3.3.4 Brake Option
For frequency converters 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 (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.
External placement of the brake resistor has the
advantages of selecting the resistor based on application
need, dissipating the energy outside of the control panel,
and protecting the frequency converter from overheating
when 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.
Internal Adjustable Frequen... Service Manual
42 Danfoss A/S © Rev. 2014-02-10 All rights reserved. MG94A222
33
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