2014 PV Distribution System Modeling Workshop: Data and Models for High Penetration Using Advanced Inverters: Roger Dugan, EPRI

1. Roger C. Dugan
Sr. Technical Executive
Sandia-NREL-EPRI PV Distribution System Modeling Workshop
May 6, 2014
Santa Clara, CA
Data and Models for High-Penetration
PV Using Advanced Inverters

2. 2© 2014 Electric Power Research Institute, Inc. All rights reserved.
Objective
• Data and modeling requirements for advanced, or smart,
inverter functions will be illustrated using the modeling
requirements for the EPRI OpenDSS program

3. 3© 2014 Electric Power Research Institute, Inc. All rights reserved.
The OpenDSS PVSystem Model With Smart
Inverter Control Can Demonstrate Benefits

4. 4© 2014 Electric Power Research Institute, Inc. All rights reserved.
The basic volt-var control function can be
described by four P, Q points
This control is effective where the voltage level will respond to
vars – where the system impedance is Inductive

5. 5© 2014 Electric Power Research Institute, Inc. All rights reserved.
Adding hysteresis to the volt-var curve is
sometimes beneficial in controlling voltage
Implementations of this model may require more points simply
implement shifting logic to a base curve

6. 6© 2014 Electric Power Research Institute, Inc. All rights reserved.
Modeling the advanced inverter is demonstrated
with an OpenDSS example based on this circuit

7. 7© 2014 Electric Power Research Institute, Inc. All rights reserved.
An actual 10-min PV system Active Power
measurement will be used for the example
New "LoadShape. PV_ls" npts=600 sinterval=1.0 mult=(File=“Solar-600s.csv")
OpenDSS Script for Defining This as a “Loadshape”: File containing 600 pts

8. 8© 2014 Electric Power Research Institute, Inc. All rights reserved.
This OpenDSS script snippet defines the four
PV systems
New PVSystem.3P_ExistingSite4 phases=3 bus1=B51854_sec kV=0.4157 kVA=523
~ irradiance=1 Pmpp=475 pf=1 %cutin=0.1 %cutout=0.1 yearly=PV_ls
New PVSystem.3P_ExistingSite1 phases=3 bus1=X_5865228330A kV=0.4157 kVA=314
~ irradiance=1 Pmpp=285 pf=1 %cutin=0.1 %cutout=0.1 yearly=PV_ls
New PVSystem.3P_ExistingSite3 phases=3 bus1=X_5891328219_Cust1 kV=0.4157
~ kVA=836 irradiance=1 Pmpp=760 pf=1 %cutin=0.1 %cutout=0.1 yearly=PV_ls
New PVSystem.3P_ExistingSite2 phases=3 bus1=B4832_sec kV=0.4157 kVA=209
~ irradiance=1 Pmpp=190 pf=1 %cutin=0.1 %cutout=0.1 yearly=PV_ls
•Bus Name (Bus1)
•Voltage rating (kV)
•kVA rating (kVA)
•Base irradiance (kW/m2)
•Power at MPP (Pmpp)
•Base power factor (pf)
•Cut in/cut out percentage values
•Irradiance Loadshape for OpenDSS solution mode (yearly in this case to get desired
monitoring)
•Inverter Efficiency curve (optional)
•Pmpp vs Temperature curve (optional)
Data for PVSystem Model

9. 9© 2014 Electric Power Research Institute, Inc. All rights reserved.
The base-line simulation reveals voltage and
power excursions
Note: Unity PF assumed for base-line

10. 10© 2014 Electric Power Research Institute, Inc. All rights reserved.
Implementation of a simple volt-var control
requires definition of a curve and an InvControl
New XYCurve.vv_curve npts=4 Yarray=(1.0,1.0,-1.0,-1.0) XArray=(0.5,0.95,1.05,1.5)
New InvControl.InvPVCtrl mode=VOLTVAR voltage_curvex_ref=rated
~ vvc_curve1=vv_curve EventLog=yes
Volt-Var Control Curve Definition
Inverter Control Definition
pu Voltagepu Rated Vars

11. 11© 2014 Electric Power Research Institute, Inc. All rights reserved.
Results with simple volt-var control show the
voltage is reduced about 2% to less than 105%

12. 12© 2014 Electric Power Research Institute, Inc. All rights reserved.
Modeling hysteresis is accomplished by adding
an offset to the voltage (x axis)
New XYCurve.vv_curve npts=4 Yarray=(1.0,1.0,-1.0,-1.0) XArray=(0.5125,0.9625,1.0625,1.5125)
New InvControl.InvPVCtrl mode=VOLTVAR voltage_curvex_ref=rated
~ vvc_curve1=vv_curve hysteresis_offset=-0.025 EventLog=yes

