Eaton PowerXL DC1, Manual

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6 Parameters
6.2 Digital and analog inputs
132
DC1 Frequency Inverter 10/12 MN04020003Z-EN www.eaton.com
6.2.11.2 Regenerative braking
If the rotor of an asynchronous motor is driven oversynchronously in the
operating direction of the rotating field, it generates electric power via its
stator windings. The motor then becomes a generator. In the frequency
inverter, this generative energy causes an increase in the DC link voltage.
Oversynchronous speeds occur, for example, when the output frequency in
frequency inverter operation is reduced with short deceleration times, the
connected machine has a large flywheel mass or when the flowing medium
in pumps and fans works against the speed reduction.
The increase in the DC link voltage is monitored by the DC1 frequency
inverter and always enables a braking torque of approx. 30 % of the rated
motor torque. A higher braking torque can be achieved with a more powerful
frequency inverter. A brake chopper is integrated into DC1 frequency invert-
ers of size FS2 and larger. When used in conjunction with an external high-
capacity resistor, this brake chopper makes it possible to achieve braking
torques of up to 100 % of the rated motor torque.
The external braking resistor is connected via terminals DC+ and BR.
Figure 79: Regenerative braking with external braking resistance
a
Machine flywheel mass
b
Inverter with brake chopper (braking transistor)
c
Braking resistance (R
B
) Energy flow (braking torque)
The brake chopper can be activated in parameter P-34. This function is only
available in frequency inverters of size FS2 and FS3.
￫
In frequency inverters without a braking transistor, parameter
P-34 has no function.
M
R
B
3
˜
a
b
c
i
R+
R-