Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS)

Transcription

1 Renewable Energy Applications: Photovoltaic and Wind Energy Conversion Systems (WECS) Josep Pou Antoni Arias Page 1

2 Outline 1. Renewable Energy Perspectives 2. Solar Photovoltaic (PV) 3. Wind Generation 4. Power Electronics Page 2

3 Outline 1. Renewable Energy Perspectives 2. Solar Photovoltaic (PV) 3. Wind Generation 4. Power Electronics Page 3

4 1. Renewable Energy Perspectives Primary Energy Use Estimation of primary energy Source: German Advisory Council on Global Change 2003, WBGU Page 4

5 Energy Sources There will be a decrease in the use of power sources based on fossil fuels (especially coal and oil) and also nuclear. On the other hand, it is expected an increase in the use of the renewable energy, mainly photovoltaic, wind and waves. 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. Page 5

6 Outline 1. Renewable Energy Perspectives 2. Solar Photovoltaic (PV) 3. Wind Generation 4. Power Electronics Page 6

7 2. Solar Photovoltaic (PV) Page 7

8 Maximum Power Point Tracking (MPPT) Power (W) 1000 W/m 2 Page 8

9 Single-Phase PV System Solar Radiation PV LC FILTER L v dc C Single- Phase Inverter (DC-AC) a b L g ELECTRICAL GRID AC Voltage Low Power Systems (up to 5kW 10kW) Page 9

10 Three-Phase PV System LC FILTER L ELECTRICAL GRID Solar Radiation PV v dc C Three- Phase Inverter (DC-AC) a b c L g L g L g v R v S v T AC Voltages High Power Systems (above 10kW) Page 10

11 Autonomous PV System DC-DC Converter (Boost) Batteries PV a Solar Radiation v dc Regulator Inverter (DC-AC) b Page 11

12 Example in Terrassa Science Museum Page 12

13 Example in Barcelona Forum Area Page 13

14 Outline 1. Renewable Energy Perspectives 2. Solar Photovoltaic (PV) 3. Wind Generation 4. Power Electronics Page 14

15 3. Wind Generation Main classification: - Fixed-speed wind turbines. - Variable-speed wind turbines. Page 15

16 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. Page 16

17 Induction generator operating at fixed speed Advantages: - Robust design. - No need for maintenance. - Well enclosed. - Produced in large series. - Low price. - Can withstand overloads. Fixed-Speed Wind Turbines Disadvantages: - Uncontrollable reactive power consumption. - Fixed speed means more mechanical stress. Page 17

18 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. Page 18

19 Reactive Power Compensation Example of reactive power as a function of the active power (The reactive power is compensated by capacitors at no-load) Page 19

20 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 Page 20

21 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 Page 21

22 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). Page 22

23 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. Page 23

24 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. Page 24

25 Multipole Synchronous Generators (MPSG)? -Multipole synchronous generators may not need a gearbox (these generators have a large diameter). - The rotational speed can change within a wide range. ENERCON E-126 (7 MW) - This is expected to be the most common wind turbine configuration in the future. Page 25

26 Outline 1. Renewable Energy Perspectives 2. Solar Photovoltaic (PV) 3. Wind Generation 4. Power Electronics Page 26

27 4. Power Electronics Power electronics is the engineering study of converting electrical power from one form to another. 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 ( Page 27

28 Power Electronic Semiconductors Diode Thyristor or SCR (Silicon Controlled Rectifier) Triac N OFF N i ON v N OFF OFF i ON F v OFF N F i ON F OFF v N ON Page 28

29 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 F OFF v OFF OFF v Page 29

30 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. Page 30

31 Application of Power Semiconductors Page 31

32 Classification of Power Electronic Converters FROM: AC Rectifier TO: DC V 1, f 1 V 2 DC/DC Converter DC AC Inverter V 1 V 2, f 2 Page 32

33 Classification FROM: AC Static AC Switches TO: AC V 1, f 1 V 2, f 2 = f 1 Cycloconverter (f 2 <f 1 ) Rectifier Matrix Converter DC Inverter AC V 2, f 2 Page 33

34 Rectifier Examples (from AC to DC) Three-phase half-controlled rectifier CN ψ = 0 v R v L π 2π α CP Three-phase fully-controlled rectifier + T 3 T 1 ψ = 0 D D2 3 T 2 D 1 CN v R π 2π α v L CP + T' 1 T 3 T' T' T 1 T 2 T' T 3 Page 34

35 DC-DC Converter Examples + E - T i T id Buck D i v L L + - i L + U DC motor Mechanical load i L i T 0 T ON 1 1 αt D E U ON 1 L 2 ΔI I Lm U 2 L 2 T i D Voltage Source Current Source 0 αt T v L Boost T Buck-Boost D E L T D U E L U Page 35

36 Inverter Example (from DC to AC) 30 v a0 /10 i a, i b, i c + v dc v dc 2 v dc 2 2C (0) 2C sa sa (a) sb sb (b) sc (c) s c v a0 v b0 v c Time (s) Page 36

37 Cycloconverter (from AC to AC) Page 37

38 Matrix Converter (from AC to AC) Bi-directional switch SAc D1 T2 T1 D2 Page 38

39 AC-DC-AC System Example Wind-Turbine NPC Converter Grid-Connected NPC Converter Multipole Synchronous Wind Turbine v C2 C Electrical Grid v r a b c V d i wt (NP) i g r s t 3*L g v s v t v C1 C Back-to-back-connected three-level converters. These converter topologies can provide three voltage a the outputs. Example of application to wind turbines. Page 39