Naturally-Clamped Snubberless Current-fed Soft-Switching ...

Naturally-Clamped Snubberless Current-fed Soft-Switching DC/DC Converters

Akshay Kumar RathoreAssociate Professor

Electrical and Computer EngineeringConcordia University, Montreal, Canada

[email protected]

IEEE IAS Distinguished Lecture

1

mailto:[email protected]

© Dr. Akshay K. Rathore, Associate Professor, Electrical and Computer Engineering, Concordia University, Montreal, Canada

2

Major Research Focus

1) High-frequency power converters• Low voltage medium power applications• High device switching frequency• Soft-switching techniques• Compact, low cost, light weight

• Current-fed topologies (high voltage gain)

2) Low-frequency power converters• Multilevel converters• Medium voltage high power applications• Low device switching frequency• High efficiency• Industrial applications


3

Current-Fed DC/DC Converters• Boost derived• Voltage gain


4

Major Research Highlights

1) Naturally-clamped Snubberless Current-fed Topologies

2) Impulse Commutated Current-fed Converters

3) Current-fed direct unfolding inverter

1) Single Reference Six-Pulse Modulation (SRSPM)

2) Dual Three-Pulse Modulation

*to realize capacitorless three-phase inverter with reduced magnetics and device count

1) Fundamental frequency control of medium voltage multilevel inverters

2) Common mode elimination in open-end winding machines


5

First Glance…

• Short circuit protection• Voltage gain (10x with voltage doubler)• Limits peak and circulating current• High Voltage Gain High current applications• Inductor Reliability vs Capacitor• Input inductor vs. output inductor• Low magnetizing to leakage inductance ratio


6

Outline …• High Voltage Gain Applications• Traditional Current-fed Converters• Major issues with Current-fed Converters• Current-fed Converters for low voltage high current

applications requiring high voltage conversion ratio• Advanced Current-fed Converters• Analysis, Results & Conclusion


7

Low Voltage High Current Applications• UPS• Battery/Storage• Renewables• Fuel cells• HEV/FCV


8

Low Voltage High Current Applications1) UPS: 12 V

2) HEV: 48 V

3) FCV: 12 V

4) PV/FC: 22-41 V

5) Telecommunications: 48 V

6) Energy Storage: 48 V


9

Typical Applications(1) UPS


10

(2) Solar PV/Fuel Cells


11

(3) DC Microgrid


12

(4) Fuel Cell Vehicle


(5) Low Voltage DC Fuel Cells/Battery Applications

DC source/battery

• soft switching capability

• Flexibility of interfacing different voltage levels

• High power density and symmetric structure

Pros of front end dc-to-dc converter

AC source/load DC

3Ø AC

DC

DC

Isolated dc-dc converter cascaded with a 3 phase VSC

13


Fuel Cell Characteristic

14


15

High-Frequency Power Converters• Soft-switching• Compact, low cost, light weight


Power Electronics

Major portion of volume, cost, and weight is covered by heat sink, magnetics and filters.

16


17

Reduced size of:

• Magnetics• Filters• Passive Components


18

Hard SwitchingOverlap of device voltage and device current during switching transition results into switching losses that is proportional to device switching frequency.

Switch Voltage & Currents

vSW iSW

Switch turn-on Switch turn-off

Switching Power Loss

Turn-on loss Turn-off loss

G

D

S

CsDb

© Dr. Akshay K. Rathore, Associate Professor, Electrical and Computer Engineering, Concordia University, Montreal, Canada19

Soft-switchingTo realize compact, low cost, light weight converter

G

D

S

CsDb

vsw isw

vgate

Switch Voltage & Current

Gating Signal

isw vsw

vgate

Switch Voltage & Current

Gating Signal

Zero-voltage switching (ZVS)

Zero-current switching (ZCS)


20

Soft-switching is realized and implemented by:

• Modulation Technique (PWM Converters)• Auxiliary Transition Circuit (ZCT and ZVT)• Resonance (Resonant Converters)


21

Resonant Topologies

Series resonant converter

Parallel resonant converter

Series parallel resonant converter


22

- Variable Frequency Modulation*makes the design of filters and control circuit difficult. ** variation in switching frequency required is very large due to wide variations in the input voltage and load conditions

- Fixed Frequency Modulation*soft-switching cannot be maintained with the load and source variability.

