NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Testing Distributed PV as Part of a Larger Electric System

Presenter: Anderson Hoke, P.E. - NREL

Integrating PV in Distribution Grids: Solutions and Technologies Workshop October 23, 2015

2

Device-level Testing vs. System-level Testing

• Device-level testing

• Evaluate DER response to external inputs (voltage, frequency, communications, HMI, time)

• No attempt to characterize effect of DER on larger system

• E.g. interconnection conformance testing, TrOV testing, efficiency characterization, open-loop advanced grid support function testing

• System-level testing

• Evaluate DER as part of a system (e.g. distribution feeder, EPS, microgrid)

• Characterize response of DER to system, response of system to DER, and dynamic interactions between the two

• System may include many DERs

• Tests may look at DER-DER interactions

• May focus on system-level stability, controls, optimization, communications, interoperability, cybersecurity, …

3

System-level Testing: Two Categories

• Hardware-only • Lab testing of multiple integrated hardware articles (e.g. microgrids)

• Demonstrations of one or more DERs in the field

• Power hardware-in-the-loop (PHIL) • Hybrid of simulation and hardware test

• Part of system tested in hardware, and part simulated in real-time software model

• Test device(s) in environment that emulates real-world dynamics

• Useful when:

• Real system cannot be easily experimented with (e.g. the grid)

• High-fidelity model of hardware not available

• Hardware DERs can be scaled to represent larger DERs

• Hardware elements may or may not be co-located (remote HIL)

Hardware System Level Testing Examples

5

Basic Microgrid Controller Testing

Example: Raytheon, CSIRO

BATTERY INVERTER

M1 M2

M3 M4 SOLAR INVERTER

MIID CB

IPEM CONTROLLER

DC-DC CONVERTER

GRID SIMULATOR

LOAD BANK

BATTERY SIMULATOR

PV SIMULATOR

SOLAR INVERTER

PV SIMULATOR

ESIF VLAN

208 Vac

Bus

DC

• Third-party validation of microgrid controller and other components

PHIL System-level Testing Examples

7

PHIL Testing of DER Grid Support Functions

• Hardware testing of advanced inverter/DER features with grid voltage and frequency dynamics simulated using PHIL

• Can simulate multiple PCCs simultaneously

PHIL real-time computer simulation

Voltage commands to AC source

ZTh

Grid dynamic model Inverter model

Va, Vb, Vc

Ia, Ib, Ic

LP filter

++Pgrid

Pinv

-Pload

Load profile

∆f1/R+-

Power set point

Governor

Turbine a

b

Measured currents

ZTh

ZTh

Thévenin voltage modelGrid/turbine freq. model

1/(2Hs+D)

Inverterunder test PV array /

DC source

Controlled AC voltage

source

~

LoadHardware-simulated grid

PHIL test emulating major grid frequency event, with commercial advanced inverter performing frequency ride-through:

0 10 20 30 4056

58

60

62

freq

uen

cy,

Hz

time, seconds

0 10 20 30 40-1

0

1

2

time, seconds

p.u

.

0 10 20 30 400.95

1

1.05

1.1x 10

10

pow

er,

p.u

.

f

P

Q

Vrms

Irms

8

Distributed PV with Energy Storage

• Simulation of high penetration of rooftop PV with battery storage on • IEEE123 feeder in GridLAB-D

• Historical residential commercial load profiles

• Added control strategies to inverter model: o Local Volt-VAR, Inverter smoothing, Transformer

smoothing, PV firming, PV curtailment

• PHIL testing at ~10kW scale • Replaced one inverter / PV / battery system in

the simulation with hardware

9

System-level Evaluation of Microgrid Controller

Example: SDGE- Borrego Springs, EPRI

• Evaluation of microgrid controller using hardware at-scale with simulated power systems via power hardware-in-the-loop (PHIL) or controller hardware-in-the-loop (CHIL)

