Overview of CGI/Dynos/PHIL 

Platform

Przemyslaw Koralewicz, Robb Wallen, 

and Vahan Gevorgian

November 16, 2018

5th Annual International Workshop on 

Grid Simulator Testing of Energy Systems and Wind 

Turbine Powertrains 

NREL/PR-5000-72923
NREL | 2

National Wind Technology Center

New: 1-MW/1-MWh battery

New: 430-kW PV array

2.5 MW Dynamometer

5 MW Dynamometer NWTC Wind Turbines

Existing SunEdison

1 MW PV Array

Controllable Grid Interface (CGI)

for Grid and Fault Simulation

Switchgear 

Building

Xcel

Substation

(Eldorado Canyon)

1 MW / 1 MWh BESS

CGI Bus

Xcel Bus

(7 MVA continuous / 40 MVA s.c.)

13.2 kV 115 kV

10 MW line capacity

(upgrade to 20 MW by 2018 with new 115 

kV transmission line, NWTC on-site 

substation and 35.4 kV collector system)

GE 1.5 MW

Siemens 2.3 MW Alstom 3 MW

Gamesa 2 MW

ESIF

DC

AC

AC

DC

DC

AC

DC

AC

DC

AC

13.2 kV 

Link with ESIF grid simulator, HPC, 

visualization and PHIL capabilities

Research Electrical 

Distribution Bus (REDB) 

AC and DC

CART2 and CART3

Future load for 

microgrid testing 

13.2 kV 

First Solar

430 kW PV array

DC coupled

250kW PV

1.4MW/250kWh BESS

Source: NREL

Source: NREL

Source: NREL / Dennis Schroeder (40806)
NWTC Dynamometers

Specifications

2.5-MW Dyno

• 5.8 MW 

(on the low-speed shaft)

• 12–24 rpm (at full power) 

• 4.6 MNm (3.4 M ft-lb) 

max torque

• Non-torque loads,

5 degrees of freedom

• Dual 75-t cranes, 

45-ft (14-m) hook height

• 20 x 12-m test bay

• 5-degree fixed-drive 

table tilt.

5-MW Dyno

• 2.5 MW 

(on the low-speed shaft)

• 17–31 rpm (at full power)

• 1.64 MNm (1.2 M ft-lb) 

max torque

• Non-torque loads,

3 degrees of freedom

• 50-t crane, 

30-ft (9-m) hook height

• 12.2 x 15.2-m test bay

• 0–6-degree adjustable- Source: NREL/Robb Wallen (17400) drive table tilt.

Source: NREL/Dennis Schroeder (25887)

Source: NREL/Mark McDade (27249)
NREL | 4

2.5-MW Dynamometer Projects

– Multiple projects in 2017–2018 for validating wind turbine power train 

low-voltage ride-through (LVRT) response to foreign grid codes (50 Hz using 

controllable grid interface [CGI])

– Preinstallation verification of Gearbox Reliability Collaborative 1.5 data 

acquisition system. The gearbox was installed in the U.S. Department of 

Energy-owned (DOE-owned) GE 1.5-MW turbine and is subjected to grid 

events using the CGI.

– Year 2019 projects include 

validation of two different 

wave energy devices.

GE 1.5-MW high-speed shaft 

instrumentation checkout at 

2.5-MW dynamometer. 

Installation of instrumented 

gearbox at NWTC. Source: NREL/Mark McDade (49050)

Source: NREL / Jonathan Keller (49498)
NREL | 5

C-Power wave energy device installation at the 

NREL 5-MW dynamometer. 

C-Power wave energy device installation at the 

NREL 5-MW dynamometer C-Power

• 2016–2018: Validation of the Columbia Power Technologies (C-Power) utility-scale wave energy device. The device was tested 

using realistic, oscillating, bidirectional speed and torque profiles. Testing was complete as of Nov. 2018.

• 2018: Validation of multimegawatt, medium-voltage, doubly-fed induction generator power train via direct coupling with 5-MW 

motor

• 2019: Projects include upgrading non-torque loading system to achieve 10-MNm moment capacity and potential wind turbine 

power train tests

• 2019: The 2.5-MW and 5-MW facilities will be upgraded with additional 13.2-kV medium-voltage feeds selectable between CGI 

or Xcel 

utility.

5-MW Dynamometer Projects

Source: NREL / Mark McDade (44103)

Source: C-Power website / www.columbiapwr.com/how-it-works/
NREL | 6

NWTC 7-MVA Controllable Grid Interface

Power rating

• 7-MW continuous

• 39-MVA short-circuit capacity (for 2 s)

• 4-wire, 13.2 kV.

Frequency control

• Fast output frequency control (3 Hz/s) within a range of

45–65 Hz

• 50/60-Hz operation

• Can simulate frequency conditions for any type of power system.

Voltage control (no load total harmonic distortion <2%)

• Balanced and unbalanced voltage fault conditions (zero-voltage ride- through and 130% high-voltage ride-through [HVRT])—independent voltage control for each phase on 13.2-kV terminals

• Response time: 1 ms (from full voltage to zero, or from zero back to full

voltage)

• Long-term symmetrical voltage variations (+/- 10%) and voltage magnitude modulations (0–10 Hz)—subsynchronous resonance conditions

• Programmable impedance (strong and weak grids).

