Research in
New & Renewable Energy
Dr,Li Ran
Wind Power
Recent Studies in Wind Power
Gearbox
Wind Turbine
Doubly Fed
Induction Generator
4Q Converter
Filter
Grid
DFIG Grid Fault Ride Through
Renewable Energy Networks
? Grid code sets out requirements for grid
interconnection,
? Most current renewable generation systems are
treated as,negative” load,
? Future systems MUST contribute to system
frequency and voltage control,
? Grid interconnection usually,makes or breaks” a
project,
? Development of many (ALL?) renewable energy
converter systems have concentrated on the
device itself without detailed thought of how to
convert the power for grid interconnection,
? Future developments MUST consider the system
as a whole – REQUIRES INTEGRATED SYSTEM
Grid Code - Example
● The value of grid-fault ride-through is increasingly
appreciated,
● Grid code,e.g,Scottish Hydro-Electric Guidance Note
A wind farm must remain connected under the following conditions
depending on fault voltage reduction and registered capacity of wind farm,
wind farm registered capacity
voltage during fault <30 MW >=30 MW
0% July 2005 January 2004
15% January 2004 before January 2004
● The voltage refers to that on the transmission system (275 or 132 kV),
Transformer impedance and fault infeed from the wind farm are likely
to result in a higher voltage at generator terminal,
● Fault is cleared in 140 ms for 132 kV and 100 ms for 275 kV system,
Backup clearance time can extend to 300 ms,
Initial Control Idea – why
can’t it work?
stator voltage
rotor voltage
control
ir
fault
Recent Studies in Wind Power
Gearbox
Wind Turbine
Doubly Fed
Induction Generator
4Q Converter
Filter
Grid
DFIG Grid Fault Ride Through
- 0, 3 - 0, 2 - 0, 1 0 0, 1 0, 2 0, 3
0
0, 0 5
0, 1
0, 1 5
0, 2
0, 2 5
Pre -f a u l t si l p, s0 (p u )
F
a
u
l
t
vo
l
t
a
g
e
l
e
ve
l
:
U
s
(p
u
)
R i d i n g -t h ro u g h o p e ra t i o n ra n g e
ri d i n g -t h ro u g h o p e ra t i o n ra n g e
Feasibility Region with
Proposed Control
{ super-synchronous sub-synchronous
This plot says that the DFIG can successfully ride through a grid fault which
brings terminal voltage down to 0.3 pu,even it initially operates at full speed,
Durham 30 kW DFIG Test Rig
prime drive with programmable
direct torque control
DFIG
XPC Targetbox
real time system Filter
Grid
VARIAC 4Q conv
Laboratory verification
9.95 10 10.05 10.1 -2
-1.5
-1
-0.5
0
0.5
1
1.5
2
ir-a
bc
(pu
)
Time (s) 9.95 10 10.05 10.1
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
ir-a
bc
(pu
)
Time (s)
Rotor current constrained by control
Simulation Experiment
Grid Fault Ride Through
ωr
{
Power tracking
control
D.C,link voltage
control
Configuration with direct-in-line converters
A Proposed Research
? Study on the transient behaviour of and interaction in an
integrated machine-converter system,including
- Transient FE modelling of machine (HTU discovered that
the equivalent ckt model of a DFIG gives fault current that
is about 10% too low – ICEM 2004.);
- Transient thermal modelling of semiconductor devices;
- Control of converters to satisfy machine and power system
requirements,
Objective,optimized design and control strategy,
Recent Studies in Wind Power
Direct Drive (Gearless)
Wind Turbines
The Nacelle of a Geared Turbine
Generator
Gearbox
Drive
Shaft
Blades
Pitch
Mechanism
Lightning
Arrester
Anemometer
Mechanical
Brake
Hub
Tower
Yaw
Drive
Vernier hybrid machine
for direct drive wind turbine
? Flux switching machine
? Incorporates magnetic gearing
? High shear stress
? High force/torque at low speed
? Low power factor
Four-pole,three-phase,
prototype
The SLiM Concept (from EGL)
Three key aspects
? Large diameter using pre-tensioned
spokes and pre-compressed rims
? Ironless stator avoids magnetic pull
? Permanent Magnet Rotor
Ironless Stator Version
Rotor steel rim
Large Rare Earth
Magnets
Stator
non-metallic
rim
Stator coils
Magnet flux
pattern
Spoked Lightweight
Direct Drive Wind Machine
(SLiM)
Evolving
Generation
Ltd
Initial Power Conversion Arrangement
Stator coils
Inverter
module
Inverter
module
Output
to grid
Load C h ar ac te r i s ti c s
P r e di c t e d us i ng p r e di c t e d E,R and L M e as ur e d V and I
0
50
100
150
200
250
0 2 4 6 8 10
Cur r ent (A dc)
Voltag
e
(V
dc)
60 r pm
50 r pm
40 r pm
30 r pm
60 r pm
50 r pm
40 r pm
30 r pm
EGL
On Going Research
Research on power conversion and control
Schemes trying to achieve
? Fault tolerant operation
? Air-gap support
? Transformerless grid interface that satisfies
grid codes
? Low cost 100% rated converter
? Integration of PE and machine coil?
