Energy and Power Engineering, 2013, 5, 1120-1125

doi:10.4236/epe.2013.54B214 Published Online July 2013 (http://www.scirp.org/journal/epe)

Harmonic Currents of Semiconductor Pulse Switching

Converters

Petr Bilik1, Jan Zidek1, Vaclav Kus2, Te r eza Josefova2

1Faculty of Electrical Engineering and Computer Science, VSB – Technical University of Ostrava, Czech Republic

2Department of Electromechanics and Power Electronics, University of West Bohemia, Pilsen, Czech Republic

Email: {petr.bilik, jan.zidek}@vsb.cz, kus@kev.zcu.cz, terkajos@kev.zcu.cz

Received March, 2013

ABSTRACT

Due to the operation of power semiconductor switching converters, the content of harmonic currents, which these

switching converters take from the feed array, is still increasing. One of the possible ways of minimizing these currents

is the use of pulse switching converters. On one hand, the original, characteristic harmonic ones are minimized, but, on

the other hand, new frequencies caused by the modulation frequency appear in the current spectrum. The level of the

currents of these frequencies is small and is scarcely dependent on the load of the converter. It may happen that the

proportional value of the monitored harmonic one is high, although the absolute value is low. In the article presented,

there is a description of the activity of the pulse voltage rectifier and an analysis of the current taken. The other part

contains the results of the harmonic analysis of the stated current, including both the absolute and proportional values

according to the load. In the conclusion, there are results of measurements of pulsed switching converters taken from

the real measurement.

Keywords: Rectifiers; Harmonic Analysis; Harmonic Distortion; Power System Harmonics; Current Measurement

1. Introduction

Conventional controlled rectifiers designed for speed

regulation of DC motors were characterized by both the

consumption of harmonic currents and, especially, the

variable power factor (proportional to the steering angle

of the converter). There were mostly high power con-

verters, so the negative effects on the power network

were dealt with by experts. In the spectrum of the current,

there mostly occurred so called characteristic harmonic

ones and their level was computed using the amplitude

principle. When mentioning small power sources for the

use in electronics (charging of capacitors), there were, on

the contrary, very low powers and very small amount of

appliances, so that negative effects were ignored.

A significant increase of negative effects of the con-

verters on the power network occurs with the increase of

frequency converters with a DC voltage intermediate

circuit. These converters usually contain uncontrolled

rectifiers at the input. The converter thus works with a

negligible phase shift between the voltage and the current,

and the power factor (fundamental harmonic cos φ1) is

close to 1. However, the current harmonic ones become a

problem. The very first converters even worked without

sufficient circuits for limitation of the harmonic ones. In

principle, it is a rectifier working to capacitive load; the

values of harmonic currents are very high. In a simplified

calculation, there can be used a so-called "generalized

amplitude principle" (1) [1,2].

h1

hd

sin

12

II.

d

hsin 2

(1)

where: h – harmonic order, I1 – magnitude of fundamen-

tal harmonic, d – diode conduction time.

Detailed information about calculations of characteristic

harmonics, non-characteristic harmonics and interharmonics

can be found in [2-5]. Topic of harmonics elimination

and power factor improvement of three-phase rectifier is

described in [6].

Equation (1) advantage is that it also applies to con-

ventional controlled rectifiers, to calculation of the har-

monic ones with intermittent currents, to calculation of

harmonic voltage converters as well as to frequency

converters or other rectifiers working to capacitive loads.

See the calculated shape of current in Figure 1.

The unambiguous result of this relation is the fact that

the values of harmonic ones depend on the time during

which the diode is open (the capacity is recharged). As

for large capacities, the time is very short and thus the

harmonic ones are even higher. This, paradoxically, re-

sults in a situation where the load requires large voltage

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