Harmonic Modeling And Investigation On Harmonic Characteristics For Typical Single-phase Nonlinear Loads

A large number of nonlinear loads are widely distributed in low voltagedistribution system, and the number of these nonlinear loads will further increase withthe development of power electronic technology. Due to the high current distortion ofthese nonlinear loads—the ITHD of these loads even more than100%—and their widedistribution in all over the electric network, these loads seriously affect the powerquality of the power system. So it is very important to study and characterize theharmonic character of these loads. This paper developed a precise frequency-domainharmonic model based on harmonically coupled admittance matrix for single-phasediode-bridge converter-based loads, with which harmonic attenuation effect of suchloads was investigated and study of the relationship between harmonic Norton modeland harmonic coupled admittance matrix model was done. Two new indices, namelyconduction angle attenuation factor and peak voltage attenuation factor are proposed forcharacterizing the harmonic attenuation effect of nonlinear loads. Research on problemsof harmonic Norton model, such as the applicability of the model and model parameterscalculation, was also carried out.①By improving the method for solving the circuit, a precise frequency-domainharmonic model of single-phase nonlinear loads, which use uncontrolled rectifiers withdc-smoothing capacitors as their power supply, was proposed by this paper. This modelwas verified by simulations and measurements as well.②An approach for estimating the parameters of a general equivalent circuit thatrepresents the single-phase diode-bridge converter-based loads, such as PC and LCD,was presented. Both the parameter estimation approach and the above-mentionedharmonic model were verified by simulations and measurements.③Model-based analyses of the harmonic character and harmonic attenuationeffect of these loads were performed, and two new indices, namely conduction angleattenuation factor and peak voltage attenuation factor, were proposed for characterizingthe harmonic attenuation effect. Good correlation between these indices and totalattenuation factor of harmonic current is verified by simulation, so these indices can beused to characterize the influence of system voltage on harmonic current. Furthermore,quantitative analysis of harmonic attenuation effect can be done by using these indices.④Analysis of the relationship between harmonic admittance matrix model and harmonic Norton model and three problems of harmonic Norton model were carried outby this paper. Besides the improvement of model parameters calculation of harmonicNorton model, the difference of harmonic modeling by harmonic admittance matrixmodel and harmonic Norton model were presented in this paper.