Source variability is critical than load variability.


23

- Series Resonant Converters (SRC) and Series-Parallel Resonant

Converters (SPRC) can operate with ZVS only for a narrow range

of source (input) voltage.

- For a fixed input voltage value, it is easy to design the converter to

maintain ZVS at light load (35%) or up to 10%.

- In the case of PRC, the inverter peak current does not

decrease much with reduction in load.


Soft-switching is lost at higher input voltage and converter enters hard-switching region.

- Efficiency reduces drastically.

-Input current ripple : poor source utilization at lower load i.e. waste of hydrogen in case of fuel cells.

- Requirement: Flat efficiency curve

24

Efficiency Curve with Source Voltage Variation


LCL Series Resonant Converters

RLLs

nt:1HF Tr

DR2

Co

Io

Vo

DR1 DR3

DR4

iLsVin

Cin

S2

D2

C2

Iin

+

-

S1

D1

C1 S3

D3

C3

S4

D4

C4

Cs Lp

LCL Resonant Circuit

25

RLLs

nt:1HF Tr

DR2

Co

Io

Vo

DR1 DR3

DR4

iLsVin

Cin

S2

D2

C2

Iin

+

-

S1

D1

C1 S3

D3

C3

S4

D4

C4

Cs Lp

LCL Resonant Circuit

- Relatively better soft-switching range by reducing the value of

magnetizing inductance (parallel inductor).


26

Modulation Technique (PWM Converters)-Simple control to implement

Auxiliary Transition Circuit (ZCT and ZVT)-Additional components including switches and driver

Resonance (Resonant Converters)-Design is tricky-Optimization is needed-Analysis and control is relatively complex- Peak and circulating currents


27

Major Concerns with Traditional Voltage-fed PWM and Resonant Converters for Low Voltage High Current Applicationsand SOURCE VARIABILITY

1) Excessively high peak and circulating currents

2) Poor efficiency with voltage and load variation due to high conduction losses

3) Poor performance if voltage conversion ratio is quite high (high voltage gain)

4) Loss of soft-switching with variability of the source and/or load


28

Low Voltage High Current Applications

1) Excessively high peak currents, circulating currents2) Poor efficiency with voltage and load variation due to high

conduction losses3) Poor performance if voltage conversion ratio is quite high


29

Duty Cycle Loss

0

-20

-40

-60

20

40

60

I(L1)

0.02702 0.027025 0.02703 0.027035 0.02704Time (s)

0

-20

-40

-60

20

40

60

I(MOS1)

0

0.5

1

1.5

2

2.5

3

I(D1) I(D2)

0.02702 0.027025 0.02703 0.027035 0.02704Time (s)

0

-10

-20

-30

10

20

30

VP3

The ‘zero’ voltage duration over a HF cycle is called Duty Cycle Loss.

Higher value of transformer leakage inductance will cause higher Duty Cycle Loss.Needs to increase transformer turns ratio to compensate

The current through the inductor cannot be changed instantaneously.

Transfer leakage inductance will cause slow change in the direction.


30

Rectifier Diode Ringing

The transformer leakage inductance and the diode parallel capacitance (of the order of pF) resonates.

Voltage ringing/stress needing overrated devices with higher cost and Rds,on. Otherwise needs external snubber to clamp the diode voltage.

RLLs

nt:1HF Tr DR2

Co

Io

Vo

DR1 DR3

DR4

iLsVin

Cin

S2

D2

C2

Iin

+

-

S1

D1

C1 S3

D3

C3

S4

D4

C4


31

Current-Fed Converters-Issues


32

Fundamental issue with Current-fed Isolated TopologiesShort-circuit protectionCurrent limitingDevice voltage spike/overshoot at device commutation (turn-off)

Needs snubber, either active-clamp or passive to absorb the voltage spike and clamp the device voltage.

