09-07-2012, 12:26 PM
Single-Phase Pulse Width Modulated Rectifier
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Introduction
At the beginning of the 19th century, electric energy came
into use in many technical fields. From the beginning ways
were sought to change parameters such as voltage, frequency
and current. The converters of electric parameters can
be divided into two main groups. The first group uses for
change the Faraday’s law of induction e.g. the Ward-Leonard
drive. The second group includes converters that work on the
controlled switching principle, i.e., semiconducting rectifiers,
inverters, etc.
Phase controlled rectifiers
The electric energy conversion made by semiconducting
converters is being used more and more. This had led to the
growth of negative phenomenons, that appeared negligible,
when only a few converters being used. However the development
of semiconductor structures has enabled higher power
to be transmitted and has also led to wide spread of converters.
In this way, converters have a negative effect on the
supply network. The regressive effects of overloads with harmonics
and reactive power consumption are becoming major
disadvantages of phase controlled (mostly thyristor) rectifiers.
These side effects need to be compensated by additional filtering
circuits with capacitors or inductances. However, such
circuits raise the costs and also increase material and space
requirements for the converter.
PWM rectifiers
In order to suppress these negative phenomena caused by
the power rectifiers, use is made of rectifiers with a more sophisticated
control algorithm. Such rectifiers are realized by
semiconductors that can be switched off IGBT transistors.
The rectifier is controlled by pulse width modulation. A rectifier
controlled in this way consumes current of required
shape, which is mostly sinusoidal. It works with a given phase
displacement between the consumed current and the supply
voltage. The power factor can also be controlled and there are
minimal effects on the supply network.
Control of the PWM rectifier
The rectifier consists of 4 IGBT transistors, which form
a full bridge, the input inductance and the capacitor at
the output. It is controlled by pulse width modulation. Supply
voltage Us and the voltage at the rectifier input Ur are
sinusoidal waveforms separated by the input inductance.
Measurement results
A functional sample of the PWM rectifier was built. The
control algorithm was realized on the basis mentioned
above. Four IGBT transistors act as the power part, and a
MOTOROLA 56F508 controller microprocessor was chosen.