19-01-2013, 11:53 AM
Current Ripple Factor Performance of Half-Wave Rectifier With and Without Freewheeling Diode
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Abstract
The objective of this work is to investigate ripple
factor of half-wave rectifier circuits. The ripple factor is one of
important characteristic necessary when designing a power
electronic converter. The ripple factor measures how much
deviation the converter output parameter has, such as the
output current, from its nominal designed value. In this paper
the ripple factor of the output current of half-wave rectifiers will
be investigated. More specifically, the ripple factor of output
current from more practical half-wave rectifiers that include
inductive load with or without a freewheeling diode will be
analyzed and then compared to that of the basic half-wave
rectifier consisting only of a resistive load. Derivation of the
equations for the ripple factor for the three half-wave rectifier
circuits will first be presented. From these results, plots will be
generated using Pspice that will allow us to conveniently
compare the ripple factor performance of each of the rectifiers
INTRODUCTION
In power conversion circuits, the actual output waveform
of any converter constructed from the input sources will in
general be different from the input. This tells us that the
output must contain unwanted components along with the
wanted components. These unwanted components are
unfortunately unavoidable and they can be described as the
Fourier components. The complete collection of unwanted
components defines distortion. The terms harmonic distortion
or simply harmonics refer to this unwanted behavior.
Particularly in dc application such as that of rectifier circuits,
the collected unwanted components are typically referred to
by the term ripple. A more specific definition is ripple factor
which is a tool to measure how much deviation the converter
output parameter has from its nominal designed value
THE BASIC HAW-WAVE RECTIFIER
Rectification is the process of converting ac power to dc
power. An uncontrolled rectifier uses only diodes as
rectifying elements. The dc output voltage is fixed in
magnitude by the amplitude of the ac supply voltage.
However, the dc output is not pure, that is, it contains
significant ac components or ripple. To suppress this ripple, a
filter is typically inserted after the rectifier. The simplest
circuit configuration of rectifier is the half-wave rectifier and
is shown in figure 1. Here, the half-wave rectifier circuit
whose source voltage is a sine wave is supplying a purely
resistive load. During the positive half cycle, when the
voltage at the anode is positive with respect to the cathode,
the diode turns on. This allows current through the load
resistor. Thus, the load voltage follows the positive half sine
wave. During the negative half-cycle, the voltage at the anode
becomes negative with respect to the cathode and the diode
turns off. There is no current flows through R. Figure 2
shows the output voltage waveform of the half-wave rectifier
using an input waveform of i, sinm and with frequency of
60Hz.
CONCLUSIONS
In this paper, the ripple factor characteristics of three
different circuit configurations of the half-wave rectifiers
were investigated. Several examples on how to derive the
equations for the average and rms values were presented from
which the expression for the ripple factor can further be
obtained. Results from computer simulations were provided
and several plots were included from five different cases.
From these results, it is clear that the smallest and therefore
the best ripple factor can be obtained when inductive load
with the extra freewheeling diode is used. Further work for
this project will include, but not limited to, lab
implementations and measurements of these circuits to
supply us with empirical results which can then be compared
with those results that are obtained from the computer
simulations.