RL

S4

Llk

1:nHF Tr

DR2

Co

Io

Vo

DR1 DR3

DR4

D4

C4

ilkVinCin

S2

D2

C2

L iin

+

-

A

B

S1

D1

C1 S3

D3

C3


33

Snubbers , a traditional solution

LD

DC

D

CR

C

R

S

C

CRD

(a) (b) (c)

(e) (f)

DC

(d)

R

Snubbers for suppressing the voltage spike: (a) Dissipative RC snubber, (b)-(d) Dissipative RCD snubber, (e) Non-dissipative energy recovery LC snubber, and (f) active-clamping snubber.


34

Snubbers, a traditional solution

RLHF TrCo Vo

Vin+

-

S1

S2 S4

S3 D1

Fuel Cell

D2

D3

D4

Cin

L

Cau

Lau

Dau1

Sau

Dau2

Auxiliary Circuit

RLHF TrCo Vo

Vin+

-

S1

S2 S4

S3 D1

Fuel Cell

D2

D3

D4

Cin

L

Lau

Cau

Sau

Auxiliary Circuit

RLHF TrCo Vo

Vin+

-

S1

S2 S4

S3 D1

Fuel Cell

D2

D3

D4

Cin

L

Cau

Sau1

Auxiliary Circuit

Sau2

RLHF TrCo Vo

Vin+

-

S1

S2 S4

S3 D1

Fuel Cell

D2

D3

D4

Cin

L

Cau

Lau

Dau1

Sau

Dau2

Dau3

Auxiliary Circuit


35

Current-fed Full-bridge Isolated DC/DC Converter

RL

S4

Llk

1:nHF Tr

DR2

Co

Io

Vo

DR1 DR3

DR4

D4

C4

ilkVinCin

S2

D2

C2

L iin

Cax

Ca

+

-S a

x

Dax

+-

Lm

iLm

iS1

A

BvAB

S1

D1

C1 S3

D3

C3

iCa

Assuming 0.05 < Dx 0.1, then-Vo > Vin for D > 0.55, i.e. boost converterVo < Vin for D < 0.55, i.e. buck converter

)1(2 x

ino DD

VnV

+−⋅⋅

=

Active-clamp: Floating active deviceA high value high frequency capacitor

Demerits • Higher peak currents and circulating current • Reduced boost capacity • Increased complexity, footprint, cost


Active-clamped Current-fed Half-Bridge Converter

RL

S2

Ls

nt:1HF Tr

DR2

Co

Io

Vo

DR1 DR3

DR4D2

C2

iLs

Vin

Cin

S1

D1

C1

L1 L2

Iin

Ca1

Sa1

Da1

Ca2

Sa2

Da2

Ca

+

-A

BvAB

IS1 +ID1

IS2 +ID2

ISa1+IDa1 iLmLm

36

Active-clamp: Two floating active devices due to two inductorsFloating devices have high gating requirementsA high value high frequency capacitor

Demerits • Higher peak currents and circulating current • Reduced boost capacity • Increased complexity, reduced reliability, footprint, cost

)1( x

ino DD

VnV+−⋅

=


37

“Naturally Clamped Snubberless” A New Class of Current-fed

Converter Topologies

Dr. Pan XueweiAssociate ProfessorHarbin Institute of Technology, China

Dr. Prasanna RajagopalTexas Instruments, Dallas, USA


38

(1) Snubberless Naturally-clamped Current-fed ConvertersInnovative and Novel Modulation Naturally device voltage clamping Zero current commutation of devices Soft-switching of all devices SNUBBERLESS Bidirectional – Several applications True isolated boost converter (preserves boost converter capacity) Negligible circulating current (low peak current and components rating) Inherent natural clamping and soft-switching, i.e., maintained with variability of source

and/or load Reduced switch peak current (half) and circulating currents Higher efficiency (at least 2% improvement) Lower components count-high density* Solves the traditional problem associated with current-fed converters

