Brake Option; Load Sharing; Control Interface - Danfoss VLT AutomationDrive FC 301 Series Design Manual

Basic Operating Principles

3.3.4 Brake Option

For adjustable frequency drives equipped with the
dynamic brake option, a brake IGBT along with terminals
3 3
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. Excess DC bus
voltage is generally a result of an overhauling load causing
regenerative energy to return to the DC bus. This occurs,
for example, when the load drives the motor causing the
voltage to return to the DC bus circuit.
Placing the brake resistor externally 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.

3.3.5 Load Sharing

Units with the built-in load sharing option contain
terminals (+) 89 DC and (–) 88 DC. Within the adjustable
frequency drive, these terminals connect to the DC bus in
front of the DC link reactor and bus capacitors.
The use of the load sharing terminals can take on two
different configurations.
In one method, the terminals are used to tie the DC bus
circuits of multiple adjustable frequency drives together.
This allows one unit that is in a regenerative mode to
share its excess bus voltage with another unit that is
running a motor. Load sharing in this manner can reduce
the need for external dynamic brake resistors while also
saving energy. In theory, the number of units that can be
connected in this way is infinite; however, each unit must
be the same voltage rating. In addition, depending on the
size and number of units, it may be necessary to install DC
reactors and DC fuses in the DC link connections and AC
reactors on line power.
16
Design Guide
Attempting such a configuration requires specific consider-
ations and should not be attempted without first
consulting Danfoss application engineering.
In the second method, the adjustable frequency drive is
powered exclusively from a DC source. This is a bit more
complicated. First, a DC source is required. Second, a
means to soft charge the DC bus at power-up is also
required. Last, a voltage source is required to power the
fans within the unit. Again such a configuration should not
be attempted with out first consulting Danfoss application
engineering.

3.4 Control Interface

3.4.1 Control Principle
The adjustable frequency drive receives control input from
several sources.
•
•
•
When wired and properly programmed, the control
terminals provide feedback, reference, and other input
signals to the adjustable frequency drive; output status
and fault conditions from the adjustable frequency drive,
relays to operate auxiliary equipment, and serial communi-
cation interface. A 24 V common is also provided. Control
terminals are programmable for various functions by
selecting parameter options through the local control
panel (LCP) on the front of the unit or external sources.
Most control wiring is customer supplied unless factory
ordered.
Rev. 2014-04-04 All rights reserved.
Local control panel (hand mode)
Programmable analog, digital, and analog/digital
control terminals (auto mode)
The RS-485, USB, or serial communication ports
(auto mode)
MG33BF22