Operation
7.11 Closed-loop control
SINAMICS DCP
Operating Instructions, 09/2019, A5E34382853K
347
● p55321 = 1 (activated):
As a result of the optimized pulse pattern, the power semiconductors are also clocked in
the transition range, so that all of the required modulation depths can be realized.
As a consequence, the current controller has a steadier control response in the transition
range.
● p55321 = 2 (activated with frequency derating):
Corresponds to the response for p55321 = 1; however, in the transition range, the pulse
frequency is additionally reduced, therefore reducing the switching losses.
In the transition range, the current ripple on both sides of the DCP is very low as the
voltages at both sides of the DCP are very low; as a consequence, reducing the switching
frequency does not noticeably influence the control response.
7.11.12 PV array flying restart
This function is required for SINAMICS DCP applications in photovoltaic systems with high
no-load voltage.
PV fields with a no-load voltage of up to 1000 V can be operated at the SINAMICS DCP
using this function - even if this voltage exceeds the continuous operating range of the
SINAMICS DCP.
When operated without load, a no-load voltage is available at the output terminals of a PV
array.
This high output voltage can be reduced by applying a load.
As a consequence, when the SINAMICS DCP is switched on, the "PV array flying restart"
function attempts to reduce the output voltage of the PV array by impressing a load current
so that it lies in the continuous operating range of the SINAMICS DCP:
● 30 kW device: U ≤ 800 V
● 120 kW device: U ≤ 920 V
See also Chapter "Technical specifications (Page 425)".
Clocked operation of the device is not possible for voltages that lie outside the continuous
operating range of the SINAMICS DCP. As a consequence, the load current is generated by
connecting side 1 and side 2 of the SINAMICS DCP with one another via the power
semiconductors (that are permanently turned on), the reactor (see function diagram 6830 in
the SINAMICS DCP List Manual) and the series resistors.
For p55110 = 1 or 2, function "PV array flying restart" is automatically executed after each
ON command (r0898.0 = 1). This is the reason that the function is already active during
precharging (operating state < o7) and the load current is limited by the precharging resistors
on that side of the DCP that is connected to the PV array.
These precharging resistors must be dimensioned so that on one hand the PV array voltage
can be reduced down into the continuous operating range of the SINAMICS DCP as a result
of an adequately high load current - and on the other hand, the voltage difference when
closing the main contactor is sufficiently low that the contactor is not damaged when it is
closed.
Function "Flying restart PV array" is exited once the SINAMICS DCP has reached the
operating state (o0), and the PV array voltage has reached the continuous operating range
of the device.
The load current that is obtained during the "Flying restart PV array" is then maintained for
5 s. Further, this load current is indicated in r55112 and can be used as starting value by
other functions (for example, the MPP tracker).
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