The second lecture of the inverter , let's continue our course about that :
In this lecture we will educate the fillter of the inverter :
Output Line Filters For PWM Inverter Fed Induction Motor :
It is well known that inverter could produce very asymptotic stream to form sinus
(sinusoidal) but abroad effort inverter not as sinus where exposed to high for cutting,
which may cause the collapse of the isolation of the engine directly due to high
voltage which may result due to the switching or also causes a breakdown of the
insulation after a period of operating.
If it is clear that the frequency of switching directly on unarmed affects motor and
cable nutritious too.
In practice chipping up to 12KHz frequency and which leads to a very high rate of
voltage change with time dv / dt, which in turn causes the extreme diligence
insulation.The following figure, for example, shows the shape of the voltage wave emerging
from inverter works at a rate cutting 6KHz and at a frequency of 50Hz and the
distance between the engine and inverter 750ft voltage of 400 volts. It has been
observed that there is an effort for waves of up to 1460 volts.
In this example conductive cables inverter represent to the engine as if it T.L transfer
high-voltage lines on the outskirts of the motor causes the well-known phenomenon
of a counter waves Reflected waves.
high-voltage lines on the outskirts of the motor causes the well-known phenomenon
of a counter waves Reflected waves.
It is also noted that the engine is exposed to changes in the high-voltage dv / dt any
voltage pulses are changing too high a value in a very small time. And the number of
these pulses in a given time determined by the switching frequency or rate used in
the shredder inverter . This may in turn lead to the collapse of isolating the engine.
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| The Output Voltage of the inverter |
This prompted the designers of engines to be considerate design spectrum at the
same engine for example NEMA category B engine is designed to withstand
momentary voltage up to 1000 V a time of rising Rise time is not less than 2
microseconds or dv / dt less than 500 volts per microsecond one.
And here it appeared the urgent need to use filters to reduce the dv / dt value
experienced by the engine.
When the engine is fed long cables, it works as lines transfer the equivalent circuit
and him are as shown in the figure below. And based the value of C capacitance, L
inductance along the cable.
same engine for example NEMA category B engine is designed to withstand
momentary voltage up to 1000 V a time of rising Rise time is not less than 2
microseconds or dv / dt less than 500 volts per microsecond one.
And here it appeared the urgent need to use filters to reduce the dv / dt value
experienced by the engine.
When the engine is fed long cables, it works as lines transfer the equivalent circuit
and him are as shown in the figure below. And based the value of C capacitance, L
inductance along the cable.
 |
| The equivalent circuit for T.L |
And recovery of transmission lines when the impedance characteristics of the
transmission line be less than the impedance load rebound occurs Reflection voltage
and current phenomenon and that my cases of Switching and the voltage on the
outskirts of the biggest pregnancy. The following table shows the increase coefficient
relationship effort apostate p with an engine capacity of:
transmission line be less than the impedance load rebound occurs Reflection voltage
and current phenomenon and that my cases of Switching and the voltage on the
outskirts of the biggest pregnancy. The following table shows the increase coefficient
relationship effort apostate p with an engine capacity of:
Types of the fillter :
1-Sine wave filter :
The second method, a so-called low pass sine wave filter is composed of inductive
reactance reactor and inductive reactance capacitor imp on the outskirts of inverter .
As in the following figure :
2- Reactor Filter :
The third way is to use only reactor in a row with the parties inverter The following
figure shows the way plug and voltage after the filter. It is noted that the effort began
to be affected by the impact of prompt PWM and have the time of high voltage greater
than 4 microseconds and this is very desirable.
1. engine from the bad influence of the length of the cable connection protection.
2. reduce the dv / dt of the effort on the outskirts of the engine.
3. extend the life of power components inverter.4- reduce the harmonic.
5. Reduce the high currents sudden surge current.
6. Reduce the temperature of the engine.
7. improve the ability to run the engine plants.
The following figure illustrates the delivery of the filter on the outskirts of inverter :
Connecting the Inverter with the engine :
First explain programmed and the Key Pad its own ways:
AC DRIVE MICRO MASTER 420 Type :
AC DRIVE MICRO MASTER 420 TERMINALS
AC DRIVE MICRO MASTER 420 PARAMETERS
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