Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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1
Evolution of PV inverter technologies
for addressing high penetration utility issues
Soonwook Hong
Solectria Renewables
soonwook.hong@solectria.com
2
Alamosa NM 30MVA PV plant: PVI 82kW x 504EA
World Largest CPV Site: Commissioned in early 2012
3
Solectria Renewables’ Products Evolution in 3 years
Residential (1.8 ~ 7.6kW) Commercial (10 ~ 100kW) Utility Scale (225 ~ 500kW)
Commercial (14 ~ 28kW) Utility Scale (500 ~ 750kW)
What are the driving factors for this evolution?
4 Topics What happened during the last three years? What are opportunities for the PV inverter? What are the challenges for the PV inverters? A Case Study with high penetration
5
DoE Sunshot initiative
Goals
…reduce the total installed cost of solar energy systems to $.06 per kilowatt-hour
(kWh) by 2020. Since SunShot's launch in 2011, price has dropped from about $0.21
to $0.11. (60% achieved in 3 years)
It is equivalent to $1.00 per watt installation cost for utility scale solar project (50%
for panel, 40% for BOS and 10% for inverter)
…Solar energy could meet 14% of U.S. electricity needs by 2030 and 27% by 2050.
http://energy.gov/eere/sunshot/mission
Cost Reduction and High Penetration!
6 State RPS Policies
7
PV Installations and System Price Reduction
Source: GTM Research/SEIA March 2013
PV Installation exceeded wind Installation in 2013!
8 Challenges and Opportunities with High Penetration (aside from all benefits) Utility Side - Intermittency - Dispatchability - Over-voltage issue - Coordinating with the existing utility assets Manufacturers Consideration - Cost reduction - Efficiency/Reliability enhancement - Energy density increase - New features to resolve utility side challenges
9 Concept changes with High Penetration Independent resources Resources to be integrated Intermittent resources Dispatchable resources with ESS Distribution resources Power System resources Resources with ‘credit’ Resources to compete with Invited guest with privileges team member sharing responsibilities
10
PV Inverter Evolution
External High Voltage String Innovative New
Transformer String Inverters Topology Devices
Cost reduction √ √ √ √ √
Performance increase √ √ √
Energy density increase √ √ √
Reliability increase √ √ √
Efficiency increase √ √ √ √
Component Size reduction √
√ √ √ √
Modularity √ √
Harmonics reduction √11
PV Inverter Communication Capabilities
- Remote Monitoring & Control
- More processor HP at very little additional cost allows for multiple
COM interfaces:
Protocols: Medium:
IEC 61850
• Allowing different sets of settings when feeder reconfigures
• Allowing different modes of operation for different times of the day
Closing the loop for the system integration12
Possibilities as a dispatchable grid asset
Irradiation
+
Reactive Power Control
Voltage Regulation +
Flicker mitigation Power Dispatch
Real power Generation Power Factor Correction Emergency Backup Operation
Power curtailment Fault Ride Through Micro Grid Operation13
Several Grid Supporting Features in PV inverters
Volt var Frequency Watt
Fault Ride Through DRCS14
Several Grid Supporting Function Characteristics
Fast Response Voltage Regulation
Fault Ride Through Slew Rate Control15
Grid Supporting Feature influencing PV Operation
Fewer String Sizing Choices:
Minimum DC voltage rises:
18 19 20
Vdc
Vmppt-max
800 V
Current shifts from IGBTs to diodes.
565 V
535 V
Vmppt-min
inductive 0.8 0.9 1.0 0.9 0.8 capacitive16
Grid supporting features affecting the inverter operation
Example: 500kVA inverter, rated current
Unity PF 0.8 capacitive PF 0.8 inductive PF
98.3% CEC 97.9% CEC 97.4% CEC
• Current shifts from IGBTs to diodes.17 Grid Supporting Features influencing inverter reliability Automobile best warranty - 100,000 miles 2 hours per day with 40 mph average speed Net operating time:= 2,500 hours PV Inverter standard warranty - 5 years 8 hours per day on an average Net operating time:= 14,600 hours PV Inverter warranty is about 6 times as that of an automobile The PV inverter warranty model is designed to work for the increased hours and/or higher operation density when the grid supporting functions are provided.
18
High Penetration Scenario Example:
1.7 MW site in Cedarville NJ
4.7 miles from substation 12kV feeder, 6MW mid-day load
Concerns of local overvoltage
Utility has closed circuit for more PV
0.5 MW
1.7 MW19
Overvoltage Concerns
3.0% of points
exceed +5% limit20
Mitigating overvoltage issue with Power Factor control
• Feeder could be reopened for PV after PF adjustment to 0.97
• “Flicker” Mitigation (cloud induced voltage transients)
• Generation reduction due to PF control < 0.4% or less
< 0.1% of points
exceed 5% limit21
How power factor control helps the voltage regulation?
• If the X/R ratio of the feeder is
known, the grid voltage can be
regulated by adjusting power
factor.
• The controlled power factor will
be usually higher than 0.9522
Simulation with IEEE 34 Node Test Feeder
848
822 846
820 844
864
818 842
802 806 808 812 814 850 824 826 834 860 836
858 840
816
832 862
800 888 890
810 Regulator PV 838
852
Load
828 830 854 85623
XR Compensation (Power Factor Control)
Sunny Day Cloudy Day
1.05 1.05
1.045 1.045
1.04 1.04
1.035 1.035
1.03 1.03
1.025 1.025
With No PV
With No PV 1.02
1.02 Generation mode
Generation mode 1.015
1.015 PF Control
PF Control 1.01
1.01
5:27 8:19 11:12 14:05 16:58 19:51
5:27 8:19 11:12 14:05 16:58 19:51
Number of operations of the regulator at 850
40 40
30 30
20 20
10 10
0 0
No PV Generation Mode PF Control No PV Generation Mode PF Control24
Power Factor Control Advantages
Regulates the self-induced voltage change issue
Steady state as well as dynamic voltage regulation
Autonomous function without need for communication
0.4% generation reduction when pf = 0.97 on sunny days
Open up the generation to load ratio, thereby reduce high penetration
issues with a minimum investment.25
Evolution possible with Teamwork!
with leaders from different organizations in the industries26
Thank you!
Soonwook Hong
soonwook.hong@solectria.comYou can also read
