User Experience with New Solar PV ModelsCalifornia ISO

Irina GreenRegional Transmission Engineering LeadCalifornia ISO

WECC Renewable Energy Modeling WorkshopJune 17, 2014

Solar PV Plant Representation

Slide 2

Q Control

P Control

Current Limit Logic

IqcmdIqcmd’

IpcmdIpcmd’

Generator Model

Network Solution

Plant Level V/Q Control

Plant Level P Control

VrefVreg

QrefQbranch

PrefPbranchFreq_ref

Freg

Qext

Pref

REPC_A

Pqflag

REEC_B REGC_AVt Vt

Iq

Ip

Power Flow

Transient Stability

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

  Slide 3

3-Phase Fault on the Solar Switching Station. Voltage on the equivalent PV generator terminals

Slide 4

a) Trv = 0.2, Kvi = 100 - BLUE

b) Trv = 0.02, Kvi = 100 - RED

c) Trv = 0.02, Kvi = 40 - GREEN

Study Example 2023 Heavy Summer Case. 800 MW Solar PV Plant.

Composite Load Model for all WECC

Slide 5

Three-phase 6 cycles fault at the Switching Station 230 kV, double-line outage Switching Station – Morro Bay

Study Example. Surrounding Area

Slide 6

Bus 6 230 kV

Load Bus 1

115 kV Load Area

to solar PV plant

Study Scenarios

1. 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.

2.  Same as 1), but A/C stalling enabled.

3. 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.

4.  Same as 3), but A/C stalling enabled.

5. The Solar PV plant is replaced by a fictitious combined-cycle plant. Stalling of the single-phase air conditioner motor load components is disabled.

6.  Same as 5), but A/C stalling enabled.

Slide 7

Study Results. Switching Station Voltage

Slide 8

• 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.

Study Results. Switching Station Frequency

Slide 9

• 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

Study Results. Voltage on Equivalent Generator Terminals

Slide 10

• 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

Study Results. Frequency on Equivalent Generator Terminals

Slide 11

• 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

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

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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

Slide 13

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-conditionersSlide 14

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

Slide 15

Conclusions

Slide 16

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

High Normal Yes

3 Solar PV, no vlt and Q control, induction motors don’t stall

Normal Low No

4 Solar PV, no vlt and Q control, induction motors stall

Normal Low Yes

5 Thermal, induction motors don’t stall

Low Normal No

6 Thermal, induction motors stall

Low Normal Yes

Questions? Comments?

Slide 17