Power Electronics in Renewable Energy Systems
Power Electronics in Renewable Energy Systems by Prof. Frede Blaabjerg Aalborg University Institute of Energy Technology
[email protected] http://www.iet.aau.dk
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28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
Power Electronics in Renewable Energy Systems
Power Electronics in Renewable Energy Systems Outline 1. Development in Energy Technology 2. Wind energy systems 3. Solar energy systems 4. Summary
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28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
1. Institute of Energy Technology Power Electronics in Renewable Energy Systems
Where are we from?
• 13000 students • Founded in 1974 3
28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
1. Development in Energy Technology
Power Electronics in Renewable Energy Systems
Electricity production in 2004
The share of renewable energy production is still very modest!
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28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
1. Development in Energy Technology
Power Electronics in Renewable Energy Systems
Power capacities perspective until 2020
• The installed capacity has to increase by over 80% • New power sources becomes interesting • More efficient use of the existing sources •From production to end user •Power balance extremely important •New energy storage devices
☺ Distributed Power Generation Systems (DPGS) necessary 5
28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
1. Development in Energy Technology
Power Electronics in Renewable Energy Systems
Overview of DPGS
Advantages of DPGS: • • • • •
Load management (peak shaving) Power quality (required by standards!) Enhanced voltage stabiliity Reduced transmission losses Potential for improving grid reliability/stability
Disadvantage - high cost! 6
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• • • • •
Wind energy – highest development Solar energy – next highest development Wave energy – largely unexplored Tidal energy – largely unexplored Small hydro ( MPPT --> variable-speed WT
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems Power Conversion and control Electrical Power Wind power
Power Electronics in Renewable Energy Systems
Rotor
Power converter (optional)
Generator
Gearbox (optional)
Supply grid
Consumer Power conversion & power control
Power transmission
Power conversion & power control
Power conversion
Power transmission
Electrical control
Power control
Basic Topologies
Pref
Qref
Fixed speed with capacitor bank (old system, not used today anymore!) Two-generator principle –two pole-pairs (exists in many systems) Rotor resistance control Doubly-fed induction generator DFIG - wounded rotor (very common now!) Squirell cage induction generator SCIG Synchronous generator - External magnetized Synchronous generator - Permanent magnets 14
28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems Basic topologies for variable-speed wind turbine
Power Electronics in Renewable Energy Systems
Fixed speed with capacitor bank (Danish concept) Simple and robust No slip ring using SCIG Fixed speed and uncontrollable Needs soft-starter Gearbox Needs capacitor bank High mechanical stress
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28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems Basic topologies for variable-speed wind turbine
Power Electronics in Renewable Energy Systems
Rotor resistance control
Higher speed range Lower mechanical stress Less grid pulsations Improvement in Optislip (no rings) Still reactive power compensation Use basically slip-rings Speed range still limited to 5-10 % of nominal speed (above synchronous speed) Higher power losses in the rotor
IV Induction generator
Rr < Rr < Rr Grid
Gear
Pitch
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Resistance control
Reactive compensator
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems Basic topologies for variable-speed wind turbine
Power Electronics in Renewable Energy Systems
Doubly-fed induction generator - wounded rotor Limited speed range (-30% to +20%, typical) Small-scale power converter (Less power losses, price) Complete control of active Pref and reactive power Qref Need for slip-rings Need for gear V Doubly-fed induction generator Grid Gear
Pitch DC
AC DC
Pref
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AC
Qref
