Sequence Of Operation; Rectifier Section; Intermediate Section; Inverter Section - Danfoss VLT AQUA Drive FC 202 Design Manual

Product Overview
The adjustable frequency drive manages various motor
2 2
control principles such as U/f special motor mode and VVC
+
. Short-circuit behavior of the adjustable frequency drive
L1 91
L2 92
L3 93
Figure 2.10 Adjustable Frequency Drive Structure

2.3 Sequence of Operation

2.3.1 Rectifier Section

When power is applied to the adjustable frequency drive, it
enters through the line power terminals (L1, L2, and L3)
and on to the disconnect and/or RFI filter option,
depending on the unit configuration.

2.3.2 Intermediate Section

Following the rectifier section, voltage passes to the
intermediate section. A sine-wave 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
optimal performance and minimal losses in the motor.
20
Load sharing +
Load sharing -
P 14-50 R Filter
+ PWM principle at the control card, provides
Danfoss A/S © 09/2014 All rights reserved.
®
VLT AQUA Drive FC 202
depends on the three current transducers in the motor
phases.
LC Filter +
89(+)
(5A)
R inr Inrush
88(-)
LC Filter -
(5A)

2.3.4 Brake Option

For adjustable frequency drives equipped with the
dynamic brake option, a brake IGBT along with terminals
81(R-) and 82(R+) are included for connecting an external
brake resistor.
The function of the brake IGBT is to limit the voltage in the
intermediate circuit whenever the maximum voltage limit
is exceeded. It does this by switching the externally
mounted resistor across the DC bus to remove excess DC
voltage present on the bus capacitors.
External brake resistor placement has the advantages of
selecting the resistor based on application need,
dissipating the energy outside of the control panel, and
protecting the drive from overheating if the brake resistor
is overloaded.
The brake IGBT gate signal originates on the control card
and is delivered to the brake IGBT via the power card and
gate drive card. Additionally, the power and control cards
monitor the brake IGBT and brake resistor connection for
short circuits and overloads. For pre-fuse specifications,
refer to chapter 7.1 Electrical Data. See also
chapter 7.7 Fuses and Circuit Breakers.
R+ Brake
82 Resistor
R-
81
U 96
V 97
M
W 98
MG20N622