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i

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

August 2017 

3. REPORT TYPE AND DATES COVERED

Technical Report

4. TITLE AND SUBTITLE

Hybrid Locomotive for Energy Savings and Reduced Emissions

5. FUNDING NUMBERS

FR-RRD-0015-10-01 6. AUTHOR(S)

Brent Ballew, Gibson Barbee, Timothy Cleary, Lincoln Scott Keegan, Andrew Wilson, 

Stephen Sean Woody

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Norfolk Southern

209 Shenandoah Avenue, NE

Roanoke, VA 24016

8. PERFORMING ORGANIZATION 

REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation 

Federal Railroad Administration

Office of Railroad Policy and Development

Office of Research, Development and Technology

Washington, DC 20590

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AGENCY REPORT NUMBER

DOT/FRA/ORD-17/13

11. SUPPLEMENTARY NOTES

COR: Melissa Shurland

12a. DISTRIBUTION/AVAILABILITY STATEMENT

This document is available to the public through the FRA Web site at http://www.fra.dot.gov. 

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13. ABSTRACT (Maximum 200 words)

Norfolk Southern Corporation (NS) and Pennsylvania State University tested several different battery systems in hybrid 

locomotives. Advanced lithium-ion battery technology was the only kind that displayed the capacity to perform in heavy 

switching or local service. Testing proved hybrid locomotives could reduce emissions and save fuel, sometimes in significant 

amounts. However, even with the best assumptions taken into consideration, these locomotives would require high annual 

operating subsidies.

14. SUBJECT TERMS

Hybrid locomotive, battery, lithium-on battery, advanced lithium-on battery technology

15. NUMBER OF PAGES

32

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NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. 239-18

298-102
ii

METRIC/ENGLISH CONVERSION FACTORS

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE)

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in)

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in)

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft)

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd)

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE)

1 square inch (sq in, in2) = 6.5 square centimeters (cm2) 1 square centimeter (cm2) = 0.16 square inch (sq in, in2) 

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, yd2) 

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2) 

1 square mile (sq mi, mi2) = 2.6 square kilometers (km2) 10,000 square meters (m2) = 1 hectare (ha) = 2.5 acres

1 acre = 0.4 hectare (he) = 4,000 square meters (m2) 

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE)

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz)

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb)

1 short ton = 2,000 pounds 

(lb)

= 0.9 tonne (t) 1 tonne (t) =

=

1,000 kilograms (kg)

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE)

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz)

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt)

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt)

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal)

1 pint (pt) = 0.47 liter (l)

1 quart (qt) = 0.96 liter (l)

1 gallon (gal) = 3.8 liters (l)

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3) 

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT)

[(x-32)(5/9)] °F = y °C [(9/5) y + 32] °C = x °F

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 3 4 5

Inches

Centimeters 0 1 2 3 4 5 6 987 1110 1312

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSIO

 -40° -22° -4° 14° 32° 50° 68° 86° 104° 122° 140° 158° 176° 194° 212°

 

°F

 °C -40° -30° -20° -10° 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100°

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286 Updated 6/17/98
iii

Contents

Executive Summary ........................................................................................................................ 1

1. Introduction ................................................................................................................. 2

1.1 Background ................................................................................................................. 2

1.2 Objectives .................................................................................................................... 6

1.3 Overall Approach ........................................................................................................ 7

1.4 Scope ........................................................................................................................... 8

2. NS 999 Operation and HLS Testing ............................................................................ 9

2.1 NS 999 Operation ........................................................................................................ 9

2.2 HLS Testing .............................................................................................................. 10

3. Penn State University Testing ................................................................................... 11

3.1 Accelerated Switcher ................................................................................................. 11

3.2 Hybrid Pulse Power Characterization ....................................................................... 12

3.3 Capacity Tests ........................................................................................................... 13

3.4 SIL and HIL ............................................................................................................... 14

3.5 Hybrid Locomotive Analysis .................................................................................... 18

4. Conclusion ................................................................................................................. 23

5. References ................................................................................................................. 24

Abbreviations and Acronyms ....................................................................................................... 25
iv

Illustrations

Figure 1. NS 999 under test at Rose Yard in Altoona, PA ............................................................ 2