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems Basic topologies for variable-speed wind turbine
Power Electronics in Renewable Energy Systems
Induction generator - Squirrel cage rotor Full speed range No brushes on the generator Complete control of active og reactive power Proven technology Full-scale power converter Need for a gear
VI Induction generator Grid Gear
AC
DC DC
Pitch
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Pref
AC
Qref
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems Basic topologies for variable-speed wind turbine
Power Electronics in Renewable Energy Systems
Synchronous generator - External magnetized Full speed range Possible to avoid gear (multi-pole generator) Complete control of active and reactive power Small converter for field Need of slip-rings Full scale power converter Multi-pole generator may be big and heavy
DC AC
VII Synchronous Generator
Gear
AC DC
Pitch
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Pref
Grid
DC AC
Qref
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems Basic topologies for variable-speed wind turbine
Power Electronics in Renewable Energy Systems
Synchronous generator - Permanent magnets Full speed range Possible to avoid gear (multi-pole generator) Complete control of active and reactive power Brushless (reduced maintenance) No power converter for field (higher efficiency) Full scale power converter Multi-pole generator big and heavy Permanent magnets needed in large quantities
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PM-synchronous Generator Multi-pole
AC DC
Pitch
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Pref
Grid
DC AC
Qref
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems Technology comparison
Power Electronics in Renewable Energy Systems
2001 Design Concept Fixed speed (Stall or active stall regulation, fixed speed operation, gearbox, poleswitchable asynchronous Dynamic slip control (Limited variable speed, pitch regulation, gearbox, poleswitchable asynchronous generators with variable slip) Doubly-fed generator (Variable speed operation, pitch control, gearbox, double-fed generator utilizing power electronics in the inverter) Direct-driven variable speed synchronous (generators with large-diameter synchronous ring generator, including pitch control, but no gearbox, utilizing power electronics in the inverter) Total
World-Market Share
Market Share Germany
23%
22%
11%
0%
50%
49%
16%
29%
100%
100%
- Power electronics is now in wind turbines 21
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems
Power Electronics in Renewable Energy Systems
Control of wind turbines
Basic demands: Electrical:
• Interconnection (conversion, synchronization) • Overload protection • Active and reactive power control
Mechanical: • Power limitation (pitch) • Maximum energy capture • Speed limitation/control • Reduce acoustical noise •Damp mechanical resonances
Control loops with different bandwidth 22
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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2. Wind Energy Systems
Power Electronics in Renewable Energy Systems
DFIG Control Structure
The back-to-back converter is typically full-bridge VSI or NPC (multi-level, high power)
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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2. Wind Energy Systems
Power Electronics in Renewable Energy Systems
Control of Multi-pole Synchronous Generator
PMG
Generator rectifier
Grid inverter
Inductance Grid
vDC
Pref
Power control
vDC
Grid control Q
vga,v gb, v gc iga, igb, igc ref
Control of Multi-pole Synchronous Generator
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems
Power Electronics in Renewable Energy Systems
Current developments, Vestas A/S Denmark
Target market: Big off-shore farms
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Vestas V120 off-shore turbine Rated power: 4,500 kW Rotor diameter: 120 m Hub height: 90 m Turbine concept: Gearbox, variable speed, variable pitch control Generator: HV DFIG
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
2. Wind Energy Systems
Power Electronics in Renewable Energy Systems
Current Developments, Enercon GmbH Germany
Enercon E-112 gearless turbine Rated power: 4,500 - 6,000 kW Rotor diameter: 114 m Hub height: 124 m Turbine concept: Gearless, variable speed, variable pitch control Generator: Enercon ring generator
Target market: Large on-shore and off-shore farms.
