P R E S E N T E D B Y

Sandia National Laboratories is a multimission

laboratory managed and operated by National

Technology & Engineering Solutions of Sandia,

LLC, a wholly owned subsidiary of Honeywell

International Inc., for the U.S. Department of

Energy’s National Nuclear Security

Administration under contract DE-NA0003525.

Grid Forming Inverters in

Interconnected Systems

Abraham Ellis

ael l i s@sandia .gov

SAND2018-11666 C

C O - AU T H O R S

• Brian Johnson, University of Washington

• Rober t Lasseter, University of Wisconsin

• Yashen Lin, National Renewable Energy Laborator y

• Ryan Ell iott , Brian Pier re, Sandia National Laboratories

• Joseph Eto, Lawrence Berkeley National Lab

The grid of the future

More wind and solar generation, more storage, more electronic load (e.g., EV). All distributed and inverter-based

Lower system inertia, faster dynamics, more challenging control requirements.

Extremely difficult to approach 100% share in large interconnected systems.

Grid Forming Inverters deserve careful consideration as a potential solution.

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Grid following Vs grid forming inverter controls

Two fundamental types of inverter controls

Grid Following Control (GFL) Grid Forming Control (GFM)

Controls current and phase angle Controls voltage magnitude and frequency

Control of active & reactive power as well as fault currents

Instantaneously balances loads withoutcoordination controls

Cannot operate standalone Can operate standalone

Cannot achieve 100% penetration Can achieve 100% penetration

Two 1.2 MW backup diesel generators

Distributed Energy Resources Management System (DERMS)

2 MW/4 MW-hrenergy storage system

1 MW fuel cell

1.2 MW rooftop solar PV system

Five 2.3 kW wind turbines

Static disconnect switch at the

“point of common coupling”

Utility Interface

When a disturbance to the utility grid occurs, the automatic disconnect switch enables the facility to “island” itself from the main utility grid.

GFM inverters were studied and deployed in DOE/CERTS microgrids

Santa Rita Jail Microgrid, dedicated 3/22/2012.

GFM inverters were studied and deployed in DOE/CERTS microgrids

Seamlessly switches between grid and island operation and back

Stable without communications

Sources are plug-and-play

Proven in microgrid applications

E. Alegria, T. Brown, E. Minear, R. Lasseter,

“CERTS Microgrid Demonstration With

Large-Scale Energy Storage and Renewable

Generation,”, IEEE Transactions on Smart

Grid, Vol. 5, No. 2, March 2014.

C. Marnay, N. DeForest, M. Stadler, J.

Donadee, C. Dierckxsens, G. Mendes, J.

Lai, and G. F. Cardoso, “A green prison:

Santa Rita Jail Creeps Towards Zero Net

Energy (ZNE),” in Proc. ECEEE, 2011.

What about GFM inverters operating as part of large grids?

Many open questions…

How do GFM inverters behave in a large interconnected system?

How does a system defined by GFM inverters behave? What are the fundamental dynamic characteristics?

What are the most promising GFM control architectures? What functions & operating modes are required?

How are the GFM inverter hardware requirements?

How do we protect the network?

What are the modeling gaps for large-scale simulation?

etc., etc.

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Preliminary observations – frequency control with low inertia

Simulated frequency response for 5% load drop event, as a function of residual inertia

(a) (b) (c)

20% 50% 80%

Time(s) Time(s)

Grid following (GFL)

inverters with freq-

watt functionality

Grid forming

(GFM) inverters

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Aggregated PV outputFrequency

Case study – O’ahu, Hawai’i, 50% distributed PV

System at 920 MW load, 466 MW PV

Event is loss of 62 MW load

GFL controls w/

frequency-watt function

GFM CERTS controlsGFM inverters

responds much faster

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Total System LoadFrequency

Case study – O’ahu, Hawai’i, 50% distributed PV

System at 1,080 MW load, 540 MW PV

Event is loss of 200 MW generator

GFL controls with

frequency-watt function

GFM CERTS controls

Load tripping

events

Better frequency control

avoids load tripping

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M. E. Khatib, W. Du, R. Lasseter, “Evaluation of Inverter-based

Grid Frequency Support using Frequency-Watt and Grid Forming

PV Inverters”, SAND ID #659600

A current USDOE GFM controls project, led by NREL

Develop and implement in hardware GFM controls, specifically Virtual Oscillator Controls (VOC)

Study methods to aggregate distributed inverters for large-scale simulations

Assess GFM modeling requirements for large-scale simulation platforms (e.g., PSSE, PSLF)

Compare performance vs. GFL inverters for increasing % share

Identify research gaps and priorities for possible future investment

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GFM/VOC project – Controls development, hardware implementation

The VOC is implemented and tested in two sets of hardware test beds:

◦ NREL customized multi-inverter hardware test bed.

◦ Off the shelf multi-inverter hardware test bed with SunPower.

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Johnson BB, Sinha M, Ainsworth NG,

Dörfler F, Dhople SV. Synthesizing

virtual oscillators to control islanded

inverters. IEEE Transactions on

Power Electronics. 2016

Aug;31(8):6002-15.

GFM/VOC project – Model aggregation for system studies

Developed model aggregation method, validated using prototype VOC inverters

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[2] Scaling laws for grid forming: M. Khan, B.

Johnson, V. Purba, and S. Dhople, “A Reduced-

order Aggregated Model for Parallel Inverter

Systems Controlled with Virtual Oscillator

Control,” Workshop on Control and Modeling

for Power Electronics, 2018.

GFM/VOC project – Model aggregation for system studies

Custom PSLF model of GFM VOC controls

Preliminary simulation results with 39-bus system representative of large grid (e.g., WECC)

Refinement and validation efforts under way

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System at ~50% share of inverter-based generation (PV)

Simulated a generator trip (Unit 10, ~4% of pgen)

Upcoming USDOE Workshop – You are Invited!14

Grid-Forming Inverters for Low-inertia Power Systems

February 26-27 *, 2019 – NREL, Golden Colorado, USA

Confirmed Speakers:Vijay Vittal (ASU), ark Ahlstrom (NextEra Energy), Danny Zimmanck (Enphase), Thibault Prevost (RTE), Alejandro

Domingues Garcia (UIUC), Aranya Chakraorty (NCSU), Marcelo Colombino (NREL), Scott Mason (SEL), Kevin Schneider (PNNL), Duncak Calloway (UC-Berkeley), David Porter (S&C Electric), Deepak Romasubramanian

(EPRI), Ulrich Muenz (Siemens), Philipp Strauss (Fraunhofer-IWES)

For more information, contact:

Brian Johnson, brianbj@uw.edu Yashen Lin, yashen.lin@nrel.gov Abraham Ellis, aellis@sandia.gov

This workshop will gather experts from universities, research institutes, equipment manufactures and utilities interested in Grid Forming Inverters. Participants will review

the state-of-the-art, and identify future research needs.