JOl KNALOFSC H NC K&IKCIINOLv/v i ^ I "^li ( y 13 itij I \ C ONTROL OF HI DIRKC IIONAL CONVERTER IN BATTERY ENERGY S T 0 R A ( ; E S \ S lEM (BESS) FOR PEAK POWER SHAVING DILU KlllLN B( )Bn,N DOI IlAl[.]
Trang 1JOl KNALOFSC H.NC K & I K C I I N O L v / v i ^ I "^li ( y 13 - itij I \
C ONTROL OF HI-DIRKC IIONAL CONVERTER IN BATTERY ENERGY
S T 0 R A ( ; E S \ S lEM (BESS) FOR PEAK POWER SHAVING
DILU KlllLN B(.)Bn,N DOI IlAl 11U(')NG I KON( I 1 IL I JCl 1 fRlT NANG LUONG
DUNG AC(.)UY (BfSS) BU (•(")N(i SUAf DlNll
N}iO Due Minh Thainguyen ('niveisilv
Nguyen Van Lien
Hanoi Ihiiversitv ofScience and 'I'echnology
ABSTRACT
The issue that the isolated flexible electric grid face is shod time peak power (active and reactive) demand for starting of induction motor, in this shod time the generation can not ramp up for keeping up with the demand and then the starting up can be failled This paper presents a scaled down Battery Energy Storage System (BESS) for peak load shaving applications The design includes
a bidirectional converter capable of intedacing a battery bank with the AC power gird In order to match dynamic response of the BESS and to take simplicity for implementation algorithms based on microprocessor or digital signal processing systems (DSP), the authors propose a convetional PID controller for the BESS The experiment shows good results
IOM TAT
l^ang dien cue bd linh hoat phdi ddi mat vdi thwc ti Id thwdng xuyen cd nhu ciu phu tai cdng suit dinh (tdc dung vd phdn khdng) ngdn han di khdi ddng cdc ddng ca khdng ddng bd, trong khodng thai gian rit ngdn nay mdy phdt khdng kip huy ddng cdng suit, kit qud Id cdc ddng ca khdng khoi ddng dwgc Ndi dung bai bdo nay danh cho viec thiit ki he thing Iwu trir dien acquy (BESS) img dung di san phu tdi dinh Thiit bi bao gdm mdt bd biin ddi hai hwdng cd khd nang lien kit ddn acquy vdi Iwdi dien xoay chiiu Di ddp wng ddng hoc cua BESS du nhanh vd dan gian, bat bdo nay da sif dung thuat diiu khiin dwa tren vi xir ly hodc he thing xw ly tin hieu sd (DSP), cdc tdc gid sw dung bo diiu khiin PID thdng dung Viec tiin hdnh thwc nghiem da cho cdc kit qud khd tdt va qua dd cd thi diic rut kinh nghiem cho thiit ki he thing
Nomencleature
PLL-Phase Look Loop
PCC-Point of common ccnipling
L INTRODUCTION
In Flexible AC Transmission Systems
(FACTS), the Batterv Lncrgv Storage Svsiems
(BESS) arc used as compensators connected
parallelly with loads at a PCC in thc grid
Specifications of BI-^SS have been researched to
stabilize voltage of the grid (compensation o\'
reactive power), to shave daily load trend
(receiving and generating active power al
different time-interval at a da> ) etc In the case
of small hydro-electric canal-type power
station, BESSs play an important role when
they integrate a function of peak power
compesation for starting motors
As motors start, a large amount of power (about 5-7 times of norminal power) must be required in some seconds However, characteristics of active power control of small hvdro-elcctric generators have long delay-time,
so the\ could not response in time (Fig 2) That time makes a chance for BESS to generate supplementary power to help the motors start successfullv and stabili/c the grid
C»nal(L, q.)
