Silicon-Carbide Inverters for Small-Wind
Addressing the Single-Phase Gap
Rob Wills, Intergrid, LLC
Temple, NH
rwills @ intergrid.us
About the Presenter..
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Renewable Energy since 1982
Power Electronics & Inverters
Skystream Design Team
AWEA rep on NEC (with R. Preus)
Chaired NEC Committees on
Microgrids
• UL1741 / 2030.7
Intergrid gratefully acknowledges support from NREL & DOE
Silicon Carbide-Based Inverters for
Intermediate Wind Applications
Contract NFC-5-52012-0
CIP Program
The US Rural Market
• There is a sweet spot at 25 kW because of State
and Federal incentives
• Most farm residences are single phase
• Farm irrigation service is typically three-phase,
but often does not qualify for incentives
• 200A 240V single-phase service supports 38.4
kW interconnection
• There are few single-phase inverter options –
especially over 10 kW
We Need Single-Phase 20-40 kW
Inverter Solutions
• Larger Turbines are more cost effective
• Most of the market is rural, not urban
• Mainly 200A Single Phase Services
• 200A x 240V = 48 kW
• Max Interactive Feed 80% -> 38.4 kW
The Single Phase Gap – SMA 2013
The Single Phase Gap - ABB
ABB / Power One ended support
for its Wind inverter products in 2014
… And It was Not Optimal
Lots of Parts..
INTERGRID’s Solution
Single & Three Phase Inverters
25-75 kW for Wind and Storage.
19” Rack
Or
Wall Mount
Variable Speed Drives
(VFD) as active front-end.
INTERGRID’s Solution
“Wide Bandgap” Silicon Carbide FETs
(Field Effect Transistors)
Have 1/10th the switching losses of Silicon
IGBT devices
They allow switching at 30 kHz rather than
5-10 kHz which reduces the size of filter
Inductors and the inverter overall
Specifications
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100A DC Input
100A AC Output
Single phase 240 V
Three phase 120/208 V and 277/480 Vac
DC Bus voltage to 800 Vdc
Output Power:
• 24 kW single phase 240 V
• 36 kW three phase 120/208 V
• 75 kW three phase 277/480 V
Can be ganged for higher power
Progress
• First unit operating at Chava Wind site in
Florida with Hitachi VFD
• Second about to be deployed in Iowa for VAWT
testing
• Implementing a 6 x 2 kW turbine VAWT array
in Igiugig Alaska in the fall (DC Microgrid)
Architecture
Controller
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Microchip DSPic Based
10” x 2.5”
Three gate drives
Voltage and current monitoring
Contactor and precharge control
Isolated CAN and RS-485 Communication
UL1741 / 6142 Certification underway
Master Controller
• Open source software development
• Dual-core CPU and single core micro-controller
• Complex data collection in a low power
package
• Integrated Wi-Fi
• Bluetooth® 4.0
• 1GB DDR and 4GB flash memory
• 40 multiplexed GPIO interfaces
MICROGRIDS
http://www.greentechmedia.com/articles/featured/resiliency-how-superstorm-sandy-changed-americas-grid
Present Technology
Multi-mode Inverters
Some problems with the multimode approach are:
• Only a subset of building loads are supported
• Essential loads have to be rewired to an emergency sub-panel
• Paralleling multiple units becomes awkward; they all have to be in the same location
• The transfer switch has limited capacity and functionality.
• Integration with renewable energy sources is complicated (dc coupling).
Microgrid Concepts
• Distributed Generation, Distributed Control
• Terminology:
• Grid Forming, Grid Supporting, Grid Sustaining
• Impedance Controlled Voltage Sources & Controlled Current Sources
• Droop control for power and frequency
Contact:
Dr. Rob Wills, PE
Intergrid
PO Box 48
Temple, NH 03084
603-801-4749
rwills @ intergrid.us
Allan Villiers, 1929
PortandStarboard.com