Feed-in inverters must assist with frequency stability in the grid. If the grid frequency leaves the normal tolerance range
(e.g. ±200 mHz), then the grid is in a critical state. In the event of overfrequency, there is a generation surplus, in the
event of underfrequency, there is a generation deficit. In the case of overfrequency, photovoltaic systems and electrical
storage systems must reduce their active feed-in power in relation to the increase in frequency. The P(f) function is avail-
able for this purpose.
That being said, the availability or the adjustability of the functions may be limited depending on the country setting se-
lected. This is particularly true if the applicable grid connection guidelines make this restriction compulsory.
P constant
The function "P constant" is available for managing load flows in a plant. If necessary, this can be used to reduce the feed
of a photovoltaic inverter.
P constant has been conceived for use with Plant Controllers and is therefore only available via communication and can-
not be adjusted on the display/web interface. You can find detailed information on the communication protocol at
in the “Software” subsection of the “Downloads” section.
When a target value is received for P limit, the specified power value is set by the inverter. If the specification is changed
(e.g. via communications interfaces), the new value is adopted by way of a filter and a gradient limit. Depending on the in-
verter series, the settling time and gradient limitation may be adjustable.
If the applicable grid connection guidelines call for the active power to be adjusted to the target value with a defined gra-
dient or a defined settling time, then the blueplanet 87.0 TL3 to 150 TL3 can be configured in such a way that this gradi-
ent is adhered to. In addition, the gradient can also be implemented on the plant controller. This second solution is to be
used for all other inverters.
Dynamics / accuracy
In all of the control methods described below the specified target value at the inverter’s connection terminals is adjusted
using a stationary deviation of the reactive power of maximum 2% S
N
.
The transient response of the control methods is determined by a PT-1 filter. In this case, the set settling time corre-
sponds to 5 Tau, or in other words, achieving approx. 99% of the final value for a PT-1 filter. Subject to the control
method selected, there are also other parameters that determine dynamic behavior.
Methods for controlling the active power of feed-in inverters may be necessary for local management of load flows, for
voltage stability in the distribution network and for ensuring the stability of the interconnected network.
The device makes use of the following functions in order to control the active power. These are described in the following
section:
P set (MPPT/communication) Active power limitation [See section 10.4.1
P limit (communication) Active power limitation [See section 10.4.1
P(U) (characteristic) Voltage-dependent power reduction P(U) [See section 10.4.2
P(f) (characteristic) P(f) [See section 10.4.3
10.4.1 Active power limitation
P set
The function P set is intrinsically integrated in PV inverters in the MPP-tracking of the inverter. The P set value is con-
stantly recalculated based on the MPP tracking algorithm.
P limit
The function "P limit" is available limiting the maximum infeed power. If necessary, this can be used to reduce the in-feed
of an inverter e.g. for congestion management of the distribution system operator.
P limit is available via MODBUS/SunSpec inverter model 123
WMaxLimPct
and RS485 communication only. For detailed
information on the communication protocol please refer to the download section at
“Software”.
KACO blueplanet 87.0 TL3 KACO blueplanet 92.0 TL3 KACO blueplanet 110 TL3 KACO blueplanet 125 TL3
KACO blueplanet 137 TL3 KACO blueplanet 150 TL3
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