On Going Research
condition monitor
Voltage
regulator
Auxiliary pow er
pick up
Main output coils
D.c.-d.c,converter Brake resistor H-bridge
Cascade in
series w ith
other bridges
in the same
phase
Bypass
sw itch
Optical gate signals
&
Thyristor and diode
rectifier
Figure 1,A possible module design
On Going Research
Sa i
a
ib
ic
ec,eb,ea
Sb
Sc
+ -
+ -
+ -
+ -
+ -
+ -
grid
Circuit Diagram
? Chopper cut out speed,
9m/s
? Current at cut out,3A
? Generator cut out (using
circuit breaker),18.5m/s
? Generator cut out
current,17A
? Maximum high frequency
ripple current,3A
? Maximum transistor
current,3A
? Maximum diode current,
17A
Converter design,system simulation 0.0
50.0
100.0
150.0
200.0
250.0
2 3 4 5 6 7 8 9 10
Wind s pe e d (m /s)
Ele
ctri
cal
powe
r (W)
Max im um pow e r Batte ry co nne ctio n
Tracking Simulation
Annual Energy Capture
Average wind
speed (m/s)
Annual Energy Capture (kWh)
Battery Part Converter Full Converter Maximum
5 371 451 453 454
6 690 762 771 779
7 1083 1144 1168 1229
9 1848 1891 1954 2520
Average wind
speed (m/s)
Partially rated converter Fully rated converter
Increase from
direct connection
(kWh)
Percentage
increase
Increase from
direct connection
(kWh)
Percentage
increase
5 80 21.6% 82 22.1%
6 72 10.4% 81 11.7%
7 61 5.6% 85 7.9%
9 43 2.3% 106 5.7%
Wave Energy
Demonstration of Absorbing
Wave Energy
a
b
c
d
Wave Energy Converters
? Shoreline devices
Simple maintenance and grid connection
cost of land intrusion
Example,OWC
? Nearshore devices,typically 10-25 m deep,devices
can be tight moored to the sea bed
? Deep water devices,slack moored to maintain
geographical position only
Wave Energy Converters
? Terminator type
Principle axis parallel to incident wave crests
Waves are stopped as they reach the device
Example,Salter Duck
? Attenuator type
Principle axis perpendicular to wave crests
Energy conversion by relative motion of parts
of the device as a wave passes underneath
Example,Pelamis
? Point absorber
Oscillating body (next slide)
Concept of Direct Drive Wave
Energy Converter
? Couple moving part direct to generator
? Remove intermediate mechanical systems
? Slow reciprocating motion
Wave Energy
? Wavegen
? Oscillating water column,Islay
? Ocean Power Delivery
? Pelamis,SRO contract for
Machir Bay
? Teamworks Technology
? Archimedes Wave Swing
Direct Drive Wave Machine
Sea dev i ce
El ect r i ci t yLi near
G ener at orDi re ct D riv e
F l o a t
Rod
m u t u a l l y b u o y a n t
p o w e r t a k e o f f
m e ch a n i sm
d ra g p l a t e
st a t o r
t ra n sl a t o r
W a t e r su rf a ce
l i n e a r e l e ctr i ca l
g e n e r a to i r
3 - p h a se m a i n s
g r i d vo l ta g e
C
V
dc
3-phase ac/ac converter
? Power output - 300W per
half phase
? dc link 150V
? new inverter,800V dc link
Converter Power
Current,I
Voltage,V
Power in
=VxI
Power out of Machine
Into Converter
Direct Drive Machine
Electrical Requirements
? At 1m/s,100 kW,Force = 100 kN
? Conventional machines,? = 20-30
kN/m2
? Transverse Flux Machines,? =
200 kN/m2
High force density electrical
machines-problems
?High airgap closing forces
?Maxwell stress α B2
?Airgap closing force
?Force at zero current
High force density electrical
machines-problems
?Low power factor
?High open circuit voltage
(e.g,60 volts)
?Internal resistance = 1.5
Ohm
?Expected short circuit
current 40 A?