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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2. Distributed Renewable Power Sources
Power Electronics in Renewable Energy Systems
Current developments –off-shore wind farms
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• Horns Reef, Denmark, 80 x 2MW (Vestas V80, pitched, variablespeed, DFIG with gearbox) • In operation for more than 3 year • Extreme corrosion and mechanical stress • Experienced problems with transformer and generators, premature corrosion • Horns Reef experience-->higher price per kWh, more than 50% higher than on-shore • The planned developments with new off-shore farms are delayed slightly Workshop Energy Technology, April 27 2006 by Frede Blaabjerg 28-04-2006 www.iet.aau.dk
3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
Europe Potential
☺ Annual total potential in NW Europe: ca.1000 kWh/m2/year (ca 50% direct and 50% diffuse radiation) In southern Europe : ca.2000 kWh/m2/year 28
28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
Introducing Photovoltaics Direct sunlight conversion to electricity using semiconductor materials (ex. Si, Ga-As, etc) ☺ ☺ ☺ ☺ ☺ ☺ ☺
Over 30 years experience Modular (mW to MW) Noise and pollution free No moving parts Reliable, long life (>20 year) Low operation cost Abundant resource (Si) High manufacturing cost Typical efficiency 15-18%
Roof-integrated PV system Skyskrapper on Broadway, New York
4.6 MWp, Springerfield, Tucson, Arizona, USA, 29
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6.3 MWp, Solar Park Muhlhausen,
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
Germany,
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3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
Efficiency
The thermodynamic ideal limit is ~45%
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
Photovoltaic Systems- stand-alone
Solar lighting in Mexico
PV/Wind in Korea
Solar/FC Source: IdaTech
Mobile Solar. Source Nasa
Source: Helios
A large variety of applications 31
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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3. Solar Energy Systems Photovoltaic Systems - Grid connected Power Electronics in Renewable Energy Systems
PV Buildings. Source BCIT , Burnaby, British Columbia
Residential, not-integrated roof Residential, integrated roof
Residential PV is developing very fast in Japan and Germany
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Power plants
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
Power configuration for grid-connected PV systems
Central inverters • 10 kW-250kW, threephase, several strings in parallel • high efficiency, low cost, low reliability, not optimal MPPT •Used for power plants
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String inverters • 1.5 - 5 kW, typical residential application • each string has its own inverter enabling better MPPT • the strings can have different orientations •Three-phase inverters for power < 5kW
Module inverters • 50-180W, each panel has its own inverter enabling optimal MPPT • lower efficiency, difficult maintenance •Higher cost/kWp
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
Converter topologies for PV inverters on the LF side with isolation with DC-DC converter
on the HF side without isolation
PV Inverters with isolation without DC-DC converter without isolation
• Without boost / with boost of dc voltage • Galvanic isolation necessary some places • LF/HF transformer (cost-volume issue) • A large variety of possibilities • The optimal topology is not matured yet as for drives • Transformerless topologies having higher efficiency are emerging 34
28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
PV inverters with dc-dc converter and isolation
PV Array
DC
DC
PV Array
Grid DC
AC
DC
AC
DC Grid
AC
DC
AC
On high frequency (HF) side
On low frequency (LF) side
The HF transformer leads to more compact solution but complex design High frequency bridge High frequency inverter
Line frequency inverter
Filter
vx Filter
PV array
C
~
vgrid
High frequency tranformer
Typical solution with push-pull dc-dc converter with HF transformer and PWM fullbridge inverter with filter (LCL, LC,L)
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
3. Solar Energy Systems Transformerless PV inverters with boost Power Electronics in Renewable Energy Systems
Boost Converter
PV Array
DC
Full bridge inverter
DC Grid DC
AC PV array
VDC bus
C
Filter
~
vgrid
•Compact design •Leakage current problem •Safety issue
•Boost converter, full-bridge PWM inverter, grid filter
•Time sharing configuration •Extra diode •Boost with rectified sinus reference •PWM full-bridge inverter •Efficiency>96%
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
PV inverters without boost With isolation
Full bridge inverter Line frequency transformer
DC
PV Array
Grid AC PV array
C
~
Filter
vgrid
•Grid side trafo •High volume Without isolation Cascaded inverter I1
DC
PV Array
Grid AC
PV array 1
C1
E1
iinv vinv
I2
PV array
C
Filter
~
vgrid
