Baumuller b maXX 5500, Instruction Handbook Manual

Page: 219 / 316

Operation
Instruction handbook b maXX BM5500, BM5600, BM5700
Document No.: 5.13008.10
219
of 314
8
8.2 Power on switching frequency / DC link charging
8.2.1 Power supply switch-on frequency BM551X and BM552X
The devices use a rectifier with 6 diodes (B6U circuit). There is a resistor between rectifier
and DC link capacitor limiting the charging surge. The resistor is bridged by a relay after
the charging. Smaller waiting periods between the DC link discharge and charge reduce
the lifetime of the devices. The specified waiting time of the device is increased to at least
90 seconds when an additional external DC link capacitance is connected. The maximum
permitted external DC link capacitance depends on the power supply voltage (refer to
Z Figure 36 – on page 66).
8.2.2 Power supply switch-on frequency BM5X3X to BM5X7X
The devices use a rectifier with 3 diodes and 3 thyristors (B6HK circuit). The circuit mea-
sures the voltage on the phase conductor and the DC link. The corresponding thyristor is
fired if the phase conductor voltage minus DC link voltage is lower than a fixed threshold.
Thereby an almost constant voltage time area is applied to the series connection of phase
conductor and DC link capacitor. The charge of the DC capacitor is done with current
pulses of approx. same level. This level depends on the inductance of the commutation
choke, the impedance of the power supply and the power supply voltage. The thyristors
are fired if the DC link is charged to 50 V difference between peak power supply voltage
and DC link voltage and there is a potential drop in blocking direction. The thyristor shows
a behavior like a diode.