RL

S4

Llk

1:nHF Tr

DR2

Co

Io

Vo

DR1 DR3

DR4

D4

C4

ilkVinCin

S2

D2

C2

L iin

Cax

Ca

+

-

S ax

Dax

+-

Lm

iLm

iS1

A

BvAB

S1

D1

C1 S3

D3

C3

iCa


39

“Naturally Clamped Snubberless” Current-fed Topologies

RL

S2

Llk

1:nHF Tr

Co

Io

Vo

C2

VinCin

S1 C1

L1 L2

iin

+

-

ABvAB

S5

S6

D1 D2

S3

S4

D3

D4

D5

D6

Current-fed half-bridge dc/dc converter


40

Bi-directional Snubberless Naturally-clamped ZCS Current-fed Half-bridge Isolated DC/DC Converter

RL

S2

Llk

1:nHF Tr

Co

Io

Vo

C2

VinCin

S1 C1

L1 L2

iin

+

-

ABvAB

S5

S6

D1 D2

S3

S4

D3

D4

D5

D6

• Elimination of Active-Clamp Circuit• Reduced switch peak current stresses• Reduced switch conduction losses• Higher efficiency• Lower components count


41

Characteristics-

TRUE Isolated Boost converter

)1( DVnV in

o −⋅

=


Equivalent Circuit

S2

Llk

Vo´VinCin

S1

L1 L2

iin

+

-A

BvAB

iS1 = Iin/2 + iLlk

iS2 = Iin/2 - iLlk

KCL at point A

KCL at point B

Inductor equationn

Vt

IL oLlklk =

∆∆

42


Operation and AnalysisGS1

GS3

GS2

GS4

iS1 + iD1

t1 t2 t3t4

t5 t6 t7 t8

Iin/2

ilk Iin/2

-Iin/2

vAB

vLs

Iin/2

ILs,peak

iS2 + iD2

-ILs,peak

Iin

Iin/2

Iin

Isw,peak

iS3 + iD3

iS4 + iD4

nVo

nVo

nVo−

nVo

Iin/2

Isw,peak

RL

S2

Llk

1:nHF Tr

Co

Io

VoVinCin

S1

L1 L2

iin

+

-

ABvAB

D4

D5

RL

S2

Llk

1:nHF Tr

Co

Io

VoVinCin

S1

L1 L2

iin

+

-

ABvAB

S4

S5

RL

S2

Llk

1:nHF Tr

Co

Io

VoVinCin

S1

L1 L2

iin

+

-

ABvAB

S4

S5

D1

RL

S2

Llk

1:nHF Tr

Co

Io

Vo

C2

VinCin

S1

L1 L2

iin

+

-

ABvAB D2 D4

D5 t1 < t < t2

t2 < t < t3

t3 < t < t4

t4 < t < t5

43


Equivalent Circuit

S2

Llk

Vo´VinCin

S1

L1 L2

iin

+

-A

BvAB

iS1 = Iin/2 + iLlk

iS2 = Iin/2 - iLlk

KCL at point A

KCL at point B

Inductor equationn

Vt

IL oLlklk =

∆∆

44


GS1

GS3

GS2

GS4

iS1 + iD1

tot1 t2 t3

t4t5 t6 t7 t8

Iin/2

ilk Iin/2

-Iin/2

vAB

vLs

Iin/2

ILs,peak

iS2 + iD2

-ILs,peak

Iin

Iin/2

Iin

Isw,peak

iS3 + iD3

iS4 + iD4

nVo

nVo

nVo−

nVo

Iin/2

Isw,peak

RL

S2

Llk

1:nHF Tr

Co

Io

VoVinCin

S1

L1 L2

iin

+

-

ABvAB

S4

D1

C1

D6

D4

RL

S2

Llk

1:nHF Tr

Co

Io

VoVinCin

S1

L1 L2

iin

+

-

ABvAB

S4

D1

C1

D6

D4

RL

S2

Llk

1:nHF Tr

Co

Io

VoVinCin

S1

L1 L2

iin

+

-

ABvAB

S4

D1

C1

D6

D4

t5 < t < t6

t6 < t < t7

t7 < t < t8

45


Design

46

Leakage/series inductance

Switch current-LV side

Switch current-HV side

Transformer primary current

Input inductors

Switch voltage-LV side

Voltage gain


Simulation Results…

47



48


49

Picture of Lab Prototype: 500 W

Input Boost Inductor

PSoC 5

SecondarySwitches

Input FilterOutput Filter

HF Transformer

Primary Switches

• Input voltage = 12 V• Output voltage = 300 V• Switching freq. = 100 kHz• Output power = 200 W


