Cree PV Inverter Tops 1kW/kg with
All-SiC Design
Alejandro Esquivel
September, 2014
Copyright © 2014, Cree Inc.
Presentation Outline
1. Meeting an Industry Need
a)
1kW/Kg
b)
No electrolytic capacitors in DC link
2. 50+kW SiC based PV Inverter Design
a) Boost Stage
b) Inverter Stage
c) Auxiliary Power Supply
3. Performance Comparison
Copyright
© 2013
Cree,
Copyright
© 2014,
Cree
Inc. Inc.
2
Cree SiC Power Portfolio – Products and Support
Reference Designs:
SiC Schottky Diodes:
• Solar - Boost and Inverter
• SMPS - PFC, ZVS, Flyback
• 600V, 650V, 1200V, 1700V
• 1A to 50A
• Packaged and bare die
C2M SiC MOSFETs:
• 1200V, 1700V
• 1Ω to 25mΩ (4A to 60A)
• Packaged and bare die
Gate Drivers:
• Single and dual
• Cree designed
• Partnered designs
Package Styles:
• TO-220
• TO-247
• Full-PAK
• DPAK (TO-252)
• D2PAK (TO-263)
• QFN
• Isolated TO-220
SiC Power Modules:
• 1200V, 1700V
• 100A to 300A Half-bridges
• 50A Six-pack
Bare die for power modules
Copyright © 2014, Cree, Inc.
pg. 3
Commercial PV installation 100kW – 1 MW
•
Commercial three-phase roof top system
•
Need for:
•
–
Small size
–
Light weight
–
High power density
–
Lower installed system cost
SiC devices enable the best solution to
achieve this need
Power density needed
> 1 kW/Kg
Copyright © 2014, Cree Inc.
4
What Is Used Today - Example
50 kW, TL3 series
Kaco Blueplanet 50.0 TL3
Full Power MPPT Voltage Range
480 – 850 VDC
Operating MPPT Voltage Range
200 – 850 VDC
No. Independent MPPT Input
Nominal output power
1
50 kW
CEC Efficiency
97.5%
Peak Efficiency
98.3%
Power Factor
> 0.99
Output Voltage
480 Vac
Operating Temperature Range
-30 °C to 60 °C
(de-rated > 45 °C)
Cooling
Forced convection
Weight
173 kg
Isolation Transformer
Volume
Copyright © 2014, Cree Inc.
Power density = 0.29 kW/Kg
Need: Increase this value > 3×
No
840 × 355 × 1360 mm
Cree SiC Technology
can achieve this…
5
Cree SiC Technology Enables ½ Volume and <1/3 Weight
Cree SiC based 3-ph, PV String Inverter comparison
Full Power MPPT
Voltage Range
480 – 850 VDC
450 – 800 VDC
Operating Voltage
Range
200 – 850 VDC
400 – 950 VDC
No. Indep MPPT Input
1
2
Nominal output power
50 kW
50 kW
CEC Efficiency
97.5%
97.8%
Peak Efficiency
98.3%
98.7%
Power Factor
> 0.99
> 0.99
Output Voltage
480 Vac
480 Vac
-30 °C to 60 °C
(de-rated > 45 °C)
-30 °C to 60 °C
(no de-rating)
Cooling
Forced air
Forced air
Weight
173 kg
50 kg
No
No
Operating Temperature
Range
Isolation Transformer
Volume (m3)
Copyright © 2014, Cree Inc.
0.41
840 x 355 x 1360 mm
0.21
700 x 300 x 1000 mm
SiC based 3-ph PV string
Inverter
Power Density = 1 kW/Kg
6
Cree All-SiC PV Inverter Reference Design Overview
Aux. Power Supply
Aux. Power Supply
450 to 800 VDC
2x MPPT channels
Driver
Driver
Channel B
~
Scalable to any numbers
of MPPT channels
MPPT Boost,
75kHz
480 Vac rms l-l
Channel A
LC line
Filter
825 VDC
3-ph Inverter,
48kHz
Control Plane
Copyright © 2014, Cree Inc.
7
3LT-Type Inverter Chosen for High Frequency Efficiency
2L
2L Si
3L-NPC Si
3L-T Si
2L SiC
3L-T SiC
100.0%
Power Stage Efficiency
99.5%
99.0%
3L-NPC
98.5%
98.0%
97.5%
97.0%
3L-T
96.5%
96.0%
0
5
10
15
20
25
30
35
40
45
50
Swithcing Frequency
Frequency (kHz)
Switching
(kHz)
Copyright © 2014, Cree Inc.
8
Inverter Schematic: All SiC Active Power Semiconductors
Input
Filter
4-ph interleaved
Boost Converter
2x C2M0080120D, SiC MOSFET in
parallel per phase leg.
2x C4D10120D, SiC MPS diodes in
parallel per phase leg.
Copyright © 2014, Cree Inc.
DC
Link
10x 700uF
600VDC film
3-ph T-Type
Inverter
2x C2M0025120D, SiC MOSFET in parallel
