Bi-directional DC/DC converter topology comparison and design

Power Supply Design Seminar

Bi-directional DC/DC converter topology comparison and design

Reproduced from 2016 Texas Instruments Power Supply Design Seminar SEM2200

TI Literature Number: SLUP343 © 2016, 2017 Texas Instruments Incorporated

Power Seminar topics and online power training modules are available at:ti.com/psds

Texas Instruments – 2016/17 Power Supply Design Seminar

Bi-directional DC/DC converter topology comparison and design

HEV/EV and server applications

Sanatan RajagopalanZhong Ye

Texas Instruments – 2016/17 Power Supply Design SeminarTexas Instruments – 2016/17 Power Supply Design Seminar

Agenda• Application overview and specifications

o Automotive applicationo Server and Datacenter

• Topology comparisono Four-phase interleaved fixed frequency Bi-directional Buck convertero Four-phase interleaved ZVS transition-mode Bi-directional Buck converter

• UCD3138-based control scheme and implementation • Test data comparison

o Switching waveform comparisono Efficiency comparisono Loss Breakdown Comparisono Thermal o EMI

• Conclusions4-2


Application overview-automotive• Continuous increase of electrical power consumption• 12-V system running into limitations • Improve efficiency for high-power loads (AC comp.,

pumps, …)• Mild hybrid functionality asking for high cycling perform-

ance (lead acid not good fit for more recuperation)• Additional savings due to intelligent networks

(partial shutdown loads in the network)• Reduce copper diameter and cost

12-V lead-

battery

12-Vload

12-Vgenerator12-V

load

12 V

GND

Today: 12-V system

12 V

GND

48-VLi-Ion

battery

48-Vmotor/

generator

12-V / 48-V

DC/DCconverter

48 V

GND

48-Vload

48-Vload

Next step: 48-V power network extension

12-Vlead-

battery

12-Vload

12-Vload

12-Vload

4-3


48-V / 12-V electrical system with start/stop

12-V electrical system

12-V battery

48-V Li-Ion battery management 48-V traction motor inverter

Activesuspension control

AC compressor Water pump

Electricpower

steering

Coolingfan

Transmissionoil/fluid pump

Fuelpump

Parts using 48 V

48-V / 12-V bi-directionalDC/DC converter

4-4


Typical 48-V / 12-V converter specification for automotive• >96 percent efficiency• No air or liquid cooling needed• Multi-phases interleaved • Phase current sharing• Can be stacked to deliver 3 kW (3-kW buck-mode and 800-W boost-mode)• 12-V reverse connection prevention • Failed phase isolation• Auto phase-shedding and offset for light-load management• Protection including OCP, OVP, OTP• 70 V/100 ms load-dumping BN48 surge • 100 uA quiescent current when disabled (after 48 V is disconnected)• CAN bus or SPI communication

4-5


Microsoft reinvented data center

Traditional data center

Bi-directional DC/DC

Advantages of local energy storage data center deployments• Reduce cost up to 5 times• Eliminate up to 9% losses associated with UPS• No requirement for a UPS or battery room

o 25% facility footprint reduction• Improve serviceability significantly

o Hot-swappable o Minimize potential failure impact zone

Other applications: data centers and servers

* Reference from Microsoft Publication

Generators

UPS

IT load

Substation Substation

IT loadGenerators

4-6


Topology investigation

Hard-switching, non-Isolated DC/DC (sync-buck) converter

Transition-mode ZVS DC/DC (sync-buck) converter

PROS• Simple control• Fixed-frequency• Low inductor current ripple

• Soft-switching, potentially high efficiency

• Low common-mode noise

CONS• High-switch ringing• High common-mode noise

• High inductor current ripple• Variable frequency• Complex control

4-7


Hard-switching and soft-switching bi-directional converter

Buck-mode

Boost-mode

Buck-mode

Boost-mode

Energy transfer direction

Energy transfer direction

Soft-switching converterHard-switching converter

Buck-mode

Boost-mode

4-8


UCD3138 overviewKey features• Multi-nested loop isolated digital controller• 3 loop with 14-bit DAC reference• 2-pole 2-zero PID filters with multi-coeff

banks• PWM, phase-shift and resonant-mode

control • Constant voltage, current and power

modes• Input voltage feed-forward and Vpri-

sensing• Peak current mode with internal slope

comp.• Cycle-by-cycle current limit with CLF

counter• 8x over sampling or averaging at EADC

4-9


UCD3138 key features (cont.)• 12-bit ADCs with hardware filters• 12-bit ADCs with dual hold-sampling • Auto PWM-LLC and PWM-PS mode

switching• Burst-mode for light load operation• Integrated copper trace current-sensing• Integrated current-sharing circuit• 8 high resolution DPWM outputs (250 ps) • 32-bit, 32-MHz ARM 7 (32 KB PFlash, 4

KB DFlash)• Multi-channel, 12-bit 256 ksps GP ADC• On-chip (BOD / POR)• Single-supply operation (3.3 V)

• Single supply operation (3.3 V)• On-chip reference + oscillator• 2 UART’s + programmable PMBus

interface• 2 MHz max switching frequency• 4 ns frequency resolution• External interrupt + fault input and output• –40°C to +125°C extended temp range• 64 pin and 40 pin QFN packages• Power-saving features• And MORE!!!