?Expected power 2.4 kW?
High force density electrical
machines-problems
?Actual short circuit current
1.5 Amps
?Actual power approx,3.3 W !
?Require active rectifier
Low force density electrical machines
?Good magnetic circuit for high shear force
is root of its problems
?Presence of iron in circuit
?No iron = poorer magnetic circuit
?No Maxwell stress
?Lower inductance
?Ironless / air cored
?Cylindrical opposed rare earth PMs
?Coils not supported in steel
N SNSSN
Stee l
Ma g n e t
N SNS
Stato r
Co il
SN
Mo vin g
Ro tor
Air cored tubular machine
Power Conversion Scheme 1
1’ 1 2’ 2 8’ 8
R R’
1’ 1 2’ 2 8’ 8
Y Y’
1’ 1 2’ 2 8’ 8
B
B’
R
Y
R,Y,B R’,Y’,B’
~700 V
peak V and I,
370 V /phase
75 A
Large coil resistance,by pass inactive coils
Power Conversion Scheme 2
e(t)
L R
control target,
i(t)=|e(t)|/(2R)
common
d.c,link
from other
coils
coil
Power Conversion Scheme 2
e m f _ p h a s e A,,,
L _ p h a s e A, I,,,
1 0, 0 0
1 0, 0 0
2 0, 0 0
2 0, 0 0
1 2, 0 0
1 2, 0 0
1 4, 0 0
1 4, 0 0
1 6, 0 0
1 6, 0 0
1 8, 0 0
1 8, 0 0
- 7 3, 2 5 - 7 3, 2 5
7 5, 6 8
0 0
- 3 3, 3 3 - 3 3, 3 3
3 3, 3 3 3 3, 3 3
6 6, 6 7
- coil EMF
- coil current
Down Stream Power Conversion
<
v
coil 15
coil 14
coil 1
search
coil
i
+dc1
-dc1
+dc1
-dc1
+dc1
-dc1
v
i
+dc2
-dc2
R
Y
B
current
controller
buffer
amp
boost d.c.-d.c,chopper
including,1,air core choke
2,Skiip 942GB120
Alstom ALSPA MV3000C
power
smoothing
controller
duty ratio
Phase A
Phase B
Phase C
1,v<200V 200 V
Title
Power Conversion Stage,Block Diagram
Size Rev Document Number,001
energy storage
capacitor bank
Inverter Panel
dSPACE
(including grid filter)
v
Solar Power
Solar powered pump
Durham University
Solar Powered Car
Durham University
Solar Powered Car
Power Systems
Grid Integration – HV/MV AC or DC?
