Power electronic topologies for wind turbines

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1 XIX JORNADAS de CONFERENCIAS JCEE 14 Power electronic topologies for wind turbines Author: Source: ALSTOM WIND

2 Presenttion of the wind systems: lrge numbers Annul offshore wind instlltion (011) Source: EWEA Size evolution of wind turbines over time Source: EWEA

3 Rules for connecting wind frms to the grid Generl wind frm lyout Locl wind turbine grid Collecting point Trnsmission system Wind frm grid interfce PCC WT Wind frm elements: Wind turbines (WT). WT connected in prllel to rdils. Locl wind turbine grid. Collecting point. To increse the voltge for trnsmission. Trnsmission system. HVAC or HVDC trnsmission. Wind frm interfce. To dpt the voltge, frequency nd the rective power demnd of the grid in the PCC. Point of common connection.

4 Fixed nd vrible speed wind turbines Wind Turbine configurtions ) Wind turbine using n induction genertion (IG). b) Wind turbine using doubly-fed induction genertor (DFIG). c) Wind turbine using permnent mgnet synchronous genertor (PMSG).

5 Fixed-speed wind turbines Wind Turbine configurtions The electricl genertor is connected directly to the grid. An induction genertor is normlly used. Since the grid frequency is fixed, the speed of the wind turbine is settled by the rtio of the gerbox nd by the number of poles in the genertor. n f 60 3

6 Fixed-speed wind turbines Induction genertor operting t fixed speed Advntges: - Robust design. - No need for mintennce. - Well enclosed. - Produced in lrge series. - Low price. - Cn withstnd overlods. Source: AEROSTAR Disdvntges: - Uncontrollble rective power consumption. - Fixed speed mens more mechnicl stress. 4

7 Fixed-speed wind turbines Cpcitor bnks Cpcitors bnks compenste for rective power from the induction genertor. Mxim use of the electricl grid is done operting t unity power fctor. Voltge Current C C C 5

Fixed-speed wind turbines Soft-strter If you connected (or disconnected) lrge wind turbine genertor to the grid with norml switch, you would be quite likely to dmge both the genertor nd the gerbox.

8 Fixed-speed wind turbines Soft-strter If you connected (or disconnected) lrge wind turbine genertor to the grid with norml switch, you would be quite likely to dmge both the genertor nd the gerbox. Also lrge currents in the neighborhood grid would be produced. - To prevent this sitution, wind turbines connect nd disconnect grdully to the grid using thyristors. - To void thyristor losses under norml opertion mode, bypss switch is ctivted (min contctor). Induction Genertor 8

9 Vrible-speed wind turbines Doubly-fed induction genertor A frequency converter control the currents in the rotor. The slip of the rotor cn chnge within wider rnge. Power converters hve to stnd only frction the nominl power (0% or 30%). It is the most common topology produced by lrge mnufcturers nowdys. Less expensive compred to the full power converter. Source: ALSTOM WIND 9

10 Vrible-speed wind turbines Multipole synchronous genertor ENERCON E-16 (7 MW) Multipole synchronous genertors my not need gerbox (these genertors hve lrge dimeter). This is expected to be the most common wind turbine configurtion in the future. 10

11 Vrible-speed wind turbines Vrible speed The frequency of the genertor voltges cn be different from the electricl grid (50-60 Hz) nd therefore the turbine speed cn chnge. Advntges: - More energy production. - Less mechnicl stress. - Reduce power fluctution. - Cpcity of noise reduction. - My hve more control on the grid currents. Drwbcks: - The system requires power electronic converters. - More expensive. 11

12 Vrible-speed wind turbines Wind turbine components 1

13 Vrible-speed wind turbines Permnent mgnet synchronous genertor 13

14 Wind turbine system bsed on PMSG Wind Turbine Modeling Vrition of Power coefficient C p with Tip Speed Rtio (for fixed vlues of β) 0.5 C p P P mechnicl wind Cp C pmx = 0.48 ß=0 ß=.5 ß=5 ß=7.5 ß=10 ß=1.5 ß=15 ß=17.5 ß=0 0.1 λ opt = Tip speed rtio λ 16

15 Control opertion Are of different control opertion Control regions for the WT PN Power (kw) 1 3 Vmin Wind speed (m/s) Vmx First intervl Second intervl Third intervl vrible speed nd fixed pitch vrible speed nd vrible pitch fixed speed nd vrible pitch 18

