sinusoidal power theory is not feasible for non-sinusoidal condition. The existing non-sinusoidal power theories have no clear physical meanings. To solve this problem, this paper presents a time-varying power theory based on the instantaneous sinusoidal expression of DFT (Discrete Fourier Transform). For arbitrary voltage and current signals, use the DFT to get their sinusoidal expression, and calculate the time-varying active power and the time-varying reactive power. This definition is feasible for any periodical and non-periodical signals. It has a distinct physical meanings, especially the time-varying reactive power can show the scale and direction of load´s electromagnetic energy oscillation. It can embrace the sinusoidal power, Budeanu power and Fryze´active power. Finally, the rationality and feasibility of this time-varying power is demonstrated by theoretical analysis and work examples.