150kV dc cable to network
Isolator
Rectifier 123kV AC BUS
Transformers
Circuit breakers
41 kV rms AC
Six-step inverters
Isolators
50kV dc cables from
generators
Summary
? Grid fault ride through
- DFIG,Direct-in-line converter
semiconductor device,machine modelling,
control
? Direct drive wind power
- Fault tolerance,air-gap support,grid
interface,cost,integration
? Direct drive linear wave machine
- Low voltage high current,energy storage,
active damping
? Solar power
? Power systems
Discussion on Collaboration
? Fees
? Subsistence
? Visiting scholar
? Ph.D,studentship
? Industrial projects from China (local)
? Government research projects from China
? Application for China-UK or China-Europe
projects
New & Renewable Energy
Dr,Li Ran
Wind Power
Recent Studies in Wind Power
Gearbox
Wind Turbine
Doubly Fed
Induction Generator
4Q Converter
Filter
Grid
DFIG Grid Fault Ride Through
Renewable Energy Networks
? Grid code sets out requirements for grid
interconnection,
? Most current renewable generation systems are
treated as,negative” load,
? Future systems MUST contribute to system
frequency and voltage control,
? Grid interconnection usually,makes or breaks” a
project,
? Development of many (ALL?) renewable energy
converter systems have concentrated on the
device itself without detailed thought of how to
convert the power for grid interconnection,
? Future developments MUST consider the system
as a whole – REQUIRES INTEGRATED SYSTEM
Grid Code - Example
● The value of grid-fault ride-through is increasingly
appreciated,
● Grid code,e.g,Scottish Hydro-Electric Guidance Note
A wind farm must remain connected under the following conditions
depending on fault voltage reduction and registered capacity of wind farm,
wind farm registered capacity
voltage during fault <30 MW >=30 MW
0% July 2005 January 2004
15% January 2004 before January 2004
● The voltage refers to that on the transmission system (275 or 132 kV),
Transformer impedance and fault infeed from the wind farm are likely
to result in a higher voltage at generator terminal,
● Fault is cleared in 140 ms for 132 kV and 100 ms for 275 kV system,
Backup clearance time can extend to 300 ms,
Initial Control Idea – why
can’t it work?
stator voltage
rotor voltage
control
ir
fault
Recent Studies in Wind Power
Gearbox
Wind Turbine
Doubly Fed
Induction Generator
4Q Converter
Filter
Grid
DFIG Grid Fault Ride Through
- 0, 3 - 0, 2 - 0, 1 0 0, 1 0, 2 0, 3
0
0, 0 5
0, 1
0, 1 5
0, 2
0, 2 5
Pre -f a u l t si l p, s0 (p u )
F
a
u
l
t
vo
l
t
a
g
e
l
e
ve
l
:
U
s
(p
u
)
R i d i n g -t h ro u g h o p e ra t i o n ra n g e
ri d i n g -t h ro u g h o p e ra t i o n ra n g e
Feasibility Region with
Proposed Control
{ super-synchronous sub-synchronous
This plot says that the DFIG can successfully ride through a grid fault which
brings terminal voltage down to 0.3 pu,even it initially operates at full speed,
Durham 30 kW DFIG Test Rig
prime drive with programmable
direct torque control
DFIG
XPC Targetbox
real time system Filter
Grid
VARIAC 4Q conv
Laboratory verification
9.95 10 10.05 10.1 -2
-1.5
-1
-0.5
0
0.5
1
1.5
2
ir-a
bc
(pu
)
Time (s) 9.95 10 10.05 10.1
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
ir-a
bc
(pu
)
Time (s)
Rotor current constrained by control
Simulation Experiment
Grid Fault Ride Through
ωr
{
Power tracking
control
D.C,link voltage
control
Configuration with direct-in-line converters
A Proposed Research
? Study on the transient behaviour of and interaction in an
integrated machine-converter system,including
- Transient FE modelling of machine (HTU discovered that
the equivalent ckt model of a DFIG gives fault current that
is about 10% too low – ICEM 2004.);
- Transient thermal modelling of semiconductor devices;
- Control of converters to satisfy machine and power system
requirements,
Objective,optimized design and control strategy,
Recent Studies in Wind Power
Direct Drive (Gearless)
Wind Turbines
The Nacelle of a Geared Turbine
Generator
Gearbox
Drive
Shaft
Blades
Pitch
Mechanism
Lightning
Arrester
Anemometer
Mechanical
Brake
Hub
Tower
Yaw
Drive
Vernier hybrid machine
for direct drive wind turbine
? Flux switching machine
? Incorporates magnetic gearing
? High shear stress
? High force/torque at low speed
? Low power factor
Four-pole,three-phase,
prototype
The SLiM Concept (from EGL)
Three key aspects
? Large diameter using pre-tensioned
spokes and pre-compressed rims
? Ironless stator avoids magnetic pull
? Permanent Magnet Rotor
Ironless Stator Version
Rotor steel rim
Large Rare Earth
Magnets
Stator
non-metallic
rim
Stator coils
Magnet flux
pattern
Spoked Lightweight
Direct Drive Wind Machine
(SLiM)
Evolving
Generation
Ltd
Initial Power Conversion Arrangement
Stator coils
Inverter
module
Inverter
module
Output
to grid
Load C h ar ac te r i s ti c s
P r e di c t e d us i ng p r e di c t e d E,R and L M e as ur e d V and I
0
50
100
150
200
250
0 2 4 6 8 10
Cur r ent (A dc)
Voltag
e
(V
dc)
60 r pm
50 r pm
40 r pm
30 r pm
60 r pm
50 r pm
40 r pm
30 r pm
EGL
On Going Research
Research on power conversion and control
Schemes trying to achieve
? Fault tolerant operation
? Air-gap support
? Transformerless grid interface that satisfies
grid codes
? Low cost 100% rated converter
? Integration of PE and machine coil?