Figure 2. NS 999 traditional lead-acid battery voltage variation across a string of 54 batteries 

after charging. Top histogram (w/ equalization). Bottom histogram (w/o equalization) ..... 3

Figure 3. HLS lead carbon battery voltage variation across a string of 54 batteries after charging

................................................................................................................................................. 4

Figure 4. NS 999 battery ISO container manufactured at DropBox, Inc. ...................................... 4

Figure 5. Battery ISO container in place on NS 999 ..................................................................... 5

Figure 6. IntraPack battery trays in place on NS 999 .................................................................... 5

Figure 7. NS 999 charge and discharge testing at Juniata locomotive shop .................................. 6

Figure 8. NS 999 material yard switching load profile .................................................................. 9

Figure 9. HLS outfitted with East Penn UltraBattery string ........................................................ 10

Figure 10. Graph demonstrating typical Accelerated Switcher cycle current demand ................ 11

Figure 11. AV900 current and voltage output during Corvus battery pack Advanced Switcher 

cycling ................................................................................................................................... 12

Figure 12. Corvus voltage during HPPC test ............................................................................... 13

Figure 13. Corvus amperage during HPPC test ........................................................................... 13

Figure 14. Corvus battery pack capacity test results.................................................................... 14

Figure 15. Top-level of locomotive powertrain model ................................................................ 15

Figure 16. FLC fully discharges the battery with steady state battery operation ........................ 15

Figure 17. FLC logic commands a series of constant current cycles to operate the battery in a 

steady state manner ............................................................................................................... 16

Figure 18. Corvus battery system enclosed in ESPEC chiller ..................................................... 17

Figure 19. Interface diagram of HIL testing station .................................................................... 18

Figure 20. Multi-Vari chart displaying annualized CO2 pollution (lbs.) offset ........................... 20

Figure 21. Multi-Vari chart displaying annualized battery cost .................................................. 21

Figure 22. Surface plot displaying effects of varying battery cost and fuel cost vs. annualized 

savings due to hybridization ................................................................................................. 22
v

Tables

Table 1. FLC performance metrics .............................................................................................. 16
1 

Executive Summary

From April 2014 to December 2015, Norfolk Southern Corporation (NS) continued the project it

started in 2008 to develop the NS 999 battery electric switcher locomotive by moving the unit to 

Roanoke, VA, for use in switcher service. NS found the lead-carbon batteries currently installed 

on the NS 999 had approximately 50% of expected capacity and could not complete a full shift 

of switcher duty. After about 3 months of service, several electrical parts on the NS 999 failed 

while the unit was charging. Failure analysis was underway at the time of this research project. 

The Federal Railroad Administration (FRA) sponsored the study through continued laboratory 

testing of two other battery chemistries for use in both switcher and road service locomotives. 

Testing of a high-capacity lead-carbon battery string for switcher use at NS showed that this 

battery better withstood simulated switcher duty than previously tested lead-carbon batteries did. 

Pennsylvania State University (Penn State) tested an advanced-chemistry lithium-ion battery 

pack for use on both a switcher and road locomotive. This testing showed that the lithium-ion 

pack provided significant energy storage and would be suitable for more rigorous switching 

duties, local service, and road use. Penn State also characterized the lithium-ion pack with

Hybrid Pulse Power Characteristic (HPPC) testing and capacity tests. Using this information, 

Penn State created a hybrid locomotive model that shared the load between a diesel engine and 

the lithium-ion pack. The model allowed dynamic braking energy to recharge the battery pack. 

Penn State checked the model’s accuracy by comparing the model’s results to hardware tests 

using the lithium-ion pack. NS then used this model to run a designed experiment that showed a 

hybrid locomotive could reduce emissions of pollutants. However, the resulting fuel savings do 

not offset the capital cost of the battery pack; so, each hybrid locomotive would need a large 

annual subsidy. 
2

1. Introduction

Wide fluctuations in diesel fuel costs and advances in battery energy storage technology have 

prompted renewed interest in electric locomotives and hybrid locomotive systems. In switching 

service, a battery Energy Storage System (ESS) would allow for a zero-point source emission 

locomotive in non-attainment areas while a line-haul (road) hybrid would reduce emissions and 

improve efficiencies by an estimated 8–15% in some freight applications. The Norfolk Southern 

Corporation (NS) strategic research plan was to develop a battery electric switcher locomotive as 

an ESS research platform with the ultimate goal of developing a road hybrid locomotive capable 

of recovering dynamic braking energy by means of an ESS.

