Design and implementation of a LLC-ZCS Converter for ... · 1/7/2016 · Infineon Italy s.r.l. ATV division Design and implementation of a LLC-ZCS Converter for Hybrid/Electric Vehicles

Infineon Italy s.r.l.ATV division

Design and implementation of a LLC-ZCS Converter for Hybrid/Electric Vehicles

Davide GIACOMINI Principal, Automotive HVICs

HV Battery LV Battery

M

12Vbus

Traction Network

Power Distribution Network

Hybrid and Full Electric vehicles allow pollution reduction this make them the new generation of transportation

Traction and power distribution networks are highly impacted by this evolutionHV battery in hybrid/electric vehicles allow traction as well as services to run out of the battery for a medium/long time.

Need for clean

22016-01-07 Copyright © Infineon Technologies AG 2016. All rights reserved.

HV Battery LV Battery

M

12Vbus

Traction Network

Power Distribution Network

Variable Min. Typ. Max.

Input HVB [V] 250 350 450

Output LVB [V] 13

Load power [W] 400 2400

System has been designed considering these ranges

Power distribution network: exploiting the energy of a HV battery for traction and services

System Specification

› While the traction inverter is directlysupplied by the HV battery, all services in a car today still run out of a 12V battery, therefore a HV-DC/DC converter is neededto supply this battery line


1. Galvanic isolated topology2. Soft switching

Lr

LV

n:1

GD

GD

GD

IG1 IG2

IG3 IG4

M1

M2

HV

HV

Gate

Dri

ver

LV Gate Driver

Cr

Controller board

and isolation

• Behaves as current generator intrinsically protected @ short circuit at the output.• ZCS has the advantages of using IGBT with co-packed fast diode;• Simplified output filtering uses only capacitors;• No need to control the DC current through transformer, resonance Cap solves it.

System design: converter topology choice


Lr

LVB

n:1

GD

GD

GD

IG1 IG2

IG3 IG4

M1

M2

HVB

HV

Gate

Dri

ver

LV Gate Driver

Cr

Analog

ControllerOptocoupler

-

+ Vref

Error Amplifier

Cr voltage

sense

Primary High Voltage Side Secondary Low Voltage Side

Inner Loop

Voltage Control Loop

Cf

IRS27951SSO8 analog controllerGrounded in the HV side

Error amplifier and OV protectionGrounded on the LV side

HV caps protectionloop

System design: control strategy

AU

IRS

11

70

S

1

2

3

4

8

7

6

5

VCC

SYNC

MOT

EN

VGATE

VS

VD

NC

AUIRS1170S synch. Rect.PSO8 analog controller

AU

IRS2191S

AUIRS2191S Fast HVIC driverSO16


LLC DC/DC board, prototype picture


Board Layout Resonant Capacitor tank

Pri

mary

sid

e I

GBTs

Resonant Inductor at primary side

Transformer

Center tappedoutput

SynchronousrectificationFets and control IC

Pri

mary

sid

e

gate

dri

vers

Loop control board

Output Capacitors

Layout is optmised for system testing and debugging.


• It is made with only Organic Conductive Polymer capacitor, 4mF in total no need for output inductor

• System volume and cost are reduced

• SR MOSFET voltage rating = 60V-80V higher power density and cheaper system

Output Flter

• Resonant inductor at primary side reduces size and weight; resonant capacitors also take care of balancing the magnetizing current

Magnetics and Resonant Tank

• Resonant inductor and capacitor values have been optimized vs. load and input voltage variation

Mathlab routine has been implemented in order to design

main parameters

•Magnetizing inductance Lm = abut 6 times resonant inductor value

•Transformer ratio is 16:1+1; Isec. = 170Arms

•Variable frequency from 60kHz to 125kHzTransformer

•Lr = 128uH

•Irms~15A

•System Resonant freq.: 125kHzResonant inductor

•Cr = 12,6nF

•3kV

•C0G (low ESR)Resonant Capacitor

•Rds-on = 2,4mW max, 80V

•3x each leg in parallelSynchronous rectification Fets

•650V – 40A IGBTs

•Vce_sat= 1,80V @125CPrimary switching section

System design: main BOM components


Simulation results

Transfer Function: switching from 70k to 120kHz at Vin=350V

~70kHz ~120kHz

Simulation at Vin = 350V, Vout = 12V and different power output


Measurements: Operating Frequency vs Input Voltage and load

96

98

100

102

104

106

108

110

112

200 250 300 350 400 450

Fsw vs Vin at Io=100A

V

KHz

0

20

40

60

80

100

120

25 75 125 175

Fsw vs Io at Vin=350VKHz

A

Low switching frequency variation vs. input voltage and load changes

Good matching with simulation


Operation at nominal input voltage:400V – 100A

Sec.Center tap current

100A/d

Primary current

25A/d

Capacitor voltage

500V/d

Clean sinusoidal voltage across resonance capacitors, someringing noise visible on transformer‘s secondary current


