Estimation of Energy Storage Capability for Hybrid Electric Drivetrain Systems

PUTTING POWER TO WORK

ADVANCED COMPONENTS AND SYSTEMS DIVISION

Caterpillar Confidential: Green

Estimation of Energy Storage Capability for Hybrid Electric Drivetrain Systems

by

Wellington Y. Kwok*, Igor S. Ramos, Andrew A. Knitt, and Justin D. Middleton -- Caterpillar Inc. --

PUTTING POWER TO WORK CAT ELECTRONICS


Presentation Outlines

•  Background –  Hybrid systems in machines and heavy-duty equipment –  High-level battery / capacitor energy management algorithm

•  Technical Approach –  Measurements to High-Level Controls –  Calculations for Power Capability –  Calculations for Energy Availability and Acceptance –  Efficiency evaluation (for optimizing energy utilization on

complete machine operations)

•  Concluding Remarks



Background Example of Hybrid Electric Vehicle (Automotive)

CONVENTIONAL

ENGINE TRANS- MISSION

TIRE

TIRE

PARALLEL HYBRID

ENGINE TIRE

TIRE

DIFFEREN

TIAL

GEA

R

ELECTRIC MOTOR

CONVERTER/ INVERTER

ESS

SERIES HYBRID

TIRE

TIRE

ELECTRIC MOTOR

CONVERTER/ INVERTER

ESS

GEN ENGINE - Main engine power to drive tires - Downsize engine for hybrids - Direct reduction in fuel consumption



Background Example of Hybrid Excavator Configuration

Reference: - Komatsu Introduces the World�s Hydraulic Excavator: Hybrid Evolution Plan for Construction Equipment - M. Ochiai and S. Ryu, 7th JFPS International Symposium on Fluid Power, 2008 - D.Y. Jo, S. Kwak and N. Kim, 8th International Conference on Power Electronics, 2011

ENGINE HYDRAULIC PUMP

SWING MOTOR

CONVERTER/ INVERTER

DRIVE MOTOR

GEN

ARM / BOOM / BUCKET

M/G DRIVE

MOTOR

MAIN CONTROL VALVE

ESS

-  Shared engine power -  Multiple energy sources / sinks -  Multiple functions at once -  Single high-power operation -  Difficult for machine hybridization



Energy Storage Capability Method for Reporting Power and Energy

ENERGY STORAGE

MEAS

SOC (State of Charge)

SOH (State of Health)

POWER CAPABILITY

AVAILABLE ENERGY

HIGH LEVEL CONTROLS

OU

TPU

T REQUEST

CAPABILITIES

OCV, R

CAPACITY

Developed / Well-understood

Less focused / Application specific




ENERGY STORAGE

MEAS

SOC

SOH

POWER CAPABILITY

AVAILABLE ENERGY

HIGH LEVEL CONTROLS

OU

TPU

T REQUEST

CAPABILITIES

OCV, R

CAPACITY

WHAT? -  Potential functions -  Engine assist -  Regenerative braking



Energy Storage Capability Determine Discharge Pulse Power Capability – Baseline (Ideal)

FreedomCAR HPPC

D

DMINEQMDMINDMAX R

VVVP

)( ___

−=

Assumptions - Power capability at min. op. voltage - No limit to discharge current