1.1 Background

Project Work 2008-2010 

In 2008, NS began to develop a prototype battery powered all-electric switcher locomotive that

used an array of 1,080 conventional 12-volt lead-acid batteries. NS unveiled the all-electric 

battery powered switcher locomotive, NS 999, at its Juniata locomotive shop in Altoona, PA, on 

September 28, 2009. 

Figure 1. NS 999 under test at Rose Yard in Altoona, PA

Operating the NS 999 switcher locomotive identified numerous challenges associated with

charging and discharging long strings of lead-acid batteries. Poor battery management caused

large variations in individual battery voltage and State of Charge (SoC) across the battery strings. 

The voltage and SoC variations resulted in premature battery failure, reduced reliability and 

lower locomotive horsepower. Due to the premature battery failures, initial testing of the NS 

999 was concluded in March 2010, and the ESS was disassembled in February 2011. 

Project Work 2011-2013

Follow-up work in 2011 through 2013 focused on testing solutions to several shortcomings 

identified from initial NS 999 field trials. These included redesign of the Battery Management 
3

System (BMS), exploration of alternative battery technologies and repackaging of the energy 

storage system to improve maintenance and battery thermal issues (seen in laboratory testing). 

To support the test program, design and construction of an NS battery test laboratory, or Hybrid 

Locomotive Simulator (HLS), was completed in November 2011. The HLS included BMS 

design enhancements and a new battery technology to be tested prior to reassembling the 

locomotive. Comprehensive full-scale (charge/discharge cycle testing of two 700v battery 

strings) laboratory testing combined with energy modeling was initiated to understand and 

optimize battery performance for both switcher and road service duty cycles. 

The new battery technology was a lead carbon battery developed by Axion Power International 

Inc., referred to as the Axion pack hereafter. This battery technology removes the sulfation 

failure mode occurring from poor battery management, which reduced the expected life of the 

conventional lead acid batteries in the original NS 999. Further, the battery’s higher dynamic 

charge acceptance appeared to offer a greater opportunity to capture the dynamic brake energy 

with less energy fade and a longer projected service life.

Figure 2. NS 999 traditional lead-acid battery voltage variation across a string of 54 

batteries after charging. Top histogram (w/ equalization). Bottom histogram (w/o 

equalization) 
4

Figure 3. HLS lead carbon battery voltage variation across a string of 54 batteries after 

charging

The approach to the redesign of the NS 999 battery packaging was to design a packaging system 

that utilizes passive cooling based on current industrial Uninterruptible Power Supply (UPS) 

designs that can then be ruggedized for the railroad environment. IntraPack Corp, a leader in 

stand-by power battery systems, designed and manufactured the battery trays, and DropBox, Inc, 

a custom ISO container modification specialist, designed and manufactured the battery container 

to hold the battery trays.

Figure 4. NS 999 battery ISO container manufactured at DropBox, Inc. 
5

Project Work 2014 

The NS 999 rebuild at the Juniata locomotive shop was completed in October 2014, and the 

battery switcher returned to Rose Yard in Altoona, PA, during the fourth quarter of 2014 for 

initial testing. After testing, the locomotive was placed in revenue service in the NS Roadway 

Material Yard in Roanoke, VA. The NS 999 has been in operation in this service since February 

2015. 

Figure 5. Battery ISO container in place on NS 999 

Figure 6. IntraPack battery trays in place on NS 999 
6

Figure 7. NS 999 charge and discharge testing at Juniata locomotive shop 

In parallel to NS 999 rebuild efforts and continued HLS testing, NS worked with researchers at 

the Penn State Battery Application Technology Testing & Energy Research Laboratory 

(BATTERY) for exploration into and testing of “next generation” battery technologies, such as 

lithium-ion variants and nickel metal hydride, for the road hybrid locomotive application. 