4-10


UCD3138-based control• Three control loops: current loop, 12-V

voltage loop, 48-V voltage loop• Total current is sensed for current loop

control• Current source operation before voltages

reach set points• Phase currents are sensed for current

balance• Current command set by digital

communication port or ADC input

Additional control for ZVS operation:• Phase 1 negative current sensed• Negative current thresholds programmed

by PWM0, one to generate a sync signal• Sync signal controls frequency modulation

4-11


Current ripple and phase number selection

• Duty cycle directly determines phase number selection• Optimal phase numbers for 48-V /12-V buck and boost power conversion are: 4, 8, 12• Adding phases reduces current ripple further when duty cycle is away from:

o 0.25 in buck-modeo 0.75 in boost-mode

IL2

/ V

0.2

0.4

0.6

0.8

1

IL1

/ V

0

0.2

0.4

0.6

0.8

time/uSecs 5uSecs/div

0 5 10 15 20 25 30

IL_T

otal

/ V

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Time

IL1

IL2

IL1+ IL2

0

1

0

1

0

1.50.66A

Ripple Current Cancellation

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 2 3 4 5 6 7 8 9 10 11 12Normalized Inductor Current Ripple vs Phase NumberPhase Number

Normalize

d Cu

rren

t Ripple

Zero current ripple at 12V

4-12


System block diagram for circuit test

4-13


Power stage component selection and designHard-switching Soft-switching

Switching frequency 140 kHz 100 kHz- 450 kHz

Current ripple at full load 16.25 A (±25% ripple) 65 A

Inductor value 4.7 uH 1.4 uH

Inductor DC resistance 1.86 mΩ 0.618 mΩ

Inductor part number SER2915H-472KL (Coilcraft ) Litz wire: AWG# 32, 110 strands PQ26/20 core -TDK B65877B0000R097

Inductor photos

4-14


Power stage component selection and design (cont)Hard-switching Soft-switching

Main MOSFETs Infineon IPB017N100N5:100 V, 1.7 mΩ

Infineon IPB015N08N5:80 V, 1.5 mΩ

Reverse protection FETs

CSD16556Q5B:TI, 20V, 1.062 mΩ @ 75ºC

CSD16556Q5B:TI, 20 V, 1.062 mΩ @ 75ºC

48-V fuses Littlefuse: 0891030 30A, 2.06 mΩ @ 25ºC,2.18 mΩ @ 90ºC

Littlefuse: 0891030 30 A, 2.06 mΩ @ 25ºC,2.18 mΩ @ 90ºC

Low inductance shunt-sensing resistor

Panasonic ERJ-M1WTF2M0U: –2 mΩ

Panasonic ERJ-M1WTF2M0U: –2 mΩ

48-V input filter inductor

Coilcraft XAL1580-102 MEB:1 uH 73.5 A, 0.93 mΩ typical

Coilcraft XAL1580-102 MEB: –1 uH 73.5A, 0.93 mΩ typical

4-15


Bi-directional DC/DC converter prototype 110 A

5.0” x 7.5”

48 V

12 VUCD3138

48 V

12 V

4-16


ZVS buck-switching waveform

ZVS Buck at 20A Io

• Max frequency = 450 kHz• Min frequency = 104 kHz

Switching node voltage

Inductor current

4-17


Buck-switching waveform comparison 20 A

Soft-switching: negative current and ZVS Deadtime from SyncFET turn-off to main FET turn-on = constant 220 nS Deadtime from main FET turn-off to sync FET turn-on varies based on Io

Hard-switching

Soft on/off edges

6V overshoot

Hard switching

No overshoot

4-18


Buck switching waveform comparison 110 A

Soft-switching: Negative current and ZVS (104 kHz)

• Deadtime from sync FET turn-off to main FET turn-on = constant 220 nS• Deadtime from main FET turn-off to sync FET turn-on varies based on Io

Hard-switching (140 kHz)

20V overshoot

Soft on/off edgesHard switching

No overshoot

small undershoot

4-19


Boost-switching waveform comparison 20 A

• Deadtime from SyncFET turn-off to Main FET turn-on = constant 220nS

• Deadtime from Main FET turn-off to SyncFET turn-on varies based on Io

Soft-switching: Negative current and ZVS (353 kHz)Hard-switching (140 kHz) • Deadtime from sync FET turn-off to main FET turn-

on 37.5 nS• Deadtime from main FET turn-off to sync FET

37.5nS

Soft on/off edgesHard switching

4-20


Boost-switching waveform comparison 110 A

• Deadtime from sync FET turn-off to main FET turn-on = constant 220 nS

• Deadtime from main FET turn-off to sync FET turn-on varies based on Io

Soft-switching: Negative current and ZVS (104 kHz)Hard-switching (140 kHz)• Deadtime from sync FET turn-off to main FET turn-on

