Siemens sinamics dcp - 7.11.13 Switching frequency; 7.11.14 Actual value acquisition

Operation
7.11 Closed-loop control
SINAMICS DCP
Operating Instructions, 09/2019, A5E34382853K
349
7.11.13 Switching frequency
Either a fixed or variable switching frequency can be selected. The variable switching
frequency should be selected for those applications where it is required that at each
operating point the DCP achieves the highest possible efficiency.
● p55322 = 0: fixed switching frequency (factory setting)
– 30 kW device: 20 kHz
– 120 kW device: 15 kHz
● p55322 = 1: variable switching frequency
– At each operating point (= ratio, input/output voltage), the switching frequency is
reduced as far as possible.
–
Advantage: Improved efficiency
The efficiency increases at lower switching frequencies as a result of lower switching
losses in the power semiconductors.
– Disadvantage: The current control can be somewhat less steady.
– Note: Reducing the switching frequency can increase the current ripple inside the
device. As this ripple may neither result in overloading the power semiconductors nor
saturating the internal reactor, the possibility of reducing the frequency is restricted,
depending on the particular operating point.
For a voltage ratio of 1:2 or 2:1, in principle, the internal current ripple is the highest; in
this case, the frequency cannot be reduced. For a voltage ratio of 1:1, in principle, the
internal current ripple is the lowest; in this case, the frequency can be reduced the
most. However, the switching frequency is reduced by a maximum of 5 kHz.
● r55325: displays the actual switching frequency
Note
In addition, the switching frequency can also
be reduced for an overtemperature condition,
see Chapter "
Derating (Page 357)".
7.11.14 Actual value acquisition
See function diagram 6850 in the SINAMICS DCP List Manual.
The actual value acquisition provides all the actual values required for the closed-loop
control.
The most important values are available as BICO in standardized representation and also as
display parameters in physical units.
Basic information about current actual values:
The current actual value acquisition in the SINAMICS DCP acquires the reactor current. The
reactor is an energy store that takes the current from one voltage level to another. The
reactor current is always the current that flows on the side with the lower voltage. A lower
current flows on the side with the higher voltage.