For full-scale road hybrid battery testing at BATTERY, NS selected the Corvus Energy AT6500 

Energy Storage Modules (6.5kWh) featuring Dow Kokam’s Lithium Nickel Manganese Cobalt 

(NMC) polymer cells. The Corvus Modules are a viable candidate for a road hybrid due to their 

favorable combination of energy density, cycle life, advanced BMS and industrial experience 

with hybrid marine watercraft. After selection of the Corvus battery, preliminary work began 

into the development of a locomotive model that would be used in hybrid locomotive Software 

in the Loop (SIL) computer simulations and Hardware in the Loop (HIL) battery testing using 

actual locomotive duty cycles. 

1.2 Objectives

The general objective of this project is to continue the FRA grant activities initiated under

Agreements FR-RRD-0015-10-01-00 through FR-RRD-0015-10-01-04, of researching the 

feasibility and ultimate development of a hybrid battery powered road locomotive. 

Specific objectives for the grant period include: 

1. Continuing to operate the NS 999 switcher locomotive in revenue service to trend 

capacity and efficiency for comparison to diesel engines. Thus far, the NS 999 reliability 

has proven poor; largely due to non-battery systems including choppers, insulated-gate

bi-polar transistor (IGBT) and cooling system failures. The NS 999 prototype provides a 

unique opportunity to further study and define the technical challenges and long-term 
7

economics of battery-based energy storage systems. Ultrabattery testing – underway 

since December 2014 will continue. Thus far, the East Penn UltraBattery has tested with 

higher capacity, lower variation, and higher efficiency (resulting in less heating) then

previously proposed systems. 

2. Continuing laboratory testing of a 104-kWh string of 16 Corvus Energy AT6500 48V LiNMC battery modules, hereafter referred to as the Corvus string. It includes:

A. Accelerated switcher cycle testing. Findings will be compared against the results

obtained from previous evaluations of advanced lead-carbon battery technologies in 

terms of charge/discharge efficiencies, battery/cell variations, heat loads generated, 

etc. This item has been updated to run between 6 and 8 strings of Corvus AT6500 

battery modules against defined switcher load profiles. Coupled with the capacity 

testing this should give an indication of the feasibility of the Corvus system in an 

electric switcher locomotive. The series of tests will include the ability of the 

batteries to achieve this service as the battery modules age.

B. Hybrid Pulse Power Characterization testing (HPPC) of the Corvus string to further 

define the ideal operating range and potential for battery overheating by estimating 

the instantaneous resistance at various states of charge.

C. Additional capacity checks to confirm the manufacturer’s energy ratings for the 

Corvus string, noting cell variations and its influence on the overall useable energy. 

This test will be repeated as the Corvus string is tested to define life cycle 

degradation. 

D. Accelerated line-haul cycle testing using representative load profiles (“drive cycle”) 

derived from event recorder data in revenue service. Testing will explore various 

hybrid configurations (diesel engines), ESS size and utilization strategies. This task 

has also been updated to include running a Design of Experiment (DoE) including a 

full factorial of five different variables including: temperature, charge/discharge 

power, number of strings, two different load profiles, and gain (range of State of 

Charge and the speed at which the hybrid controller allows the batteries to change 

SoC). This DoE will include 32 different runs with two replicates or an estimated 64 

runs to optimize application of the Corvus string and define potential deficiencies. 

The end points of the DoE will be run first for evaluation prior to completing all the 

runs and replicates. This line-haul testing is also known as HIL testing and SIL 

simulations. 

1.3 Overall Approach

To further development of a zero-point source emission battery electric switcher the Corvus 

string will be tested using the previously developed “advanced switcher cycle.” Integration of 

these more energy dense batteries onto a switcher platform will allow more onboard capacity and 

less downtime due to recharging. Other switcher activities will be continued operation of the NS 

999 and HLS testing of the East Penn UltraBattery.
8

To determine viability of a road hybrid locomotive, NS and the Penn State BATTERY lab will 

perform HPPC tests to assess the effectiveness of the Corvus string. From these tests a battery 

model can be developed and integrated with the previously created locomotive model for SIL

computer simulations. With the SIL model we can simulate various road hybrid locomotive 

scenarios to determine the most viable configurations. Ultimately the battery model within the 

road hybrid SIL model will be “replaced” with the physical Corvus string and tested under the 

same conditions to determine fidelity between the computer simulations and physical cycling of 

the battery. If the fidelity is high, we can use the SIL as a surrogate for time consuming (1 run is 

approximately 30 hrs) physical testing.

