Active Current Limiting; Reactive And Apparent Current Limiting - Siemens SINAMICS S120 System Manual

7.10.2

Active current limiting

The limits for the active current can be set to different values for the two energy flow
directions "motoring" and "generating".
If the motoring current limit is reached, then less active current is injected into the DC link
than is specified by the active current setpoint. Generally, the DC link voltage would
decrease; however, only up to the rectified value (V
load. Below this DC link voltage, as a result of the design, uncontrolled recharging currents
flow, similar to those of a diode bridge circuit. As a consequence, the active current limiting
when motoring is only effective under the condition that the DC link voltage is appropriately
high.
For example, the active current limiting can be used to reduce the magnitude of the grid
current peaks during load cycles (this has the disadvantage of higher DC link voltage
fluctuations) - or if the DC link voltage control, at least temporarily, is realized using another
component in the DC link.
7.10.3

Reactive and apparent current limiting

The reactive current can be limited, separately for capacitive (r0075 > 0) and inductive
(r0075 < 0) reactive current setpoint (p3525, p3526). Dynamic limits are also possible using
the appropriate BiCo interconnection (p3524).
When using the apparent current limit p3527, initially, the reactive component is reduced
(possibly down to 0) before the active current setpoint is adapted.
The associated display parameters for current actual values and status signals should be
taken from function block diagram FP8945.
Here we would like to make reference to the derating characteristic (SINAMICS Low Voltage
Engineering Manual) for continuous operation with cosφ not equal to one.
Figure 7-10
Grid infeed
System Manual, 04/2015, A5E03347436A
Derating characteristic for cosφ not equal to one
7.10 Commissioning supplementary controls
≈ 1.35 V ), which is dependent on the
dc grid
Commissioning
133