Experimental Results…

50


Comparison between Active-clamp and Snubberless Current-fed Bidirectional HB ConverterVin = 22 V, Vo = 350 V, Po = 200W, fs = 100 kHz

51


52

Bi-directional Snubberless Naturally-clamped ZCS Current-fed Full-bridge Isolated DC/DC Converter

• Modular: Easy interleaving, scalable for high power• Low device voltage rating• Elimination of Active-Clamp Circuit• Reduced switch peak current stresses• Reduced conduction losses; Higher efficiency• Lower components count



53


54


• Input voltage = 12 V• Output voltage = 300 V• Switching freq = 100 kHz• Output power = 500 W



55

Primary side waveforms500 W



56

Secondary side waveforms

500 W



57

Primary side waveforms

250 W



58

Secondary side waveforms

250 W


Comparison of VFDAB and CFDAB Bidirectional Converters(Low Voltage High Current Applications)

59


60

Interleaved Current-fed Full-bridge Voltage Doubler: Bidirectional Snubberless Naturally Clamped

• Reduced switch current • Reduced conduction losses• Higher efficiency


61




62

Gating Signal waveforms

at source end

Gating Signal waveforms at load end



63

Cell-1 waveforms: soft-switching ZCS of primary side devices and ZVS of secondary side devices



64



65

50% load waveforms: soft-switching ZCS of primary side devices and ZVS of secondary side devices


66

Current-fed Push-Pull Converter: Bidirectional Snubberless Naturally Clamped

• Two primary devices and grounded• Reduced gate driver circuit requirements


67


• Input voltage = 12 V• Output voltage = 300 V• Switching freq = 100 kHz• Output power = 250 W


Experimental Results (250 W)

68


Experimental Results (100 W)

69


70

Naturally clamped Snubberless Current-fed Topologies

RL

S2

Llk

1:nHF Tr

Co

Io

Vo

C2

VinCin

S1 C1

L1 L2

iin

+

-

ABvAB

S5

S6

D1 D2

S3

S4

D3

D4

D5

D6

Current-fed half-bridge dc/dc converter

Current-fed full-bridge dc/dc converter


71

Current-fed push-pull dc/dc converter

Interleaved current-fed full-bridge voltage doubler


72

S3

Llk1

D3

C3

Vin

S1

D1

C1

L1 L3iin

S2

D2

L2

C2

Llk3

Llk2

+-

+-

+-

A

BC

+ -+ -

+ -RL

Co

Io

Vo

+

-S8

D8

C8+-

D5 +-C5

S9

D9 +-

D6

S6+-S5 C6

C9S7

D7

C7+-

D4 +-C4S4

3-PhaseHF Tr

iLlk1

iLlk2

iLlk3

S1 1:n3- Ph HF transformer

Cin

S2 S3

Iin ILlk1

ILlk2

ILlk3

Lin

Llk1

Llk2

Llk3

S5 S7 S9

S4 S6 S8 Io

Co

Ro VoVin

S6

Llk1Vin

Cin

S2

iin

S4

Llk3

Llk2

+-

+-

+-

A

BC + -

RLCo

Io

Vo

+

-S10+-

+-

S12+-

S11+-S9

S8+-

+-S7

3-PhaseHF Tr

iLlk1

iLlk2

iLlk3

+-

+-

+-S1 S3 S5

+ -+ -

L

Current-fed current divider three-phase dc/dc converter

Current-fed three-phase dual 6-pack (D6P) dc/dc converter

Current-fed three-phase push-pull dc/dc converter


73

Publications1. P. Xuewei and A. K. Rathore, "Small Signal Modeling of Snubberless Soft-switching Current-fed

Bidirectional Converter and Control Implementation using PSoC," IEEE Transactions on Vehicular Technology, vol. 64, no. 11,Nov 2015, pp. 4996-5005.

2. S. Bal, A. K. Rathore, and D. Srinivasan, “Naturally commutated current-fed three-phase bidirectional soft-switching dc-dc converter with 120o modulation technique,” in Press, IEEE Transactions on Industry Applications, Jan 2016.

