Design, Control and Application of Modular Multilevel Converters for HVDC Transmission Systems by Kamran Sharifabadi, Lennart Harnefors, Hans Peter

Transcription

1 Desgn, Control an Applcaton o Moular Multleel Conerters or HVDC Transmsson Systems by Kamran Sharaba, Lennart Harneors, Hans Peter Nee, Staan Norrga, Remus Teoorescu ISBN 0: Copyrght Wley 06 Chapter 4 Control uner Unbalance Gr Contons

2 Gr Requrements Challenges: VDE AR N 40 GC (D) Neg.sequence q Pos. sequence q Internal balancng o MMC cu, l Current saturaton

3 Conentonal Vector Control Fltere PLL remoe neg. seq. n oltage Can not control current sequence components to GC res. * s * sq * P 3 Q 3 *

4 Conentonal Vector Control BAD! Double req oscllatons n Reerence * s goes to sat! Unesre neg. seq. s s GOOD! Reuce P rpple Reuce c rpple s No rpple n c Flterng o n orer oscllaton s necesarry!

5 PLL wth Notch Flter Notch lter Resonant lter h= H n s ns s s s s s n n Secon orer BW LPF H LPF s s b bsb Resultant prelter H s H s H s p n LPF The notch lter wll lter out the secon orer harmonc rom the gr oltage

6 Conentonal Vector Control BAD! Can not nject negate sequence! GOOD! The secon harmonc oscllatons are remoe n s Same reuce c oltage an crculatng current rpple Component base control s necesarry!

7 Synchronzaton n Decouple Double Synchronous Reerence Frame DDSRF PNSE Bascs cos( t ) cos( t ) s V V sn( t ) sn( t ) cos( t) T V V q 0 sn( t ) cos( t) T V V q sn( t ) 0 T cos( ) sn( ) T T sn( ) cos( ) Soluton: Challenge: Couplng between comp. n Double requency oscllatons Decouplng Network!

8 Synchronzaton n Decouple Double Synchronous Reerence Frame DDSRF PNSE Decouplng Network * * * q F T * * * * q F T * T T sn( t) cos( t) T F s 0 cos( t) sn( t) 0 s Due to LPF, PLL can be UNFILTERED s θ s TF n statonary!: Decouplng network s s s s s s s - Teoorescu, R.; Lserre, M.; Rorguez, P., "Control o Gr Conerters uner Gr Faults," n Gr Conerters or Photooltac an Wn Power Systems,, Wley-IEEE Press, 0

9 Synchronzaton n Double Secon Orer Integrator DSOGI PNSE s s s q T ; T q s q T ; T q SOGI S S QSG, q α β ω α β SOGI QSG α, β q β PNSE α α - β - S- TF n statonary!: s k s s ks s s s ω k SOGI x x s s s' q s' α qα β qβ / / s s - Dynamcs o DSOG etermne by No couplng between components! Teoorescu, R.; Lserre, M.; Rorguez, P., "Control o Gr Conerters uner Gr Faults," n Gr Conerters or Photooltac an Wn Power Systems,, Wley-IEEE Press, 0

10 Synchronzaton n s DDSRF PNSE s DSOGI PNSE Same ynamcs wth: K,, k DSOGI more robust as t epens on oppose to DDSRF () DSOGI nul rotatonal transormatons DDSRF 4 DSOGI No Decouplng Network!

11 Synchronzaton n Recap: Instantaneous Power Theory n or ac c conerters p P P cos t P sn t c s p qq Q cos t Q sn t c s q 4 egrees o reeom Q c, Q s - neglecte P q q Q 3 q q q Pc q q P s q q q A * P * q * A Q 3 Pc * P q s Only poste seq: * V, 0 * * q q 0 * q P 3 Q 3

12 Injecton Reerence Strategy Flexble Poste Negate Control FPNSC * k k k k P Q * p * q Inst. Power Theory Droop actors: K acte K reacte abc ; a ; abc 3 a 0 0 q 0 o k = : Injecton o pos. seq. Q => Gr oltage pos. seq. support o k = 0: Injecton o neg. seq. Q => Gr oltage unbalance compensaton (reucton o oltage neg. seq.) o 0<k < : Smultaneous Injecton o pos. an neg. seq. Q

13 Injecton Reerence Strategy Flexble Poste Negate Control FPNSC Instantaneous P elere to the gr: p P p P p Pk P k P k P k Q k Q k p 0 Not possble to sole or K an K!