Fig I Small hydro-power station
16
Trang 2JOUHNAL OF SCIENCE & TECHNOLOGY * No 79B - 2010
50
N 40
I
i ^ 3 0
^ 2 0 ^
2 3 4 5 6 7 8
Time (s)
Fig 2 Unstable frequency when induclicvi
motor begins to start
In order to control BESS, one can use
grid voltage-oriented approach (VOC) with
PID convential controllers or direct povver
control approach with hvstercsis of 2- or
3-position controllers [2 4] Both of these
approaches have advantages and disadvantages
as well However VOC approach with PID
controllers is more appropriate due to it does
not require stricly in identification of svstem s
parameters
IL MATHEMATICAL BACKGROUND
AND DESIGN OF A CONTROLLER
2.1 Instantaneous power control
In the rectangular coordinate (dq), that
rotates synchronously with space voltage vector
at PCC, components id iq Ud Uq will be
slow-varying quantities According to the concept of
space vector, vve can get:
u = u^+ju^ l = 'j+J'a
thenp — Re(u.i ) ; q = Im(w./ )
(4) (S)
That leads the similar expressions for
calculating instant power
P = -(Uj-ij+Uc,f,) 'I 'I'
m
-{u^.i,-Uj.l)
If the axises d,q are oriented exactly on
the grid-voltage space we will have
and:
P = ~^'.i-'.i
(7)
'/ — u,.i
0 '' '/
At PCC, (Fig 3), we have equations for balancing power
Pr = P, + P,
Qr=Lf+Q,
(8)
If the source is isolated and soft, BESS will create power buffer between the load and the source to ensure stabilization and to improve economics of the system in load-varv ing mode, especially in the worst case, when induction motor begins to start The model in our study has been described in Fig 3
PCC
Source
IN IT
I
Load
Battery;
^
— ( Q ) Motor
BESS
Fig 3 Block diagramn of soft power network integrated with BESS
Set values for power BESS can be calculated as follows:
Due to the voltages at PCC are equal, then (9) can be
^clB^ref ~~ ^cIT ^cIN
(10)
c/H_rcJ v-v
where ijN and i,jN are given constants depended
on limited power barie of the source
2.2 Designing of current regulator
From [3, 4] one can have mathematical model on coordinate system dq as follows:
Trang 3l O l U N A L Ol S( IEN( K & TECHNOLOGY * No 79B - 2010
',v,/ = /^'
^ , f<'.l
\ L-f- \ u,,-.el.i
dt
dl
1 / ; +//,,+^./,/,
dl
(11)
where /,/,, current inputs of convcilci
//\,/,, voltages at PCC
//>,/,, voltage inputs of converter
Thc purpo.sc o\' current controllers is to
control the actual currents tracking to thc set
value and to eliminate coupling effections
between components d.q and disturbance from
grid-voltage ii\.i That helps to design current
controllers with decoupling structure as
described in Fie 4
Closed transfer function of the current loop can bc calculated as
ik.i
•- coL
- K
P
Us
Fig 4 Current Controllers
In order lo calculate parair.ctcrs of
current controllers, vve assume the coupling
effect be eliminated (due to the compensation
of decoupling) The current loops have a
simpler structure as depicted in Fig 5
/,„ Lp-+(R + K)p + K, (12)
/,/
P p
R^L.p
R+Lp
Pig 5 Simplified structure of current loops
lo avoid possible svstem saturations the control action was kept below 1 Dynamics of current loop will be improved when poles of plant are eliminated by controller Then zeros of the loop will be set as time-constant of current controller, linallv the parameters of current controllers can be calculated as below
R_
Block diagram for controlling BESS coiinet.n.u wiil, sni.i!! isolated hydro-electric grid in this case can be designed in Fig 6 [3]
PCC,
•t- ' Load
t ' l e i
\ I ' " ' "
'Sd OqA, ' B « 'so 'flc