per phase leg upper and lower switch.
Output
Filter
3x 4uF, 470Vac film
3x 230uH, metglas core
1x C2M0025120D, SiC MOSFET per T-leg.
1x C5D50065D, SiC MPS Diode per T-leg.
9
50kW 4-Channel Boost Front End
Boost Chokes*
2pcs C2M0080120D
per each phase
EMI Filter Choke
MPPT
Ch A
Controller
MPPT
Ch B
Phase Gate
driver
Copyright © 2014, Cree Inc.
10
3-Level, T-Type Inverter Topology
3500 µF
270 µH
• Main lower & upper MOSFET position: 2x Cree 1.2kV SiC Mosfet, 50A, 25 mOhms
• Uses Cree SiC MOSFET body diode in main anti-parallel with main power switches
• T-Branch MOSFET position: 1x Cree 1.2kV SiC Mosfet, 50A, 25 mOhms
• T-branch Diode position: 2x Cree 650V, 50A, C3D50065D
Copyright © 2014, Cree Inc.
11
SiC System Efficiency v/s Si based system*
Better Overall efficiency
@ 1/3rd the weight
CEC Efficiency:
• Kaco – 97.5%
• Cree – 97.8%
* Independent test data for KACO BluePlanet 50.0 TL3 provided by gosolarcalifornia.ca.gov
Copyright © 2014, Cree Inc.
12
Thermal Images of Boost With 400VIn/800VOut at Full Load
C2D0080120D
C4D10120D
Boost Inductor
Part
Tc (°C)
Part #1
Tc (°C)
Part #2*
C2M0080120D
92.6
94.4
C4D10120D
67.5
64.9
Boost Inductor
69.7
* Note excellent sharing between paralleled devices.
Note: Testing is based on full load operation after 30min with fan to cool system
Ambient temperature = 25ºC
Copyright © 2014, Cree Inc.
13
Operating Temperature Data
Vin = 600 / 700VDC
Tamb = 22ºC
Po = 48 kW
LC output filter
Tcore = 66 (with potting)
103ºC (no potting)
Tcore = 38/35ºC
Tc = 54/53ºC
Tc = 70//68ºC
Tc = 39/38ºC
Tc = 61/54ºC
Copyright © 2014, Cree Inc.
Tc = 46/42ºC
14
60W SiC Based Auxiliary Power Supply
Cree 60W Single-end Flyback reference similar to that used in 50kW:
–
Input voltage: Wide input range 200Vdc to 1000Vdc
–
Output voltage: 12Vdc/4.5A; 5V/0.5A; -12Vdc/0.25A
–
Operating frequency: 75KHZ
PQ2625
transformer
Cree 1700V SiC MOSFET:
C2M1000170D
Cree 60W Aux Power Demo board with 1700V SiC MOSFET
Cree 1700V, 1Ω MOSFET:
• Higher blocking than available silicon
• Higher efficiency for cooler operation
• Enables higher reliability than comparable silicon designs
Copyright © 2014, Cree Inc.
pg. 15
All SiC 50kW PV String Inverter Test Assembly
Boost converter
DC Link Film Capacitors
2x 3.5mF, 1.1kV
Controller
Output Power = 47.8kW
Output Voltage = 492 Vac l-l rms
Output Current = 56A rms
DC link Voltage = 850 VDC
3-phase, balanced resistive load
Output filter
Copyright © 2014, Cree Inc.
Inverter Power stage
16
50kW Physical Specifications
All aluminum enclosure
30cm
100cm
Weight distribution shown in Kg
Total weight = 50 Kg
70cm
Copyright © 2014, Cree Inc.
17
Summary

Using SiC MOSFETs available today from Cree enables up to 3x the
power to weight ratio when compared to current Si based systems.

Higher Fsw reduces cost of the magnetics in the boost and output filter
while delivering improved efficiency compared to Si solutions.

Installing smaller, lighter inverters will lower installation costs.

Less parts and the use of film capacitors in the DC link can improve
reliability of the system.

Cree is developing a complete range of SiC discrete and module
devices to support the power conversion market.

SiC makes economic sense today!
Copyright © 2014, Cree Inc.
18
50 kW PV inverter – impact of “C2M” FETs
C2M0025120D MOSFET
Decreased BOM cost
Size, weight reduced
Efficiency improved
Reference: See Cree booth.
Copyright © 2014, Cree, Inc.
Size
Weight
Inverter
BOM
50% ↓
60% ↓
30% ↓
Inverter
install
cost
$/kW
savings
50% ↓
3-4% ↓
19