Power definition and energy measurement based on waveform similarity

For the characteristics of non-linear, imbalance and fluctuation, a large quantity of harmonic and negative sequence current will be injected to the power grid by the traction load of electric railway, which will lead to the serious distortion of the source voltage. Under this circumstance, the original definition of reactive power in the form of sine wave is unsuitable and inconvenient. Meanwhile, the harmonic and negative sequence current will also affect the measurement of electric energy directly. Thus, the research on the definition and measurement of the reactive power considering the power quality factors such as harmonics and negative sequence becomes necessary. The existing power theories under non-sinusoidal condition are analyzed and compared in this paper. In view of the waveform similarity of the voltage and current, the definition of the power and the project meaning of the power factor are studied thoroughly. The results indicate that the difference between the voltage and current is the existing fundamental of the reactive power. It is also a key factor to weigh the energy transmission or conversion in the whole system. An effective energy measuring method is also designed in this paper, which can reflect the consumed energy correctly and reasonably.