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Ind
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ial E
lectr
ica
l E
ng
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Au
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© Mats Alaküla EHS
Hybrid Drive Systems for Vehicles
• More on Auxilliary Systems and EMC
Ind
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© Mats Alaküla EHS
High voltage?
• > 1.5 V
• > 15 V
• > 50 V
• > 150 V
• > 300 V
• > 3 kV
• > 50 V is regarded
as high
• 48 V common
• 36/42 V …
Ind
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© Mats Alaküla EHS
What is a dangerous equipment?
• Equipment where a fault can cause harm
to a person or property.
• 12 V system can also be dangerous
– Can cause fire
– Hydrogen explosion possible
• Even if the voltage is low, the short circuit
current is high and thus also the possible
heat dissipation
Ind
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© Mats Alaküla EHS
Hybrid vehicle system
• Grounding
– 14 V negative earth in chassis
– 48 V negative earth in chassis?
– 400 V floating
chassie
12 V 42 V 300 V
Gen FAS RDU
48 V 400 V
Ind
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© Mats Alaküla EHS
Toyota Prius safety system
Ind
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© Mats Alaküla EHS
Basic dangers
1. Direct current through body
2. Short circuit current that cannot be interrupted
3. High output voltage from switching converters
– Also EMC
4. Parasitic currents from switching converters
5. Fire or explosion
Ind
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© Mats Alaküla EHS
Current through body
• Current depends on
– Voltage
• AC, especially 50 Hz, is
worst
• But, DC is also
dangerous
– Resistance
• Skin + body fluid. Skin
most important
• Moisturous skin worst.
”Murare” ...
• > 80 mA in more than
0.2 seconds can lead to
cardiac arrest
Ind
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© Mats Alaküla EHS
Approximate values for body
sensitivity to current
Ind
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© Mats Alaküla EHS
Body Resistance
Dry Skin, Hand-to-Hand
resistance=100 kOhm
Wet or broken skin, Hand-to-Hand
resistance < 1000 Ohms.
Conclusion on contact:
• Already at 125 V is life
threatening !
• 400 V is VERY
DANGEROUS!
0 50 100 150 200 250 300 350 400 450 500500
1000
1500
2000
2500
3000Kroppens inre resistans i Ohm
0 50 100 150 200 250 300 350 400 450 5000
0.2
0.4
0.6
0.8Ström genom kroppen i Ampere
Spänning i Volt
1000 V
220V
Ind
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© Mats Alaküla EHS
Thus:
• Have the greatest respect for the traction
battery!
– It is dangerous!
Ind
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© Mats Alaküla EHS
Short circuit current
• Very large short circuit currents
– Low inner resistance
– Several 1000 Ampére short circuit current
– Difficult to interrupt due to the inductance of
the cables and the lack of zero crossings
Ind
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© Mats Alaküla EHS
Inductance
• Stored energy in the magnetic field.
• Unit is Henry
• Single conductor, 1 mikroHenry/m
• Equation u=L*di/dt
• What does that mean?
Ind
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© Mats Alaküla EHS
To breake an inductive current
• The inductance
sets up a voltage to
keep the current
going.
• Arcs
• Used in ignition
coils and in light
tube igniters
Ind
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© Mats Alaküla EHS
Light tube
u
-
nät
Lys
rör
Bimetallkontakt
Glimlampa
Glim
tändar
e
Induktor
Ind
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© Mats Alaküla EHS
Electric strength of air
• 3 MV/m
• Whe the air is ionized the temperature
reaches several 1000 C in a plasma with
strong light
• Burns
• Eyes damaged
• Used in welding
Ind
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© Mats Alaküla EHS
Conclusions on braking an
inductive current:
• Very large voltages are created that may
start sparcs.
• Use fuses, protective clothing, fire
extinguisher
• Don’t let it happen!
Ind
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© Mats Alaküla EHS
Power Electronics
• To convert electric energy
• Range: 0 – 1000 MW
• Switching amplifiers
Ind
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© Mats Alaküla EHS
Why Switch?
• Traditional converters have low efficiency,
e.g. 25-60 %.
• Switching converters >95 %.
Ind
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© Mats Alaküla EHS
Classes
A B och AB
20 – 25% 60 %
Ind
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© Mats Alaküla EHS
Class D Audio Amplifiers
Ind
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© Mats Alaküla EHS
Modulation
PWM
Spänning
Bärvåg
Tid
Önskad
spänning
till last
Tid
Pulsad utspänning
Verklig
spänning
till last
Ind
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© Mats Alaküla EHS
PWM
A variable voltage is created with a pulse
width / pulse period.
Pulsad utspänning
Bärvåg
Tid
Önskad
spänning
till last
Verklig
till last
Ind
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© Mats Alaküla EHS
PWM in Car
Long cables
Square voltages contain wide spectrum
Noise generated
Can be heard in the radio ...
