Socrates – Erasmus Visit
Renewable Energy Applications:
Photovoltaic and Wind Energy
Conversion Systems (WECS)
Josep Pou
Antoni Arias
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
Page 1
Socrates – Erasmus Visit
Outline
1.
2.
3.
4.
Renewable Energy Perspectives
Solar Photovoltaic (PV)
Wind Generation
Power Electronics
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Outline
1.
2.
3.
4.
Renewable Energy Perspectives
Solar Photovoltaic (PV)
Wind Generation
Power Electronics
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
1. Renewable Energy Perspectives
Primary Energy Use
Estimation of primary energy
Source: German Advisory Council on Global Change 2003, WBGU
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Energy Sources
ƒ
There will be a decrease in the use of power
sources based on fossil fuels (especially
coal and oil) and also nuclear.
ƒ
On the other hand, it is expected an increase
in the use of the renewable energy, mainly
photovoltaic, wind and waves.
ƒ
In the long term, the photovoltaic generation
will be the key to cover power demand.
Great changes in the photovoltaic cell
technology are expected that will increase
the ratio efficiency/cost.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Outline
1.
2.
3.
4.
Renewable Energy Perspectives
Solar Photovoltaic (PV)
Wind Generation
Power Electronics
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
Page 6
Socrates – Erasmus Visit
2. Solar Photovoltaic (PV)
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Maximum Power Point Tracking (MPPT)
Power
(W)
1000 W/m2
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Single-Phase PV System
LC FILTER
L
ELECTRICAL
GRID
PV
Solar
Radiation
vdc
C
SinglePhase
Inverter
(DC-AC)
a
Lg
AC
Voltage
b
Low Power Systems (up to 5kW – 10kW)
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Three-Phase PV System
LC FILTER
L
PV
Solar
Radiation
a
vdc
C
ThreePhase
Inverter
(DC-AC)
b
c
ELECTRICAL
GRID
Lg
vR
Lg
vS
Lg
vT
AC
Voltages
High Power Systems (above 10kW)
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Autonomous PV System
DC-DC Converter
(Boost)
Batteries
PV
Solar
Radiation
a
vdc
Regulator
Inverter
(DC-AC)
b
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Example in Terrassa
Science Museum
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Example in Barcelona
Forum Area
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Outline
1.
2.
3.
4.
Renewable Energy Perspectives
Solar Photovoltaic (PV)
Wind Generation
Power Electronics
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
3. Wind Generation
Main classification:
- Fixed-speed wind turbines.
- Variable-speed wind turbines.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Fixed-Speed Wind Turbines
The electrical generator is connected directly to the grid.
- An induction generator is normally used.
- Since the grid frequency is fixed, the speed of the wind turbine is settled
by the ratio of the gearbox and by the number of poles in the generator.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Fixed-Speed Wind Turbines
Induction generator operating at fixed speed
Advantages:
- Robust design.
- No need for maintenance.
- Well enclosed.
- Produced in large series.
- Low price.
- Can withstand overloads.
Disadvantages:
- Uncontrollable reactive power consumption.
- Fixed speed means more mechanical stress.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Capacitor Banks
- Capacitors banks compensate for reactive power from the induction
generator.
- Maxim use of the electrical grid is done operating at unity power factor.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Reactive Power Compensation
Example of reactive power as a function of the active power
(The reactive power is compensated by capacitors at no-load)
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Static VAr Compensator (SVC)
This device allows for a continuous compensation using switched
capacitor banks and some inductors. They are connected to the grid by
thyristors (SCR: Silicon Controlled Rectifier).
Induction
Generator
Δ
Δ
Δ
Δ
…
x3
x3
x3
x3
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Gearbox
Why a gearbox is needed?
-The gearbox is used to increase the
speed of the electrical generator.
- Without a gearbox, for a wind
turbine rotational speed of 30 rpm, a
generator of 100 pair of poles (!!!!)
would be needed (assuming 50-Hz
grid frequency).
- Furthermore, the mass of the rotor
has to be roughly proportional to the
torque.
T=P/ω; if ω↓ then T↑ for a constant P.
T: Torque, P: Power, ω: Rotational speed
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Soft-Starter
- If you connected (or disconnected)
a large wind turbine generator to the
grid with a normal switch, you would
be quite likely to damage both the
generator and the gearbox. Also
large currents in the neighborhood
grid would be produced.
- To prevent this situation, wind
turbines connect and disconnect
gradually to the grid using thyristors.
- To avoid thyristor losses under
normal operation mode, a bypass
switch is activated (main contactor).
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Variable-Speed Wind Turbines
Variable speed
The frequency of the generator voltages can be different from the
electrical grid (50-60 Hz) and therefore the turbine speed can change.
