SiC MOSFET based 50kW DC/DC Boost

Converter in PV Application Rev 2, 12/3/13

Cree Power Applications

1

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

2 Copyright © 2012, Cree Inc.

Typical 3-ph String Inverter Topology with Si Devices

Copyright © 2013, Cree Inc.

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

3

ZVT Three-level Boost Converter Topology

Copyright © 2013, Cree Inc.

Source: Michael T. Zhang, Yimin Jiang, Fred C. Lee in APEC1995 ZVT aux circuit

ZVT Three-level Boost Benefits:

600V Si MOSFET devices

Higher frequency operation

Zero voltage soft switching

Higher efficiency

ZVT Three-level Boost Drawbacks:

Additional switcher for aux circuit

Complicated control method

Output DC link voltage unbalance issue

4

Key Advantages of Using SiC MOSFETs

Copyright © 2013, Cree Inc.

SiC power semiconductors are superior to

silicon in 3 critical properties:

– 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

No current tailing for IGBT Turn-on Turn-off

On State

Off State Off State

5

Key Advantages of Using SiC Schottky diodes

I C

urr

en

t (A

)

-10

-8

-6

-4

-2

0

2

4

6

8

10

-1.0E-07 -5.0E-08 0.0E+00 5.0E-08 1.0E-07 1.5E-07 2.0E-07

CSD10060

TJ = 25, 50, 100, 150°C

600V, 10A Si FRED

TJ = 25°C

TJ = 50°C

TJ = 100°C

TJ = 150°C Silicon’s

Wasted Energy!

Cree’s SiC Switching

Waveform –

Constant over Temp

Time (s)

Almost zero reverse recovery energy independent of device temperature.

6

50kW, 4 phase Interleaved Boost Converter Features

2x devices hard paralleled per phase

4 phase interleaved Boost with full SiC devices Input voltage: 400V-600Vdc

Output voltage: 800Vdc

Output power: 50KW (12.5KW per channel)

Controller preset

2x independent MPPT channels

Copyright © 2013, Cree, Inc.

2pcs

C4D10120D

2pcs

C4D10120D

2pcs

C4D10120D

2pcs

C4D10120D

Inverter

StageA B C

A

B

C

800V-1000Vdc

2pcs

C2M0080120D

A Channel

4pcs

150uF/

600V

B Channel

C Channel

D Channel

Solar Panel

MPPT 1

400Vdc~800Vdc

Solar Panel

MPPT 2

400Vdc~800Vdc

2pcs

C2M0080120D

2pcs

C2M0080120D

2pcs

C2M0080120D

Phase A

Phase B

Phase C

Phase D

7

Electrical Specifications

8 Copyright © 2012, Cree Inc.

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

Hardware designed as an evaluation platform and not a qualified product.

* Restriction imposed due to limited testing for evaluation products.

PCB Assembly Of The 50kW Evaluation Unit

EMI Filter Choke

Boost Chokes*

Controller

2pcs C2M0080120D

per each phase

Phase Gate

driver

MPPT

Ch B

MPPT

Ch A

Copyright © 2013, Cree, Inc. 9

Measured Versus Calculated Efficiency Over Varying Load

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.

97.13%

98.28%

98.75%

98.92%

99.06% 99.11% 99.06%

98.87%

98.52%

97.80%

98.60%

98.91%

99.20% 99.28% 99.36% 99.41% 99.34%

99.14%

96.0%

96.2%

96.4%

96.6%

96.8%

97.0%

97.2%

97.4%

97.6%

97.8%

98.0%

98.2%

98.4%

98.6%

98.8%

99.0%

99.2%

99.4%

99.6%

5% 10% 20% 30% 40% 50% 60% 80% 100%

Eff

icie

ncy

Loading (%)

50KW Interleaved Boost Converter with 800V DC Output

Prototype @400VDC Input

Prototype @600VDC Input

Predicted @600VDC Input

10

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

Vds1 (500V/div)

Vds2 (500V/div)

Il(10A/div)

Copyright © 2013, Cree, Inc.

Turn-Off detail Turn-On detail

Hard paralleled

MOSFETs

on each phase

5uS/div

200nS/div 200nS/div

11

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

Vds1 (200V/div)

Vgs (10V/div)

Il(10A/div)

Copyright © 2013, Cree, Inc.

Turn-Off detail Turn-On detail

5uS/div

200nS/div 200nS/div

12

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

C2D0080120D C4D10120D

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

Boost Inductor

Copyright © 2013, Cree, Inc. 13

Electrical Connectors

14 Copyright © 2012, Cree Inc.

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 PWR Ground

CON 6

CON 5

CON 3

CON 4

CON 2

CON 1

2x 94mm, 12VDC fans

connected to CON 20. CON 21

CON 22

CON 16

Top View

Bottom View

Mechanical Detail

15 Copyright © 2012, Cree Inc.

Unit size: 530mm X 365mm X 174mm

Weight (as shown): 10Kg

Cooling: 2x 94mm, 12VDC Fans

Mounting: 10x M6 bolts

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.

17 Copyright © 2012, Cree Inc.