t = 0

VEQM DVEQM

VMIN_D

I = 0

P = 0

Dt



Energy Storage Capability Determine Discharge Pulse Power Capability – Practice

t = 0

VEQM DVEQM

VMIN_D

I = 0

P = 0

Dt

IMAX_D

Current Limited

Voltage Limited

CALCULATE

CALCULATE

CALCULATE

CALCULATE

DEFINE

( )D

D_MINEQMD_MIND_MAX R

VVVP

−=

( )D

D_MINEQMD_MAX R

VV −=Ι

D_MIINV

IF

?D_MAXD_MAX Ι≤Ι$

DD_MAXEQMD_MIN RVV ×Ι$+=$

D_MAXD_MIND_MAX VP Ι$×$=

N

Y

END



Current Limited

Voltage Limited

Energy Storage Capability Determine Regen Pulse Power Capability – Practice

CALCULATE

CALCULATE

CALCULATE

CALCULATE

DEFINE

( )C

EQMC_MAXC_MAXC_MAX R

VVVP

−=

( )C

EQMC_MAXC_MAX R

VV −=Ι

C_MAXV

IF

?C_MAXC_MAX Ι≥Ι$

CC_MAXEQMC_MAX RVV ×Ι$+=$

C_MAXC_MAXC_MAX VP Ι$×$=

N

Y

ENDt = 0

VEQM

DVEQM

VMAX_C

I = 0

P = 0

Dt

IMAX_C




ENERGY STORAGE

MEAS

SOC

SOH

POWER CAPABILITY

AVAILABLE ENERGY

HIGH LEVEL CONTROLS

OU

TPU

T REQUEST

CAPABILITIES

OCV, R

CAPACITY

WHY? -  Continue operation -  Scale back / ramp up engine -  Charge energy storage device -  Dissipate excess energy

HOW? - E = ∫ P dt -  Min. Power ! overcharge / overdischarge -  Max. Power ! under utilized -  Avg. Power ! ??



Energy Storage Capability Determine Energy Availability / Acceptance – Concept

SOCHSOCLSOCOP

∆QL ∆QH

Usable Range

SOCH = 80%

SOCL = 20%

SOCH = 100%

SOCL = 50%

BATTERY CAPACITOR



Energy Storage Capability Determine Energy Availability / Acceptance – Concept

SOCHSOCLSOCOP

∆QL ∆QH

( )LOPPdL

PdPdPd

SOCSOCdtQ

dtVE

→Ι=Δ

Ι=

∫∫

Maintain at/above SOCL

( )HOPPcH

PcPcPc

SOCSOCdtQ

dtVE

→Ι=Δ

Ι=

∫∫

Maintain at/below SOCH

Remarks Energy ≠ Capacity



Energy Storage Capability Determine Energy Availability – Concept

SOCHSOCLSOCOP

∆QL ∆QH

Constant Power DischargeP1(t) = V1(t) * I1(t) = {Const}P2(t) = V2(t) * I2(t) = {Const}P3(t) = …:Pn(t) = ...

Vol

tage

Cur

rent

OCV

I = 0

V1(t)

I1(t)

∆QL = ∫t1 I1(t) dt

E1 = ∫t1 P1(t) dtE2 = ∫t2 P2(t) dtE3 = ∫t3 P3(t) dt

:En = ∫tn Pn(t) dt

V2(t)

I2(t)∆QL = ∫t2 I2(t) dt

Dis

char

ge E

nerg

y

Discharge Power

Time

{P1, E1}

{P2, E2}

{Pn, En}

t1t2

Energy Availability as a function of Discharge

Power at SOCOP



Energy Storage Capability Determine Energy Acceptance – Concept

SOCHSOCLSOCOP

∆QL ∆QH

Constant Power ChargeP1(t) = V1(t) * I1(t) = {Const}P2(t) = V2(t) * I2(t) = {Const}P3(t) = …:Pn(t) = ...

Vol

tage

Cur

rent

OCV

I = 0

V1(t)

I1(t) ∆QH = ∫t1 I1(t) dt

E1 = ∫t1 P1(t) dtE2 = ∫t2 P2(t) dtE3 = ∫t3 P3(t) dt

:En = ∫tn Pn(t) dt

V2(t)

I2(t)

∆QH = ∫t2 I2(t) dt Cha

rge

Ene

rgy

Charge Power

Time

{P1, E1}

{P2, E2}

{Pn, En}

t1t2

Energy Acceptance as a function of Charge

Power at SOCOP



Energy Storage Capability Determine Energy Availability / Acceptance – Practice

Interpolate Energy-Power at any SOC

between calibration curves

SOCHSOCL

∆QL4

∆QH4

Cha

rge

Ener

gy

Charge Power

Dis

char

ge E

nerg

y

Discharge PowerSOC1

SOC2

SOC3

SOC4

SOC1

SOC2

SOC3

SOC4

SOC1 SOC2 SOC3 SOC4

∆QL3

∆QH3∆QL2

∆QH2∆QL1

∆QH1

SOCH

SOCL



-2,500

-2,000

-1,500

-1,000

-500

0

500

1,000

1,500

2,000

2,500

-2,000 -1,500 -1,000 -500 0 500 1,000 1,500 2,000

Power, W

Ene

rgy,

JC - 2.40V to 2.50V D - 2.40V to 1.00V C - 2.20V to 2.50V D - 2.20V to 1.00VC - 2.00V to 2.50V D - 2.00V to 1.00V C - 1.80V to 2.50V D - 1.80V to 1.00V

