Update of High-Frequency Soft-Switching Three-Phase ...

VII- 1Jun. 22nd, 2018 Milpitas, CA CPES Proprietary

Update of High-Frequency Soft-Switching

Three-Phase Inverter/Rectifier

Zhengrong Huang, Qiang Li, Fred C. Lee


3Φ-Grid Charging Station EV

Bi-Directional Three-Phase Rectifier/Inverter

3Φ

AC/DCDC/DC EV


Research Goal for Rectifier/InverterP

ow

er

density (

W/in

3)

Efficiency

30

60

0

SiC Device

> 300 kHz

> 100 W/in3

~ 99% eff.90

97%

Si Device

~ 20 kHz

< 20 W/in3

97 ~ 98% eff.

98% 99%


Why SiC?

Half turn-on energy, negligible turn-off energy compared with Si

0

400

800

1200

1600

2000

10 15 20 25 30 35 40 45 50

Energy (μJ)

ICE or IDS (A)

Eon, SiC MOSFET

CREE

C2M0025120D

Eoff, SiC MOSFET

CREE

C2M0025120D

Eoff, Si IGBT

Infineon

IKW40N120H3

Eon, Si IGBT

Infineon

IKW40N120H3

* Eoss has been compensated

Turn-on energy can be eliminated with CRM ZVS


System Benefit with CRM

CRM outperforms CCM on efficiency

0

2

4

6

8

10

Lo

ss(W

)

CRM, 20kHz

(Soft turn-on)

0

2

4

6

8

10

Lo

ss(W

)

CCM, 20kHz

(Hard turn-on)

Conduction Turn-on Turn-off Driving TotalTotal

Vin=800V, Vo=400V, Po=4kW, Buck Converter

Device Loss with SiC: CCM vs. CRM


Opportunity for High Frequency

Vin=800V, Vo=400V, Po=4kW, Buck Converter

SiC-based System at CRM

0

4

8

12

16

20

0 100 200 300 400 500

Devic

e L

oss (

W)

Switching Frequency (kHz)

300 kHz is selected for trade-off between efficiency and density

0

4

8

12

16

20

0 100 200 300 400 500

Devic

e L

oss (

W)

Switching Frequency (kHz)


Extremely wide frequency range

(>> 10:1) in this application

Prior-Art of Three-Phase CRM:

Decoupled Three-Phase H-Bridge

CRM Three-Phase H-Bridge(UCF, 2012)

• Three phases are decoupled

• Each phase operates at CRM

independently

[Ref]: D. Zhang, Q. Zhang, H. Hu, A. Crishina, J. Shen, and I. Batarseh, “High efficiency current mode control for three-phase micro-

inverters,” in Proc. IEEE Energy Appl. Power Electron. Conf. Expo., Feb. 2012, pp. 892–897

VDC = 800 V, VAC = 277/480 V

FS

(MH

z)

0 ̊ 60 ̊ 180 ̊

16

120 ̊0

4

0.3

8

12


Proposed DPWM + CRM

Frequency range still wide (~ 10:1)

Applying DPWM with CRM

• One phase is clamped

VA

VB

VC

0

0

0

0 ̊ 60 ̊ 180 ̊120 ̊

Clamping CRM

Two-phase decoupled control

for ZVS

• Other two phases are controlled

as CRM independentlyF

S(M

Hz)

0

2

0.3

3

1

FS_A FS_C FS_B

0 ̊ 60 ̊ 180 ̊120 ̊

VA+-

VB+-

VC+-


Frequency range shrinks to 300 ~ 500 kHz

Frequency Synchronization (FS Sync.)

FSA = 2MHz

FSC = 300kHzFS

Sync Sync

FSA = 300kHz

FSC = 300kHz

DPWM + CRM DPWM + CRM + FS sync.

