ABB ACS1000i air-cooled, User Manual

Page: 50 / 174

03 POWER ELECTRONICS AND CABINET FEATURES
3BHS206977 E01 REV H ACS1000I AIR-COOLED USER MANUAL 50/174
3.4.12.1 Control principle
If the DC-link voltage rises above a preset limit, the control system of the ACS1000
automatically activates the braking chopper. A rise of the DC-link voltage can be caused by a
machine, feeding into the DC link or by an increase of the voltage in the rectifier of the
ACS1000.
Figure 3-21: Braking chopper design
3.4.12.2 Monitoring and protective functions
3.4.12.2.1 Current monitoring
Input currents of the braking chopper are monitored for overcurrent and imbalance in order to
detect any defective component in the circuit. The current can become imbalanced if one of the
IGCTs conducts a current permanently or if an IGCT fails to be switched on.
If a short-circuit or an imbalance is detected in the braking chopper, the drive is shut down.
3.4.12.2.2 Thermal protection
The braking chopper and the braking resistors are monitored for over-temperature by
the ACS1000.
In addition, an external thermal protection device can be connected to a digital input. As soon
as the temperature of the braking resistors exceeds the response threshold of the external
thermal protection device, the operation of the braking chopper is disabled and an alarm
message is displayed on the control panel of the ACS1000. Braking is then only possible when
the temperature falls below the threshold.
(1) Semiconductor stack
1