Effectiveness of the method of two measurements in determining the parameters of equivalent circuits of electrical network elements for the highest harmon-ic components of currents and voltages

The feasibility of applying the method of two measurements in determining the parameters of equivalent circuits of electrical network elements for the highest harmonic components is analyzed. Experiments were carried out using a MATLAB Simulink model of the common coupling point that includes a distorting load in the form of a three-phase rectifier, a nondistorting linear load and a generalized power system without distortion sources. The parameters of an equivalent circuit in the form of active bipoles, consisting of current distortion and conductivity sources, were determined using the method of two measurements of mode parameters. Modes with variations in the active and reactive power of the studied distorting load and loads in the external electrical network were considered. The results of determining the equivalent circuit parameters under 20% and more variations in the power loading were established to be unstable (400% dispersion of actual values). Therefore, these parameter values appear to be unreliable due to their dependence on the value of external load power. At the same time, the simulation of random variations in loading parameters within 10% of the initial value allowed the parameters of an equivalent circuit to be correctly determined. It was shown that the equivalent circuit of a nondistorting linear load consists solely of conductivity, while the equivalent circuit of a distorting load can contain non-zero conductivity on the considered harmonic component. Thus, according to the performed study, the method of two measurements produces the results acceptable in terms of accuracy (deviation from actual values of less than 1%) not at a single significant variation in the mode parameters, but during a continuous monitoring of small natural variations in the parameters of the electric power system. The results obtained can be used when solving the problem of online assessing the effect of loads on the quality of electricity, since the initial data for this problem include the equivalent circuit parameters.

electric power quality, voltage waveform distortion, higher harmonics, two-measurement method, Thé-venin's theorem, equivalent circuit, active one-port device, MATLAB Simulink