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3.3.4 Brake Option
For adjustable frequency drives equipped with the dynamic brake option, a brake IGBT along with
terminals 81(R-) and 82(R+) is included for connecting an external brake resistor.
The function of the brake IGBT (see Figure 3-8) 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 be returned
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 appli-
cation need, dissipating the energy outside of the control panel, and protecting the adjustable
frequency 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.
Figure 3.8: Brake option
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives
3 Internal Adjustable Frequency Drive Opera-
tion
MG.90.L1.22 - VLT
®
is a registered Danfoss trademark
3-11
3
Содержание VLT HVAC FC 100
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