1. User Experience with New Solar PV Models California ISO
Irina Green
Regional Transmission Engineering Lead
California ISO
WECC Renewable Energy Modeling Workshop
June 17, 2014

2. Solar PV Plant Representation
Power Flow
Transient Stability

3. Transient Stability Models. Large Solar PV Plant
REGC_A  module - Generator/Converter interface with the grid. Typical parameters from the WECC Guidelines
REEC_B module - Electrical Controls of the inverters. Typical parameters from the WECC Guidelines except for Integral Gain (Kvi) and Transducer Time Constant (Trv). Reduced Kvi from 100 to 40 to avoid oscillations. Kvi=40 typical for the PV1E model. Was a typo in the Trv, changed from 0.2 to 0.02
REPC_A module - Plant Controller. It processes voltage and reactive power output to emulate Volt/Var control at the plant level. Typical parameters from the WECC Guidelines

4. 3-Phase Fault on the Solar Switching Station
3-Phase Fault on the Solar Switching Station. Voltage on the equivalent PV generator terminals
Trv = 0.2, Kvi = BLUE
Trv = 0.02, Kvi = RED
Trv = 0.02, Kvi = 40 - GREEN

5. Study Example 2023 Heavy Summer Case. 800 MW Solar PV Plant
Study Example Heavy Summer Case. 800 MW Solar PV Plant. Composite Load Model for all WECC
Three-phase 6 cycles fault at the Switching Station 230 kV, double-line outage Switching Station – Morro Bay

6. Study Example. Surrounding Area

7. Study Scenarios Same as 5), but A/C stalling enabled.
Solar PV with 0.95 lead/lag power factor. Reactive power and voltage control; priority is reactive power. Plant controller controls voltage. Stalling of the single-phase air conditioners disabled.
 Same as 1), but A/C stalling enabled.
Solar PV with unity power factor. No reactive support or voltage regulation. Priority is real power. Stalling of the single-phase air conditioner motor load disabled.
 Same as 3), but A/C stalling enabled.
The Solar PV plant is replaced by a fictitious combined-cycle plant. Stalling of the single-phase air conditioner motor load components is disabled.
 Same as 5), but A/C stalling enabled.

8. Study Results. Switching Station Voltage
Voltage recovered to the pre-fault values. Solar PV with unity power factor voltage recovered to a slightly lower value.
Solar PV showed faster recovery than the combined-cycle plant.
Single-phase air conditioners stalling did not have almost any impact on the voltage on this bus.

9. Study Results. Switching Station Frequency
Inverter-based generators had better damping than conventional generators
No impact from the air-conditioner stalling
Higher frequency in the first 0.5 second after the fault with solar PV

10. Study Results. Voltage on Equivalent Generator Terminals
Voltage recovered to the pre-fault values, except for solar PV with unity power factor, especially with A/C stalling
Faster voltage recovery and better damping with solar PV
Voltage spike in the first 0.5 sec after the fault with solar PV with voltage regulation
Only slight impact of A/C stalling in PV scenario with unity power factor

11. Study Results. Frequency on Equivalent Generator Terminals
Inverter-based generation has better damping than conventional generation
Slow frequency recovery with solar PV that has voltage regulation
May appear as a criteria violation in transient stability studies, but this may be a numerical issue
No impact of A/C stalling

12. Study Results. Real Power Output from Equivalent Generator
Solar PV generators have better damping than the thermal unit
Solar PV units have slower recovery
A/C stalling doesn’t have any impact

13. Study Results. Reactive Power Output from Equivalent Generator
Solar PV generators have better damping than the thermal unit
As expected, solar PV with unity power factor did not respond
A/C stalling has very slight impact by increased reactive output, except for the unit with unity power factor

14. Study Results. Adjacent Load Bus
Generator type doesn’t have any impact on voltage, very slight impact on frequency
Delayed voltage recovery due to stalled air-conditioners

15. Loss of Load
Scenario 1: PV with voltage regulation, A/C stalling disabled – 66 MW
Scenario 2: PV with voltage regulation, A/C stalling enabled – 91MW
Scenario 3: PV with unity power factor, A/C stalling disabled – 67 MW
Scenario 4: PV with unity power factor, A/C stalling enabled – 96 MW
Scenario 5: Combined cycle plant, A/C stalling disabled – 69 MW
Scenario 6: Combined cycle plant, A/C stalling enabled – 97MW

16. Conclusions Scenario Transient voltage on generator terminals
Post-fault steady state voltage
Slow voltage recovery on adjacent load buses
1 Solar PV, voltage control, induction motors don’t stall
High
Normal No
2 Solar PV, voltage control, induction motors stall
Yes
3 Solar PV, no vlt and Q control, induction motors don’t stall
Low
4 Solar PV, no vlt and Q control, induction motors stall
5 Thermal, induction motors don’t stall
6 Thermal, induction motors stall

17. Questions? Comments?