Tereza Josefova

Current harmonics of voltage-source active rectifier with random switching frequency

This paper presents the issue of current harmonics drawn from the grid by three-phase voltage-source active rectifiers when the switching frequency of the devices is random; it is not an integer multiple of the supply frequency (50 Hz). The first part compares the harmonic analysis calculations derived for the piecewise linearized simplified current waveform and the simulations in the random frequency case. The second part presents a comparison of the current harmonic analysis when the switching frequency is the integer multiple of the supply frequency and when it is not. The second part also shows a dependence of the current spectrums on the random switching frequencies. This paper verifies, that the same conclusions of the previous publications apply to both the switching frequency that is the integer multiple of the supply frequency and the random switching frequency.

Analysis of current drawn by the voltage-source active rectifier from the electricity network

This paper deals with analysis of the current drawn from the grid by the voltage-source active rectifier. These converters are designed and controlled so that the current drawn from the grid approaches sine wave and power factor approaches one. Analytical calculations of harmonic analysis of this current based on the Fourier series are performed on a simplified model. These analytical calculations of the simplified model are compared with simulations. It is proved that even when the simplified model is used; the results of the analytical calculations differ very little from simulations. Little effect of active rectifier load on the absolute values of the current harmonics is proved in this paper. Absence of characteristic harmonics produced by diode rectifier in the spectrum of the current and the effect of the switching frequency for the presence of new harmonic current are shown in simulations.

Effect of dead times on the values of input current harmonics drawn from the grid by a voltage-source active rectifier

This paper presents an effect of dead times on values of an input current harmonics drawn from an electric grid by a voltage-source active rectifier. The first part shows a derivation of the effect on one pulse of the voltage and then the values of the current harmonics are derived. The main section discusses a description of voltage with the pulse width modulation with respect to the dead time. A voltage waveform at the input terminals of the inverter, its harmonic analysis, and calculations of the current harmonics values are derived. The last part shows simulations and comparison of the harmonic analysis of the current with and without dead times.

DC link voltage ripple of voltage-source active rectifiers

The paper deals with the DC link voltage ripple of voltage-source active rectifiers switched by PWM. The DC link voltage is maintained constant by a converter control; it fluctuates around the desired value. Therefore the first part of the paper describes the influence of voltage-source active rectifier parameters on the DC link voltage ripple. The effects of capacitors, loads and switching frequencies on the DC link voltage ripple are investigated. Also the paper discusses the influence of the DC link voltage ripple on current harmonics drawn from the grid by voltage source active rectifiers. The harmonics in the input current spectrum appear around the switching frequency. The last section analyzes the deviations of the current harmonics caused by the DC link voltage ripple.

Influence of a dead time duration on the input current spectrum of voltage-source active rectifiers

The paper discusses the influence of a dead time duration on the input current spectrum of voltage-source active rectifiers. The main body shows the simulations of a three-phase voltage-source active rectifier with respects to the dead times. This section especially describes the figures which present the harmonics analysis of the input current and its dependence on the dead time duration. The last part of the paper discusses the Total harmonic distortion of the current and effect of the dead times on this comprehensive indicator of the distortion. The higher dead time duration causes additional harmonics and it mainly affects odd harmonics.

The use of voltage-source active rectifier to minimize the effect of supply voltage drops on converters

The paper presents the possibilities of the use of voltage-source active rectifiers to minimize the effect of voltage drops on the DC link voltage magnitude of frequency converters. The control of voltage-source active rectifiers can compensate the short-term voltage drops within a certain range. The paper describes principle of the operating of voltage-source active rectifiers and the range of the voltage drops that can be compensated. The paper points out that it is important to observe the load current and the DC link voltage of converters.