IEEE Power & Energy Magazine - Grid Edge 2023 - 33

PV
η (PV, Grid)
η-MPP-Tracking
Grid
PV
η (PV, Grid)
DIN EN 50530, IEC 61683
Grid
Battery
η (Battery)
(a)
(b)
figure 6. (a) Different energy conversion paths in PV battery systems require tracking of dynamic, time-dependent system
behavior. (b) Applicable norms for the individual conversion paths serve as guidelines for the new benchmarking concept.
single-branch feeders longer than 1 km.) Cost-benefit analyses
on these so-called smart grid technologies have identified
a significant cost savings potential for DSOs.
Figure 8 shows the outcome of a cost-benefit analysis for
two actual LV grids in Germany. In addition to various forms
of local reactive power provision and active power control
through state-of-the-art PV inverters, MV/LV OLTCs are
also monetarily benchmarked. The figure depicts the grid
reinforcement costs as well as the network and PV feedin
losses, expressed as NPVs, that arise in when a defined
amount of PV capacity is hosted and assuming the application
of the smart grid technologies mentioned above. Comparing
this approach with classical grid reinforcement reveals that
potential cost savings of more than 50% are associated with
the application of these smart grid technologies. The results
coincide with the outcomes of other studies in this field.
From a technical perspective,
volt/var control-which in Germany
is commonly known as Q(U) or
Q(V) control-through PV inverters
and other RES is currently
considered controversial by German
DSOs, inverter manufacturers,
and research institutions.
While some DSOs appreciate the
efficiency of volt/var control (reactive
power is provided only if it is
needed for voltage support), others
worry about potential instabilities
resulting from the voltage dependency
of many autonomously
controlled entities. Although the
stability question has not been
conclusively answered, there are
strong indicators that instabilities
associated with volt/var control
may be caused by inadequate
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figure 7. Development of active power flows 2009-2013, measured at a
110-kV/20-kV substation in the Bayernwerk AG service area.
ieee power & energy magazine
33
controller designs rather than the nature of the control itself.
Park controllers of utility-sized PV systems are good examples.
Unusually long communication dead times within a
park controller in combination with fast-acting PV inverters
can lead to unstable reactive power outputs that are solely
based on the control system's architecture. This problem may
seem arbitrary but can become a serious issue when park controllers
from third parties that do not technically match up
with the internal controller settings of the installed inverters
are used. Against this background, it is highly likely that German
grid codes will need to incorporate new requirements
specifying the relevant controller settings (permissible dead
times, filter time constants, and so on) in the years to come.
Active power curtailment of PV systems is presently just
allowed to guarantee the power system security. It is not yet
facilitated from the regulatory design to use active power
Measured at 110/20-kV Substation, Courtesy of Bayernwek AG
η-Load Adjustment
η (Battery, Loads)
Loads
Battery
η (Battery, Loads)
IEC 62509
Loads
Winter Peak Load
DIN EN 50530,
IEC 61683
η (Battery, Grid)
η (Battery, Grid)
η (PVs, Loads)
η (PVs, Loads)
η (PVs, Battery)
IEC 62509
η (PVs, Battery)
η-MPP-Tracking
Load Flow (MVa)
Reverse Power Flows
IEC 62509
Summer Peak Load

IEEE Power & Energy Magazine - Grid Edge 2023

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - Grid Edge 2023