Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs

 
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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    Evolution of PV inverter technologies
for addressing high penetration utility issues

                   Soonwook Hong
                 Solectria Renewables
             soonwook.hong@solectria.com
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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Alamosa NM 30MVA PV plant: PVI 82kW x 504EA

     World Largest CPV Site: Commissioned in early 2012
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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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?
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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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
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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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!
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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State RPS Policies
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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PV Installations and System Price Reduction
                      Source: GTM Research/SEIA March 2013

      PV Installation exceeded wind Installation in 2013!
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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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
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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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
Evolution of PV inverter technologies for addressing high penetration utility issues - Soonwook Hong Solectria Renewables - IEEE PEs
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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                                                     √
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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 integration
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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 Operation
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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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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   capacitive
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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.
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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 MW
                                                            1.7 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

         • 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% limit
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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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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     856
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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 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
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