Renewable Energy Applications: Photovoltaic and Wind Energy Conversion … · 2017-11-23 ·...

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

Socrates – Erasmus Visit


Josep PouAntoni Arias



Outline

1. Renewable Energy Perspectives2. Solar Photovoltaic (PV)3. Wind Generation4. Power Electronics



1. Renewable Energy Perspectives

Primary Energy Use

Estimation of primary energySource: German Advisory Council on Global Change 2003, WBGU



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.

Energy Sources



Outline




2. Solar Photovoltaic (PV)



1000 W/m2

Power (W)

Maximum Power Point Tracking (MPPT)



Single-Phase PV System

Solar Radiation

AC Voltage

Lga

vdc

b

ELECTRICAL GRID

PV

C

Single-Phase Inverter (DC-AC)

LLC FILTER

Low Power Systems (up to 5kW – 10kW)



Three-Phase PV System

Solar Radiation

AC Voltagesvdc

ELECTRICAL GRID

PV

C

Three-Phase Inverter (DC-AC)

LLC FILTER

vT

vS

vRLg a

Lg b

Lgc

High Power Systems (above 10kW)



vdc Regulator Inverter (DC-AC)

Batteries

a

b

Solar Radiation

PV

DC-DC Converter(Boost)

Autonomous PV System



Science Museum

Example in Terrassa



Example in Barcelona

Forum Area



Outline




3. Wind Generation

Main classification:- Fixed-speed wind turbines.- Variable-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.

Fixed-Speed Wind Turbines



Induction generator operating at fixed speedAdvantages:- 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.

Fixed-Speed Wind Turbines



- Capacitors banks compensate for reactive power from the induction generator.

- Maxim use of the electrical grid is done operating at unity power factor.

Capacitor Banks



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

Reactive Power Compensation



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).

Static VAr Compensator (SVC)

InductionGenerator

…

x3 x3 x3 x3

Δ Δ Δ Δ



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

Gearbox



- 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).

Soft-Starter



Variable speedThe 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.

Variable-Speed Wind Turbines



- 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.

ALSTOM-ECOTECNIA

Doubly-Fed Induction Generator (DFIG)



-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.

?

ENERCON E-126 (7 MW)

Multipole Synchronous Generators (MPSG)




Outline



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 (http://www.ece.ncsu.edu/research/pes)

http://www.ece.ncsu.edu/research/pes



v

iN

NON

OFF

Diode

v

i

N

ON

OFFOFF

Thyristor or SCR (Silicon Controlled

Rectifier)

F

OFF

Triac

v

i

F

ON

OFF

ON

F

N

N

Power Electronic Semiconductors



v

i

FF

ON

OFF

Transistor(BJT, MOSFET, IGBT,...)

v

i

N

ON

OFFOFF

GTO (Gate Turn-Off) Thyristor,IGCT (Integrated Gate Commutated

Thyristor)

FF




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.




Application of Power Semiconductors



DC AC

AC DC

V1 V2 , f2

V1 , f1 V2

Inverter

DC/DC Converter

Rectifier

FROM: TO:

Classification of Power Electronic Converters



Inverter

V1 , f1

DC AC

AC AC

V2 , f2

V2 , f2= f1

Static AC Switches

FROM: TO:

• Cycloconverter (f2<f1)• Matrix ConverterRectifier

Classification



π 2π α

0ψ =

2T1T3T

3T '1T '

3T

2T ' 1T '

Rv

CP

CN

Lv

+

−

π 2π α

1D2D 3D

2T1T3T

0ψ =

Three-phase half-controlled rectifier

Three-phase fully-controlled rectifier

Rv

CP

CN

Lv

+

−

Rectifier Examples (from AC to DC)



DC-DC Converter Examples

E U

T

D

L

iT

iD

iL

i

+

-

++ -

Lv

Current Source

Voltage Source

DC motor

Mechanical load

E UT

DLLv

E U

T D

L

ONT

mLI

Tα T

Tα T

0

0

OND E UL−

UL−

1

1

1

2

2

2

IΔ

iTiD

LiBuck

Boost Buck-Boost



Inverter Example (from DC to AC)

2dcv

)0(dcv

C2

C2

as bs cs

as bs cs

+

−2dcv

)(a)(b

)(c

0av0bv0cv

0 0.01 0.02 0.03 0.04 0.05 0.06-30

-20

-10

0

10

20

30

Time (s)

va0/10 ia, ib, ic



Cycloconverter (from AC to AC)



Bi-directional switch

SAc

T2

D2

T1

D1

Matrix Converter (from AC to AC)



Back-to-back-connected three-level converters. These converter topologies can provide three voltage a the outputs. Example of application to wind turbines.

AC-DC-AC System Example

(NP)

CvC2

vC1C

rVd

st

a

b

c

Wind-Turbine NPC Converter Grid-Connected NPC Converter

vr

vs

vt

3*Lgiwt ig

Multipole Synchronous Wind Turbine

ElectricalGrid

Renewable Energy Applications: Photovoltaic and Wind Energy Conversion … · 2017-11-23 ·...

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Transcript of Renewable Energy Applications: Photovoltaic and Wind Energy Conversion … · 2017-11-23 ·...