Power Management and Energy Storage Systems

1. 20EE603PE-ELECTRIC VEHICLES
UNIT-IV
POWER MANAGEMENT AND ENERGY STORAGE
SYSTEMS
CONTENTS
• Energy storage,
• Battery based energy storage and simplified models of battery
Fuel cells
• Super capacitor,
• Flywheels and their modelling for energy storage in HEV /BEV
• Energy management strategies and its general architecture
• Rule and optimization based energy management
strategies(EMS)
• Case study of design of a HEV and BEV.

2. ENERGY STORAGE
“Energy storages” are defined as the devices that store energy, deliver energy
outside (discharge) and accept energy from outside (charge).
Types of energy storages that have been proposed for electric vehicle (EV) and
hybrid electric vehicle (HEV) applications.
Chemical batteries, ultra capacitors or super capacitors, and ultrahigh-speed
flywheels. The fuel cell is a kind of energy converter.
Battery based Energy Storage and Simplified models of battery
Batteries
A battery consists of two or more electric cells joined together. The cells convert
chemical energy to electrical energy. The cells consist of positive and negative
electrodes joined by an electrolyte.
The ‘lead acid’ battery is the most well-known rechargeable type, but there are
others.

3. Cell and battery voltages
Battery Parameters
The battery is represented as having a fixed voltage E, but the voltage at the terminals
is a different voltage V , because of the voltage across the internal resistance R.
Assuming that a current I is flowing out of the battery, then by basic circuit theory ,
V = E − IR
Figure. Simple equivalent circuit model of a battery

4. • Charge (or Ahr) capacity
• Energy stored
𝐸𝑛𝑒𝑟𝑔𝑦 𝑖𝑛 𝑊ℎ𝑟 = V × Ahr
• Specific energy
• Energy density
• Specific power
• Ahr (or charge) efficiency
• Energy efficiency
• Self-discharge rates
• Battery temperature, heating and cooling needs
• Battery life and number of deep cycles

5. Energy management strategies and its general
architecture
Classification of Hybrid ECU
The hybrid ECU is the heart of the control architecture of any HEV and it is also
known energy management strategy (EMS). The EMS can be classified into
following broad categories:
Rule based
Optimization based
The Rule Based strategies consist of following subcategories:
Fuzzy based:
The fuzzy based control strategies are of three types
a. Predictive,
b. Adaptive
c. Conventional
ii. Deterministic Control:
The deterministic controllers are subdivided into
a. State Machine
b. Power follower
c. Thermostat Control.

6. Lead Acid Batteries
Lead Acid Battery Basics
• The negative plates have a spongy lead as their active material,
whilst the positive plates have an active material of lead
dioxide.
• The plates are immersed in an electrolyte of dilute sulphuric
acid. The sulphuric acid combines with the lead and the lead
oxide to produce lead sulphate and water, electrical energy
being released during the process.
• The overall reaction is:
Pb + PbO2 + 2H2SO4 ↔ 2PbSO4 + 2H2O



10
02
.
0
cells
of
no.
C
R
• The internal resistance of a lead acid battery is

7. The overall characteristics of the battery
Specific energy 20–35Wh kg−1 depending on usage
Energy density 54–95Wh l−1
Specific power ∼250Wkg−1 before efficiency falls very greatly
Nominal cell voltage 2V
Amphour efficiency ∼80%, varies with rate of discharge and temperature
Internal resistance Extremely low, ∼0.022 per cell for 1Ah cell
Commercially available Readily available from several manufacturers
Operating temperature Ambient, poor performance in extreme cold
Self discharge ∼2% per day (but see text)
Number of life cycles Up to 800 to 80% capacity
Recharge time 8 h (but 90% recharge in 1 h possible)

8. The reactions during the
charge and discharge of the
lead acid battery

9. Lithium Batteries
Well-established feature of the most expensive laptop computers
and mobile phones that lithium rechargeable batteries are
specified, rather than the lower cost NiCad or NiHM cells.
The lithium batteries are of following types:
 Lithium polymer batteries
 Lithium ion batteries
The lithium polymer battery
• Uses lithium metal for the negative electrode and a transition
metal intercalation oxide for the positive.
The overall chemical reaction is:
xLi +MyOz ↔ LixMyOz

