three-phase interleaved llc converter with capacitive ...pel.ee.ibaraki.ac.jp/img/file858.pdfpower...

May 28th, ICPE 2019-ECCE ASIA

May 28th, 2019

ICPE 2019-ECCE ASIA

Highlights

Three-Phase Interleaved LLC Converter with

Capacitive Current Balancing and

Reduced Switch Voltage Stress

Yoshiya Tada, Yusuke Sato, and Masatoshi Uno

Ibaraki University, Japan

Automatic current balancing despite component tolerance

Reduced RMS currents by asymmetric resonant operations

96.8% full-load efficiency at 1 kW


Outline

• Background

- Interleaved PWM converter

- Conventional interleaved LLC converter

• Proposed three-phase interleaved LLC converter

- Asymmetric resonant operation

- Automatic current balancing mechanism

- Operation modes and reduced switch voltage stress

• Experimental verification

- Current balancing

- Switch voltage stress

- Power conversion efficiency

• Conclusions 1-kW Prototype

1/27


Background

2/27


Interleaved Converter

Required current balancing to avoid current concentration

• Reduced current stress

• Reduced current ripple of

input or output port

Time

Cu

rren

t iout

Current concentration

due to component tolerance

Converter(Phase)

Converter(Phase)

Converter(Phase)

Vin Load

iout

3/27


Interleaved PWM Converter

H.C. Chen, C.Y. Lu, and U.S. Rout, IEEE Trans. Power Electron., vol. 33, no. 5, May 2018, pp. 3683–3687.

Vin

LA

LC

LB

QA QB QC

DA

DB

DC Vin

LA

LC

LB

QA QB QC

DA

DB

DC

Imbalanced Balanced

Without Current Balancing Control

Individual duty cycle adjustment

to balance phase currents

With Current Balancing

Control

Additional feedback control loops and current sensors required

4/27


Interleaved LLC Converter

LLC converter

• Galvanic isolation

• Low EMI

• High efficiency

• Frequency-dependent

gain characteristics

Cannot simply apply interleaving operation to LLC converter

Individual switching frequency

adjustment to balance phase current

QAL

QBH

QAH

QCL

QCH

QBL

Vin LkgB

LkgC

LkgA

LmgB

LmgC

LmgA

CrB

CrC

CrA

5/27


Numerous switchesBulky inductor

With Current Balancing Control

E. Orietti et al, in Proc. Brazilian Power Electron. Conf., 2009, pp. 298–304, Oct. 2009. †

Z. Hu, et al., IEEE Trans. Power Electron., vol. 29, no. 6, pp. 2931–2943, Jun. 2014. † †

With Variable Inductor† With Switch-Controlled Capacitor † †

Current concentration caused by

capacitance mismatch (e.g., 5%)