On Going Research
condition monitor
Voltage
regulator
Auxiliary pow er
pick up
Main output coils
D.c.-d.c,converter Brake resistor H-bridge
Cascade in
series w ith
other bridges
in the same
phase
Bypass
sw itch
Optical gate signals
&
Thyristor and diode
rectifier
Figure 1,A possible module design
On Going Research
Sa i
a
ib
ic
ec,eb,ea
Sb
Sc
+ -
+ -
+ -
+ -
+ -
+ -
grid
Circuit Diagram
? Chopper cut out speed,
9m/s
? Current at cut out,3A
? Generator cut out (using
circuit breaker),18.5m/s
? Generator cut out
current,17A
? Maximum high frequency
ripple current,3A
? Maximum transistor
current,3A
? Maximum diode current,
17A
Converter design,system simulation 0.0
50.0
100.0
150.0
200.0
250.0
2 3 4 5 6 7 8 9 10
Wind s pe e d (m /s)
Ele
ctri
cal
powe
r (W)
Max im um pow e r Batte ry co nne ctio n
Tracking Simulation
Annual Energy Capture
Average wind
speed (m/s)
Annual Energy Capture (kWh)
Battery Part Converter Full Converter Maximum
5 371 451 453 454
6 690 762 771 779
7 1083 1144 1168 1229
9 1848 1891 1954 2520
Average wind
speed (m/s)
Partially rated converter Fully rated converter
Increase from
direct connection
(kWh)
Percentage
increase
Increase from
direct connection
(kWh)
Percentage
increase
5 80 21.6% 82 22.1%
6 72 10.4% 81 11.7%
7 61 5.6% 85 7.9%
9 43 2.3% 106 5.7%
Wave Energy
Demonstration of Absorbing
Wave Energy
a
b
c
d
Wave Energy Converters
? Shoreline devices
Simple maintenance and grid connection
cost of land intrusion
Example,OWC
? Nearshore devices,typically 10-25 m deep,devices
can be tight moored to the sea bed
? Deep water devices,slack moored to maintain
geographical position only
Wave Energy Converters
? Terminator type
Principle axis parallel to incident wave crests
Waves are stopped as they reach the device
Example,Salter Duck
? Attenuator type
Principle axis perpendicular to wave crests
Energy conversion by relative motion of parts
of the device as a wave passes underneath
Example,Pelamis
? Point absorber
Oscillating body (next slide)
Concept of Direct Drive Wave
Energy Converter
? Couple moving part direct to generator
? Remove intermediate mechanical systems
? Slow reciprocating motion
Wave Energy
? Wavegen
? Oscillating water column,Islay
? Ocean Power Delivery
? Pelamis,SRO contract for
Machir Bay
? Teamworks Technology
? Archimedes Wave Swing
Direct Drive Wave Machine
Sea dev i ce
El ect r i ci t yLi near
G ener at orDi re ct D riv e
F l o a t
Rod
m u t u a l l y b u o y a n t
p o w e r t a k e o f f
m e ch a n i sm
d ra g p l a t e
st a t o r
t ra n sl a t o r
W a t e r su rf a ce
l i n e a r e l e ctr i ca l
g e n e r a to i r
3 - p h a se m a i n s
g r i d vo l ta g e
C
V
dc
3-phase ac/ac converter
? Power output - 300W per
half phase
? dc link 150V
? new inverter,800V dc link
Converter Power
Current,I
Voltage,V
Power in
=VxI
Power out of Machine
Into Converter
Direct Drive Machine
Electrical Requirements
? At 1m/s,100 kW,Force = 100 kN
? Conventional machines,? = 20-30
kN/m2
? Transverse Flux Machines,? =
200 kN/m2
High force density electrical
machines-problems
?High airgap closing forces
?Maxwell stress α B2
?Airgap closing force
?Force at zero current
High force density electrical
machines-problems
?Low power factor
?High open circuit voltage
(e.g,60 volts)
?Internal resistance = 1.5
Ohm
?Expected short circuit
current 40 A?
