Solar Integration Workshop, Berlin, 24.10.2017 Mathias Schoeneberger, Sören Patzack, Hendrik Vennegeerts Forschungsgemeinschaft für elektrische Analgen und Stromwirtschaft e.V. (FGH) Marco Lindner, Rolf Witzmann Technical University of Munich (TUM) Derivation of a Q(U)-control tolerance band for inverters in order to meet voltage quality criteria
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Mathias Schoeneberger , Sören Patzack, Hendrik Vennegeerts
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Solar Integration Workshop, Berlin, 24.10.2017
Mathias Schoeneberger, Sören Patzack, Hendrik Vennegeerts
Forschungsgemeinschaft für elektrische Analgen und Stromwirtschaft e.V. (FGH)
Marco Lindner, Rolf Witzmann
Technical University of Munich (TUM)
Derivation of a Q(U)-control toleranceband for inverters in order to meetvoltage quality criteria
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 2
SIW 2016
„Stability Assessment for Automated Voltage Controlling Equipment in
Distribution Grids“
one key finding:
Q(U)-control with PT1 behavior can ensure voltage stability in distribution
networks, while increasing the hosting capacity
last years outlook: tolerance band for stability evaluation of controls
what are testing scenarios in order to ensure sufficient limitation of over-
shoot and setting time for all real situations?
what are the maximum allowed deviations from the ideal PT1 behavior?
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 3
SIW 2016
„Stability Assessment for Automated Voltage Controlling Equipment in
Distribution Grids“
one key finding:
Q(U)-control with PT1 behavior can ensure voltage stability in distribution
networks, while increasing the hosting capacity
last years outlook: tolerance band for stability evaluation of controls
what are testing scenarios in order to ensure sufficient limitation of over-
shoot and setting time for all situations?
what are the maximum allowed deviations from the ideal PT1 behavior?
what is a reasonable value for x?
Q
t
x %
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 4
Agenda
motivation for Q(U)-control in distribution networks
dynamic behavior, stability and voltage quality
requirements in standards for inverters with Q(U)-control
methodology for tolerance band derivation
results
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 5
Distributed Generation with Q(U)-control
Dynamic Modelling of Automated Voltage Controlling Equipment
ideal model of DG with Q(U)-control
simplified block representation
PT1-output-characteristic required in EN 50438
slope gradient
hysteresis
Q
U
dead-band
measurement
U
QDGUPCC
Q(U)-
characteristic PT1
grid
U
Q
UQset
Q(U)-control
PCC: point of common coupling
Q(U) Parameters
measurement delay Tm
slope gradient Kslope
PT1 time constant TPT1
PT1 gain KPT1
FGH e.V. | M. Schoeneberger | Stability Assessment for Automated Voltage Controlling Equipment in Distribution Grids 6
Distributed Generation with Q(U)-control
Dynamic Modelling of Automated Voltage Controlling Equipment
ideal model of DG with Q(U)-control
simplified block representation
PT1-output-characteristic required in EN 50438
Q(U) Parameters
measurement delay Tm
slope gradient Kslope
PT1 time constant TPT1
PT1 gain KPT1
measurement
U
QDGUPCC
Q(U)-
characteristic PT1
grid
U
Q
UQset
Q(U)-control
first order lag element
PCC: point of common coupling
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 7
Motivation for Q(U)-control in distribution networks
characteristic rural network
scenario
reg
ula
rtr
an
sfo
rma
r
no voltage-
control
Q(U) 0.95
Q(U) 0.9
cosϕ(P) 0.95
cosϕ(P) 0.9
VR
DT
no voltage-
control
Q(U) 0.95
Q(U) 0.9
cosϕ(P) 0.95
cosϕ(P) 0.9
70
90
104
98
123
231
226
222
217
205
0 200 400 600
0 100 200 300
1
2
3
4
5
6
7
8
9
10
Maximale Netzanschlusskapazität
Investitionen Spannungshaltungskonzept
Investitionen konventioneller Netzausbau
source: FNN-study on new methods for static voltage control
investment in €/kWp
hosting capacity in kWp
maximal hosting capacity
investment voltage controlling equipment
investment network expansion
0.95; 0.9: cosϕ(P)min
voltage rise can limit the further
integration of distributed generation (DG)
static voltage control of DG shows
a significant cost benefit
in comparison to network expansion
positive interplay of Q(U)-control