Advantages:
- More energy production.
- Less mechanical stress.
- Reduce power fluctuation.
- Capacity of noise reduction.
- May have more control on the grid currents.
Drawbacks:
- The system requires power electronic converters.
- More expensive.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Doubly-Fed Induction Generator (DFIG)
ALSTOM-ECOTECNIA
- The slip of the rotor can change within a wide range (and therefore the
wind-turbine speed as well).
- It is the most common topology produced by large manufacturers
nowadays.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Multipole Synchronous Generators (MPSG)
?
ENERCON E-126 (7 MW)
-Multipole synchronous generators may not need a gearbox (these
generators have a large diameter).
- The rotational speed can change within a wide range.
- This is expected to be the most common wind turbine configuration in
the future.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
Outline
1.
2.
3.
4.
Renewable Energy Perspectives
Solar Photovoltaic (PV)
Wind Generation
Power Electronics
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
4. Power Electronics
ƒ
Power electronics is the engineering study of
converting electrical power from one form to
another.
ƒ
At a world-wide average rate of 12 billion kilowatts
every hour of every day of every year, more than
40% of the power generated is being
reprocessed or recycled through some form of
power electronic systems. By 2010, it is
expected this will increase up to 80%.
Source: North Carolina State University, Department of Electrical and Computer
Engineering (http://www.ece.ncsu.edu/research/pes)
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Power Electronic Semiconductors
Thyristor or SCR
(Silicon Controlled
Rectifier)
Diode
i
i
i
ON
N
ON
F
v
OFF
OFF
v
ON
F
N
N
N
OFF
Triac
OFF
v
N
OFF
F
ON
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Power Electronic Semiconductors
Transistor
(BJT, MOSFET, IGBT,...)
GTO (Gate Turn-Off) Thyristor,
IGCT (Integrated Gate Commutated
Thyristor)
i
i
ON
ON
F
F
N
F
OFF v
OFF
OFF
F
v
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Power Electronic Semiconductors
Source: L.M. Tolbert, “High Power Electronics for a Sustainable 21st Century,” NSF
Workshop for Sustainable Energy Systems, The University of Tennessee, Dec.
2000, Atlanta, Georgia.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Application of Power Semiconductors
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Classification of Power Electronic Converters
TO:
FROM:
AC
V1 , f1
Rectifier
DC
V2
DC/DC Converter
DC
V1
Inverter
AC
V2 , f2
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Classification
FROM:
Static AC
Switches
TO:
AC
V2 , f2= f1
AC
V1 , f1
• Cycloconverter (f2<f1)
Rectifier • Matrix Converter
DC
Inverter
AC
V2 , f2
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Rectifier Examples (from AC to DC)
ψ =0
Three-phase half-controlled rectifier
−
CN
vR
π
vL
+
T3
CP
2π
T1
T2
D3
D2
ψ =0
α
D1
Three-phase fully-controlled rectifier
−
CN
vR
π
2π
vL
+
CP
T1 '
T3 '
T2 '
T3
T1
T1 '
T2
T3
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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α
Socrates – Erasmus Visit
DC-DC Converter Examples
TON
Buck
iL
i
+
+
D
iT
-
1
ΔI
2
DC motor
vL
T
E
DON
L
-
0
+
iL
U
iD
αT
Mechanical
load
E −U
L
2
−U
L
I Lm
T
2
1
iT
1
iD
Voltage
Source
vL
E
T
Buck-Boost
Boost
L
αT
0
Current
Source
D
T
D
U
T
E
L
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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U
Socrates – Erasmus Visit
Inverter Example (from DC to AC)
30
+
vdc
2
sa
sb
vdc
2C
−
(b)
(0)
vdc
2
sa
sb
(c)
sc
ia, ib, ic
20
sc
(a)
va0/10
va 0
vb 0
vc 0
10
0
-10
2C
-20
-30
0
0.01
0.02
0.03
0.04
0.05
Time (s)
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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0.06
Socrates – Erasmus Visit
Cycloconverter (from AC to AC)
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Matrix Converter (from AC to AC)
Bi-directional
switch
SAc
D1
T2
T1
D2
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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Socrates – Erasmus Visit
AC-DC-AC System Example
Wind-Turbine NPC Converter
Grid-Connected NPC Converter
Multipole
Synchronous
Wind Turbine
a
b
c
vC2
Electrical
Grid
C
vr
Vd
ig
iwt
s
t
(NP)
vC1
r
3*Lg
vs
vt
C
ƒ Back-to-back-connected three-level converters. These
converter topologies can provide three voltage a the
outputs. Example of application to wind turbines.
Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)
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