FS

(MH

z)

0 ̊ 60 ̊ 180 ̊120 ̊0

2

3

1

FS_A FS_C FS_B

0.3

FS_C FS_B

FS

(MH

z)

0 ̊ 60 ̊ 180 ̊120 ̊

0.3

0

2

3

1

FS_A

ILA

(CRM)

ILC

(CRM)

t0

0 t

ILA

(DCM)

ILC

(CRM)

t0

0 t


Operation Mode

Clamping CRM DCM

DPWM + CRM + FS sync.

0 ̊ 60 ̊ 180 ̊120 ̊

VA

VB

VC

0

0

0

VA+-

VB+-

VC+-


Off-Time Extension

0

0

t

VGS_S1

IL

VDS_S2

VGS_S2

S2

S1

IL

w/o Toff extension

ZVS is achieved with off-time extension

A

B

C

0

0

t

t

t

t0

0

VGS_S1

IL

VDS_S2

VGS_S2

w/ Toff extension

t

t

t

0

0


Two-Channel Interleaving

A

B

C

IL

0

Before interleaving

t

IL

After interleaving

IL

0 t


A

B

C

Negative Coupling

Sub-harmonic oscillation is avoided with negative coupling

Non-coupled

0

0

IL IL1

IL1

IL

t

IL1

IL

t

0

0

Negative-coupled

tt


95.0%

96.0%

97.0%

98.0%

99.0%

100.0%

30% 50% 70% 90% 110%

Eff

icie

ncy

Load Percentage %

Previous Achievement:

High-Frequency Three-Phase Rectifier/Inverter

43.5 cm (17.13 in)

19.0

cm

(7.4

8 i

n)

Height: 3.9 cm (1.54 in)

Power density: 127 W/in3

99% peak efficiency

VAC = 277/480 V, VDC = 800V, P = 25 kW, FS > 300 kHz


3Φ-GridPV Inverter PV Panel

Extension to PV Application

3Φ

AC/DCDC/DC


Leakage Current (iLK) Requirement in PV System

Typical Cpv: 60 ~ 160 nF/kW[1]

Below 30 kVA: iLK (RMS) ≤ 0.3 A [2]

[1] “Capacitive Leakage Currents”, SMA technical information.

[2] “Safety of power converters for use in photovoltaic power systems - Part 2: Particular requirements for inverters”, IEC 62109-2:2011

Based on 12.5 kW system, Cpv is 0.75 ~ 2 μF

Cpv

iLK


Issue: Large Leakage Current

DPWM + CRM + Fs sync.

iLK

0VA

0VB

0VC

180 ̊60 ̊ 120 ̊0 ̊

iLK

0

30

-30

RMS = 4.2 A >> 0.3 A

180 ̊60 ̊ 120 ̊0 ̊

Clamping CRM DCM

Leakage current much larger

than standard

High leakage current peak

exists every 60 ̊

VA+ -

VB+ -

VC+ -


Change of Equivalent Circuit Every 60 ̊

A

B

C

N

0 ̊ 60 ̊ 180 ̊120 ̊

VA

VB

VC

0

0

0

VDC

+

Before 60 ̊

A

B

C

N

After 60 ̊

A

BC

N

Applying Superposition:

iLK

iLKiLK

L

Cpv

L/3

Cpv

+

-

iLK𝑽𝑨𝑵 + 𝑽𝑪𝑵

𝟑Cpv

L/3+

-

VDC/3+

-

iLK𝑽𝑩𝑵 + 𝑽𝑪𝑵

𝟑

Veq Veq

Clamping

Clamping

CRM

CRM

DCM

PVA

+ -

VB+ -

VC+ -


Veq

iLK

0

0

L/3

Cpv

iLK+

-

Veq

Low-Frequency Dynamics of Leakage Current

𝒊𝒑𝒌 ≈∆𝑽

𝒁𝒏=

∆𝑽

𝑳 𝟑 𝑪𝒑𝒗

How to increase characteristic impedance Zn to suppress iLK?