with voltage regulated distribution
transformers (VRDTs)
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 8
Motivation for Q(U)-control in distribution networks
0
5
10
15
20
25
30
35
40
45
Re
act
ive
En
erg
y[G
varh
]
Grid 1 Grid 2 Grid 3 Grid 4
Grid 5 Grid 6 Grid 7 Grid 8
voltage rise can limit the further
integration of distributed generation (DG)
static voltage control of DG shows
a significant cost benefit
in comparison to network expansion
positive interplay of Q(U)-control
with voltage regulated distribution
transformers (VRDTs)
significant reduction of reactive energy
infeed from distributed generators
with Q(U)-control
Q(U)-control should be default setting for
voltage control
source: “U-Control – Recommendations for Distributed and
Automated Voltage Control in Current and Future Distribution
Grids”, SIW 2017
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 9
Voltage Stability
Closed Control Loop
Q(U)-control represents a closed control loop
and can in some cases be prone to unstable behavior
oscillation of reactive power infeed
<-> oscillation of voltage
0
0 ? t
Q
t
Q
ideal dynamic
behavior
unwanted
oscillations
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 10
Voltage Stability
Closed Control Loop
Q(U)-control represents a closed control loop
and can in some cases be prone to unstable behavior
oscillation of reactive power infeed
<-> oscillation of voltage
example shows
slow oscillation: f ≈ 0.05 Hz
Stability assessment required
0
0
Source: ETG/FNN Schutz- und Leittechnik Tutorial 2016,
„Auswirkung von Parkregelungskonzepten auf die Netzstabilität“
-3,00
-2,00
-1,00
0,00
1,00
2,00
3,00
19,80
20,00
20,20
20,40
20,60
20,80
21,00
21,20
Voltage Reactive Power
Uref
U [kV]
Q[Mvar]
exemplary field test data with
erroneous controller parameters
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 11
Worst-Case Assumptions for Stability Assessment
Critical Network
impact of Q(U)-control on the local voltage increases with
increasing available reactive power (Qmax)
increasing impedance (X) /increasing line length (l)
increasing slope gradient (Kslope)
identification of a critical network using the reactive power impact
parameter QIP
analysis of more than 200 low voltage networks*
highest QIP for a network with 19 DG units
with ∑ 1000
critical unit at the end of a 700 m line
(X = 0.057 Ω) with a nominal power of 200 kW
worst-case assumption
no power factor limitation (Qmax = Smax)
network parameters
controller parameter
∑ ∗ ,
*QIP network identification was part of the analysis in: „Aktuelle Musternetze zur Untersuchung von Spannungsproblemen in der Niederspannung,“
M.Lindner, C. Aigner et al., 14. Symposium Energieinnovation, Graz, 2016
20 kV 0.4 kV
V
UVS
UPCC , QDG
…
critical unit
U(-Qmax)
Q
U
-Qmax
linear
section
1 p.u.
examined Q(U)-characteristic
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 12
Worst-Case Assumptions for Stability Assessment
Trigger
impact of Q(U)-control on the local voltage increases with
increasing available reactive power (Qmax)
increasing impedance (X) /increasing line length (l)
increasing slope gradient (Kslope)
reaction of the voltage controllers triggered by sudden voltage change
of ∆Utrigger = 6 % upstream of the transformer
reference value for sudden voltage change in medium voltage level according
to DIN EN 50160
network parameters
controller parameter
20 kV 0.4 kV
V
UVS
UPCC , QDG
…
critical unit
0,96
0,98
1,00
1,02
1,04
-4 -2 0 2 4 6 8 10
UOS[V]
t [s]
sudden voltage change at transformer
∆U = 6 %
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 13
Criteria for Voltage Stability Assessment
Stability and Voltage Quality
sudden voltage change - ∆Ust < 3 %
German standard VDE-AR-4105 defines ∆Ust as a change in voltage between
two consecutive rms-values
short term flicker - Pst < 1
maximal voltage change - ∆Umax < ∆Utrigger
∆Utrigger: voltage jump triggering a reaction of the inverter with Q(U)-control
∆Umax: maximal change in voltage after trigger
all criteria are met
one criterion violated
more than one criterion violated
unstable – the dynamic process after the trigger does not reach a stationary
terminal value
stable – a stationary terminal
value is reached
FGH e.V. | M. Schoeneberger | Derivation of a Q(U)-control tolerance band in order to meet voltage quality criteria 14