37.5 nS• Deadtime from main FET turn-off to sync FET 37.5 nS

3V overshoot

Soft on/off edges

Hard switching

8V overshoot

4-21


Bi-directional operation

Ibat

IL

VSN

Programmable parameters• 12-V battery current at

buck- and boost modes• Current ramp-up and ramp-

down time• Idle time between buck and

boost operation• 48-V and 12-V battery OVP

and UVP thresholds

4-22


GUI control screen

Device GUI for circuit configuration and debug• Facilitate firmware and hardware debug• Change parameters while circuit is running• Monitor register values firmware execution• Converter status reporting

Control GUI for system test and monitoring• Facilitate system test• Ease system parameter setting• Monitor system operating state and status• Monitor battery voltage and phase currents

4-23


Loss breakdown chart at 110 A, 12-V output

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11

Hard Switching Buck

ZVS Buck

Sw

itchi

ng

loss

Con

duct

ion

loss Gat

e dr

ive

loss

Cor

e lo

ss

Win

ding

loss

Saf

ety

FET

loss

Shu

nt lo

ss

Fuse

loss

Filte

r L lo

ss

Bia

s lo

ss

Oth

er lo

sses

Pow

er L

oss

/ W

*Calculated data with test data recertification

4-24


Efficiency comparison: buck-mode

84.00%

86.00%

88.00%

90.00%

92.00%

94.00%

96.00%

98.00%

0 20 40 60 80 100 120

ZVS Buck

Hard Switching Buck

ZVS Buck w/o safety parts

HS Buck w/o safety parts

Effic

ienc

y

12 V Current / A

4-25


Efficiency comparison: boost-mode

84.00%

86.00%

88.00%

90.00%

92.00%

94.00%

96.00%

0 20 40 60 80 100 120

ZVS BoostHard Switching Boost

Mode-switching and phase-sheddingcan improve light-load efficiency.

Effic

ienc

y

12 V current / A

4-26


Light-load management (LLM)• DCM operation improves efficiency by around 2%

at 10 A load, compared with CCM operation• Ideal diode emulation (IDE) can further improve

light-load efficiency (by around 0.3%-0.7%)• Phase-shedding can be used to improve light-

load efficiency when switching loss becomes dominant

• Mode switching needed for LLMo CCM DCM/IDE phase-sheddingo ZVS transition-mode DCM/IDE phase-

shedding

DCM control (buck-mode)

Ideal diode emulation (boost mode)

Vds

IL

Vds

IL

Vg_top

Vg_bot

4-27


Thermal data comparison 110 AZVS buck-modeHard-switching buck-mode

Top FET / C Bottom FET / C Core / C Winding / C

72.0/73* 61.5/64 56.5//59 62.3//64


84.75/92 68.25/69 64/65 77.5/78

*Avg. temp / max temp

Top FET

Bottom FET

Top FET

Bottom FET

CoreWinding

Core

Winding

4-28


Thermal data comparison 110 AZVS boost-modeHard-switching boost-mode


64.3/66* 75.3/76 65/66 66.75/71


67.25/72 75.25/77 63/64 69.25/73

Top FET

Bottom FET

Top FET

Bottom FETCoreWinding

Winding

Core

*Avg. temp / max temp4-29


EMI floor and bias noise (quasi-peak)

Noise floor

Bias noise

Class B QP Class 5 avg

4-30


EMI comparison (quasi-peak)Hard- versus soft-switching at buck-mode and full-load

15 dB

Class B QP Class 5 AvgSoft-switching

Hard-switching

4-31


Summary and conclusionsHard-switching Soft-switching

Efficiency Better efficiency at light-load range Better efficiency potential at heavy loads

Voltage spike, dv/dtand current ripple

Higher voltage spike and dV/dt but lower current ripple

Softer dv/dt and lower voltage spike, but much higher current ripple

Control complexity Fixed frequency, less complexity Hardware is required for cycle-by-cycle phase synchronization

Thermal Higher FET temperature rise Lower temperature rise and less than 75ºC FET case temperature and windings

• One power stage designed for both hard- and soft-switching converter comparison tests• Efficiency advantage of soft-switching at heavy load is insignificant• Soft-switching converter can improve efficiency by optimizing inductor design• Light-load management can improve light-load efficiency to a similar level for both controls• EMI under 1 MHz has insignificant difference, but soft-switching exhibits up to 15 dB lower noise at higher

frequency • UCD3138 is capable of doing both hard-switching and soft-switching control • GUI eases circuit debug and facilitates system test and monitoring

o Download firmware with Fusion GUI here: www.ti.com/ucd3138.4-32

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Bi-directional DC/DC converter topology comparison and design