10. Nominal battery parameters for nickel cadmium batteries
Specific energy 40–55Wh kg−1 depending on current
Energy density 70–90Wh l−1 depending on current
Specific power ∼125Wkg−1 before becoming very inefficient
Nominal cell voltage 1.2V
Amphour efficiency Good
Internal resistance Very low, ∼0.06 per cell for a 1 Ah cell
Commercially available Good in smaller sizes, difficult for larger batteries
Operating temperature −40 to +80 ◦C
Self discharge 0.5% per day, very low
Number of life cycles 1200 to 80% capacity
Recharge time 1 h, rapid charge to 60% capacity 20 min

11. A continuation of the charging current results in the generation of
oxygen at the positive electrode via the reaction.
4OH- → 2H2O + O2 + 4e−
The resulting free oxygen diffuses to the negative electrode,
where it reacts with the cadmium, producing cadmium
hydroxide, using the water produced by reaction .
The normal charging reaction will be taking place at this
electrode, using the electrodes produced by reaction .
2Cd(OH)2 + 4 e− → 2Cd + 4OH−
The internal resistance of a NiCad battery is



3
C
0.06
cells
of
no.
R

12. The lithium ion battery
It uses a lithiated transition metal intercalation oxide for the positive electrode
and lithiated carbon for the negative electrode. The electrolyte is either a
liquid organic solution or a solid polymer.
The overall chemical reaction for the battery is:
C6Lix + MyOz ↔ 6C + LixMyOz
Table.Nominal battery parameters for lithium ion batteries
Specific energy 90 Wh.kg−1
Energy density 153Wh.L−1
Specific power 300 W. kg−1
Nominal cell voltage 3.5V
Amphour efficiency Very good
Internal resistance Very low
Commercially available Only in very small cells not suitable
for electric vehicles
Operating temperature Ambient
Self-discharge Very low, ∼10% per month
Number of life cycles >1000
Recharge time 2–3 h

13. Metal Air Batteries
The aluminium air battery
Aluminium is combined with oxygen from the air and water to form
aluminium hydroxide, releasing electrical energy in the process. The
reaction is irreversible. The overall chemical reaction is:
4𝐴𝐼 + 3𝑂2 + 6𝐻2 𝑂 ⟶ 4𝐴𝐼(𝑂𝐻)3
Table. Nominal battery parameters for aluminium air batteries
Specific energy 225 Wh.kg−1
Energy density 195Wh.L−1
Specific power 10 W. kg−1
Nominal cell voltage 1.4V
Amphour efficiency N/A
Internal resistance Rather high, hence low power
Commercially available Stationary systems only available
Operating temperature Ambient
Self-discharge Very high (>10% per day) normally, but the
electrolyte can be pumped out, which makes it
very low
Number of life cycles 1000 or more
Recharge time 10min, while the fuel is replaced

14. Super Capacitor
Capacitors are devices in which two conducting plates are separated by an insulator.
Capacitors are devices in which two conducting plates are separated by an
insulator.iarasan

15. Flywheels
Figure. Principle of flywheel used as an energy store

16. • Whether mechanical or electrical, the system can also be used
to recover kinetic energy when braking.
• The flywheel can be accelerated, turning the kinetic energy of
the vehicle into stored kinetic energy in the flywheel, and
acting as a highly efficient regenerative brake.
• The total amount of energy stored is given by the formula
E = 0.5Iω2
where E is the energy in joules, I is the moment of inertia and
ω is the rotational speed in radians per second.
 When a flywheel reduces from ω1 to ω2 radians per second
the energy released will be given by the formula
 
