SiC MOSFET based 50kW DC/DC Boost Converter in PV Application Rev 2, 12/3/13

Cree Power Applications

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Overview 1. Typical PV Boost systems in PV applications 2. Why consider a design with SiC devices? 3. 50kW Boost converter evaluation unit 4. Test results 5. Availability and other details

Copyright © 2012, Cree Inc.

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Typical 3-ph String Inverter Topology with Si Devices

MPPT BOOST+3Level Inverter:  1200V IGBTs for Booster+600V IGBTs for three-level inverter  Low frequency with10kHZ-20kHZ because of Si IGBT limitation  Heavy weight and large size, thus low power density  High passive magnetic cost because of low frequency Copyright © 2013, Cree Inc.

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ZVT Three-level Boost Converter Topology Source: Michael T. Zhang, Yimin Jiang, Fred C. Lee in APEC1995

ZVT Three-level Boost Benefits:

ZVT aux circuit

ZVT Three-level Boost Drawbacks:

600V Si MOSFET devices

 Additional switcher for aux circuit

Higher frequency operation

 Complicated control method

Zero voltage soft switching

 Output DC link voltage unbalance issue

Higher efficiency

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Key Advantages of Using SiC MOSFETs SiC power semiconductors are superior to silicon in 3 critical properties:

Off State

Off State

–

Wider bandgap: SiC supports 10 times higher electric fields than Si

–

Higher thermal conductivity: SiC supports 3 times the power density of Si

–

Reliability: 10X better than silicon

SiC MOS Key Benefits Vs Si: Low conduction losses

Low switching losses Enabling high frequency On State

No current tailing for IGBT Turn-on Copyright © 2013, Cree Inc.

Turn-off 5

Key Advantages of Using SiC Schottky diodes

Almost zero reverse recovery energy independent of device temperature.

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Cree’s SiC Switching Waveform – Constant over Temp

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I Current (A)

4 2

CSD10060 T J = 25, 50, 100, 150°C 0

600V, 10A Si FRED TJ = 25°C TJ = 50°C TJ = 100°C TJ = 150°C

-2 -4

-6

Silicon’s Wasted Energy!

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-1.0E-07

-5.0E-08

-10 0.0E+00

5.0E-08

1.0E-07

1.5E-07

2.0E-07

Time (s)

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50kW, 4 phase Interleaved Boost Converter Features 2x devices hard

paralleled per phase Phase A A Channel

4 phase interleaved

Boost with full SiC devices

 Input voltage: 400V600Vdc

400Vdc~800Vdc

2pcs C2M0080120D

2x independent MPPT

2pcs C4D10120D

800V-1000Vdc

Phase C C Channel

Inverter Stage

C

 Output power: 50KW Controller preset

2pcs C4D10120D

Phase B B Channel

Solar Panel MPPT 1

Output voltage: 800Vdc (12.5KW per channel)

2pcs C2M0080120D

B A A

2pcs C2M0080120D

2pcs C4D10120D

B

C

4pcs 150uF/ 600V

400Vdc~800Vdc

Phase D D Channel Solar Panel MPPT 2 2pcs C2M0080120D

2pcs C4D10120D

channels

Copyright © 2013, Cree, Inc.

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Electrical Specifications

Parameter

Unit

Value

DC output voltage

VDC

800

Max. output power

kW

50

DC input voltage

VDC

400 – 600

Efficiency

%

97.8 – 99.14

Switching Frequency / phase

kHz

75

Operating temp*

ºC

-25 to +35

Storage temperature range

ºC

-35 to +85

Isolation voltage

kV

tbd

* Restriction imposed due to limited testing for evaluation products.

Hardware designed as an evaluation platform and not a qualified product. Copyright © 2012, Cree Inc.

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PCB Assembly Of The 50kW Evaluation Unit Boost Chokes* 2pcs C2M0080120D per each phase

EMI Filter Choke

MPPT Ch A

Controller

MPPT Ch B

Phase Gate driver

Copyright © 2013, Cree, Inc.