LV

LAQAL

QBH

QAH

QBL

LkgB

LkgA

LmgB

LmgA

CrB

CrA

Vin

CSB

CSAQAL

QBH

QAH

QBL

LkgB

LkgA

LmgB

LmgA

CrB

CrA

Vin

Current balancing control required

Current imbalance under

light load condition

6/27


Additional

inductors

With Inductive Current Balancing

H. Wang et al., IEEE Trans. Power Electron., vol. 32, no. 9, pp. 6694–7009, Sep. 2017.

With Common Inductor

• Automatic current balancing

• Current imbalance under light load conditions

LB

LAQAL

QBH

QAH

QBL

LkgB

LkgA

LmgB

LmgA

CB

CA

Vin

7/27


Designed for only two phase topology

With Capacitive Current Balancing

iB iA

irec

Cu

rren

t

Increased current ripple

O. Kirshenboim and M.M. Peretz, IEEE Trans. Power Electron. vol. 33, no. 7, pp. 5613–5620, Jul. 2018.

iB

iA irecLkgAQAH

QBL

QBH QAL

LkgB

LmgA

LmgB

CFCrA

CrB

Cout

Vin

With Flying Capacitor

Charge conservation law

8/27


Research Objectives

Proposed interleaved LLC converter

•Automatic current balancing

• Reduced current ripple

•High extendibility

• Soft switching characteristics

9/27


Proposed 3-Phase Interleaved LLC Converter

10/27


Flying

capacitors

Proposed 3-Phase Interleaved LLC Converter

CoutCin

Phase CPhase BPhase A

Vin Vout

QBHQAH QCHCrC

QAL QBL

LkgC

LmgC

C1

C2

CbC

TrC

CrBLkgB

LmgB

CbB

TrB

CrALkgA

LmgA

CbA

TrA

QCL

iA

iB

iC

• Automatic current balancing

• Reduced switch voltage stress

• Asymmetric resonant operation

• High extendibility

• d = 0.33 for high-side switches

• 120º out of phase

• PFM control

11/27


Extension for Multiple Phases

Concept of Extension

Q1H

Q1L

Cin

CF1

Cr1

Vin

Lkg1

Lmg1

Tr1

QnH

QnL

CrnLkgn

Lmgn

Trn

QH

QL

CF

CrLkg

Lmg

Tr

Phase 1 Additional circuit Phase n

Four-phase interleaved LLC converter

QAH QBH QCH QDH

QAL QBL QCL QDL

C1

C2

C3

CrA

CrD

CrC

CrB

LkgA

LkgD

LkgC

LkgB

LmgA

LmgD

LmgC

LmgB

CoutCin

Vin

CbA

CbD

CbC

CbB The number of phases can

be arbitrarily changed

12/27


Operation Principle

13/27


Asymmetric Resonant Operation

Current Waveforms

Vin

QAH

QAL

C1

CrALkgA

LmgA

Vin

QAH

QAL

C1

CrALkgA

LmgA

Current Flows in Phase A

Positive Half Cycle

Negative Half Cycle

Reduced RMS currents thanks to asymmetric resonant operation

1

1

1

2

rPrA

kgArA

fC C

LC C

1

2rN

kgA rA

fL C

14/27


• C1 takes part in resonance in Phase A

• iA charges C1

Operation: Mode 1

Vin

CbA

CbB

CbCQAH QBH QCH

QAL QBL QCL

C1

C2

CrC

CrB

CrA

LkgC

LkgB

LkgA

LmgC

LmgB

LmgA

TrC

TrB

TrA

iA

iB

iC

qA

2Vin/3 Vin/3

Vin/3

qA

15/27


• C1 is discharged by iB

• Balanced iA and iB due to charge conservation of C1

• C1 and C2 take part in resonance in Phase B

Vin

CbA

CbB

CbCQAH QBH QCH

QAL QBL QCL

C1

C2

CrC

CrB

CrA

LkgC

LkgB

LkgA

LmgC

LmgB

LmgA

TrC

TrB

TrA

Operation: Mode 2

iA

iB

iC

qB

qB

qAqB

qA = qB

2Vin/3 Vin/3

Vin/3

16/27


• C2 is discharged by iB

• Balanced iB and iC due to charge conservation of C2

• C2 takes part in resonance in Phase C

Vin

CbA

CbB

CbCQAH QBH QCH

QAL QBL QCL

C1

C2

CrC

CrB

CrA

LkgC

LkgB

LkgA

LmgC

LmgB

LmgA

TrC

TrB

TrA

Operation: Mode 3qC

iA

iB

iC

Vin/3

Vin/3

Vin/3

qBqC

qB = qC

17/27


• Automatic current balancing: iA = iB = iC

• C1 and C2 reduce switch voltage stress less than 2Vin/3

Vin

CbA

CbB

CbCQAH QBH QCH

QAL QBL QCL

C1

C2

CrC

CrB

CrA

LkgC

LkgB

LkgA

LmgC

LmgB

LmgA

TrC

TrB

TrA

Operation: Summary

iA

iB

iC

18/27


Design Consideration

19/27


Designing Method of Flying Capacitors

Optimum design of flying capacitor

frP : frN = 2 : 1

Current WaveformsTime

Curr

ent

1/frP

1/frN

Still room for

RMS current reduction

C2

QCH

QCL

CrCLkgC

LmgC

iC

Phase C

C1

QBH

QBL

C2

CrBLkgB

LmgB

iB

Phase B

Vin

QAH

QAL

C1

CrALkgA

LmgA

iA

Phase A

Current Flows of

Positive Half Resonance

20/27


Experimental Verification

21/27


Experiments were performed with

• Asymmetric resonant operation

• Symmetric resonant operation

Prototype150 mm

10

0 m

m

Front Side

1-kW Prototype

Parameters of transformers

Experimental conditions

• Input voltage Vin = 400 V

• Output voltage Vout = 48 V

Value

Phase A

N1 : N2 = 9 : 7

Lkg = 2.98 μH,

Lmg = 60.7 μH

Phase B

N1 : N2 = 9 : 6

Lkg = 3.51 μH

Lmg = 61.2 μH

Phase C

N1 : N2 = 8 : 7

Lkg = 3.49 μH

Lmg = 49.3 μH

Rear Side

Transformers

C1C2

22/27


Automatic Current Balancing

• Automatic current balancing despite severe mismatch in the

transformers’ parameter

• Reduced peak currents thanks to asymmetric resonance

• Current errors less than 2% over the entire power range

Output power [W]

Curr

ent

[A]

IA

IB

IC

Average Absolute Value of

Primary Phase Currents

Current Waveforms of

Primary Phase Currents at 1 kW

23/27


Switch Voltage Stress

High-side Switch Voltage (200 V/div.) Low-side Switch Voltage (200 V/div.)

Suppressed to approximately less than 2Vin/3

24/27


ZVS Waveforms

Phase A Phase B

Phase C

Verified ZVS operation

for all switches

25/27


Improved efficiency compared with those of symmetric

Power Conversion Efficiency

99.0%

97.5% 96.8%

91.1%

Asymmetric

Symmetric

Output power [W]

Eff

icie

ncy

[%

]

Power Conversion Efficiencies

Asymmetric Resonance (1 kW)

Symmetric Resonance (700 W)

Primary Phase Current Waveforms

26/27


Conclusions

• 3-Phase interleaved LLC converter has been proposed

• The proposed converter adopts asymmetric resonant

operation using flying capacitors to reduce RMS currents

• Experimental results demonstrated the automatic current

balancing despite mismatched transformer parameters

• Switch voltage stresses were reduced to less than around

2Vin/3

• Power conversion efficiency was improved thanks to

asymmetric resonance

27/27

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