Bi-directional DC-DC converter Bi-directional DC-DC converter with Soft Switching Cellwith Soft Switching Cell

Student: Marek Ryłko

Co-ordinators: Dr. Michael G. Egan

Dr. John G. Hayes

EPE-PEMC 2006, Portoroz 31th Aug 2006

Topology basics

• Introduce Soft Switching Cell

• 5 extra elements

– 2 aux. Switches

– 2 aux. Diodes

– Autotransformer

Hard Switching

Soft Switching

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Fundamentals of operation

Continous conduction mode• Fixed bus-voltages• Operating frequency – above audible noise

Maximum frequency limited by system topology and devices properties

• Efficiency 92-98%• Hardware overcurrent protection• Main switches operates as thyristor-dual• Fully ZVCS switch-on main switches and snubber assisted

switch-off• ZCS switch-on and ZVCS turn-off of auxiliaries• Main diodes reverse recovery limited by soft-switching cell

inductance

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Main inductor current

Resonant ind. current

Main switch current

Flywheeling diode current

Pole voltage

Low voltage bus current

Main inductor voltage

Basic waveforms - BOOST

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Main inductor current

Resonant ind. current

Main switch current

Flywheeling diode current

Pole voltage

Low voltage bus current

Zero Current Crossing Mode

Basic waveforms - ZCCM

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Main inductor current

Resonant ind. current

Main switch current

Flywheeling diode current

Pole voltage

Low voltage bus current

Main inductor voltage

Basic waveforms - BUCK

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Soft Switching boundary

22 cos1 Vtaavp

1cosmin t

0)1(0min

2 aatvt

p

2

1a

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Pole voltage swing (boost):

Minimum value is achieved for:

Pole voltage must reach zero:

Soft Switching boundary is:

Transformer turn ratio

• Presented boundary for soft switching refer to auxiliary voltage VS

• Damp resistance is present Rd and take part as voltage drop

• Initial conditions are significant factor when main current is large

• Diodes voltage drop affect soft switching

• Voltage swing must be overestimated to take into account main-switch turn-

on time 22

22

542

42max

2

11

1

12

Di

Di

DD

DVL

dV t

t

VVV

VVaI

V

R

e

an

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Duty factor

• Hard switching (square pole voltage)

• Soft switching rr = 0 (deformation of rising and falling edge)

2

1

V

rIVD rLeffective

Because bus voltages are fixed, the duty factor depends on main inductor current as derivative of average value of pole voltage

20

222

2

20

2220

22

2

1

2 1

211arccos

1arccos

2

1

1 ZIVa

ZIaVZIaaV

a

a

TV

rIV

TVa

LID

L

LLLrLapp

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

0 100 200 300 400

I

0.2

0.4

0.6

0.8

1

D

DvsIL, Blue:Pspice, Green&Red:Ideal rr0, 150kHz

System characteristic DvsI

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Damped Cell – non ideal case rr ≠ 0

• Damped cell Duty factor

20

222

2

20

2220

22

22

22

22

22

2

22

2

2

2

1

1

211arccos

1arccos

2

1

21arccos

arccos2

11

1

1ln

ZIVa

ZIaVZIaaV

a

a

VrIa

rIaVVr

V

Ia

VrIa

rIa

Va

a

Va

aVVa

TrIVa

Va

Tr

L

V

rIVD

L

LL

rL

rLr

L

rL

rL

rLr

rLapp

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

0 100 200 300 400I

0.2

0.4

0.6

0.8

1

D

DvsIL, Red:Pspice, Purple&DarkGreen:Damped rr0.3, 150kHz

System characteristic DvsI

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

100 200 300 400IL

0.2

0.4

0.6

0.8

1

D

DvsIL, Blue&Black:HS, Red&LightGreen :Ideal, Purple&DarkGreen:Damped, 150kHz

Difference between ideal and damped system

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Summary of soft switching system

• EMI improvement

• Good efficiency

• Decreased switching losses

• Distributed heat radiation

• Silent operation (over audible frequencies)

• No significant volume improvement

• More complex system

• Gain affected due to cell operation

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

Further research plan

• Development of systems above 10kW• Compare with other bi-directional topologies

– Interleaved, multiphase converters – Comparison of high ripple current and low ripple

current cases– Investigation of IGBT operation in soft-switched

regimes– MOSFETs in interleaved systems for high power– Inductor design– Coupled inductor approaches– Fully resonant approach– Hardware, FPGA’s for control– Conference papers

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END

THE END

Thank you for your attention!

Topology

Fundamentals

BOOST

ZCCM

BUCK

SS Boundary

Turn ratio

Duty – ideal

Duty – damped

Summary

Further plans

END