共振電流を利用した低圧配電系統背後インピーダンスの推定

抄録

Two estimation methods for a backward impedance of a power distribution system are proposed in this paper. A frequency response of a transient current flowing into a capacitor, which connected to a distribution line, has information of the backward impedance. The impedance is obtained from an attenuation constant and a resonance frequency determined by the capacitance and the impedance of power distribution system. These parameters are stably obtained from a frequency response of the transient current using a least square method. The accuracy of the method heavily depends on the origin on the time-axis for Fourier transform. Additional time-origin estimation is required for an accurate estimation of the backward impedance. The second method estimates the backward impedance using two transient current waveforms obtained by connecting alternately different capacitors to a distribution line. The backward impedance can be represented as a function of the frequency responses of these current. This method is suitable for an automatic measurement of the backward impedance because the method is independent from the time-origin. The proposed methods are applicable to an estimation of a harmonic current of the distribution system. In this paper, a harmonic current flowing through a distribution wire is estimated from the estimated backward impedance and the measured results of harmonic voltages obtained by an instrument developed by the authors.