With SIL and HIL results NS will determine the viability of a road hybrid locomotive. The 

analysis will include sections dedicated to energy recovery, emissions reductions and a financial 

analysis.

1.4 Scope 

The work contained within and performed during the grant period pertains to North American 

freight railroads. Load profiles, locomotive characteristics and engineering considerations have 

been developed with this specific industry in mind. Due to the flexible design of the test 

protocols, HIL and SIL models modifications can be made to accommodate other rail segments 

if given the appropriate inputs. 
9

2. NS 999 Operation and HLS Testing

2.1 NS 999 Operation

The Juniata locomotive shop completed construction of the second-generation NS 999 in 

September 2014. After a brief checkout in Altoona Yard, NS moved the unit to the Roanoke 

Roadway Material Yard in the 1st quarter of 2015. NS researchers checked and recorded data 

for 2 months while the locomotive was in use. 

During cold weather, the Axion pack had less capacity than it had shown during the previous 

laboratory testing. NS began charging the unit for one-hour at mid-shift to try to extend the 

unit’s run time to complete an entire shift. However, the Axion pack could not complete an 

entire shift even with the mid-shift charge or with warmer weather. NS estimated the Axion 

pack capacity was at approximately 50% of expected, but could not quantify the exact capacity 

because the unit’s software lacked a standardized capacity test. 

Figure 8. NS 999 material yard switching load profile 

After completing 22 switcher shifts, several electrical parts on the NS 999 failed while the unit 

was charging. A ruptured cooling line that leaked coolant onto the high-voltage bus likely 

caused the part failures, but a power surge from severe electrical storms in the area may have 

also caused the failures. Several improvements were made to the control software during the 

unit’s repairs: 

• Doubling the BMS CAN bus speed to fix a communication problem 

• Adding an improved state-of-charge (SoC) algorithm 

• Adding a standardized capacity test (20-amp discharge) similar to the laboratory tests 
10

Capacity testing after the repairs and upgrades showed the control software intermittently 

disabled strings to protect the equipment. This prompted further investigation, which found 

possible shorts within three of the battery trays and other potential issues with the power 

electronics. Analysis of these problems is still underway. 

2.2 HLS Testing

To address runtime issues with the NS 999, NS sought out a higher capacity lead-carbon battery. 

As a result, NS began testing a string of East Penn UltraBatteries in the Roanoke HLS. In 2015, 

The UltraBattery string completed about 425 (9900kWh) simulated switcher shifts. The testing 

has shown low within-string voltage variation and double the capacity compared with other leadcarbon batteries previously evaluated. These results make the UltraBattery a strong candidate for 

use in the current switcher service but not for more rigorous switcher service. 

Figure 9. HLS outfitted with East Penn UltraBattery string
11

3. Penn State University Testing

3.1 Accelerated Switcher

The purpose of the Accelerated Switcher cycle is to estimate the battery run-time in a switcher 

locomotive. It consists of simple charges and discharges that simulate the NS 999 in service. 

The cycle repeats until the battery has reached its lower voltage or SoC limit. 

Figure 10. Graph demonstrating typical Accelerated Switcher cycle current demand
12

Figure 11. AV900 current and voltage output during Corvus battery pack Advanced 

Switcher cycling

Previous Accelerated Switcher testing with the Axion pack yielded 4.5 hours of total runtime. 

This result is nearly identical with the runtime seen in NS 999 field service. Testing of the 

Corvus pack produced a runtime of 26 hours in Advanced Switcher testing. With this runtime, 

the NS 999 could complete a full day of switching without need of a recharge instead of the 

single shift that it can complete with lead-carbon packs. The Corvus pack may allow for more 

power and energy demanding switching service such as hump yard switching or even “local 

service” traveling around a city switching industry customers.

