DC/DC Converters for Automotive Applications; Systems
Training
Colin Gillmor: (HPC)
Colin Gillmor
Applications Engineer
• Career
– MEngSci, University College Cork, Ireland
– PSU designer with Artesyn,
– PSU Controller systems and Applications support with TI
• Expertise
– PSU System and Applications design
•
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Training summary
DC/DC Converters for Automotive Applications; summary:
• The demand for Electric Vehicles (EV) is increasing rapidly. This training session with a look at a typical
EV system block diagram and then focus on the DC/DC applications within these systems.
Training level: Intermediate
Course Details:
Audience: All
What you’ll learn:.
•
•
•
•
Learn about a typical EV power system block diagram
Understand why they are designed in this way
How the Phase Shifted Full Bridge topology is used in
EV applications
Specific TI Designs & Parts Discussed:
• TID #’s: PMP7246
• Part #’s: UCC28951-Q1, LM4132-Q1
UCC21520 + Others
• WEBENCH tools: N/A
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Detailed agenda
• Electric Vehicle power systems – Block diagrams
• Introduction to Battery Charging
• Designing multi-kW power supply systems using the UCC28951-Q1
– The Phase Shifted Full Bridge
– High Power Battery Charger using the UCC28951-Q1
•
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Electric Vehicle power systems
•
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HEV/EV – Powertrain EE* overview
Engine
Management
• Gasoline & Diesel
Engine ECU
• Engine Actuators
Transmission
HEV/EV
• Manual,
Automatic, & Shiftby-Wire
Transmission
• Transmission
Actuators
• Battery
Management
• On-board Charger
• Inverter
• DC/DC Converter
• Regenerative
Braking
Powertrain
Sensors
Power
Steering
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•
•
•
•
•
•
• Electric Power
Steering
• Hydraulic Power
Steering
• Steer-by-Wire
Pressure
Position
Temperature
Exhaust
Knock
Speed
Fluid
Concentration/
Quality
*EE = End Equipment
•
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HEV/EV DC/DC Converters
•
DC/DC Converter
Bidirectional 48V-12V
Bidirectional HV-LV
Unidirectional 48V-12V
Unidirectional HV to LV –
Analog Loop
On Board Charger
Unidirectional HV to LV –
Digital Loop
Auxiliary Power Supplies
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System Block Diagram
External
Grid Connection
AC Power
Signalling
DC Power
Link
EVSE*
Proximity Sensor
GFCI*
SAE
Level 1: Single phase: AC power, 1.92kW
Level 2: Split phase: AC power, 19.2 kW
Level 3: DC power, 240kW
•
Vehicle
AC/DC
Battery
This system is characterised by:
High Power levels
Dangerous voltages
Dangerous currents
Harsh environment
*EVSE – Electric Vehicle Service Equipment
*GFCI – Ground Fault Current Interruptor
http://www.ti.com/lit/ug/tidub87/tidub87.pdf
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On-Board Charger (OBC)
What is the On-board Charger?
• An On Board Charger is used in an electric vehicle (EV)
or hybrid electric vehicle (HEV) to charge the traction
battery (48V or HV usually ~400V)
• This includes:
• Converts the grid 50/60Hz into DC
• Adjusts the DC level to the levels required by the
battery and provides the galvanic isolation
• Usually includes a Power Factor correction (PFC)
What does this EE consist of?
