IBR Short Circuit Model - Considerations for VCCS Tabular ...
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© 2021 Electric Power Research Institute, Inc. All rights reserved.w w w . e p r i . c o m
Aboutaleb Haddadi, Ph.D.Sr. Engineer Scientistahaddadi@epri.com
Evangelos Farantatos, Ph.D.Sr. Project ManagerGrid Operations & Planning R&D GroupEPRIefarantatos@epri.com
IEEE PSRC MeetingSep 2021
IBR Short Circuit Model -
Considerations for VCCS
Tabular Model
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IBR Short Circuit Model
C24 –recommended table for WTG short circuit model in commercial platforms
▪ IBR is represented by a voltage-dependent current source.
▪ It is possible to have different tables for different time frames.
▪ The table format enables IBR plant owner to provide short circuit
data without revealing proprietary inverter control.
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Negative Sequence Representation of Type IV Wind Turbine
Generator/Solar Photovoltaic Inverter
▪How should the table look like when inverter injects negative sequence current?
–Challenge: Separate tables for +seq and -seq may not provide sufficient accuracy
▪ Example:
– +Seq and –Seq tables produced using
an EMT IBR model (PSCAD, EMTP, etc)V1 (pu) I1 (pu)
Angle(I1/V1)(degrees)
1.00 1.00 0
0.90 0.99 -17
0.72 0.74 -50
0.70 0.62 -60
+Seq table
V2 (pu) I2 (pu)Angle(I2/V2)
(degrees)
0.00 0.00 0
0.11 0.22 -90
0.21 0.41 -90
0.28 0.53 -90
-Seq table
Fault with
varying
resistance
If the table is used to represent the inverter under a different
fault with a different combination of V1 and V2, the table
may not give correct I1 and I2 values.
Example: For a fault with V1=0.72 pu and V2=0.28 pu, the
table gives I1 = 0.74@-50° and I2=0.53@-90°;
I1+I2 > 1.1 pu which is not realistic!
BUT
A joint +seq and –seq table is needed.
I_lim=1.1pu
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IBR Fault Ride Through (FRT) Requirement
VDE-AR-N 4120
Example: For V2=0.25 p.u. and k=2 I2=2*0.25=0.5 p.u.
I2=k*(V2)
Example: For V1=0.5 p.u. and kFRT=2 I1=2*(1-0.5)=1 p.u.
I1=kFRT*(1-V1)
+Seq dynamic reactive current injection -Seq dynamic reactive current injection
But the converter current is limited (e.g., 1.1 pu)In reality, I1 and I2 get limited by a converter current limiter logic.
I1 & I2 are coupled.
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Negative Sequence Representation – Cont’d
▪To account for the coupling between I1 and I2,
a joint table is needed.
▪What is the format (what quantities does I2
depend on)?
–V1, I1, angle(I1/V1)
–V2, I2, angle(I2/V2)
–angle(V2/V1)
–etc?
Time since initiation of a fault (cycles)
V1 (pu) V2 (pu)
3 cycles
I1 (pu)Angle(I1/V1)
(Degrees)I2 (pu)
Angle(I2/V2)
(Degrees)
0.9 0.0
0.1
0.2
0.3
0.4
0.5
0.8 0.0
0.1
0.2
0.3
0.4
0.5
0.7 0.0
0.1
0.2
0.3
0.4
0.5
….. ….. ….. ….. ….. …..
?
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▪There is no standardization for current limiter logic implementation.
▪There are several options:
Current Limiter Logic
Current limiter logic implementation
impacts I2 characteristics.
Active and reactive
components of I1 and I2
(I1r, I2r, I1p, I2p)
d- and q-axis components
of I1 and I2 (I1q, I2q, I2d,
I1d)
Phase currents
(Ia, Ib, Ic)
And other options...