Energy Storage Capability Determine Energy Availability / Acceptance – Practice

Charge at 1.5kW from 72% to 96% SOC

(1.80V to 2.40V)

Discharge at -100W from 88% to 40% SOC

(2.20V to 1.00V)




ENERGY STORAGE

MEAS

SOC

SOH

POWER CAPABILITY

AVAILABLE ENERGY

HIGH LEVEL CONTROLS

OU

TPU

T REQUEST

CAPABILITIES

OCV, R

CAPACITY

Enable Long-Term projection of

Power & Energy utilization

Overall Efficiency

Optimize among all other Energy Sources

& Sinks



Energy Storage Capability Estimating Charge and Discharge Efficiencies – Concept

t = 0

VEQM

I = 0

P = 0

Const Power

))t(V)t(V(C21E 0

2EQM

2EQMREMOVED −=

∫ Ι= dt)t()t(VEAVAILABLE

Absolute Energy Change in Equilibrium or

Thermodynamic State

Useable Energy Time Integral of

Instantaneous Power

Key Concept: Efficiency Usable vs. Absolute




t = 0

VEQM

I = 0

P = 0

Const Power

))t(V)t(V(C21E 0

2EQM

2EQMREMOVED −=

∫ Ι= dt)t()t(VEAVAILABLE

))()(()()(

022

21 tVtVC

dtttV

EE

EQMEQMREMOVED

AVAILABLED −

Ι== ∫η

)()(

)()()()(

0

0

00

00*+

+

++

++

=Ι

Ι≈

tVtV

ttVttV

EQMEQMDηt – t0 = Δt ! 0

Discharge Efficiency, ηD




∫ Ι

−==

dtttVtVtVC

EE EQMEQM

ACCEPTED

ADDEDC )()(

))()(( 022

21

η

t = 0

VEQM

Const Power

I = 0

P = 0

∫ Ι= dt)t()t(VEACCEPTED

))t(V)t(V(C21E 0

2EQM

2EQMADDED −=

t – t0 = Δt ! 0 )()(

)()()()(

0

0

00

00*+

+

++

++

=Ι

Ι≈

tVtV

ttVttV EQMEQM

Cη

Charge Efficiency, ηC



t = 0

VEQM DVEQM

I = 0

P = 0

DVEQM

t > 0

Energy Storage Capability Estimating Round-Trip Energy Efficiency – Concept

EOUT = ∫ V(t) Ι(t) dt

EIN = ∫ V(t) Ι(t) dt

CDt

t

IN

OUTRTrip

dtttV

dtttV

EE

ηηη ×=

Ι

Ι

==

∫

∫*

0

0

)()(

)()(

Round-Trip Efficiency Energy OUT vs. Energy IN



Energy Storage Capability Estimating Round-Trip Energy Efficiency – Concept

t = 0

VEQM DVEQM

I = 0

P = 0

DVEQM

t > 0 t* = 0 t*t = 0

VEQM DVEQM

I = 0

P = 0

DVEQM

t > 0 t* = 0 t*

Increased Charge Power

Decreased Charge Power

Higher ηC

Lower ηC



Energy Storage Capability Estimating Round-Trip Energy Efficiency – Practice

10

100

1,000

10 100 1,000

Discharge power, W/cell

Cha

rge

pow

er, W

/cel

l

99.5%99.2%

99%98.5%

98%97%

95%92% 90% 88% 85% 80%

75%

70%

65%

ηRTrip ~ 99%

Cycle at -30W/+20W (80.0% ! 79.9% --> 80.0% SOC)

ηRTrip ~ 97.5%

Cycle at -30W/+100W (80.0% ! 79.9% ! 80.0% SOC)

Round-Trip Efficiency Map at

80% SOC



Concluding Remarks

•  Technical Approach –  Evaluate Power Capabilities within system limits –  Predict Energy Availability / Acceptance at any charge state –  Map Roundtrip Efficiency based on charge / discharge powers

•  Benefits –  Enable system-level energy management –  Efficient projection of energy and power capabilities –  Optimization among multiple energy sources and sinks

Engineering

Estimation of Energy Storage Capability for Hybrid Electric Drivetrain Systems