2
2
2
1
51
.
0 
 

E

17. Matching the electric drive and ice
Figure. Schematic of epicyclic gear set
The governing equation for an epicyclic gear in terms of the basic
ratio and gear angular speeds can be written as
  0
1 


 c
r
s k
k 



18. Table. Epicyclic gear input–output relationships

19. Sizing the propulsion motor
Figure. Hybrid vehicle drivetrain

20. For the BEV case study evaluated here, the vehicle characteristics
and added battery mass are summarized in Table.
The design in procedure followed comprises three steps:
Step 1. Simulate the full vehicle over one or more standard drive
cycles.
Step 2. Import this P(V) file into a high performance dynamic
simulation of the battery and ultra-capacitor combination.
Step 3. Validation of the combination ESS with selected energy
management strategies (EMS).
Parameter Description Rating Parameter Description Rating
Battery pack
44S x 1P x
200 Ah
144 V, 28
kWh
Aerodynamic Cd (#) 0.25
Battery mass kg 303.6
Rolling
resistance
Crr (kg/kg) 0.08
Vehicle mass kg 920(1,127)
Tyre rolling
Radius
P205/50R16V
(rw, m)
0.4
ICE power kW 125 Frontal area Af (m) 1.96
Table. Vehicle parameters used in the performance simulations

21. Step 1 Parameters listed in Table 1 are input into an Excel spreadsheet and simulated
over a standard UDDS cycle
A nominal all electric range (AER)
of
  mi
E
SOC
E
AER
mi
batt
125
156
7
.
0
28000




Figure. Simulation of tractive power, P(V) for Miata BEV: (a) urban dynamometer
drive cycle (UDDS) and (b) vehicle P(V) data file from simulation

22. Table. Summary of vehicle level simulation
Parameter Description Value Parameter Description Value
UDDS avg.
speed
V (mph) 19.6
Motoring
power
Pmot
(KWpk)
28.5
UDDS max
speed
Vmx (mph) 56.7
Regeneratio
n power
Pregen
(KWpk)
-21.2
Distance
per cycle
mi 7.44
Average
power
Page (kW) 1.657
Step 2
For dynamic simulation the Maxwell ultra-capacitor model is used and a
functional representation of the lithium ion battery is developed. For this
representation the discharge and charge characteristics of the lithium-iron-
phosphate (LFP) cell are approximated.

23. Torque and power
• Motor–generator capability curves for torque and power define the peak
operating capability of the hybrid electric system.
• It is necessary to be clear in understanding that the capability curve defines
the operating bounds of the hybrid ac drive system.
Figure. M/G torque–speed capability envelope

24. Continuous rating:
The ac drive can be operated within its continuous rated region indefinitely,
provided the motor thermal management system is operated at or below its
cooling medium maximum inlet temperature conditions for the coolant used , the
power inverter thermal management system is within its maximum inlet
temperature of coolant and the power electronics electrical parameters are within
nominal stress levels of 50%.
Intermittent overload operation is permitted for short durations (<30 s) to
contain low energy transients such as responding to fast gear changes or clutch
actuation intervals when the M/G may be called upon to furnish additional
torque and power.
Peak overload operation is within the capability of the electric machine but
outside the capability of the power electronics. There have been attempts to
redefine this peak condition to contain fast transients having low energy, but very
high power.
Thermal management systems for passenger car hybrids consist of auxiliary
coolant reservoirs, pumps and fans, along with a small radiator. The M/G will have
a separate coolant supply from either the vehicle’s engine coolant (<115o C) or
transmission oil cooler (<1200 C).

25. Constant power speed ratio (CPSR)
Figure. M/G operating envelope for hybrid propulsion

26. • AC drives employed as hybrid propulsion components operate in both motoring
(first and third) and generating (second and fourth) quadrants.
• In mild hybrid, ISA applications, the M/G operates in the first and fourth
quadrants only because the engine is not to be back driven. However, in power
split and other hybrid propulsion architectures the M/G can and does operate
over all four quadrants.
• Motoring operation of the M/G occurs for positive torque and positive (counter
clockwise [CCW]) speed or for negative torque and negative (clockwise [CW])
speed.
• When the sign of either torque or speed are reversed, the M/G is in generating
mode. With modern power electronic controllers, the machine is capable of
operating anywhere within the confines of its torque–speed envelope.