14 Injecton Reerence Strategy Poste Sequence Injecton wth oscllatng P k = k = * P Q * * p q V, 0 q * * q P 3 Q 3 PSI LVRT requrement or reacte component: * P 3 * q k0.9 V Balance njecton wll not cancel the oscllatng terms P c, P s whch wll generate ouble requency rpple n P an Q.

15 Injecton Reerence Strategy Mxe Sequence Injecton MSI Accorng to PSI LVRT an NSI LVRT * P 3 * q k(0.9 V) * 0 * q k( V 0.05) For any gen P the poste an negate component o the reacte current are calculate accorng to GCs

16 Improe Vector Control n DDSRF PNSE Base θ PLL a b c abc a s a DDSRF a a - From measurements a b c a a - k k - abc s s DC bus oltage Controller * Poste Negate Sequence Reerence Generator s s * s -* θ DDSRF θ s s - a Negate Seq. output current controller s -* a - Poste Seq. output current controller s * abc θ abc -θ s abc θ 0 To nternal control

17 Improe Vector Control n DSOGI PNSE Base PLL a b c abc a s DSOGI-PNSE a S a S- θ a a - From measurements a b c c* a a - k k - abc DC bus oltage Controller c s Poste Negate Sequence Reerence Generator sc * s * θ Output current controller s * s * abc a * b * c * 0 To nternal control The two control methos can be esgne ynamcally equalent. In terms o mplementaton DSOGI s more smple an requre less computatonal buren!

18 Smulaton case Test conerter Recter moe 00MW c power Unbalance ault (V = 0. pu an V = 0.8 pu at t =.s) Output current controller: PR(α c = 000 ra/s, α h = 50 ra/s) PLL on pos. seq. oltage (α p = 50 ra/s, α p = 0 ra/s, α b = 000 ra/s ) PSI LVRTan MSI LVRT moes

19 DSOGI PNSE PSI LVRT MSI LVRT Goo perormance on c se or both strateges!

20 DSOGI PNSE The rpple on the c bus an crculatng current are elmnate (ater a short the transent pero), conrmng the nng n Secton 3.3.7, Equaton (3.53). The resonant control o crculatng current s proen eecte urng unbalance gr contons beng able to control the crculatng current to a c alue ater a transent. MSI LVRT s exhbtng larger rpple n the power an n the sum capactor oltage than PSI LVRT, whch s to be expecte ue to the unbalance njecte currents Due to the negate reacte current njecton, the MSI LVRT strategy s able to reuce the gr oltage negate sequence rom 0. to 0.5, whch s a esrable eect

21 Conclusons The recent gr coes or large scale generaton requres nepenent control o both poste (PSI LVRT) an negate (NSI LVRT) reacte current njecton. PSI LVRT can be ullle wth conentonal control enhance wth a notch pre lter n the PLL structure. NSI LVRT ullment requres mprong the conentonal control by ang PSNE an component base current control structures. DDSRF PNSE an DSOGI PNSE can be esgne to be ynamcally equalent. Statonary an synchronous control strateges can be esgne to be ynamcally equalent, but statonary control s less complex (ewer transormatons an controllers, no nee o ecouplng) an more robust urng unbalance aults, as t uses the gr requency nstea o the gr angle. Also, current reerence lmtaton s lesscomplexnstatonaryrameasthe sequence components can be ae algebracally. For crculatng current suppresson, the PR controller (h = ) an Ra=0 Ω proes to be ecent urng unbalance gr aults as s capable o controllng the crculatng current to acalue MMC HVDC wth PNSE an resonant control can comply wth both PSI LVRT an NSI LVRT smultaneously wthout olatng the lmts or njecte current, c bus oltage or sumcapactor oltages. O course ths stuy s usng the aerage arm moel, assumng that all capactor oltages n the arm are entcal.