• PFC Controller and Rectification
• High Efficiency rectification with lowest harmonic
impact to the grid
• Controller
• Analog or Digital Control (<2kW to >100kW)
• Adjusts the DC level to the levels required by the
battery
• Galvanic Isolation
• Galvanic Isolation Grid to Battery
• Bias Supply
• Diagnostics
• Temperature Sensing
• Current & Voltage Sensing
• Iso Barrier
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System Block Diagram
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System Block Diagram
Potential DC/DC
Applications for
UCC28951-Q1
(green)
Unidirectional
High Power
ZVS for low loss
on HV inputs
•
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Introduction to Battery Charging
•
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Lead Acid battery
Chargers operate in CI and CV modes
Compensation for battery temperature
12V / 48V nominal battery voltages are common
2.35V per cell (typ) when charged
1.9V per cell (typ) when discharged
≈70%
Lead Acid
98%
100%
33-42 Wh/kg energy density
Battery damage if not fully charged – Sulfation
Float charge compensates for self-discharge
Ideal float voltage is a function of temperature
Deep discharge damages battery
•
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Lithium Ion battery
400V nominal battery voltage
300V minimum when discharged
120-240 Wh/kg energy density
85%
Very tight end voltage tolerances
Typ 4.2V/cell ±50mV (±1.2%) → OVP
Over Charging can damage battery
Temperature rise during charging → OTP
Battery pack cell balancing – not considered here
100%
Lithium Ion
3%
Tradeoff
Charge Rate vs Charge Time vs Battery Life
Final Charge vs Battery Life vs Range - Fully charging Li Ion battery can reduce lifetime
70% charge / 20% discharge cycle for extended lifetime – but reduced range.
Preconditioning phase if deeply discharged – not shown here
Periodic ‘top up’ charge – not a continuous trickle charge
•
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Battery Charger output regulation
Two regions
Constant Voltage regulation
Regulation down to zero current
Tight regulation tolerances
Temperature dependence
Constant Current regulation
Regulation down to approx half nominal Vout
If Vo drops below this –
Micro controller decides action
Li Ion battery ‘top up’ behaviour and final
charge levels determined by MCU – this is a
system level decision and trades stored
charge against lifetime.
•
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Designing multi-kW power supply systems using the
UCC28951-Q1
•
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Systems Overview
• Problem: Electric vehicles need systems to convert AC power into DC for storage in high
(HV) and low voltage (LV) batteries and to convert the stored energy back to AC to drive
the Motors. We’ve seen the overall system block diagram now we will examine how to
design the DC/DC link between the PFC stage output and HV Li Ion and LV Lead Acid
batteries.
• Solution: The UCC28951-Q1 is a sophisticated device that controls the PSFB stage to
achieve high efficiency at high power levels in conjunction with other TI devices.
• Description of system solution: The PSFB power system is a key component of this
system, specifications are shown in the next slide.
• Key components: Texas Instruments offers a wide variety of devices for PSFB
applications in H/EV. A few examples: The UCC28951-Q1 PSFB controller. The multi
channel UCC21520 8kV isolated gate driver. The LM4132-Q1 Reference with 0.05%
accuracy. INA520-Q1 and INA199-Q1 Current sense amplifiers, TLV316-Q1 op-amp
•
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Example applications
Phase Shifted
Full Bridge
12V Lead Acid battery charger
Input from PFC stage, Output
charges battery
Min
Nom
Max
Vin
370V
390V
410V
Hold Up time
n/a
400V Li-Ion battery charger
Vout
8V
12V
15V
Input from PFC stage, Output
Power Out
1kW
charges battery
Modes
CI, CV, Float
Min
Nom
Max
Battery
Lead Acid
Vin
370V
390V
410V
Max Iout
83A
Hold Up time
n/a
Temp comp
Ext
Vout
300V
400V
420V
Power Out
3.3kW
Modes
CI/CV/OFF
Battery
Li Ion
Max Iout
8.25A
Temp comp
Ext
•
UCC28951-Q1
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The PSFB in multi-kW power supply systems
The PSFB is the topology of choice for high input voltage, high power
applications because:
• It achieves Zero Voltage Switching (ZVS) which significantly reduces
switching losses.
• It uses the full flux swing available from the transformer core so that a
smaller transformer is possible.
• The transformer primary is driven with the full input voltage minimising
primary currents.
• Efficiencies of greater than 99% can be achieved.
The main disadvantage is that it requires four active switches on the
transformer primary.