High-Frequency, PV Application:

Small L, Large Cpv Small Zn, High ipk

Veq(avg)

60 ̊

Veq

iLK

0

0

Veq(avg)

ipk

ΔV

60 ̊

t

t


0

0

VGS_S7

VGS_S8

t

t

Applying H8 Topology[ref]: Operation

[Ref] R. Rahimi, S. Farhangi, B. Farhangi, G. R. Moradi, E. Afshari and F. Blaabjerg, "H8 Inverter to Reduce Leakage Current in Transformer-less

Three-Phase Grid-Connected Photovoltaic systems," in IEEE Journal of Emerging and Selected Topics in Power Electronics.

0 ̊ 60 ̊ 180 ̊120 ̊

VA

VB

VC

0

0

0

Clamping

Clamping

CRM

CRM

DCM

Before 60 ̊ (Clamped to N)

0

I7 = I8

After 60 ̊ (Clamped to P)

0

I7 = I8

t

0

0

VGS_S7

VGS_S8

t

t

Isolation is provided in leakage current path at freewheeling period

N

P

S7

S8

I8

I7

VA+ -

VB+ -

VC+ -

t


Suppression of High Leakage Current Peak

0 ̊ 60 ̊ 180 ̊120 ̊

VA

VB

VC

0

0

0

Clamping

Clamping

CRM

CRM

DCM

6-Switch

I8iLK

I8 0

0iLK

60 ̊

Accumulation of iLK is suppressed at the end of each switching cycle

8-Switch

I8 0

0iLK

t

t

60 ̊

Same Veq

VA+ -

VB+ -

VC+ -

Coss<<Cpv: Larger ZnCpv

Coss

t

t


6-Switch 8-Switch

RMS = 1.3 A

180 ̊60 ̊ 120 ̊0 ̊

Still Large RMS Leakage Current

0

30

-30

iLK 0

30

-30

180 ̊60 ̊ 120 ̊0 ̊

iLK

RMS = 4.2 A

iLK inside each switching cycle still needs to be suppressed

0

30

-30

iLKt

How to increase inductance but not impact operation?

> 0.3 A

L/3

CpvVeq

+

-


Adding CM Choke

L Lcm

iLK

Switching frequency iLK is suppressed by Lcm

0.1

0.2

0.3

0.4

100 150 200 250

Lcm (μH)

i LK

(A, R

MS

)

Standard

180 ̊60 ̊ 120 ̊0 ̊

0

10

-10

iLK

Lcm = 150 μH, RMS = 0.23 A

Lcm = 0 μH, RMS = 1.3 A

L/3+Lcm

Cpv

iLK

Veq

+

-


ZVS for the Additional Switches

Clamping

CRM

DCM

0

ILA

0

0

0

VGS_S7

VDS_S7

t

t

t

ILA

0

0

0

VGS_S7

VDS_S7

t

t

t

VA+ -

VB+ -

VC+ -

ILA

ZVS

Additional switch achieves ZVS by negative current in clamping phase

0 ̊ 60 ̊ 180 ̊120 ̊

VA

VB

VC

0

0

0

S7+ - VA+ -

VB+ -

VC+ -


System Efficiency Estimation with H8

VDC = 800 V, VAC = 277/480 V, PO(100%) = 12.5 kW, PF = 1, Fs,min = 300kHz

Conduction loss increase has insignificant impact on efficiency

94.0%

95.0%

96.0%

97.0%

98.0%

99.0%

100.0%

30% 50% 70% 90% 110%

Eff

icie

nc

y

Load Percentage %

6-Switch Tested

8-Switch Estimated

0

20

40

60

80

100

De

vic

e L

os

s (

W)

Conduction Switching

Related

6-Switch

8-Switch


Summary

With the proposed CRM-based soft-switching

modulation technique (DPWM + CRM + Fs sync.), 99%

peak efficiency is achieved even at > 300 kHz high-

frequency operation.

25 kW bi-directional three-phase AC/DC converter

operating at > 300 kHz and achieves 127 W/in3 power

density.

With H8 topology, in PV applications, the leakage

current can be significantly suppressed, while soft-

switching is still achievable and only pay small price

on conduction loss.

Thank you! [email protected]

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