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Measured Versus Calculated Efficiency Over Varying Load 50KW Interleaved Boost Converter with 800V DC Output 99.6% 99.4%

99.20%

99.28%

99.36%

99.41%

99.34% 99.14%

99.2% 99.0%

98.91%

98.8%

98.60%

98.6%

99.06%

99.11%

98.92%

99.06% 98.87%

98.75%

Efficiency

98.4%

98.52%

98.2% 98.0%

98.28% 97.80%

97.8% 97.6%

97.4% 97.2% 97.0%

Prototype @400VDC Input

97.13%

96.8%

Prototype @600VDC Input

96.6%

Predicted @600VDC Input

96.4% 96.2% 96.0%

5%

10%

20%

30%

40% 50% Loading (%)

60%

80%

100%

Note: Gate to source turn on resistor is 15Ohm and turn off resistor is 5Ohm Ambient temperature is 25°C with fan cooling

Copyright © 2013, Cree, Inc.

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Waveforms With 600VDC Input And 800VDC Output (D=25%)

Il(10A/div) Vds1 (500V/div)

Hard paralleled MOSFETs on each phase

Vds2 (500V/div)

5uS/div

Turn-Off detail

200nS/div Copyright © 2013, Cree, Inc.

Turn-On detail

200nS/div 11

Waveforms With 400VDC Input And 800VDC Output (D=50%)

Il(10A/div) Vds1 (200V/div)

Vgs (10V/div)

5uS/div

Turn-On detail

Turn-Off detail

200nS/div

Copyright © 2013, Cree, Inc.

200nS/div 12

Thermal Images With 400V In / 800V Out at Full Load C2D0080120D

C4D10120D

Boost Inductor Part

Tc (°C) #1

Tc (°C) #2

C2M0080120D

92.6

94.4

C4D10120D

67.5

64.9

Boost Inductor

69.7

Note: Testing is based on full load operation after 30min with fan to cool system Ambient temperature = 25ºC Copyright © 2013, Cree, Inc.

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Electrical Connectors Power Terminals Use AWG2 / 35mm2 Cable CON 1

In, Ch A Pos

CON 2

In, Ch A Neg

CON 3

In, Ch B Pos

CON 4

In, Ch B Neg

CON 5

Out Pos

CON 6

Out Neg

CON 21

Out, HV aux. pos

CON 22

Out, HV aux. neg

Aux. Power CON 16 6 pin 2.54mm connector 1 Vee

-2VDC

2 PV_-Ve

PWR Ground

3 18V_HV

+18VDC

4 PV_-Ve

PWR Ground

5 n/c 6 PV_-Ve

Top View

CON 6

CON 3

CON 4

CON 2 CON 5 CON 1

Bottom View

CON 21 CON 22

2x 94mm, 12VDC fans connected to CON 20.

CON 16

PWR Ground

Copyright © 2012, Cree Inc.

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Mechanical Detail  Unit size: 530mm X 365mm X 174mm

Cooling: 2x 94mm, 12VDC Fans

 Weight (as shown): 10Kg

 Mounting: 10x M6 bolts

Copyright © 2012, Cree Inc.

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Confidential

FAQ 1.

How does this compare to a Si solution? SiC MOSFETs allows the designer to take new directions in design and its not always possible to make meaningful comparisons. It is unlikely that we would use Si in a such a hard switched, high power and high Fsw application. A comparative case study has been completed on a 10kW system by Cree in the past and its results should scale well at 50kW.

2.

What is the core and wire used to make boost inductors? 18 strand 25 AWG copper wire with polyurethane / Nylon coating.

3.

What is the highest dv/dt measured during switching? Approximately 50 V/nS.

4.

How does EMI signature compare to Si based solution? The EMI signature is highly dependent on the final package and cost effective mitigating solutions finally implemented in the product. Since the purpose of the evaluation board is to provide a platform for customers to evaluate SiC MOSFETs, the EMI aspect has not been tested. A small ferrite bead with high impedance over 10MHz is used to reduce ringing on the gate lead of the SiC MOSFETs. The bead is from Wurth Electronik p/n 74270011.

5.

What is CON15 used for? It is used for a different configuration with a digital control card and should not be used by the customer.

Copyright © 2012, Cree Inc.

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