•
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Phase Shifted Full Bridge
• Four switches, transformer, two rectifiers, inductor
– Double ended topology
Active Leg
QA, QB
Passive Leg
QC, QD
• Buck like output stage
• Four switching states per cycle
– Two power transfer
– Two freewheeling
• Four ZVS transitions per cycle
• Phase between legs controls conversion ratio
– Complex control, requires IC
• High power (1kW and upwards)
• Can achieve zero voltage switching
– Important for high Vin applications
•
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Phase Shifted Full Bridge
• Can achieve zero voltage switching
Active Leg
QA, QB
Passive Leg
QC, QD
• ZVS and reduced cross conduction requires:
– Dead time between QA OFF and QB ON
– Dead time between QC OFF and QD ON
• Reduced body diode conduction requires
– Dead time between QA OFF and QF OFF
– Dead time between QB OFF and QE OFF
•
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Phase Shifted Full Bridge
Active Leg
QA, QB
Buck Derived topology
𝑉𝑂𝑈𝑇 = 𝐷 𝑉𝐼𝑁
Passive Leg
QC, QD
𝑁𝑆
𝑁𝑃
OUTA, OUTB – reference pair
D controlled by phase shifting OUTC & OUTD
QE, QF are SRs, Diode rectification is possible
Mouse over the waveforms to play the animation
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Timing Diagram: Energy Transfer
•
•
•
•
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QA, QD, QF are ON: others are OFF
First energy transfer interval
I_PRI is Iout /N* + Imag.
QF current is Iout
Current flow in red (pri) and blue (sec) paths
Currents at end
of interval,
solid red / blue
*N is the
turns ratio
•
I_LOUT: increasing
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Timing Diagram: ZVS
• QA, QD, QF are ON: QC is OFF
• QD turns OFF
• Node B charges to Vin as I_PRI current
moves out of QD and into QC Body Diode*
• QC: turns ON
Leakage
Inductance
L_lk
*ZVS
transition
•
QD turns off
DELCD – allows time for Node B transition
QC turns on at 0V (ZVS)
Current in QD
goes to zero
during interval
Uses L_lk energy.
Faster than Node A
transition, because
I_LOUT is at maximum
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Timing Diagram: Freewheeling
•
•
•
•
•
QA, QC, QE, QF are ON: others are OFF
T1 Primary is short circuited, VXFMR = 0V
T1 Sec is short circuited by QE & QF
Output current supplied by Lout
Current flows asymmetrically in T1 Sec !
½ ΔI_Lout
QE turns ON
Secondary is
shorted
•
QE turns on
½ ΔI_Lout
+ Iout
I_LOUT: decreasing
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Timing Diagram: ZVS
• QA, QC, QE are ON: QB is OFF
• QA turns OFF
– Node A charges to GND as I_PRI current
moves out of QA and into QB Body Diode
• QB: turns ON
DELAB – allows time for node A transition
QA turns off
DELEF
QF turns off
after DELEF
Leakage
Inductance
QB turns on at 0V (ZVS)
QF turns OFF
Removes sec
short
•
Uses L_lk energy.
Slower than Node B
transition, because
I_LOUT is at minimum
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Timing Diagram: Energy Transfer
•
•
•
•
•
QB, QC, QE are ON: others are OFF
Second energy transfer interval
I_PRI is Iout /N* + Imag
QE current is Iout
Current flow in red (pri) and blue (sec) paths
*N is the
turns ratio
•
QC turns off
I_LOUT: increasing
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Timing Diagram: ZVS
• QB, QC, QE are ON: QD is OFF
• QC turns OFF
• Node B charges to Gnd as I_PRI current
moves out of QC into QD Body Diode*
• QD: turns ON
QC turns off
DELCD –allows time for
node B transition
Leakage
Inductance
*ZVS
transition
•
QD turns on at 0V (ZVS)
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Timing Diagram: Freewheeling
•
•
•
•
•
QB, QD, QE, QF are ON: others are OFF
T1 Primary is short circuited, VXFMR = 0V
T1 Sec is short circuited by QE & QF
Output current supplied by Lout
Current flows asymmetrically in T1 Sec
½ ΔI_Lout
+ Iout
QF turns on
½ ΔI_Lout
QF turns ON
Secondary is
shorted
•
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Timing Diagram: ZVS
• QB, QD, QF are ON: QA is OFF
• QB turns OFF
– Node A charges to Vin as I_PRI current
moves out of QB into QA Body Diode
• QA: is turned ON
QB turns off
DELEF
DELAB - allows time for
Node A transition
QE turns off
after DELEF
Leakage
Inductance
QA turns on at 0V (ZVS)
QE turns OFF
Removes sec
short
•
Uses L_lk energy.