3.2 Hybrid Pulse Power Characterization

Hybrid Pulse Power Characterization testing is intended to determine dynamic power capability 

over the device’s useable voltage range using a test profile that incorporates both discharge and 

regenerative pulses. The primary objective of this test is to establish, as a function of depth-ofdischarge, the discharge power capability and the regenerative power capability. 
13

Figure 12. Corvus voltage during HPPC test 

Figure 13. Corvus amperage during HPPC test

The voltage response curves are then used to derive the fixed (ohmic) cell resistance and cell 

polarization resistance as a function of state-of-charge. The resistance measurements will be 

used to evaluate resistance degradation during subsequent life testing and to develop hybrid 

battery performance models for vehicle systems analysis [1]. Penn State used the information 

from this test to develop the battery model used with the hybrid locomotive model. 

3.3 Capacity Tests

Penn State performed multiple capacity tests on the Corvus pack during 2015 to record the 

capacity loss, or State of Health (SoH), as it degraded over time. Corvus reported the pack’s

capacity at 150 A-hrs (at 100% Depth of Discharge [DoD]). Penn State’s tests did not confirm 
14

that capacity. However, Penn State limited the previous charge to about 93% SoC to prevent 

overcharging the battery.

Figure 14. Corvus battery pack capacity test results

3.4 SIL and HIL

Due to multiple unpredictable full battery charge and discharge cycles over the course of a multiday road hybrid locomotive duty cycle an accurate generic drive cycle is difficult to develop. 

The two categories of testing that can be conducted to simulate a road hybrid locomotive are 

software-in-the-loop and hardware-in-the-loop testing.

SIL is used as a development tool for locomotive/battery control logic and also is used as a 

benchmark for HIL testing. In other words, matching results from SIL and HIL validates both 

the integrity of the computer model and the proper functioning of the hardware setup. A SIL 

simulation is to be used to analyze the effectiveness of the control logic and as performance 

index that the HIL tests are expected to match. HIL test reports are to be used to validate the 

functionality of all of the systems working together. HIL results also are used to give a close 

estimate to the battery performance in a real-world application. 

3.4.1 SIL Software Setup

The MATLAB/Simulink environment was used as the main tool to develop the locomotive 

powertrain model to be used in simulation. Power demand and time are the only inputs into the 

model. This power demand is the culmination of actual data obtained from locomotives in 

operation. The power demand over various drive cycles was provided by NS for the 

development of the power split control algorithms. Figure 15 shows the highest level of the 

model with power demand as the single input and output power from the three forms of energy 

transmission (diesel generator, battery, and dynamic brake) included. 
15

Figure 15. Top-level of locomotive powertrain model

Power-split Model

As the power demand is input into the power split model a forward looking control (FLC) 

algorithm is initiated. The control method applied here is to operate the battery in a steady state 

manner. This means the control method should command the battery to output a constant current 

as often as possible. The logic here is to recognize discharge and charge cycles, and then apply a 

constant current over that cycle to reach either a discharge or charge respectively. This FLC is 

used to operate the battery in a fashion that decreases negative SoH effects that occur in 

aggressive control strategies while also resulting in minimal fuel consumption.

Figure 16. FLC fully discharges the battery with steady state battery operation

In observing the SoC over the simulation, FLC effectively discharges the battery completely just 

as each discharge cycle ends, rather than quickly discharging and sitting at a minimum SoC, 

which is an issue with the other control methods. Charge cycles are also more effective as often 

the power profile allows for charging at a maximum rate. This allows all possible available 

regenerative energy to be captured by the ESS.

The proper functionality of the steady state battery operation is more easily seen in Figure 17. 

This is a visual of the current command over a small-time window.
16

Figure 17. FLC logic commands a series of constant current cycles to operate the battery 

in a steady state manner 

FLC recognizes charge and discharge events and commands an average current over the cycle to 

operate the battery in a steady state manner. The benefit of this can be seen in the much lower 

negative effect on battery SoH. This is achieved by eliminating rapid charge and discharge 

cycling as well as commanding constant current levels during these cycles.