3. S. Bal, A. K. Rathore, D. Srinivasan, “Naturally clamped snubberless soft-switching bidirectional current-fed three-phase push-pull dc/dc converter for dc microgrid application,” IEEE Transactions on Industry Applications, vol. 52, no. 2, March/April 2016, pp. 1577-1587.

4. P. Xuewei and A. K. Rathore, "Naturally Clamped Soft-switching Current-fed Three-Phase Bidirectional DC/DC Converter," IEEE Transactions on Industrial Electronics, vol. 62, no. 5, May 2015, pp. 316-3324.

5. P. Xuewei and A. K. Rathore, "Naturally Clamped Zero Current Commutated Soft-switching Current-fed Push-Pull DC/DC Converter: Analysis, Design, and Experimental Results," IEEE Transactions on Power Electronic, Vol. 30, no. 3, March 2015, pp. 1318-1327.

6. B. Satarupa, A. K. Rathore, and D. Srinivasan, "Modular Snubberless Bidirectional Soft-switching Current-fed Dual 6-Pack (CFD6P) dc/dc Converter," IEEE Transactions on Power Electronics, VOL. 30, NO. 2, FEBRUARY 2015.

7. P. Xuewei, A. K. Rathore, and U. R. Prasanna, "Novel Soft-Switching Snubberless Naturally Clamped Current-Fed Full-Bridge Front-End Converter Based Bidirectional Inverter for Renewables, Microgrid and UPS Applications," IEEE Transactions on Industry Applications, Vol. 50, no. 6, Dec 2014, pp. 4132-4141.


74

Publications8. P. Xuewei and A. K. Rathore, "Current-fed Soft-Switching Push-pull Front-end Converter

Based Bidirectional Inverter for Residential Photovoltaic Power System," IEEE Transactions on Power Electronics, Vol. 29, no. 11, Nov 2014, pp. 6041-6051.

9. P. Xuewei and A. K. Rathore, “Novel Bidirectional Snubberless Naturally Commutated Soft-switching Current-fed Full-bridge Isolated DC/DC Converter for Fuel Cell Vehicles,” IEEE Transactions on Industrial Electronics, vol. 61, no. 5, 2014, pp. 2307-2315.

10. P. Xuewei and A. K. Rathore, "Novel Interleaved Bidirectional Snubberless Soft-switching Current-fed Full-bridge Voltage Doubler for Fuel Cell Vehicles," IEEE Transactions on Power Electronics, vol. 28, no. 12, 2013, pp. 5535-5546.

11. A. K. Rathore, and U. R. Prasanna, "Analysis, design, and experimental results of novel snubberless bi-directional naturally clamped ZCS/ZVS current-fed half-bridge dc/dc converter for fuel cell vehicles” IEEE Transactions on Industrial Electronics, vol. 60, no. 10, 2013, pp. 4482-4491.

12. U. R. Prasanna and A. K. Rathore, “Novel soft-switching snubberless current-fed half-bridge front end converter based PV inverter: analysis, design and experimental results,” IEEE Transactions on Power Electronics, vol. 28, issue 7, 2013, pp. 3219-3230.

13. U. R. Prasanna and A. K. Rathore, “Novel zero-current switching current-fed half-bridge isolated dc/dc converter for fuel cell applications,” IEEE Transactions on Industry Applications, vol. 49, no. 4, 2013, pp. 1658-1668.


Appreciation Message from Prof. Ivo Barbi

75

Federal University of Santa CatarinaDepartment of Electrical EngineeringBrazil


76

- Current-fed technologyLow voltage higher currents or high voltage gain applications

- Short circuit protection and voltage gain (built-in), and low currentrating devices

- High power density in single cell design for low voltage high currentspecifications

- Higher efficiency (performance) with wide variation in voltage and power,i.e., future deep discharge batteries for transportation, renewable powersystem, energy storage, etc.

- Full Operating Range Soft-Switching with PWM, simplified design,and control

SUMMARY


77

Naturally-Clamped Snubberless Current-fed Soft-Switching ...

Documents