Slower than Node B
transition, because
I_LOUT is at minimum
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Phase Shifted Full Bridge – reminder !
Active Leg
QA, QB
Buck Derived topology
𝑉𝑂𝑈𝑇 = 𝐷 𝑉𝐼𝑁
Passive Leg
QC, QD
𝑁𝑆
𝑁𝑃
OUTA, OUTB – reference pair
D controlled by phase shifting OUTC & OUTD
QE, QF are SRs, Diode rectification is possible
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On Board Charger < 3.3kW (UCC28951 Control)
MCU for system supervision
•
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On Board Charger: Sec Bias Flyback
•
•
•
•
•
•
Small Flyback PSU for Secondary side power
UCC28700-Q1 for example
Primary side regulation – no need for an optocoupler
Simple, low cost transformer
Small size, 6 pin SOT23
Efficiency probably about 75%
– power level is low – estimate 5W
• Variable frequency – as with all DCM flyback devices
• Cable compensation (CBC) probably not needed – tie CBC pin to GND
• Design tools available http://www.ti.com/product/UCC28700/toolssoftware
– Webench
– Reference designs
– Evaluation Modules
•
12V output
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On Board Charger: Pri Bias Flyback
•
•
•
•
•
•
Small Flyback PSU for Primary side power
UCC28700-Q1 for example
Primary side regulation – no need for an optocoupler
Simple, low cost transformer
Small size, 6 pin SOT23
Efficiency probably about 75%
– power level is low – estimate 5W
• Variable frequency – as with all DCM flyback devices
• Cable compensation (CBC) probably not needed – tie CBC pin to GND
• Design tools available http://www.ti.com/product/UCC28700/toolssoftware
– Webench
– Reference designs
– Evaluation Modules
•
12V output
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On Board Charger: Isolated Driver, Option 1
•
•
•
•
•
•
Primary/Secondary Isolation
Switching of Primary side MOSFETs
High Side and Low Side outputs needed
4 isolated outputs in total
2 high side drives, 2 low side drives
Isolation to 5.7kVRMS
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•
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2 x UCC21520-Q1, 4A, 6 A driver
Low Propagation Delays
Good Propagation Delay Matching
Adjustable Dead Time
Safety Features, UVLO etc.
As with all drivers, PCB layout is critical
•
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On Board Charger: Isolated Driver - Option 2
• Pri/Sec Isolation
• ISO7740-Q1 provides pri/sec isolation
– 5kV RMS
• 0/10V signal from UCC28951-Q1 needs
attenuation (2:1) to meet ISO7740-Q1
input level.
• Gate drivers drive the MOSFETs
• ISO7740FQDWQ
High
Side
Low
Side
• F option – outputs default LOW !
ISO7740F-Q1
•
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On Board Charger: Rectification – General
• Choice of secondary rectification depends on – Output Voltage
– Output Current
400Vout:
Diodes – Simple solution, a good choice for 400V
Full Wave or Bridge options
Reverse recovery losses makes SiC a good choice
12Vout:
SR – Good option at 12V out, body diode reverse recovery losses can be significant
Full wave with centre tap or Bridge with single secondary winding options
SRs require a MOSFET driver
Schottky diodes might be an option higher losses but easier drive and no reverse
recovery problems
Current doubler with SR is a good option – single sec. winding
•
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On Board Charger: Rectification – 12V output
• SRs are large rectifier MOSFETs.
• UCC27424-Q1 is a dual non-inverting MOSFET driver.