Table 1. FLC performance metrics

Potential Discharge Energy 34.04 MWhr (1636.6 gallons of diesel)

Potential Regenerative 

Energy

8.107 MWhr 

Energy Offset by Battery 3.58 MWhr (172.35 gallons of diesel)

Energy Captured 3.08 MWhr

Generator Diesel 

Consumption

1458.7 gallons of diesel

SoH Loss 0.1983% 

Diesel Generator Model

The diesel generator model accounts for all power demanded that the battery cannot meet. The 

diesel generator will fill the excess power demand that the battery does not output. Power in kW 

from the generator is translated into fuel consumption for later use in comparison of the effect on 

fuel consumption of each control strategy. 

Battery Model

A simple linear battery model was used for software-in-the-loop simulations. The model 

consists of lookup tables based on the data from HPPC battery characteristic tests and from 

Corvus that were used in hardware-in-the-loop simulation. The battery model is necessary to test 

that commanded battery output from the controller is as expected before implementing battery 

hardware. It was not in use under HIL testing. 
17

Dynamic Brake Model

Dynamic braking provides the method of capturing kinetic energy under braking for storage in 

the ESS. The dynamic braking model simply monitors all negative power demands. Negative 

power corresponds to braking scenarios that, without hybridization, would be wasted in the form 

of thermal energy. Energy captured from dynamic braking charges the battery for later use [2]. 

3.4.2 HIL Hardware Setup

Corvus string

Figure 18 shows the battery system enclosed in an ESPEC ETC-200L chiller for simulation of 

thermal management. The battery model being used is the Corvus AT6500-250. The battery 

modules are arranged in a 16-module series element configuration.

Figure 18. Corvus battery system enclosed in ESPEC chiller

AV900

The AV900 Electrical Loading Device gives the hardware simulation the capability to meet 

battery power output capabilities. This machine is capable of operating continuously up to 1000 

Amps, at 1000 Volts, and up to 250 kW. The AV900 has the benefit of having automatic cutoff 

switches in the case of power outage or operation exceeding load capabilities

Component Interface

The key component in this setup is the Simulink Real-Time Target with communication to both 

the AV900 and battery system. There is then also a high power/high voltage interface between 

both the AV900 and battery system which is monitored and controlled by the Simulink RealTime Target. 
18

Figure 19. Interface diagram of HIL testing station 

3.4.3 Results

Penn State performed a series of tests to compare the results of HIL and SIL simulations. 

Factors included in the tests were:

• Allowable battery DoD (SoC range)

• Two load profiles 

• Ambient temperature 

Analysis of the results showed that the SIL model was sufficiently accurate to use as a proxy for 

further work. Discrepancies between the SIL and HIL primarily resulted from:

• Minor differences between the simulation’s BMS and the real pack’s BMS 

• Temperature effects on the Corvus pack’s ability to charge and discharge, which the SIL 

model does not consider. 

These discrepancies cause the hybrid locomotive model slightly to overstate real-world 

performance.

3.5 Hybrid Locomotive Analysis

Using the hybrid locomotive model, NS conducted a full factorial design of experiment to find 

the ideal number of battery strings and best battery operating range. Factors included in the 

simulations were:

• Power factor (number of battery strings) 

• Allowable battery DoD (SoC range) 

• Route (hilly or flat), which provided load profile 

To prevent terrain for a route from unduly influencing the results, each route consisted of a 

round-trip between origin and destination. Blocks in the experiment removed undue influence 
19

from train handling and dispatching. Blocks used data from an intermodal train from each route. 

Including center points, the designed experiment consisted of 72 simulations. 

The four primary outputs used to analyze the results were: 

1. Calculated battery life in years (assumed number of trips each year)

2. Gallons of fuel saved (calculated with data from a typical Tier 0 4,000-hp road 

locomotive) 

3. kWH to recharge the pack to initial value at the end of each round trip 

4. Pounds of emissions prevented (calculated with data from a typical Tier 0 4,000-hp road 

locomotive) 

Using the first three outputs, NS calculated an Effective Uniform Annual Cost (EUAC) for each 

run to determine the financial impact. EUAC was calculated with a battery cost of $1250/kWh 

and a fuel cost of $3.00/gallon. The cost estimate of the battery pack was determined using the 

typical 2015 cost of a Li-NMC pack adding a BMS, cooling system and packaging (typically 

50%). The cost of capital used in the calculations was 10%. Expenses such as additional 

electrical components and control system upgrades necessary for hybridization were not included 

in the EUAC. As a result, the calculated EUAC understates the costs of an actual hybrid 

locomotive. 