16 Power Electronic Converter topologies of wind turbine Power electronic Semiconductors Source: L.M. Tolbert, High Power Electronics for Sustinble 1st Century, NSF Workshop for Sustinble Energy Systems, The University of Tennessee, Dec. 000, Atlnt, Georgi. 19

17 Power Electronic Converter topologies of wind turbine Bck-to-bck-connected conventionl two-level AC/DC/AC Wind-Turbine Two-Level Converter Grid-Connected Two-Level Converter Multipole Synchronous Wind Turbine PMSG b c v C C r s t 3*L Electricl Grid v r v s v t v C1 C The mximum voltge tht the trnsistors hve to withstnd is the totl dclink voltge ( ). Low qulity output voltge spectr. This implies lrge vlues of the rective components to filter the output currents 1

18 Power Electronic Converter topologies of wind turbine Modultion Strtegies The modultion stge in power electronic converter is responsible for defining the stte of the switches from continuous (or smpled) control vribles.

19 Power Electronic Converter topologies of wind turbine Modultion Strtegies Hlf-Bridge Inverter + - C (0) T ( s ) () v v C T ' ( s ) To void shortcircuits, only one trnsistor is ctivted t ny time. The control functions define the stte of the trnsistors. They cn tke two vlues s ={0,1} mening 0 =off nd 1 =on. 3

20 Power Electronic Converter topologies of wind turbine Modultion Strtegies If the upper switch is ctivted (ON stte), the output voltge becomes v 0 =+ / independently of the current direction C (0) C T T' () V v v 0 dc v v C (0) C T T' () V dc The upper trnsistor crries the output current The upper diode crries the output current 4

21 Power Electronic Converter topologies of wind turbine Modultion Strtegies If the lower switch is ctivted (ON stte), the output voltge becomes v 0 =- / independently of the current direction. + - C (0) T () v v 0 V dc + - C (0) T () v v 0 V dc + - C T' + - C T' The lower trnsistor crries the output current The lower diode crries the output current 5

22 Remrks Power Electronic Converter topologies of wind turbine Only one trnsistor from the leg cn be ctivted t ny time (ON stte). The trnsistor ctivted defines the output voltge level, independently of the output current direction. Only two voltge levels cn be obtined t the output (v 0 = /). If sinusoidl wveforms re needed, the output vrible (voltge nd/or current) hs to be filtered. The switching process is crucil (clcultion of the ON nd OFF times) to chieve good output voltge spectrum which cn be esily filtered. This process is determined by the modultion strtegy. 6

23 Power Electronic Converter topologies of wind turbine Sinusoidl PWM (SPWM) v s (modultion) v T (crrier) + - C (0) T () v v 0 V TM V SM 0 p p s t + - C T ' / v (output voltge) v 1 Fondmentl component <> instntneous men vlue Modultion signl (sinusoidl): v s (t)=v SM sin s t Trnsistors control: If v s v T T ON v=v 0 =+ / If v s <v T T ON v=v 0 =- / - / 0 p p s t 7

24 Power Electronic Converter topologies of wind turbine Bck-to-bck-connected conventionl three-level AC/DC/AC Wind-Turbine NPC Converter Grid-Connected NPC Converter Multipole Synchronous Wind Turbine v C C Electricl Grid v r b c V d i wt (NP) i g r s t 3*L g v s v t C v C1 The trnsistors hve to withstnd only hlf of the totl dc-link voltge ( /). The output voltge spectr hve better qulity. More switching frequency in the power devices 8

25 Power Electronic Converter topologies of wind turbine Three-level or neutrl-point-clmped (NPC) converter 1 1 v C C v C C s 0 s 1 i v C1 0 C b c v C1 0 C s -1 s b0 s b1 s b-1 s c0 s c1 s c-1 i b i c b c -1-1 Functionl digrm Two consecutive switches must be in on-stte 9

26 Power Electronic Converter topologies of wind turbine Sinusoidl pulse-width modultion SPWM It is bsed on compring sinusoidl modultion signls with tringulr crrier of significntly lrger frequency. v C 0 i 0 (NP) v C1 1-1 C C s 4 s 3 s s 1 s b4 s b3 s b s b1 s c4 s c3 s c s c1 b c temps/t Control pplied to define the stte of the output voltges: Reference bove both crriers High level output (1). Reference between both crriers Medium level output (0). Reference below both crriers Low level output (-1). 31

27 Power Electronic Converter topologies of wind turbine Simultion Results m=0.8 -Wye-connected lod R=1 Ω nd L= mh. -C=00 µf - =1800 V -f =50 Hz 33

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