• MOSFETs see 2 x Vin_max Ns/Np + margin
– Use 30V devices for 12V output
– Reverse recovery losses in SR can be significant
• Centre tapped secondary
• Half of sec winding ‘idle’ at a given time
• ‘Idle’ half may cause proximity losses
•
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On Board Charger: Rectification – 12V output
• Current Doubler output with Schottky Rectifiers
– Current Doubler – suited to high current outputs
– Requires Current Mode Control
– Ripple current cancellation in Cout
• Single winding on transformer secondary
– best use of transformer winding window
• Two output inductors needed
– Each inductor carries half the output current
• Vf losses are significant – depends on diode
– Heatsinking requirements significant
Secondary
Centre
Tapped
Current
Doubler
Ind Current
I_out
I_out/2
• Electrically – this is the simplest option
Ind Freq
2 fSW
fSW
• Significant losses in Diodes.
Inductance
L_out
<Lout*
•
* Depends on Duty Cycle
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On Board Charger: Rectification – 12V output
• Current Doubler output with Synchronous Rectifiers
– http://www.ti.com/lit/an/slua121/slua121.pdf
• MOSFETs see 2 x Vin_max Ns/Np + margin
• Reverse recovery losses in SR can be significant
• SRs are ground referenced – simple driver
• UCC28951-Q1 OUTE and OUTF signals are driver inputs
• May need to parallel several MOSFETs
– Use separate gate drives
– or separate gate drive resistors
– Needs careful layout to avoid HF oscillations
•
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On Board Charger: Rectification – 12V output
• Full wave rectification with SR
• Simplest transformer
– Single secondary winding
• Single output inductor
• Two SR voltage drops in current path
• SRs see Vin_max Ns/Np + margin
• Reverse recovery effects in SR diodes
• SR drive complexity
• 2 low side drives, 2 high side drives
•
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On Board Charger: Rectification – 400V output
• SiC diodes are simplest solution
• Positive temp coefficient of Vf
• Relatively low currents allow use of centre tapped
secondary
• V stresses on diodes are 2 x Vin_max Ns/Np + margin
• Use 1200V rated SiC diodes
Infineon IDH10G120C5
• Full Bridge rectification
– Halves V stresses
– Simplifies secondary
– Increases rectifier losses
•
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On Board Charger: Error Amplifiers (I and V)
•
•
•
•
•
•
•
Measure output current
Compare to reference
Output error signal (power demand)
Measure output voltage
Compare to reference
Output error signal (power demand)
Diode ‘or’ errors – lowest error ‘wins’
– Automatic CV / CI transition
– This is the usual technique
Low side sense
at 400Vout
High side sense
at 12Vout is
possible
•
Lowest error ‘wins’ and
controls the output
-
+
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On Board Charger: Input current sensing
• Current Transformer in the input power rail senses input
current
• In this position, it senses the full bridge current
• Senses any ‘shoot through’ events
– QA and QB or QC and QD ON simultaneously
• CS signal used for Peak Current Mode (PCM) control of PSFB
• PCM gives cycle-by-cycle control of peak current in primary
• Protection against transformer saturation
• CS signal is used for regulation in both CV and CI modes
• Regulation setpoint depends on whether the CV or CI error
amplifier is in control
•
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Summary
•
We have seen that the UCC28951-Q1 PSFB may be used in unidirectional DC/DC
converters for charging high and low voltage batteries from high voltage sources like PFC
outputs. This controller and topology can cover the power range from several hundred
Watts to several kW.
•
The UCC28951-Q1 can play a big role in chargers, where the power level is relatively low.
For charger applications some external intelligence needs to be added, current sensing, a
small Micro for control monitoring, temperature compensation of output voltage etc. At the
same time the UCC28951-Q1 can manage the power stage.
•
For higher power applications Micro controllers play the main role due to high power
requirement of the OBC (<20kW for on board, 50-100kW for off board). However
UCC28951-Q1 could also cover some of these applications – especially if Multiple-Phase
or Master/Slave techniques were used.
•
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Summary
MCU for system supervision
•
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Thank You
Colin Gillmor, HPC
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