• MW-scale PHIL

• RTDS and Opal-RT

PV

Energy Storage

Diesel / NG Generators

AC Loads

Aux / DC Loads

GS

Local Controller

Power Conditioningand Conversion

DC REDB AC REDB

Grid ModelDC Device Models

Bi-directionalProgrammable DC Supply

Bi-directionalGrid Simulator

M M

Local MicrogridHardware

In ESIF

ESIFEquipment

Distribution PMUWeather

Real-Time Data User Interface and Visualization

Real-TimeSimulator

LocalUser Interface

Ipv Id Rp

Rs

V

I

Market Pricing

Local UtilityConnection

GSAC Device Models

System Controller PCC

10

PHIL-based Development and Validation for ESI

PV Simulator

AC RLC Load BankInverterLocal PCC Model

Grid Simulator

M

Local Controller

Grid Model

DC

RED

B

M

AC REDB

Vpcc

Iinv

Vpcc

Vpcc

Iinv

Static

PV Array

Use of PHIL techniques to evaluate novel energy system devices and control systems connected to specific network configurations involves:

1. Validation of PHIL simulation configuration for a known condition (e.g., field data or hardware) to ensure reliability of technique with particular hardware

2. PHIL simulation with updated devices, models, or control systems to prove new developments before field implementation

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Multiple-PCC PHIL

System to be tested:

+-

+-

Z1

Inverter 1

Inverter 2

DC SourcesZ2

ZTh

Vgrid

i1

i2

VPCC1

igrid

+-

Inverter nZn

in

VPCC2

VPCCn

Vg

Inverter#1

Real-time computer simulation

Controlled AC voltage source

~

Grid dynamic model Inverter 1 model

Va, Vb, Vc Ia, Ib, Ic

Test hardware

PV / DC source

Inverter n model

Inverter#n

Controlled AC voltage source

~

Va, Vb, Vc Ia, Ib, Ic

PV / DC source

...

...

... Source and load powersGrid frequency

dynamic model

Phase angle

PCC n

PCC 1

One possible PHIL test setup:

12

Multi-inverter, Multi-PCC Volt-VAr Test

Reactive power

cycling between two

inverters with high

Q(V) slope

(a) (d)

(b) (e)

(c) (f)

(g)

(h)

(i)

Inverter#1

Real-time computer simulation

Controlled AC voltage source

~

Grid dynamic model Inverter 1 model

Va, Vb, Vc Ia, Ib, Ic

Test hardware

ZTh ZInv ZInv

PV / DC source

Inverter 2 model

Inverter#2

Controlled AC voltage source

~

Va, Vb, Vc Ia, Ib, Ic

PV / DC source

Vgrid

Test 14

1 2 3 4 5 6 7 8 90.8

1

1.2

1.4

time, seconds

voltage /

curr

ent,

p.u

.

1 2 3 4 5 6 7 8 9-2000

0

2000

4000

time, seconds

VA

Vrms1

Irms1

Vrms2

Irms2

Q1

P1

S1

Q2

P2

S2

Instability caused by

slower volt-VAr

response time • Simulated impedance in loop with actual inverters

– two different inverters from leading manufacturers

• Experimental validation with transient PHIL – no problems found in limited testing to date

13

Remote PHIL and Co-simulation Test Bed

Combines actual hardware testing using PHIL with co-simulation of larger electric power grid using off-the-shelf modeling tools. Very flexible architecture enables multi-site testing (e.g. NREL links to PNNL and CSIRO), and scenario flexibility

Very Flexible: • Arbitrary Grid: location, topology & equipment

• Demo: IEEE 8500 and 123 with no hardware changes

• Any scenario: normal ops, faults, contingencies • Demo: Cloud transients, home thermal physics

models • Actual hardware: no proprietary models required

• Demo: 2 advanced inverters at various points of common coupling

• Multi-site: hardware and/or simulation • Demo: PNNL (WA) link to NREL (CO) • CSIRO (Australia)

14

Cyber-Physical Microgrid Test Platform

• NSIL o OMNET++ for network

simulation – open source

o OPNET can be another option, but is costly

• Hardware o AC grid simulator, load

banks, DC power supplies, PV simulators, inverters

o Equipment under test

• PHIL o Opal-RT as real-time

simulation platform

o Emulation of energy storage, and distribution feeder

PVDiesel Generator

AC Load

GS

Bi-directionalDC Supply

Bi-directionalGrid Simulator

M

M

Critical AC Load

Controllable AC SupplyM

Microgrid Switch

Grid Model

PCC

Battery Model

SwitchesFilters Grid

connection

Inverter Model

Rs

RP

Microgrid

Microgrid Control Center

Network Switch

OMNET++ Communication Server

SITL

SITL

Re

al-t

ime

Sim

ula

tor

Ha

rdw

are

an

d P

HIL

NSI

L

Simulated Network in OMNET++