I2 depends on {V1, V2, I1}
I2 depends on {V1, V2, I1, angle(V2/V1)}
I2 depends on {V1, V2, I1, angle(V2/V1)}
Current limiter logic
implementation options
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Current Limiter Logic Implementation Options
▪ In one implementation, current limit may be
applied to active and reactive currents:
(I1 = I1p + j*I1r, I2 = I2r)
1. ABS(I1r)+ABS(I2r) < reactive current limit
2. I2 leads V2 by 90 degrees
3. ABS(I1p) < active current limit
▪ I2 becomes dependent on V1, V2, and I1
Suggested table formatTime since initiation of a fault (cycles)
V1 (pu) V2 (pu)
3 cycles
I1 (pu)Angle(I1/V1)
(Degrees)I2 (pu)
Angle(I2/V2)
(Degrees)
0.9 0.0
0.1
0.2
0.3
0.4
0.5
0.8 0.0
0.1
0.2
0.3
0.4
0.5
0.7 0.0
0.1
0.2
0.3
0.4
0.5
….. ….. ….. ….. ….. …..
I2=I2r
V2
V1
I1
I1p
I1r
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Current Limiter Logic Implementation Options – Cont’d
▪ In another implementation, current limit may be applied to d-
and q-axis current components:
(I1 = I1d + j*I1q, I2 = I2d + j*I2q)
1. ABS(I1q)+ABS(I2q) < q-axis current limit
2. I2 leads V2 by 90 degrees
3. ABS(I1d)+ABS(I2d) < d-axis current limit
▪ dq frame is fixed; it is established by a phase locked loop
based on V1.
▪ I2 becomes dependent on V1, V2, I1,angle(V2/V1)
Suggested table formatTime since initiation of a fault (cycles)
V1 (pu) V2 (pu) Angle(V2/V1)
3 cycles
I1 (pu)Angle(I1/V1)
(Degrees)I2 (pu)
Angle(I2/V2)
(Degrees)
0.9 0.0 0
60
120
180
240
300
0.1 0
60
120
180
240
300
0.2 0
60
120
180
240
300
….. ….. ….. ….. ….. ….. …..
I2
V2
V1
I1
I1d
I1q
I2q
I2d
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Demonstrating ResultsExample
Iq_lim=1.1 pu
Id_lim=1.1 puItot_lim = 1.1 pu
V1(pu)
V2(pu)
I1q(pu)
I1d(pu)
I2q(pu)
I2d (pu)
Case 2: angle(V2/V1) = -90 deg
0.5 0.5 0.73 0 0.37 0
Case 1: angle(V2/V1)= 0 deg
0.5 0.5 1 0 0 0.47
• Dependence of I2 on angle(V2/V1)
when current limit is applied to d-
and q-axis current components.
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Other Implications
▪ If I2 is dependent on angle(V2/V1), the phase current of IBR may be different under
different faulted phases.
FaultAngle
(V2/V1)V1 (pu) V2 (pu) Ia (pu) Ib (pu) Ic (pu)
AG 165° 0.837@21.1° 0.131@-176.9° 0.773@-3.3° 0.670@-104.9° 0.915@130.9°
BG -75° 0.842@17° 0.123@-58° 0.814@8.2° 0.680@-131.6° 0.529@132.1°
CG 45° 0.840@17° 0.123@62° 0.534@12.6° 0.815@-111.8° 0.676@108.9°
Example:
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Main Question
▪Depending on current limiter logic, I2 may depend on various quantities.
What quantities need to be included in the table
for adequate representation of I1 and I2?
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Suggested Table
▪ A table based on V1, V2, angle(V2/V1)
may be impractical; for 10 values of V1,
V2, angle(V2/V1) the table will haveto
have 1000 rows!
▪ One option is to generate the table only
based on V1 & V2 to have a more
reasonably sized table, but there will be
some error depending on the current
limiter logic implementation.
