RESEARCH INTO THE GENERATION OF HIGHER HARMONICS FROM THE OPERATION OF FREQUENCY CONVERTERS IN THE AC POWER NETWORK

Abstract

In this work, a comprehensive analysis of the influence of higher harmonics generated by a frequency converter on a three-phase power supply system of an electric drive was carried out. Attention was paid to determining the level of harmonic distortion in the input current of the converter. For experimental research, a scheme of a specialized experimental setup was developed and implemented, which provides the possibility of measuring the operating parameters of the frequency converter in real time. Experimental tests of the Altivar 71 frequency converter were carried out in three operating modes: idle, rated load and overload by 25%. The measured values ​​of current and relative line voltage were processed in the Mathcad 14 environment and presented in the form of graphs demonstrating the change in electricity parameters under different operating conditions. Analysis of the obtained spectra of harmonic components showed that the system contains mainly odd harmonics, among which the 5th and 7th harmonics have the greatest influence, especially under load conditions. It was found that increasing the load of the converter contributes to a decrease in the harmonic distortion factor, while reducing the output frequency of the frequency converter, on the contrary, leads to an increase in the level of distortion. One of the most effective methods of reducing the level of harmonic distortion, as well as increasing the power factor of the system, is the use of power factor correctors (PFC). These devices, which are based on the use of highly efficient pulse circuits with low energy losses, not only improve the current shape and increase the power factor, but also provide voltage stabilization in the DC circuit even under conditions of sharp voltage drops. As a result of the study, the levels of harmonic distortion factors for different operating modes of the frequency converter were determined, and the use of PFC was also proposed to minimize the negative impact of higher harmonics on the power supply system of the electric drive. The implementation of such measures allows to increase the efficiency of electric drive systems, ensure improved electricity quality indicators and stable operation of inverters.