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

Basic Operating Principles
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 frequency
converter, 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 2
different configurations.
In one method, the terminals are used to tie the DC-bus
circuits of multiple frequency converters 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 the mains. Attempting such a configuration
requires specific considerations and should not be
attempted without first consulting Danfoss application
engineering.
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VLT AutomationDrive FC 301/FC 302 Design Guide, 0.25-75 kW
In the second method, the frequency converter 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 frequency converter receives control input from
several sources.
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When wired and properly programmed, the control
terminals provide feedback, reference, and other input
signals to the frequency converter; output status and fault
conditions from the frequency converter, relays to operate
auxiliary equipment, and serial communication 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.
MG33BF02 - Rev. 2013-12-20
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)
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