Ind
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© Mats Alaküla EHS
PWM
sa 0 va
+50
- 50
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-200
-100
0
100
200va*, vb* & um
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-200
-100
0
100
200va
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-200
-100
0
100
200va*, vb* & um
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-200
-100
0
100
200va
Ind
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© Mats Alaküla EHS
4-Quadrant DC converter
• All combinations of u and I
i L, R + e -
id
sa
+ u -
sb 0 va vb
+Ud/2
-Ud/2
-
Ind
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© Mats Alaküla EHS
4Q PWM : II
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 -200
0
200 va*, vb* & um
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 -200
0
200 va
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 -200
0
200 vb
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 -500
0
500 u
Ind
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© Mats Alaküla EHS
3-phase
id
sa 0 va
+Ud/2
-Ud/2
sb vb sc vc
+ uab - + ubc -
- uca +
+
ua
-
+
ub
-
+
uc
- vo
Ind
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© Mats Alaküla EHS
Control of 3 phase converters.
• Symmetric
references 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02
-500
0
500
uaref & tri
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-500
0
500va
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-500
0
500vo
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-500
0
500ua
varef
tri
va
v0
u=va-v0 grundton 50 Hz
2
minmax
**
**
**
z
zcc
zbb
zaa
u
uuv
uuv
uuv
Ind
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© Mats Alaküla EHS
Ex: – UPS (Uninterruptable Power
Supply)
Likspännings-omvandling 2
Likspännings-omvandling 1
LikriktningVäxelriktning
+u
-nät
+ u -last
Batteri
Ind
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© Mats Alaküla EHS
Conclusions on PWM
• Even if the average value of the voltage is
low, the instantaneous value can be high!
Ind
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© Mats Alaküla EHS
EMC : I
• Electro Magnetic Compatibility
– Coexistence of electric and electronic systems
– Coexistence of the vehicle and sourrounding
world
• Connecting media:
– Conductive. E.g. Rectification noise from the
generator
– Inductive and Capacitive. E.g. Between cables
in the same bundle
Ind
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© Mats Alaküla EHS
Parasitic currents
• Common mode – phenomenon
• Galvanic isolation
Ind
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© Mats Alaküla EHS
This is what you think it looks like…
Induktor
Resistor
Batteri
Ind
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© Mats Alaküla EHS
… and with some experience
maybe like this…
Parasitic components in conductors and circuit board
Induktor
Resistor
Batteri
Ind
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atio
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© Mats Alaküla EHS
… but in reality like this!
Induktor
Resistor
Batteri
Internal non ideal compoents added
Ind
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© Mats Alaküla EHS
EMC problems with PWM
BatteriKraftelektronisk
omvandlareLast
Ind
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© Mats Alaküla EHS
Ex: Battery and Motor Capacitance
to Chassie
chassie
12 V 42 V300 V
Gen FAS
Ind
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© Mats Alaküla EHS
Ex: Battery and Motor capacitance
to chassie ... " 0 V"
" -300 V" " 0V"
" 0V" " 0V"
chassie
• Obs AC voltage across the parasitic capacitances, with 300 V amplitude and switching frequency !!!!
Ind
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© Mats Alaküla EHS
Communication in this environment
chassie
12 V42 V 300 V
Gen FAS
RDU controlcomputer
Vehicle controlcomputer
Ind
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© Mats Alaküla EHS
Line Charging systems
• 1-phase, 10 A = 2.3 kW = 20 km driving
distance charged per hour (=speed!)
• 3-phase, 16 A = 11 kW = 70-100 km driving
distance charge per hour
Ind
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© Mats Alaküla EHS
Example of a line charger
Optional transformer
a
b
c
Phase
Inductances
Phase
voltages
Traction
Battery
Motor Converter,
reconnected for
battery charging
Positive battery
potential
Negative batterypotential
0
Ind
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© Mats Alaküla EHS
Auxiliary Power Unit (APU) : 1
• Heavy vehicles at rest. Driver living in the
vehicle. Consuming low amounts of
electric energy.
• Energy provided via Diesel Engine at very
low power. E.g. A 300 kW diesel providing
3 kW of electric power.
• Too low efficiency.
Ind
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© Mats Alaküla EHS
APU : II
• Separate system: – Fuel Cell based
– Hybrid drive system battery
• Example: – 400 kW Diesel, max efficiency 44 %
– Can run @ 20 kW with 40 % efficiency
– 5 kWh NiMH battery (50 kg)
– SOC variation allowed to be 40 %
– 2 kW load:
• 1 hour pure battery operation
• 5...10 minutes recharging from diesel @ 20 kW / 40 % eff.
• Assume 85 % charge efficiency -> 40*0.85 = 34 %
– Probably 10 % less than Fuel Cell, but Hybrid drive benefits and single fuel.