▪ A simulation case study suggested:
– ~20% error in amplitude of I1 and I2 (on
average)
– Up to 30° error in phase angle
angle(V2/V1)=0V1
(pu)V2
(pu)I1
(pu)Angle
(I1/V1)I2
(pu)Angle
(I2/V2)0.9 0.0 1.00 -10.52 0.00 0.00
0.1 1.04 -11.09 0.20 90.000.2 0.94 -12.29 0.40 90.000.3 0.78 -14.89 0.60 90.000.4 0.50 -23.66 0.80 90.000.5 0.18 -90.00 0.92 90.000.6 0.16 -90.00 0.94 90.000.7 0.14 -90.00 0.96 90.000.8 0.12 -90.00 0.98 90.000.9 0.11 -90.00 0.99 90.00
0.8 0.0 1.10 -21.36 0.00 0.000.1 1.01 -23.49 0.20 90.000.2 0.85 -27.96 0.40 90.000.3 0.61 -41.17 0.60 90.000.4 0.37 -90.00 0.73 90.000.5 0.32 -90.00 0.79 90.000.6 0.28 -90.00 0.82 90.000.7 0.25 -90.00 0.85 90.000.8 0.22 -90.00 0.88 90.000.9 0.20 -90.00 0.90 90.00
0.6 0.0 1.10 -46.68 0.00 0.000.1 0.92 -60.21 0.20 90.000.2 0.73 -90.00 0.37 90.000.3 0.63 -90.00 0.47 90.000.4 0.55 -90.00 0.55 90.000.5 0.49 -90.00 0.61 90.000.6 0.44 -90.00 0.66 90.000.7 0.40 -90.00 0.70 90.000.8 0.37 -90.00 0.73 90.000.9 0.34 -90.00 0.76 90.00
… … … … … …
Demonstrating result:
Consider an IBR using current limiter
logic based on dq limits. The table
needs to account for angle(V2/V1).
For simplicity, we represent the IBR
using only one table with V1&V2
assuming angle(V2/V1)=0°
Assume a fault with
V1 = 0.6 pu, V2 =0.5 pu
angle(V2/V1)=90°. The IBR
contributes
I1=0.69@-90° and I2=0.86@90°
(correct values).
However, the table gives
I1=0.49@-90° and I2=0.61@90°
(estimated table values) which
means ~40% error in the amplitude
of I1&I2.
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Another Suggestion: User-Defined IBR Short Circuit Model
▪ Given the complication of VCCS table, an option is to use
a User-Defined Model (UDM) of inverter in short circuit
programs
– I1 and I2 are calculated based on generic equations
representing IBR control and current limiter scheme.
– An example is the generic equation-based model proposed
by EPRI implemented within PSS®CAPE and ASPEN
OneLiner (v15).
▪ The UDM could be a black-box
DLL-based OEM model:
– The concept is similar
to OEM DLL inverter
models used in EMT tools
(PSCAD, EMTP, etc)
and stability tools
(PSS/E, PSLF, etc).
13
FRT Current Limiter & PQ Priority Neg. Seq. Current Control
Reference: Short-Circuit Phasor Models of Converter-Based Renewable Energy Resources for Fault Studies, EPRI, Palo Alto, CA: 2017. 3002010936.
EPRI proposed IBR
short circuit model
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Type III Wind Turbine Generator
▪ VCCS tabular model of Type III is not as
complex as Type IV; Separate +seq and -seq
tables could provide sufficient accuracy.
▪ Reason:
– Under traditional coupled control, the control scheme
of Rotor-Side Converter (RSC) & Grid Side
Converter (GSC) eliminates I2.
– I2 is only contributed by the stator and can be
estimated & represented using the -seq impedance
of the machine.
– In practice, a small coupling between I1 and I2 does
exist due to the negative sequence active power
flowing from RSC to rotor; however, this coupling
can be reasonably ignored.
– Compliance with the German code may require
additional I2 injection by GSC, in which case the
table will face the same complexity issue as Type IV.
I2 = V2 / Z2,machine
I2 = 0
V2
V1 (pu) I1 (pu)Angle(I1/V1)
(degrees)
1.00 1.00 -0.05
0.90 1.10 -10.41
0.80 1.04 -22.7
0.70 0.96 -38.77
0.60 0.87 -66.63
… … …
+Seq table -Seq table
V2 (pu) I2 (pu)Angle(I2/V2)
(degrees)
0.10 0.29 99.85
0.20 0.58 99.85
0.30 0.87 99.85
0.40 1.16 99.85
0.50 1.45 99.85
… … …
I2 = 0
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