Operation at nominal input voltage: 400V – 150A


100A/d

Capacitor voltage

1kV/d

Primary current

25A/d

Frequency, capacitors voltage and Primary/Secondary currents increase


Operational waveforms at 400V -180A

Primary current

50A/d


100A/d

Capacitor voltage

1kV/d

Very close to resonance (~110kHz), waveforms are almost sinusoidal.


Secondary side synchronous rectification

AU

IRS

11

70

S

1

2

3

4

8

7

6

5

VCC

SYNC

MOT

EN

VGATE

VS

VD

NC

VCC

SYNC

MOT

EN

Vg

Vs

Vd

RMOT

RCC

CVCC

VCC

SYNC

MOT

EN

Vg

Vs

Vd

RMOT

RCC

CVCC

AUIRS1170S AUIRS1170S

VoutLon:1

GND

Cout

Rf

Cf

Rg

Rf

Rg

Cf

• In a LLC converter the secondary current and primary switching voltage are not in phase and their

phase rotation depends on the load, this effect doesn’t allow to use the primary PWM signal to

control the secondary side switches.

• A dedicated IC reading the VDS voltage across the Synch Rectification Fets solves this problem

› Typical application schematicAUIRS1170S


Secondary side waveforms at 400V and light load

Ch1= Vds [10V/d], Ch3= Vgate1 [5V/d], Ch4= Isec. [20A/d]

Waveform obtained at low current output of 30A only: the signal across the 0,8m W equivalent

Rds-on of the Fets becomes quite small but the gate command signal is regular.


Secondary side waveforms at 400V and high load

Primary current

25A/d


100A/d

Blue: Vgs

Light blue: Vds

Waveform obtained at high current output of 160A: the signal across the 0,8m W SR Fets is

much more evident as well as switching noise but the gate command signal is regular.


Power Losses Breakdown(350Vin)

0

50

100

150

200

250

300

350

400

W

Io=150A

0

20

40

60

80

100

120

140

160

180

200

W

Io=100A

• Primary side losses look still predominat and increase proportionally with the output current;

• High Vcesat of IGBTs still inpact this performances;

• Inductor losses seems to be increasing rapidly with output current, showing undersizing of the component, redesign is advisable;

• Resonant and output Capacitor losses have low inpact in the overall efficiency.

Estimation done though thermal measurement and mathematical estrapolations


Efficiency results

• Efficiency at light load is high, thanks to the low frequency operation of the input bridge;

• High Vcesat of IGBTs and inductor losses inpact overall system performances;

• At Iout=150A, only 1mW pcb trace resistance in the secondary side means 23W dissipatedand 1,3% efficiency loss.

0.75

0.8

0.85

0.9

0.95

1

40 60 80 100 120 140 160

Eff 300Vin

Eff 350Vin

Eff 400Vin

[A]


Start up and Vin transients

Fast start: Vin rise time is only limited by the Lab power supply

Vin=400V, Io=25A

Primary current

25A/d


100A/d

Capacitor voltage

1kV/div

Vin; 100V/div


Output current

30A

120A

Output voltage

Switching frequency

Experimental results: load transient

Low ESR output caps provide very low output voltage variation at load transients


Load transients : Iout from 70 to 140A

Primary current

25A/d


100A/d

Vout ripple

Load increase to 140A (traces 2 and 3 with AC coupling)


Load transients : Iout from 140 to 70A

Primary current

25A/d


100A/d

Vout ripple

Load decrease to 70A (traces 2 and 3 with AC coupling)


1. An Auxiliary DC-DC converter has been designed by using the uncommon LLC ZCS topology

2. System design flow with mathematical and electrical models have been utilized to tune the resonant tank and converter frequency operation range

3. Prototype has been built and verified

4. System efficiency over 90%, limited by high Vce_sat of IGBTs and inductor losses

5. Robustness to load transients has been verified

6. Prototype Max power is limited to around 2.0kW with air forced cooling, because of PCB and heat sinks limitations.

7. Next step: evaluate Super-Junction Mosfets performances in the same topology, adding Ultrafast diodes in parallel.

Conclusions


Documents

Design and implementation of a LLC-ZCS Converter for ... · 1/7/2016 · Infineon Italy s.r.l. ATV division Design and implementation of a LLC-ZCS Converter for Hybrid/Electric Vehicles