?Expected power 2.4 kW?
High force density electrical
machines-problems
?Actual short circuit current
1.5 Amps
?Actual power approx,3.3 W !
?Require active rectifier
Low force density electrical machines
?Good magnetic circuit for high shear force
is root of its problems
?Presence of iron in circuit
?No iron = poorer magnetic circuit
?No Maxwell stress
?Lower inductance
?Ironless / air cored
?Cylindrical opposed rare earth PMs
?Coils not supported in steel
N SNSSN
Stee l
Ma g n e t
N SNS
Stato r
Co il
SN
Mo vin g
Ro tor
Air cored tubular machine
Power Conversion Scheme 1
1’ 1 2’ 2 8’ 8
R R’
1’ 1 2’ 2 8’ 8
Y Y’
1’ 1 2’ 2 8’ 8
B
B’
R
Y
R,Y,B R’,Y’,B’
~700 V
peak V and I,
370 V /phase
75 A
Large coil resistance,by pass inactive coils
Power Conversion Scheme 2
e(t)
L R
control target,
i(t)=|e(t)|/(2R)
common
d.c,link
from other
coils
coil
Power Conversion Scheme 2
e m f _ p h a s e A,,,
L _ p h a s e A, I,,,
1 0, 0 0
1 0, 0 0
2 0, 0 0
2 0, 0 0
1 2, 0 0
1 2, 0 0
1 4, 0 0
1 4, 0 0
1 6, 0 0
1 6, 0 0
1 8, 0 0
1 8, 0 0
- 7 3, 2 5 - 7 3, 2 5
7 5, 6 8
0 0
- 3 3, 3 3 - 3 3, 3 3
3 3, 3 3 3 3, 3 3
6 6, 6 7
- coil EMF
- coil current
Down Stream Power Conversion
<
v
coil 15
coil 14
coil 1
search
coil
i
+dc1
-dc1
+dc1
-dc1
+dc1
-dc1
v
i
+dc2
-dc2
R
Y
B
current
controller
buffer
amp
boost d.c.-d.c,chopper
including,1,air core choke
2,Skiip 942GB120
Alstom ALSPA MV3000C
power
smoothing
controller
duty ratio
Phase A
Phase B
Phase C
1,v<200V 200 V
Title
Power Conversion Stage,Block Diagram
Size Rev Document Number,001
energy storage
capacitor bank
Inverter Panel
dSPACE
(including grid filter)
v
Solar Power
Solar powered pump
Durham University
Solar Powered Car
Durham University
Solar Powered Car
Power Systems
Grid Integration – HV/MV AC or DC?
150kV dc cable to network
Isolator
Rectifier 123kV AC BUS
Transformers
Circuit breakers
41 kV rms AC
Six-step inverters
Isolators
50kV dc cables from
generators
Summary
? Grid fault ride through
- DFIG,Direct-in-line converter
semiconductor device,machine modelling,
control
? Direct drive wind power
- Fault tolerance,air-gap support,grid
interface,cost,integration
? Direct drive linear wave machine
- Low voltage high current,energy storage,
active damping
? Solar power
? Power systems
Discussion on Collaboration
? Fees
? Subsistence
? Visiting scholar
? Ph.D,studentship
? Industrial projects from China (local)
? Government research projects from China
? Application for China-UK or China-Europe
projects
