Sequence Of Operation; Rectifier Section; Intermediate Section; Inverter Section - Danfoss VLT Refrigeration Drive FC 103 Design Manual

Product Overview
2.2.1 Control Structure Principle
•
2 2
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
L1 91
L2 92
L3 93
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.
18
®
VLT Refrigeration Drive FC 103
Load sharing +
89(+)
R inr
88(-)
Load sharing -
P 14-50 R Filter
Danfoss A/S © 08/2015 All rights reserved.
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
circuit behaviour of the frequency converter depends on
the 3 current transducers in the motor phases.
LC Filter +
(5A)
Inrush
LC Filter -
(5A)

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.
+
. Short-
R+ Brake
Resistor
82
R-
81
U 96
V 97
M
W 98
MG16G202