Power-Electronic Systems for the Grid Integration of Renewable Energy Sources

1. Power-Electronic Systems for the Grid Integrationof Renewable Energy Sources Based on: J.M. Carrasco, J.T Bialasiewicz, et al:Power-Electronic Systems for the Grid Integrationof Renewable Energy Sources: A Survey, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 53, NO. 4, AUGUST 2006. Zbigniew Leonowicz, PhD

2. Outline • New trends in power electronics for the integration of wind and photovoltaic • Review of the appropriate storage-system technology • Future trends in renewable energy systems based on reliability and maturity

3. Introduction • Increasing number of renewable energy sourcesand distributed generators • New strategies for theoperation and management of the electricity grid • Improve the power-supply reliability and quality • Liberalization of the grids leads to new management structures

4. Power-electronics technology • Plays an important role in distributed generation • Integration of renewable energy sources into the electrical grid Fast evolution, due to: • development of fast semiconductor switches • introduction of real-timecontrollers

5. Outline (detailed) • Current technology and futuretrends in variable-speed wind turbines • Power-conditioning systems used in grid-connected photovoltaic (PV) • Research and development trends inenergy-storage systems

6. Wind turbine technology • Wind-turbine market has been growing at over 30% a year • Important role in electricity generation • Germany and Spain

7. New technologies - wind turbines • Variable-speed technology – 5% increased efficiency • Easy control of active and reactive power flows • Rotor acts as a flywheel (storing energy) • No flicker problems • Higher cost (power electronics cost 7%)

8. DFIG http://www.windsimulators.co.uk/images/DFIG.gif

9. Variable-speed turbine with DFIG • Converter feeds the rotor winding • Statorwinding connected directly to the grid • Small converter • Low price

10. Simplified semi-variable speed turbine • Rotor resistance of the squirrel cage generator - varied instantly using fast power electronics

11. Variable-Speed Concept Utilizing Full-Power Converter • Decoupled from grid

12. ENERCON multipole synchronous generator reducedlosses lower costs increasedreliability http://www.wwindea.org/technology/ch01/imgs/1_2_3_2_img1.jpg

13. Full converter Energy Transfer Control of the active and reactive powers total-harmonic-distortioncontrol Energy storage CONTROL of Vdc driver controlling the torque generator, using a vector control strategy

14. Rectifier and chopper step-up chopper is used to adapt the rectifier voltage to the dc-link voltage of the inverter.

15. Semiconductor-Device Technology • Power semiconductor devices with better electrical characteristics and lower prices • Insulated Gate Bipolar Transistor (IGBT) is main component for power electronics

16. Integrated gated control thyristor (IGCT) - ABB

17. Comparison between IGCT and IGBT • IGBTs have higher switching frequency than IGCTs • IGCTs are made like disk devices – high electromagneticemission, coolingproblems • IGBTs are built like modular devices - lifetime of thedevice 10 x IGCT • IGCTs have a lower ON-state voltage drop- losses 2x lower

18. Grid-Connection Standards for Wind Farms Voltage Fault Ride-Through Capability of Wind Turbines • turbinesshouldstay connected and contribute to the grid in case of a disturbancesuch as a voltage dip. • Wind farmsshouldgeneratelike conventional power plants, supplying active and reactivepowers for frequency and voltage recovery, immediately afterthefaultoccurred.

19. Requirements

20. Power-Quality Requirements for Grid-Connected Wind Turbines • - flicker + interharmonics • Draft IEC-61400-21 standard for “power-quality requirements for Grid Connected Wind Turbines”

21. IEC Standard IEC-61400-21 • Flickeranalysis • Switching operations. Voltage and currenttransients • Harmonicanalysis(FFT) - rectangular windows of eight cycles of fundamentalfrequency. THD up to 50thharmonic

22. Other Standards • High-frequency (HF) harmonics and interharmonics IEC 61000-4-7 and IEC 61000-3-6 • methods for summing harmonics and interharmonicsinthe IEC 61000-3-6 • To obtain a correct magnitude of the frequency components,define window width, according to the IEC 61000-4-7 • switchingfrequencyof the inverter is not constant • Can be not multiple of 50 Hz

23. Transmission Technology for the Future • Offshore installation.

24. HVAC • Disadvantages: • High distributed capacitance of cables • Limited length

25. HVDC More economic > 100 km and power 200-900 MW 1) Sending and receiving end frequencies are independent. 2) Transmission distance using dc is not affected by cablechargingcurrent. 3) Offshore installation is isolated from mainland disturbances 4) Power flow is fully defined and controllable. 5) Cable power losses are low. 6) Power-transmission capability per cable is higher.