/ I
U P C C
Ru
0\
-
aq-Ri
' Bd ' \ ' UB^^^—T-^
J L
l—n — —
" « ^ ! SVM
•'H-battery
Fig 6 Block diagram of the system
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Isolate Circuit
^;
BAUMULLER P.Bbc IF n e i a l
I - * CT / R Ch
PS 24VDC
III EXPERIMENTAL
3.1 Experimental model of BESS
From the structure and objective of
experiment, the experimental model has been
build up at The Key Automation laboratory,
Hanoi University of Technology (Fig 7)
Main equipments include:
Dsl 104 Card in PC Computer
Power converter BUS623
Fig ~ Experimented system of BESS
in order to receive characteristics that are similar to isolate soft grid
Parameters for the controllers can be calculated as follows: BESS will provide 70%
power for starting motors, the lelf power will
be taken by the supplier
3.2 Experimental results
Some basic experimental results have been shown in Figs 8-12
Batteries of 12V/7Ah for DC voltage
source of 630V
Experimental Load:
Induction motor of 2.2 kW
Induction motor of 3kW
Sensors:
Transformers of 220V/6V ratio for
measuring voltage
Measuring load current by current
transformer with 150A/5A
As motors start with heavy load, the
starting time will be long Then in order to
check performances of BESS, we choose the
starting mode with no load The motor under
the experiment is squirrent cage induction
motor of 2.2 kW 380/220V 50 Hz Supplier
has been created from 3-phase source and
combinated with equipment for limiting power
10O0O 8O00
• 6O00 4O0O 2O00
K
iiTfviSSgssssi f''" —'V j"»"i'»ii
i %—I » I I — « — t — t — I — I — > I
BESS 3 S 3 8 4 0 4 2 4 4 4 6 4.3 t(s)
Fig 8 Active power of load and BESS
r7;0\ ,-|n|x|
15000•
10000
-f
Q-5000
0
- - - -
\l_
k-^-r-^- ttMtW
Fig 9 Active Power from the soft grid
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"1
m
,1 II II 1
' , 1 I I I I 1
' f i T i r i
1
1
i ' :• ' - : •: 4 11 4 ' •
.-.|n|
, , » ,
; •} f 4 ,-;
l-'ig 10 Reactive powers of load and BFSS
bULI
5 5 0
500 •' ••—'—'—'—'—•—'-'-^»^—'—'—'—'—'—>—I
3.8 3 9 4 0 4 1 4.2 4 3 4.4 lis)
/••/,L; / / AC-ciii i''iii\ of h)ii(l (Iiul P,ESS
IV C O N T L l S I O N S
|-^xperimcnl.'il lL•>llll^ in ini|-ilcnicnting compensation ul ptak |-)II\VL-I m var_ving4oad mode play impui-iani lolc lor developing of
small isolated solt 'i\-\i\ such a> wind generator
small hydro-eU'Lii IC NUIIIOH M'lar cell park etc
With the battciA bank ^A 4410 \ ' \ thc BESS
can supply povsci- with high rate (dP dl = 70 kW/s) In the com inu iinic wlicii B l : S S s u s c t h e energy storages liv supcr-ca|\iciotors instead of batteries, then Bi SS will be more attractive
Fig 12 DC-voltage on batterv Lh hiill, r\
REFERKNC KS
1 Xiao-PingZhang, Christian Rehtanz Bikash Pal flexible AC Tr.iMsiMi.Moii Svstems: Modelling
and Control lSBN-10 3-540-30606-4 Springer Berlin llerdelberg \CN^ ^ n k :o^K^
2 Bui Quoc Khanh, Nguyen Van Lien; Base of electric machines drive; Science cV fechnology
Publishing House, Ha Noi, 2006
3 Ngof^ucMinh, NguyenVanLien Dynamic iniprovement of B l S s nMug deadbe.ii iv pe controller
in local power networks (II'EE Viet Nam Section, International I oi um on Siratciiic fechnologies (IFOST) 2009, 21-23 October 2009 in IloChiMinh Cilv Vietnam )
4 Antti 'farkiainen, et al; Current controled line convcr using direct loniue coniiol method Euro Trans Electric Power 2004
Author s address: Ngo Due M i n h - lei.: (+84) 982.286.428 email: ngoiniiilulue238 </gmail.com
Thai Nguven University - Tan Thinh Ward, Thai N>:uven Citv