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  • SANDIA REPORT SAND2016-4856 Unlimited Release Printed May 2016

    Analysis of PV Advanced Inverter Functions and Setpoints under Time Series Simulation

    John Seuss, Matthew J. Reno, Robert J. Broderick, Santiago Grijalva

    Prepared by Sandia National Laboratories Albuquerque, New Mexico 87185 and Livermore, California 94550

    Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. Approved for public release; further dissemination unlimited.

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    Issued by Sandia National Laboratories, operated for the United States Department of Energy

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    SAND2016-4856

    Unlimited Release

    Printed May 2016

    Analysis of PV Advanced Inverter Functions and Setpoints under Time

    Series Simulation

    Matthew J. Reno, Robert J. Broderick

    Photovoltaics and Distributed Systems Integration

    Sandia National Laboratories

    P.O. Box 5800

    Albuquerque, New Mexico 87185-1033

    John Seuss, Santiago Grijalva

    School of Electrical and Computer Engineering

    Georgia Institute of Technology

    777 Atlantic Drive NW

    Atlanta, GA 30332-0250

    Abstract

    Utilities are increasingly concerned about the potential negative impacts distributed PV may

    have on the operational integrity of their distribution feeders. Some have proposed novel

    methods for controlling a PV system’s grid-tie inverter to mitigate potential PV-induced

    problems. This report investigates the effectiveness of several of these PV advanced inverter

    controls on improving distribution feeder operational metrics. The controls are simulated on a

    large PV system interconnected at several locations within two realistic distribution feeder

    models. Due to the time-domain nature of the advanced inverter controls, quasi-static time series

    simulations are performed under one week of representative variable irradiance and load data for

    each feeder. A parametric study is performed on each control type to determine how well certain

    measurable network metrics improve as a function of the control parameters. This methodology

    is used to determine appropriate advanced inverter settings for each location on the feeder and

    overall for any interconnection location on the feeder.

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    CONTENTS

    1. INTRODUCTION.................................................................................................................. 11

    2. MODELING ADVANCED INVERTER FUNCTIONS .................................................... 13

    2.1. Advanced Inverter Functions Considered ........................................................................ 13

    2.1.1. Ramp-Rate Control............................................................................................. 13

    2.1.2. Fixed Power Factor Control ............................................................................... 13

    2.1.3. Volt/Watt Control ............................................................................................... 13

    2.1.4. Watt-Triggered Power Factor Control ............................................................... 14

    2.1.5. Watt-Priority Volt/Var Control .......................................................................... 14

    2.1.6. Var-Priority Volt/Var Control ............................................................................ 14

    2.2. Example Simulations Demonstrating Advanced Inverter Functions ............................... 15

    2.2.1. Weekly Irradiance, Load Selection, and Basecase Simulation .......................... 15

    2.2.2. Ramp-Rate Control Example ............................................................................. 17

    2.2.3. Volt/Var Control Examples ................................................................................ 18

    2.2.4. Power Factor Control Examples......................................................................... 19

    2.2.5. Volt/Watt Control Examples .............................................................................. 19

    3. ANALYSIS METHODOLOGY ........................................................................................... 21

    3.1. Study Feeders ................................................................................................................... 21

    3.1.1. Feeder CO1......................................................................................................... 21

    3.1.2. Feeder CS1 ......................................................................................................... 21

    3.2. Measured Impact of Inverter Controls on Network ......................................................... 23

    3.2.1. Network Metrics Considered.............................................................................. 23

    3.2.2. Performance of Controls with Generic Parameters ............................................ 23

    3.3. Scoring Positive or Negative Controller Impacts ............................................................ 29

    3.4. Approximations Made to Reduce Computation Time ..................................................... 29

    3.5. Search Algorithm to Find Optimum Settings per PV Location ....................................... 31

    4. ADVANCED INVERTER CONTROL TYPE PERFORMANCE ................................... 35

    4.1. Inverter Ramp-Rate Limiting ........................................................................................... 35

    4.2. Constant Power Factor Control ........................................................................................ 37

    4.3. Volt/Watt Control ............................................................................................................ 39

    4.4. Watt-Triggered Power Factor Control ............................................................................. 44

    4.5. Watt-Priority Volt/Var Control ........................................................................................ 49

    4.6. Var-Priority Volt/Var Control.......................................................................................... 52

    5. GENRALIZED CONTROL SETTINGS FOR EXAMPLE FEEDERS .......................... 53

    6. CONCLUSIONS AND FUTURE RESEARCH .................................................................. 55

    7. REFERENCES ....................................................................................................................... 57

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    FIGURES

    Figure 1. Example Volt/Var droop curve with a slope of 25∆𝑸/∆𝑽 and a deadband of width 0.02V. ........................................................................................................................... 15

    Figure 2. Weekly load selected for QSTS simulation’s LDC selected as the least-square-error of

    the yearly data’s LDC. ................................................................................................. 16

    Figure 3. Weekly 1-minute resolution load and irradiance data selected for QSTS simulat