Typical solution with full-bridge inverter 37
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Linv
b2
Full bridge inverter
PV array 2
vL
a1
C2
c1
~
vgrid
E2 d2
Multi-level solution for lower dc voltage input
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
Control of PV inverters
ug SYSTEM CONTROL
System control • Different control structures • Current control (THD limits) • Specific control functions • Maximum Power Point Tracking (MPPT) • Grid synchronization (PLL) • Anti – Islanding detection (standards) • Ancillary functions (future) •Grid control 38
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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3. Solar Energy Systems Anti-islanding methods Power Electronics in Renewable Energy Systems
Passive methods • Under/Over Voltage (UV/OV) and Under/Over Frequency (UF/OF) • Voltage phase jump detection • Detection of voltage harmonics
Active methods - resident in the inverter • Output power variation • Active Frequency Drift (AFD) • Slip-Mode frequency-Shift (SMS) • Positive feedback of frequency or voltage • Impedance measurement using external device or harmonic injection •Harmonic injection is current methods for single-phase PV inverters •More info: [Asiminoaie L.,Teodorescu,R., Blaabjerg,F., Borup,U. – “A Digital Controlled PV-Inverter with Grid Impedance Estimation for ENS Detection ” IEEE Trans on PE 2005.] 39
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
www.iet.aau.dk
3. Solar Energy Systems
Cumulative installed capacity (MW)
Power Electronics in Renewable Energy Systems
Solar Photovoltaics Energy – developments
3000 2500
connected connected GridGrid grid O ff Off-
2000 1500 1000 500 0
1992 199319941995199619971998 19992000200120022003 2004 Cumulative installed capacity from 1992 to 2004 in the IEA-PVPS reporting countries (source: IEAPVPS, http://www.iea-pvps.org
☺ ☺ ☺ ☺ 40
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2.5 GW installed until 2004! (Totally installed 3700 GW!) Grid Connected PV System are growing fast Japan is the biggest solar panel manufacturer Germany is the biggest market in Europe
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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3. Solar Energy Systems
Power Electronics in Renewable Energy Systems
Solar Energy – Economics
It is expected that the production price for PV panels will be halved before 2010 The price of commercial solar electricity is now ca. 5 times higher then the conventional electricity (ca. 25-30 cents/kWh in USA) and will be comparable with the conventional kWh in 2020 (source: US Dpt. Of Energy) 41
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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Power Electronics in Renewable Energy Systems
4. Summary
• •
•
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Required total capacity installed by 2020 - 6TW (2.4 TW new installed) Wind energy - very promissing RES, huge potential,technology ready • 4 Eurocent/kWh (50% more for off-shore) • 50 GW installed in 2005 - 1.3% global penetration • 400 GW projected in 2020 - 8% global penetration • Higher penetration is possible if storage solution is found • Large off-shore is the key but needs more development to take off Solar energy - very promissing RES, huge potential • PV - c-Si technology>90% market, residential, plants, stand-alone • >2.5 GW installed by 2004, • 20 Eurocent/kWh 2005 • 4 Eurocent/kWh in 2020 • New technologies are emerging (CPV, thin-film)
28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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4. Summary Power Electronics in Renewable Energy Systems
Power electronics in RES • •
• • • • • • • 43
Renewable energy is on its move Power electronics is an important player enabling better utilization of renewable sources by implementing MPPT function (WT, PV), ridethrough capabilities, increase the capacity factor by using low wind/flow range, etc. Power converters are able to seamless transfer variable frequency power to the fixed frequency grid (ac-dc-ac). Critical for WT, Hydro. Storage solution could increase the capacity factor of RES like WT and could increase penetration. Europe goal 20% RES by 2020! Distributed Power Generation Systems (DPGS) will be a solution to avoid energy crisis in the near future. (both conventional and RES) On long-term it will decrease the power volume in the transmission level and will make the central grid control very complex. The future RES DPGS should be able to run in on-grid and off-grid modes Advanced control of grid converters including grid impedance estimation, adaptive current control are emerging Monitoring and advanced diagnosis will also be integrated 28-04-2006
Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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Power Electronics in Renewable Energy Systems 44
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Workshop Energy Technology, April 27 2006 by Frede Blaabjerg
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