Analysis of the experiment showed that variable settings that produced the best financial results 

did not correspond to the best reductions in emissions and vice versa. The analysis also showed 

that power factor and load profile (route) were the key variables. In hilly terrain, more dynamic 

brake energy is available to recharge the battery, which reduces emissions and fuel use but also 

reduces battery life with more frequent cycling. Similarly, a higher power factor and larger SoC 

range allows more dynamic brake energy to be recovered, which reduces emissions and fuel use 

but increases the initial battery cost and reduces its life with deeper discharges. 
20

Figure 20. Multi-Vari chart displaying annualized CO2 pollution (lbs.) offset

Figure 21 shows that the capital cost of the battery pack cannot be recovered at current prices for 

fuel and batteries. The overall trend in the figure indicates that a smaller battery (lower capital 

costs) operating over a longer period of time (fewer cycles in flat terrain yields longer battery 

life) is more economic than a larger battery pack recovering greater amounts of dynamic brake 

energy.

Flat Hilly

12000

11000

10000

9000

8000

7000

6000

5000

4000

3000

Flat Hilly

3

Profile

Poll Offset

8

30

40

50

Range

SoC

Multi-Vari Chart for Poll Offset by SoC Range - Power Factor

Panel variable: Power Factor
21

Figure 21. Multi-Vari chart displaying annualized battery cost 

NS created a response surface to identify “break even” points where the annualized cost of the 

battery pack was offset by fuel savings. Figure 22 uses the best-case hybrid locomotive 

simulation and the calculated annualized cost at a given fuel and battery cost. Note that this 

“break even” analysis does not consider the cost of the additional power electronics and control 

system modifications that would be needed to build a hybrid locomotive. 

Flat Hilly

-100000

-150000

-200000

-250000

-300000

Flat Hilly

3

Profile

Total Cost

8

30

40

50

Range

SoC

Multi-Vari Chart for Total Cost by SoC Range - Power Factor

Panel variable: Power Factor
22

Figure 22. Surface plot displaying effects of varying battery cost and fuel cost vs. 

annualized savings due to hybridization 
23

4. Conclusion

Based on the work detailed in this report, Norfolk Southern Corporation (NS) concluded that a 

battery switcher that could meet railroad operating demands must use an advanced lithium-ion 

battery technology. This was the only battery technology tested that displayed the capacity to 

perform in heavy switcher or local service. However, the estimated cost for such a unit would 

exceed $1 million in batteries alone and was not economically justifiable. 

Also, based on the work detailed here, NS concluded hybrid locomotives would not be feasible 

at this time. Testing proved hybrid locomotives could reduce emissions and save fuel, 

sometimes in significant amounts. However, even with the best assumptions taken into 

consideration, these locomotives would require high annual operating subsidies. 
24

5. References

1. U.S. Department of Energy Vehicle Technologies Program. Battery Test Manual For Plugin Hybrid Electric Vehicles. March 2008. 

2. Wilson, Andrew. Power Management Control Optimization of a Hybrid Electric-Diesel 

Locomotive. ASME Joint Rail Conference 2016. JRC2016-5777. 
25

Abbreviations and Acronyms

BATTERY Battery Application Technology Testing & Energy Research Laboratory

BMS Battery Management System

DoD Depth of Discharge

DoE Design of Experiment

ESS Energy Storage System

EUAC Equivalent Uniform Annual Cost

FLC Forward Looking Control

FRA Federal Railroad Administration

HIL Hardware in the Loop

HLS Hybrid Locomotive Simulator

HPPC Hybrid Pulse Power Characteristic

IGBT Insulated-gate Bipolar Transistor

NMC Nickel Manganese Cobalt

NS Norfolk Southern Corporation

SIL Software in the Loop

SoC State of Charge

SoH State of Health

UPS Uninterruptible Power Supply