A07402 — Drive: DC link voltage minimum controller active

Alarm A07402 tells you that the drive has switched in its DC link voltage minimum controller (Vdc_min controller). This happens when the DC link voltage drops below the lower switch-in threshold. For vector control and U/f the manual references the switch-in levels r1246 and r1286; for servo operation the lower threshold p1248 applies. While the controller is active, the motor's kinetic energy buffers the DC link, so the drive brakes itself, and a deviation between the speed setpoint and the actual speed can occur. Depending on the drive configuration, the same condition can also be output without any reaction (N).

• The DC link voltage undershot the lower switch-in threshold, and the drive responded by activating the DC link voltage controller.
• The manual names one possible cause for this: the line supply has failed.

1. No remedy is necessary at first: the alarm withdraws on its own once the DC link voltage distinctly exceeds the lower threshold again, and it disappears when the line supply returns.
2. If it keeps coming back, check the line supply and the infeed.
3. Increase the ramp-up time p1120.
4. As a last measure, switch the Vdc_min controller off by setting p1240 = 0.

• p1248 — lower DC link voltage threshold; in servo operation this is the switch-in threshold for the minimum controller.
• r1246 — Vdc_min controller switch-in level (kinetic buffering), which the manual references when the threshold is undershot.
• r1286 — the same switch-in level for U/f control.
• p1240 — Vdc controller configuration; set it to 0 here to shut the Vdc_min controller down.
• p1280 — the Vdc controller configuration for U/f control.
• p1120 — ramp-function generator ramp-up time; the manual's remedy is to increase it when this alarm occurs.

The alarm needs no acknowledgement and clears itself: it is withdrawn automatically once the DC link voltage distinctly exceeds the lower threshold again, or when the line supply returns.