32
Converter for armature supply using
a fully controlled three-phase bridge connection
B6C connection (6RA80..-..S22-0AA0):
Operation in one electric current direction and two
voltage directions. Fully controlled three-phase bridge connection, 2Q device
acc. to catalog.
As this is a fully controlled connection, the output voltage can accept negative values by
operation in the inverter range (see formula for calculating the output DC voltage of the
converter). This 2Q device allows driving in the speed forward direction and braking in the
speed reverse direction without any further measures, simply by offsetting the firing angle.
With this characteristic, negative output voltage in the converter range, it is possible by
switching over the motor field to implement braking operation in the forward rotation direction
and driving operation in the reverse rotation direction. By reversing the polarity of the field
current in the motor the induced motor voltage assumes negative values and the motor
outputs a negative torque (braking torque) with constant positive current direction and
negative motor voltage. So field reversal makes operation in all four quadrants possible (See
Operating Instructions Chapter 10.26). Please note that motor field reversal can only be
performed within a few seconds, demanding a 4Q device for transition to braking operation in
dynamic operations.
However, field reversal can be used to permit braking of large masses in one direction of
rotation or if operation in the opposite direction of rotation is required.
Note:
For field reversal, an overvoltage protective circuit must be configured at the output of
the field converter. This protective circuit must be able to absorb the energy content of the
field winding W[Ws] = L[H] * I
2
[A] / 2.
Any resulting overvoltages must not exceed the value of the blocking voltage of the valves of
the field converter.
Connection (B6)A(B6)C (6RA80..-..V62-0AA0):
Circulating-current-free inverse-parallel
connection of two fully controlled three-phase bridge rectifiers: 4Q device, operation in both
current directions and both voltage directions possible. Circulating-current-free means that
the current must be reduced to zero in the one current direction before the opposite current
direction is enabled. By implementing suitable current actual value acquisition in 6RA80, fast
reversal of the torque direction is possible (typically 3.3 ms at 50 Hz), allowing the retrofitting
of old circulating-current-carrying converters with 6RA80 with almost no significant
disadvantages.
With this 4Q device, driving and braking in both motor directions of rotation
is possible with high dynamic response of the control without any additional measures.
Motor operation on the converter, speed n and torque M:
n
n
M
M
B6C one current
direction
(B6)A(B6)C or B6C
with field reversal