The document discusses a proposed modular power conversion system for wind turbines to improve reliability and availability. It notes that lost revenue from non-operating turbines increases energy costs at large wind farms. The proposed system uses independent and redundant power modules to maximize uptime even if one module fails. Analysis shows that for a 30MW wind farm experiencing typical failure rates, the system could save over $165,000 per year by preventing lost energy capture from turbine downtime. With multiple annual failures averted over the farm's 20-year lifespan, the financial benefits outweigh the additional $42,000 cost per turbine for the modular system.

1. 01/29/15 1
690 V
Grid
PM
Generator
690V
690VAC,
460 Amps
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3 Phase
2.5MW
690 V
By: Dr. Sammy Germany

2. 01/29/15 2
Background:
To achieve low cost of energy, turbine manufacturers have
traditionally focused on:
• Component cost
• Component reliability
• Variable speed applications to capture more low wind
speed energy
More recent industry trends have focused on
• PMG - energy capture in wider wind speed range
• High efficiency & Reducing O&M costs
• Designs for lower class sites (Class 3)
Power System Focus – Availability + Uptime
• Uptime is the key to capture more energy
• Diminishing returns for
 power component MTBF
 power component MTTR
Uptime  kWh
Energy: Power & Time

3. 01/29/15 3
Modular Multi-MW Converters
High Reliability – High Availability
1. Designs are built to be reliable, tough inverters
2. Mechanical robustness to reduce O&M costs in harsh
turbine environments
3. Modularity: Operational redundancy, increasing
availability of system even under fault conditions
Capacity
100%
Failure
event MTTR
Without
redundancy
With
redundancy
time
Energy Savings w/
redundancy

4. 01/29/15 4
Class 4 - 30 MW Wind Farm Met Data
0
2
4
6
8
10
12
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
WindSpeedm/s)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
PerUnitTurbinePower(MW)
Wind Speed (m/s)
Average Power
• Class 3-4 Wind farm met data used for energy harvesting case studies
• Peak hourly wind speed average 80% - Optimal for parallel units.
• 10 Towers, 3MW turbines
Turbine Power
Month

5. 01/29/15 5
What is the problem?
Lost revenue from non-operation turbines increased the cost of energy in large wind farms.
• Turbine repairs occur after multiple turbines have failed (high O&M costs)
• In large farms, 3-5 turbines may need to be down before serviced (up to 3 months)
• Long MTTR of wind turbines impacts energy capture rates.
How significant is it for a 30MW Wind Farm?
• $6.6M : Yearly energy revenue for a Class 4, 30MW wind farm (6.5 c/kW.hr)
• $330k (5%): Yearly lost revenue from 3 turbine failures with 3 months downtime.
Benefits of a DRS Power System Solution:
• If one (1) turbine failure is due to an inverter, the module remains operating and capturing
energy.
• $165k Savings: 2.5% of wind farm’s yearly revenue
NPV: $0.8M – 1.8M for 1 to 2 power failures / yr over life of wind farm
(20yrs)
(Considering increased energy generated due to uptime and the cost of power system modularity)

6. 01/29/15 6
690 V
Grid
PM
Generator
690V
690VAC,
460 Amps
~
=
=
~
~
=
=
~
~
=
=
~
3 Phase
2.5MW
690 V
Topology Description
• 500kW 690V full conversion power modules
• Independent dc bus per converter stage to
maximize availability
• Isolating grid and generator contactors
• Integrated dynamic brake for LVRT
• Suitable for medium speed and direct drive.
• Optional generator dv/dt filters
Inherent Redundancy to maximize availability
Controls
• Independent power module control
electronics.
• No master controller with a single point of
failure.
Benefits
+ Lower bearing current stress
+ Open winding failure on generator
+ Hatchable converter for low MTTR

7. 01/29/15 7
DC Bus Intertie Inverters
A common approach used by commercial motor drive suppliers
- No ability to isolate inverters from the
shared dc bus reduces availability.
+ Lower Cost inverter controls, switchgear,
filters, power module ratings ($42k delta)
Investment Project Financial Analysis Date:
Unit: DRS-PCT
Project Name: 2.5 MW Wind Converter
Investment Plan 1 2 3 4 5 6 7 8
Components $420,000 $0 $0 $0 $0 $0 $0 $0
Total investment $420,000 $0 $0 $0 $0 $0 $0 $0
Revenue $0 $330,000 $330,000 $330,000 $330,000 $330,000 $330,000 $330,000
Income $0 $330,000 $330,000 $330,000 $330,000 $330,000 $330,000 $330,000
ROS % 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%
Net Cash Flow ($420,000) $330,000 $330,000 $330,000 $330,000 $330,000 $330,000 $330,000
Cost of Capital 12.0%
NPV $1,795,273.54 20 yrs
IRR 76% 7 yrs
30MW Wind Farm Benefit with a DRS Power System
Net Present Value of Investment in Modularity. $0.8M
– $1.8M: (1 to 2 failures / yr over 20 yrs)
Investment:
$42k per turbine
$420k per wind farm.
Revenue:
$165k per inverter event / yr

8. 01/29/15 8

9. 01/29/15 9
IP54

10. 01/29/15 10
Full Power Conversion Systems for Wind Applications
• Power Module and cabinet system under development
• Power modules: Grid & generator side inverters
Filters, protection, dynamic brake, controls, communications.
• Generator Compatibility: PM, Synch., DFIG
• Available: 500kW system in 2010
Major Specifications
Utility Voltage: 690V
Output Capacity: 600kVA, 500kW
Grid Freq: 50Hz or 60Hz
Generator Freq. 10Hz to >150Hz depending on
generator requirements
Cooling : Air or liquid cooled
Location: Up-tower or down-tower

11. 01/29/15 11
General Description
• 500kW, 690V grid
connection
• PM or synchronous
generators compatibility
• 1700V IGBT power
converter
• Integrated dynamic brake
for Low voltage ride through
• Liquid cooled power
converter
• Grid contactors for
protection and isolation.
Generator isolation optional
• IP54 Air cooled cabinet
• High reliability power
module design: high MTBF:
Film capacitors, low IGBT
thermal stress, liquid
cooling.

12. 01/29/15 12
DC bus
capacitors
IGBTs
Gate
drivers
Module Design under development
Control board
Bus plane

13. 01/29/15 13
Wind Farm Power (MW) 30 MW
Number of Turbines 10
Number of failures per month 1
Duration (months) 3
Lost turbine months 6
Total turbine months/ yr 120
% of lost turbine months 5%
Savings - if 1st turbine failure
is eliminated
# turbine months saved 3
% turbine months saved 2.5%
Event Description
• one turbine failure per month
• Service occurs after 3
months, 3 failures
• 1st
failure is assumed to be
the inverter – and mitigated.
• Savings shown.