evolution of pv inverter soonwook hong - ieee power & … … ·  · 2015-09-21evolution of pv...

Evolution of PV inverter technologies

for addressing high penetration utility issues

Soonwook Hong

Solectria Renewables

soonwook.hong@solectria.com

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Alamosa NM 30MVA PV plant: PVI 82kW x 504EA

World Largest CPV Site: Commissioned in early 2012

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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?

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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

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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!

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State RPS Policies

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PV Installation exceeded wind Installation in 2013!

PV Installations and System Price Reduction

Source: GTM Research/SEIA March 2013

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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

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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

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PV Inverter Evolution

External

Transformer

High Voltage

String

String

Inverters

Innovative

Topology

New

Devices

Cost reduction √√√√ √√√√ √√√√ √√√√ √√√√

Performance increase √√√√ √√√√ √√√√

Energy density increase √√√√ √√√√ √√√√

Reliability increase √√√√ √√√√ √√√√

Efficiency increase √√√√ √√√√ √√√√ √√√√

Component Size reduction √√√√ √√√√√√√√

√√√√ √√√√

Modularity √√√√ √√√√

Harmonics reduction √√√√

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PV Inverter Communication Capabilities

- Remote Monitoring & Control

- More processor HP at very little additional cost allows for multiple

COM interfaces:

IEC 61850

Protocols: Medium:

• 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 integration

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Possibilities as a dispatchable grid asset

+Reactive Power Control

Voltage Regulation

Flicker mitigation

Power Factor Correction

Fault Ride Through

+Power Dispatch

Emergency Backup Operation

Micro Grid OperationReal power Generation

Power curtailment

Irradiation

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Several Grid Supporting Features in PV inverters

Volt var Frequency Watt

Fault Ride Through DRCS

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Several Grid Supporting Function Characteristics

Fast Response Voltage Regulation

Fault Ride Through Slew Rate Control

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Current shifts from IGBTs to diodes.

Minimum DC voltage rises:

inductive 0.8 0.9 0.9 0.8 capacitive1.0

Vmppt-min

Vmppt-max

Vdc

800 V

535 V

565 V

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Fewer String Sizing Choices:

Grid Supporting Feature influencing PV Operation

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Grid supporting features affecting the inverter operation

Unity PF 0.8 capacitive PF 0.8 inductive PF

98.3% CEC 97.9% CEC 97.4% CEC

Example: 500kVA inverter, rated current

• Current shifts from IGBTs to diodes.

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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.

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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 MW1.7 MW

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Overvoltage Concerns

3.0% of points

exceed +5% limit

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Mitigating overvoltage issue with Power Factor control

< 0.1% of points

exceed 5% limit

• 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

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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 0.95

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800

806 808 812 814

810

802 850

818

824 826

816

820

822

828 830 854 856

852

832

888 890

838

862

840

836860834

842

844

846

848

864

858

PV

Simulation with IEEE 34 Node Test Feeder

Regulator

Load

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XR Compensation (Power Factor Control)

Sunny Day Cloudy Day

0

10

20

30

40

No PV Generation Mode PF Control

0

10

20

30

40

No PV Generation Mode PF Control

Number of operations of the regulator at 850

1.01

1.015

1.02

1.025

1.03

1.035

1.04

1.045

1.05

5:27 8:19 11:12 14:05 16:58 19:51

With No PV

Generation mode

PF Control 1.01

1.015

1.02

1.025

1.03

1.035

1.04

1.045

1.05

5:27 8:19 11:12 14:05 16:58 19:51

With No PV

Generation mode

PF Control

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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.

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Evolution possible with Teamwork!

with leaders from different organizations in the industries

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Thank you!

Soonwook Hong

soonwook.hong@solectria.com