Additional Closed-Loop Controls Function Module; Reactive Current/Apparent Current Limits - Siemens SINAMICS S120 System Manual
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5.3.5
Additional closed-loop controls function module
5.3.5.1
Reactive current/apparent current limits
Background
Using current limits, the operating behavior of the Active Line Module can be adapted to
address the requirements of an application. Current limits are available for various current
types, operating states and parameter types.
The following differences apply:
● Active current
Percentage grid current that is in phase with the grid voltage and which results in an
active power exchange between the load connected to the DC link and the grid.
● Reactive current
Percentage grid current with a phase shift of 90° to the grid voltage. A reactive current
results in a voltage drop across grid inductances and capacitances, as well as losses in
the ohmic components of the grid impedance. However, the reactive current is not
involved with exchanging power between the load connected to the DC link and the grid.
● Apparent current
The vectorial sum of the active current and reactive current results in the total current
called the apparent current. Limiting the current amplitude in each line phase
corresponds to apparent current limiting.
● Negative sequence system current
In the case of unsymmetrical 3 AC currents (different amplitudes in the grid phase arms),
it is possible to mathematically break down the currents into positive sequence system in
synchronism with the grid voltage (basic fundamental of active and reactive current) and
a current vector rotating in the opposite direction (what is known as the negative
sequence system).
For example, negative sequence systems occur for 2-phase line dips, and do not
participate in the average value of the active power over a fundamental (frequency)
period, but generate power harmonics with twice the grid frequency.
Note
Definition of active power
The active power exchanged between the load and grid is defined as the integral of the
product of voltage and current over one grid period. The instantaneous values for the
currents (e.g. r0076, r0078) calculated by the closed-loop control, are not average values
over a fundamental (frequency) period, but also include harmonic components.
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System Manual, 04/2015, A5E03347436A
Function modules
5.3 Description of the function modules
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