Real-time digital simulator (RTDS) – power- hardware-in-the-loop (PHIL) capability

Source: NREL / Mark McDade
NREL | 7

Open-Loop Single PCC: DER Validation

Testing of grid connected inverters and tightly 

coupled generation mixes

• Testing of frequency responses

• Characterization of droop characteristics

• LVRT/HVRT testing

• Full 4Q operation testing

• Models validation

• Wide spectrum analysis (impedance).

Source: NREL

Source: NREL Source: NREL
NREL | 8

Open-Loop Single PCC: DER Validation Examples

Source: NREL
NREL | 9

Impedance Measurements

Source: NREL
NREL | 10

Impedance Measurements

Source: NREL
NREL | 11

Open-Loop Double PCC: DER Validation

Example device:

• Microgrid feeder breakers

• Power electronic tie controllers

• AC/AC converters

• Protective relays/synchronization check logic

• Transformers.

Capabilities:

• Ability to generate any angle difference

• Ability to generate independent frequencies

• Fault testing at CGI side possible

• CGI side can run as voltage or current source inverter 

(VSI or CSI).

Source: NREL
NREL | 12

Closed-Loop Testing: PHIL

• Voltage from simulation is tracked by CGI in real 

time.

• Current measured is injected back to RTDS model.

• Allows testing device under test under various 

grid conditions and events (e.g., microgrids)

- Distances between RTDS point of interconnection 

and CGI ca. 300 ft

- 2 Gb/s RTDS optical link: Glass Optical Fiber

- 10 Mb/s CGI-ABB proprietary link: Plastic Optical Fiber

- Data exchange every 25 us (40 kHz).

Source: NREL
NREL | 13

RTDS 9-Bus Transmission Model

Source: NREL
14

Assumptions Used for PHIL Testing of 9-Bus System with BESS

Generation loss = 3.8 GW/3.8%

No BESS cases for all 

penetration levels

Conventional Generators PV & Wind Loads Total H

Renewable

penetration

PGn, MW HG,

sec

PGdispatch

,

GW

PRn,

GW

Loads

GW

HTot

60% 53.3 4 40 60 100 2.13

40% 80 4 60 40 100 3.20

20% 106.7 4 80 20 100 4.27

15% 113.3 4 85 15 100 4.53

0% 133.3 4 100 0 100 5.33

HHTTTTTT =

HHGGPPGGGG + HHBBPPBB + HHRRPPRR

PPTTTTTT

HHRR = 0

Source: NREL
15

Renewable Penetration 60%: Inertia

Battery scaling assuming 100-GW system:

• 600 MW -> 0.6% 

• 1200 MW -> 1.2%

• 1800 MW -> 1.8%

BESS controlled proportional to ROCOF using 

LabView controller. H=50 s

Frequency response improves with increasing 

BESS installed capacity at 60% renewable 

penetration. 

BESS [MW] 0 600 1200 1800

60% 2.13 2.43 2.73 3.03

40% 3.20 3.50 3.80 4.10

20% 4.27 4.57 4.87 5.17

15% 4.53 4.83 5.13 5.43

0% 5.33 5.63 5.93 6.23

2.13 2.43 2.73 3.03

3.20 3.50 3.80 4.10

4.27 4.57 4.87 5.17

4.53 4.83 5.13 5.43

5.33 5.63 5.93 6.23 Source: NREL
16

Renewable Penetration: RTAC Inertia Controller

CT/PT

Synchrophasors

P&V set points

- Implemented inertia controller based on 

commercial of-the-shelf devices

- Found limitations on maximum inertia 

depending on where frequency is measured

- Tested various frequency sources. 

Source: NREL
NREL | 17

About RTDS Distribution 

Model

• Model based on data from PG&E

• BESS can be added using PHIL to two 

locations:

– Bus 640

– Bus 647.

• Four fault locations used for fault emulation:

– Bus 630: Fault at transmission level

– Bus 650: Fault at load branch—unfused

– Bus 672: Fault at load branch—fused (F3)

– Bus 691: Fault at motor branch—unfused

• Faults can be:

– 1 x L-G, 2 x L-G, 3 x L-G, 1 x L-L, 2 x L-L, open phase

– Low impedance: 0.1 Ohm

– High impedance: 10 Ohm.

Source: NREL
NREL | 18

CGI-RTDS PHIL Interface

• Instantaneous voltage measured in model and commanded to CGI

• Very fast tracking achieved thanks to instantaneous-to-phasor (I2P) algorithm

• Compensated phase delay.

• Positive-, negative-, and zero-sequence current injection into model

• Decoupled positive- and negative-sequence DQ current measurement

• Filtered with 10-ms filter for high-frequency stability.

Source: NREL
NREL | 19

About RTDS Distribution 

Model

• RTDS automated script • Total number of fault cases executed 

per script run (ca. 15 min): 53x

• For each test case, data were captured 

using RTDS: – 100-us resolution – 7 x 3 phase voltage measurements 

(magenta dots)

– 12 x 3 phase current 

measurements (blue arrows)

– 3-s data buffer – ~ 1.5 GB of data per run.

Source: NREL
NREL | 20

FLT630 Line A to Ground

Source: NREL
NREL | 21

FLT650 Line A to Line B

Source: NREL
NREL | 22

Spectrum of LVRT Voltage During Faults

Source: NREL
www.nrel.gov

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.

Thank you