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30 Operation principle and hardware description
1
3 ~
1
AC fuses
2
LCL filter
3
Supply module (with IGBTs)
4
DC capacitors with discharge resistors
5
DC fuses
AC voltage and current waveforms
￭
The AC current is sinusoidal at a unity power factor. The LCL filter suppresses the AC
voltage distortion and current harmonics. The high AC inductance smooths the line voltage
waveform distorted by the high-frequency switching of the converter. The capacitive
component of the filter effectively filters the high-frequency (over 1 kHz) harmonics.
Charging
￭
Charging is needed to power up the DC link capacitors smoothly. Discharged capacitors
cannot be connected to the full supply voltage. The voltage must be increased gradually
until the capacitors are charged and ready for normal use. The drive contains a resistive
charging circuit consisting of fuses, contactor and charging resistors. The charging circuit
is in use after start-up until the DC voltage has risen to a predefined level.
Inverter unit
The inverter unit converts the DC back to AC that rotates the motor. It is also able to feed
the braking energy from a rotating motor back into the DC link. The inverter unit is controlled
by a type BCU control unit [A41].
2
3
4
5
DC
5
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