07 Guezennec FC Workshop OSU YG

8/2/2019 07 Guezennec FC Workshop OSU YG

1/20

Supervisory Control of Fuel Cell

Vehicles

Fuel Cell Control Workshop Irvine, CA

April 3 & 4, 2003

Yann Guezennec, Giorgio Rizzoni and Gabriel Choi

Ohio State University

Center for Automotive Research

http://car.eng.ohio-state.edu


2/20

Focus on Fuel Cell Systems for automotive applications, more

particularly PEM

Emphasis on complete systems rather than in-depth component

analysis

Treat the electro-chemistry as a black box Two levels of modeling:

Quasi-static approach, i.e., steady-state characteristics +

slow thermal dynamics (suitable for energy analysis at the

system level and vehicle level, system optimization and

supervisory control strategy) Low-frequency dynamics approach, i.e., particularly the air

supply dynamics under varying loads as seen in automotive

powertrains (suitable for low-level system control)

Strong interplay between both levels

Overview of our PEM FC

Modeling Approach (contd)


3/20

Imbedded levels of modeling:

Stack: Computationally efficient, yet accurate black-box

fuel cell stack model environment as a function of relevant

operating and control parameters implemented in a

Matlab/Simulink

System: Fuel cell system (stack and necessary auxiliaries)

model implemented in Matlab/Simulink Vehicle: Fuel cell system model implemented within our

modular, scalable vehicle performance simulator (VP-SIM)

Overview of our PEM FCModeling Approach (contd)


4/20

Fuel Cell System Model Integrated into VP-SIM, aForward Vehicle Performance Simulator

P o we r t ra i n L a y e r

1

Tract ive Force (N)

Ft_ f

F t _ r

F t

W h e e l

C o u p l i n g

alp

ha

beta

em_

ctrl

fc_

trl

c_

gear

c_

brakeVC U

Te rmin a t o r5

Te rm in a t o r4

Te rm in a t o r3

T

w

F t

v

R e a r

Whee ls1

c _ b r a k e _ r

T_i

w_ i

T_ o

w_ o

R e a r

B ra k e s

e m _ c d e

V_ba t t

i_batt

p _ f c

V _ f c

i _ f c

V_ o

i_o

P o we r A mp f c

H V _ H 2

m f _ H 2

V

I

P E M_ Fu e l_ c e l l _ s y s t e m

H v

m f

H y d r o g e n T a n k

G ro u n d

T

w

F t

v

Fro n t

Whee ls1

c _ b r a k e _ f

T_ i

w_ i

T_ o

w_ o

Front

B ra k e s

V

i

T

w

E M 1

T_i

w_ i

T_ o

w_ o

Di f f e re n t i a l 1

V

i

B a t t e ry

2B ra k e A n g le

(0 to 1 )1A c c e l A n g le

(0 to 1)


5/20

PEM Fuel Cell Vehicles: a Need for

Hybridization ?

Hybridization (i.e., batteries, supercapacitors) isprobably needed for:

Fuel cell sizing optimization Cold start and dynamic response

Energy efficiency improvement (regen + shift inoperating conditions)

Lesser needs for low-level control and dynamic

response

Hybridization creates the need for vehicle-level,energy management (supervisory) control strategy


6/20

Fuel Cell Hybridization

The directionality of the electrical energy flow must be controlled in

hybrid fuel cell vehicle (similar to power split management problem

in ICE/EM parallel hybrids)

Need for power electronics to couple fuel cell system and

batteries/supercaps due to differences in voltage/current characteristiccurves

+++

Fuel

Cell

System---

+ +

Power

Converter

DC/DC

- -

+++

Battery

---

Electric

Motor

+

Power

Converter

DC/AC

-

++++High Voltage DC Bus ++++

-----High Voltage DC Bus -----

Fuel Cell Power

Control input

Electric Motor Power

Control input

IFC

Power flow from

fuel cell to DC high

voltage battery bus

Power flow between DC high

voltage battery bus and electric motor

(positive in traction, negative in

regenerative braking)

IBatt

+++

Fuel

Cell

System---

+ +

Power

Converter

DC/DC

- -

+++

Battery

---

Electric

Motor

+

Power

Converter

DC/AC

-

++++High Voltage DC Bus ++++

-----High Voltage DC Bus -----

Fuel Cell Power

Control input

Electric Motor Power

Control input

IFC

Power flow from

fuel cell to DC high

voltage battery bus

Power flow between DC high

voltage battery bus and electric motor

(positive in traction, negative in

regenerative braking)

IBatt


7/20

Aim of Supervisory Control Strategy

(Energy Management)

To define

Real time power distribution between FC and the

electrical accumulator (Pfc: control variable)

which:

Satisfy instantaneous driver power demand (Pem)

Minimize overall fuel consumption (global)

with respect to:

Components limits

Charge-sustaining constraints (global)


8/20

ECMS Control Strategy Highlights

Initially developed for parallel HEV

Applicable to any hybrid configuration Reducing the non-realizable global minimization

criterion to a realizable local one (causal)

Based on the concept of an equivalent fuel consumption

for the electrical accumulator

Computationally cheap for real-time implementation


9/20

Concept of Equivalent Fuel Consumption

Charge sustaining => All energy depleted from electricalaccumulator has to be replaced

An average Virtual accumulator specific fuel consumptionSC (gr/kW.hr) can be calculated:Fuel Tank Electrical

Accumulator

FuelCell

fcfm _&

Pbatt

Power

Converter

Pfc

Fuel Tank Electrical

Accumulator

FuelCell

fcfm _&

Pbatt

Power

Converter

Pfc

battfbatt mE _battSC

_batt f batt P m &


10/20

ECMS Principles At each time:

Each candidate power combination is examined, combinations which dontmeet driver request are rejected

The instantaneous minimization of the equivalent fuel consumption does not

lead to a charge-sustaining strategy

To enforce the global SOC constraint, the equivalent fuel consumption isfurther modified by using an appropriately constructed multiplicative penaltyfunction to bias the optimal instantaneous split towards or away from theuse of the electrical accumulator (i.e., increase or decrease the equivalent

fuel consumption for the electric accumulator

( ) ( ) ( )fc bat t emP i P i P i+ =

( ) ( ) ( )_ _ _f fc f ba t t f e qu im i m i m i+ =& & &

Fuel CellModel

b a t t penS C f


11/20

SOC Control via Multiplicative Penalty

Function on Equivalent Fuel Consumption

Penalty function on electrical consumption should reflect not only theinstantaneous deviation from target SOC, but also the accumulateddeviation (PI-like controller). However, the integral term must be weakenough to allow enough flexibility, i.e., instantaneous and short-termdeviations from target SOC are required to best utilized the hybridizationpotential

Weak

integral

term


12/20

ECMS Supervisory Control Strategy ECMS Advantages:

Implementable (causal): requires only present and pastinformation

Computationally cheap: past information is only accumulatedsum real time implementation

Proven in simulation and in the field

Implications of ECMS control strategy w.r.t. dynamicrequirements on fuel cell system, drivability, etc. What are the implications with respect to fuel cell system dynamic

response?

If limiting rate of change of fuel cell system power (downgrading ofoptimal split) is implemented, how sub-optimal is it?


13/20

Representative Simulation Results for

Charge-Sustaining FC/Battery Vehicle

Simulation Parameters:

FCV sedan-like (Mv = 1700 Kg,

Cd = 0.35, Af= 1.8 m2)Drive cycle = FUDS (Hot Start,

T = 80C)

50 kW Fuel Cell System

(nominal)

Fuel cell system architecture and

control: pressurized with screw

compressor, optimal systemefficiency tracking

+/- 30 kW Battery Max Power

SOC Target = 0.4 - 0.8

Initial SOC = 0.6

Battery capacity = 4.4 A.h


14/20

Case 1 No hybridization

Power

split

SOC

Power

histogram

and

efficiency

Fuel

consumption

MH2 = 157.0 gr

High dynamics


15/20

Case 2 Hybridized, Optimal Power Split

Power

split

SOC

Power

histogram

and

efficiency

Fuel

consumption

MH2 = 105.9 gr

Decreased dynamics

Charge sustaining


16/20

Details of ECMS Supervisory Control

Strategy Output


17/20

Case 3 Hybridized, Optimal Split, Slew

Rate Limited to 2 kW/sec

Power

split

SOC

Power

histogram

and

efficiency

Fuel

consumption


18/20

Details of ECMS Supervisory Control Strategy

Output with Rate Limitation of 2 kW/sec


19/20

Summary Results

5.2382.91105.565.0

5.1183.59104.704.5

5.1283.58104.724.0

5.1283.41104.933.5

5.1583.22105.163.0

5.1583.42104.922.5

5.1683.18105.222.0

6.1976.98113.701.5

6.0375.99115.181.0

10.3354.70160.000.5

HEV-2

5.2982.68105.86HEV-1

8.4255.76156.97HEV-0

Standard Deviation of the

FC Power[kW]

Equivalent Mileage

[mile/gallon]

Hydrogen Consumption

[gram]

Rate Limit

[kW/sec]Hybrid Type

Effect of the Hybrid Types and Control Strategies with Screw-Type Compressor

ran with the best system-efficiency operating condition


20/20

Summary Results

Effect of the Control Strategies with Screw-Type Compressor

ran with the best system-efficiency operating condition

Hybridization with ECMSSupervisory Control Strategy

can tolerate poor dynamic

response of fuel cell system

with no fuel economy

degradation

07 Guezennec FC Workshop OSU YG

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