2.2.1 Control Structure Principle
•
The frequency converter rectifies AC voltage from
mains into DC voltage.
•
The DC voltage is converted into an AC current
with a variable amplitude and frequency.
The frequency converter supplies the motor with variable
voltage/current and frequency, which enables variable
speed control of 3-phased, standard asynchronous motors
and non-salient PM motors.
The frequency converter manages various motor control
principles such as U/f special motor mode and VVC
+
. Short-
circuit behaviour of the frequency converter depends on
the 3 current transducers in the motor phases.
Inrush
R inr
Load sharing -
Load s
LC Filter -
(5A)
LC
(5A)
Brake
Resistor
130BA193.14
M
L2 92
L1 91
L3 93
89(+)
88(-)
R+
82
R-
81
U 96
V 97
W 98
P 14-50 Rfi Filter
Illustration 2.7 Frequency Converter Structure
2.3 Sequence of Operation
2.3.1 Rectifier Section
When power is applied to the frequency converter, it
enters through the mains terminals (L1, L2, and L3).
Depending on the unit configuration, the power moves on
to the disconnect and/or RFI filter option.
2.3.2 Intermediate Section
Following the rectifier section, voltage passes to the
intermediate section. A filter circuit consisting of the DC
bus inductor and the DC bus capacitor bank smoothes the
rectified voltage.
The DC bus inductor provides series impedance to
changing current. This aids the filtering process while
reducing harmonic distortion to the input AC current
waveform normally inherent in rectifier circuits.
2.3.3 Inverter Section
In the inverter section, once a run command and speed
reference are present, the IGBTs begin switching to create
the output waveform. This waveform, as generated by the
Danfoss VVC
+
PWM principle at the control card, provides
optimal performance and minimal losses in the motor.
Product Overview
VLT
®
Refrigeration Drive FC 103
18
Danfoss A/S © 08/2015 All rights reserved.
MG16G202
2
2
Содержание VLT FC 103
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