26. HVDC LCC-based • Line-commutated converters • Many disadvantages • Harmonics

27. HVDC VSC based HVDC Light – HVDC Plus Several advantages- flexible power control, no reactive power compensation, …

28. High-Power Medium-Voltage Converter Topologies • Multilevel-converter 1) multilevelconfigurationswithdiodeclamps 2) multilevel configurations with bidirectional switch interconnection 3) multilevel configurations with flying capacitors 4) multilevel configurations with multiple three-phaseinverters 5) multilevel configurations with cascaded single-phaseH-bridgeinverters.

29. Comparison http://hermes.eee.nott.ac.uk/teaching/h5cpe2/

30. Multilevel back-to-back converter fordirect connection to the grid

31. Low-speed permanent-magnet generators power-electronic building block (PEBB)

32. Direct-Drive Technology for Wind Turbines • Reduced size • Lower installation and maintenance cost • Flexible control method • Quick response to wind fluctuations and load variation • Axial flux machines

33. Future Energy-Storage Technologiesin Wind Farms Zincbrominebattery • High energy density relative to lead-acid batteries• 100% depth of discharge capability • High cycle life of >2000 cycles at • No shelf life • Scalable capacities from 10kWh to over 500kWh systems• The ability to store energy from any electricity generating source

34. Hydrogen as a vehicle fuel • Electrical energy can be produced and delivered to the gridfrom hydrogen by a fuel cell or a hydrogen combustion generator. • The fuel cell produces power through a chemical reactionand energy is released from the hydrogen when it reacts with the oxygen in the air.

35. Variable-speed wind turbine with hydrogen storage system

36. PV Photovoltaic Technology • PV systems as an alternativeenergy resource • ComplementaryEnergy-resource in hybrid systems Necessary: • high reliability • reasonable cost • user-friendly design

37. PV-module connections The standards • EN61000-3-2, IEEE1547, • U.S. National Electrical Code (NEC) 690 • IEC61727 • power quality, detection of islandingoperation, grounding • structure and thefeatures of the present and future PV modules.

38. IEC 61000-3-2

39. Islanding PV Generator Converter AC-DC Local Loads Grid

40. Market Considerations PV • Solar-electric-energy growth consistently 20%–25% per annum over the past 20 years 1) an increasing efficiency of solar cells 2) manufacturing-technology improvements 3) economies of scale

41. PV growth • 2001, 350 MW of solar equipment was sold 2003, 574 MW of PV was installed. • In 2004 increased to 927 MW • Significant financial incentives in Japan, Germany, Italy and France triggered a huge growth in demand • In 2008, Spain installed 45% of all photovoltaics, 2500 MW in 2008 to an drop to 375 MW in 2009

42. Perspectives • World solar photovoltaic (PV) installations were 2.826 gigawatts peak (GWp) in 2007, and 5.95 gigawatts in 2008 • The three leading countries (Germany, Japan and the US) represent nearly 89% of the total worldwide PV installed capacity. • 2012 are and 12.3GW- 18.8GW expected

44. Efficiency • Market leader in solar panel efficiency (measured by energy conversion ratio) is SunPower, (San Jose USA) - 23.4% • market average of 12-18%. • Efficiency of 42% achieved at the University of Delaware in conjunction with DuPont (concentration) in 2007. • The highest efficiency achieved without concentration is by Sharp Corporation at 35.8% using a proprietary triple-junction manufacturing technology in 2009.

45. Design of PV-Converters • IGBT technology • Invertersmustbe able to detect an islanding situation and take appropriatemeasures in order to protect persons and equipment • PV cells - connected to the grid • PV cells - isolatedpowersupplies

47. Converter topologies • Central inverters • Module-oriented or module-integrated inverters • Stringinverters

48. Multistring converter • Integration of PV strings of different technologies and orientations

49. Review of PV Converters • S. B. Kjaer, J. K. Pedersen, F.Blaabjerg „A Review of Single-Phase Grid-Connected Inverters for Photovoltaic Modules”, IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 41, NO. 5, SEPTEMBER/OCTOBER 2005 • Demands Defined by the Grid • - standards (slide 37) EN standard (applied in Europe) allows higher current harmonics • the corresponding IEEE and IEC standards.