13. 13© 2014 Electric Power Research Institute, Inc. All rights reserved.
The reactive power output level is constant
when power flow between curves

14. 14© 2014 Electric Power Research Institute, Inc. All rights reserved.
The solutions on the VV curves with hysteresis
indicate the inverter drawing vars to reduce V

15. 15© 2014 Electric Power Research Institute, Inc. All rights reserved.
Volt-Var control with adaptive set point attempts
to follow the voltage more closely over time
New InvControl.InvPVCtrl mode=VOLTVAR voltage_curvex_ref=avg avgwindowlen=2m
~ vvc_curve1=vv_curve EventLog=yes

16. 16© 2014 Electric Power Research Institute, Inc. All rights reserved.
Adding a 5-s time constant on the rate of
change significantly smooths the var response
New InvControl.InvPVCtrl mode=VOLTVAR voltage_curvex_ref=rated
~ vvc_curve1=vv_curve RateofChangeMode=LPF LPFTau=5 EventLog=yes

17. Data Requirements for Other Control
Functions

18. 18© 2014 Electric Power Research Institute, Inc. All rights reserved.
The Volt-Watt Function suppresses active
power output for high voltages
New XYCurve.examplevoltwattcurve npts=4 Yarray=(1.0,1.0,0.0,0.0) XArray=(0.0,1.0,1.1,2.0)
New InvControl.InvPVCtrl mode=VOLTWATT voltage_curvex_ref=rated
~ voltwatt_curve=examplevoltwattcurve EventLog=yes
Optional DATA:
Rolling average window length
Units for Y axis
Rate-of-change mode: INACTIVE | LPF | RISEFALL
Low-Pass Filter time constant for rate of change of output power
RiseFall Limit (pu/s or kW/s)

19. 19© 2014 Electric Power Research Institute, Inc. All rights reserved.
The Dynamic Reactive Current function provides reactive current in
response to dynamic variations in voltage
New InvControl.InvTestPVCtrl mode=DYNAMICREACCURR DbVMin=0.975 DbVMax=1.025
~ ArGraLowV=10.0 ArGraHiV=10.0 DynReacavgwindowlen=120s EventLog=yes
Optional DATA:
Var change tolerance; default is 0.025 pu of available vars

20. 20© 2014 Electric Power Research Institute, Inc. All rights reserved.
The Dynamic Reactive Current control can help reduce
voltage sags and swells during transient events

21. 21© 2014 Electric Power Research Institute, Inc. All rights reserved.
Fixed Power Factor control is a simple function
that reduces voltage swings and high voltages
New PVSystem.3P_ExistingSite4 phases=3 bus1=B51854_sec kV=0.4157 kVA=523
~ irradiance=1 Pmpp=475 pf=-0.98 %cutin=0.1 %cutout=0.1 yearly=PV_ls

22. 22© 2014 Electric Power Research Institute, Inc. All rights reserved.
This example of the Max Generation Limit function limits
PV system output to 70% or Pmpp
New PVSystem.3P_ExistingSite4 phases=3 bus1=B51854_sec kV=0.415692194 kVA=523
~ irradiance=1 Pmpp=475 kvar=0.00 pctPmpp=70.0 %cutin=0.1 %cutout=0.1
~ yearly=PV_ls

23. 23© 2014 Electric Power Research Institute, Inc. All rights reserved.
This example demonstrating OpenDSS scripting
for switching from V-W control to V-V control
New XYCurve.myvw_curve npts=4
~ Yarray=(1.0,1.0,0.0,0.0)
~ XArray=(0.5,1.0,1.05,1.5)
New InvControl.InvTestPVCtrl mode=VOLTWATT
~ voltage_curvex_ref=rated
~ voltwatt_curve=myvw_curve EventLog=yes
set casename= voltwatt300_voltvar300
solve mode=yearly number=300 stepsize=1s
New XYCurve.myvv_curve npts=4
~ Yarray=(1.0,1.0,-1.0,-1.0)
~ XArray=(0.5,0.95,1.05,1.5)
InvControl.INVPVCTRL.mode=VOLTVAR
InvControl.INVPVCTRL.voltage_curvex_ref=rated
InvControl.INVPVCTRL.vvc_curve1=myvv_curve
Solve number=300

24. 24© 2014 Electric Power Research Institute, Inc. All rights reserved.
“Loadshape” data, typically in 1-s intervals, is
key to many advanced inverter simulations

25. 25© 2014 Electric Power Research Institute, Inc. All rights reserved.
Questions?