27. Figure Taxonomy of electric machines

28. Machine Dimensions
• Torque is proportional to scaling constants times the product of electric and
magnetic loading times the stator bore volume.
• Electric loading is defined as the total ampere-conductors per circumferential
length (A, in units of A/m) – in effect, it is the description of a current sheet.
• The electric loading is limited by thermal dissipation of the conductor bundles.
Magnetic loading is set by the material properties of the lamination sheets (B, in
units of Wb/m2) and of the physical dimensions of the airgap.
• The product of electric and magnetic loading is a volumetric shear force, AB
(Nm/m3). The stator bore volume, D2 L, defines the airgap surface area (pDL)
times the torque lever arm (D) of the rotor on which the volumetric shear force
acts.
• The scaling constants and coefficients are absorbed into the proportionality
constant for M/G torque in terms of its design loading and geometry.
• For electric machines of interest to hybrid propulsion, the volumetric shear force
ranges from 25,000 to 80,000 Nm/m3.
The relationship for machine torque is
T = kABD2 L

29. • where k is a constant that includes geometric variables, and excitation wave
shape variables for voltage and currents.
• The bore diameter, D, or more accurately the rotor, OD, is the main sizing
variable in electric machine design. Sizing is constrained by four fundamental
limits.
• Two of the fundamental sizing constraints have been discussed thus far: electric
and magnetic loading.
• Current carrying capacity of copper wire is limited by its thermal dissipation,
which in turn sets bounds on current density, Jcu.
• In electric machine design practice these bounds are
























s
Count
J cu
30
min
3
20
6
2
• Equation contains the thermal constraints of the machine sizing design. Higher
current densities, up to 2 x 108 A/m2 for copper, define its fusing current limit.

30. Type Symbol Airgap
(mm)
B
(Wb/m2)
Surface permanent magnet
machine
SPM <1.5 ~0.82
Interior/inset permanent
magnet machine
IPM ~1.0 0.7
Asynchronous, induction
machine (also syncrel)
IM ~0.6 0.7
Variable/switched
reluctance machine
VRM <0.5 0.8*
Table. Electric machine sizing: magnetic loading
• The electric loading, A, for the various machine technologies listed in Table., is
determined by using the current density limitations , from which the bounds on
electric loading.
 
m
A
S
VRM
IM
IPM
SPM
y
Techno
A rms /
10
5
.
4
10
5
.
4
10
8
30
/
log
10
3
10
3
10
6
min
3
4
4
4
4
4
4























31. Machine rating
(MW)
Cooling method
Rotor diameter
(m)
Rotor surface
speed (m/s)
25 Air 0.75 141
120 Air 0.95 179
150 H2 1.1 207
320 Water 1.15 217
757 Water 1.06 199
932 Water 1.25 235
Table Mechanical constraint: large electric machines
Table supports the engineering practice of limiting electric machine rotor
tangential speeds to less than 200 m/s. At higher speeds the issues of critical speed
flexing, rotor retention and eccentricity become major concerns.

32. Energy management strategies and its general
architecture
Classification of Hybrid ECU
The hybrid ECU is the heart of the control architecture of any HEV and it
is also known energy management strategy (EMS). The EMS can be
classified into following broad categories:
Rule based
Optimization based
The Rule Based strategies consist of following subcategories:
Fuzzy based:
The fuzzy based control strategies are of three types
a. Predictive,
b. Adaptive
c. Conventional
ii. Deterministic Control:
The deterministic controllers are subdivided into
a. State Machine
b. Power follower
c. Thermostat Control.

33. The Optimization based strategies are of following types:
Global Optimization:
The global optimization methods are:
a. Linear programming methods
b. Dynamic Programming
c. Stochastic Dynamic Programming
d. Genetic Algorithms
ii. Real time Optimization:
The real time optimization techniques are of following types:
a. EFC minimization
b. Robust control
c. Model predictive
d. Decoupling Control

34. Classification of control strategies

35. Rule and Optimization based energy management
strategies (EMS)
Basic Principles of Rule Based Control Methods
Rule based control strategies can cope with the various operating
modes of HEV. The rule based strategies are developed using
engineering insight and intuition, analysis of the ICE efficiency
charts shown and the analysis of electrical component efficiency
charts.
Efficiency map of ICE

36. The lines, which are drawn using engineering insight and intuition, divide
the map into three regions are: A, B, and C. The rules for operation of ICE in
these three regions are:
In the region A only EM is used because in this region the fuel efficiency of
the ICE is poor.
In region B only ICE is used since this the region of high fuel efficiency.
In region C both ICE and EM are used
Efficiency map of ICE showing upper and lower boundaries for EM operation