Simulation of Static Synchronous Compensator (STATCOM)
1
Dong Ju Lee1, Eun Woong Lee1, Jong Han Lee 1, Jong Gyeum Kim2
Department of Electrical Engineering, Chungnam National University, Daejun, Korea
2
Department of Electrical Engineering, Wongju National University, Wonju, Korea
Abstract—Two types of controllable reactive power
generator are discussed. One is static var compensator
(called as SVC) and the other is static synchronous
compensator (called as STATCOM) whose performance is
higher than SVC at a view point of a continuous
controllability of reactive power and response time. In this
paper, basic principle of STATCOM operation and the
functions of each component are explained. 30kVA
STATCOM system is practically to develop a cost-effective
and
compact
compensator.
Its
basic
operating
characteristics are verified by the simulation
absorb the reactive current. It can be treated as a shuntconnected reactive admittance. For example, thyristorcontrolled reactor (TCR), thyristor- switched reactor
(TSR) and thyristor -switched capacitor (TSC) are typical
SVC system.
The other is a static synchronous compensator (STAT
COM) whose output is adjusted continuously to inject or
absorb the reactive current. It can be treated as a shuntconnected synchronous voltage source. Comparison
results between SVC and STATCOM is shown in Table I.
1. INTRODUCTION
TABLE I. COMPARISION BETWEEEN SVC & STATCOM
Recently, most of the critical loads in an industrial low
voltage AC system have an unbalanced and/or nonlinear
characteristic because it is a single-phase rectifier with a
capacitor or thyristor-based three phase rectifier. The
unbalanced and nonlinear characteristic of the load has an
undesirable effect on the power quality of input utility
mains and adjacent load side. Therefore, reactive power
should be generated and compensated properly to
improve the power quality of input utility mains.
Typically, the response time and the bandwidth of the
closed voltage regulation loop of the STATCOM which is
a shunt-connected synchronous voltage source are
significantly better than those of the SVC which is a
shunt-connected reactive admittance. Consequently,
STATCOM can be more effective than SVC in an
industrial low voltage AC system.
In this paper, operational principle and basic control
loop of STATCOM are described. Also, control loop to
compensate the unbalanced load and nonlinear load is
discussed in detail. Its performance of the control loop of
STATCOM in unbalanced and/or nonlinear load
conditions is verified by PSIM simulation software. These
results can be used for the software implementation in the
prototype STATCOM system
Nowadays, unbalanced load or nonlinear load (e.g.,
single phase lighting load, computer load or inverter to
drive induction motor) have a bad influence upon the
power quality of utility mains. Also, it is necessary for
reactive power to be compensated because the most of
industrial loads is inductive and make a lagging
displacement power factor.
There are two type of controllable reactive power
(shunt) generator. One is a static var compensator(SVC)
whose output is adjusted discontinuously to inject or
Items
SVC
STATCOM
Function
Addition of reactive
Admittance
Voltage source to be
synchronized with
input mains
Continuity of control
Discontinuous
Continuous
Control
Phase control
PWM Control
Phase delay (max.)ax.
0.5 ~ 1 cycle
Very few
Low-order harmonics
Much
Small
Filter capacity &
Installation space
Large.
Small
(100%)
(30 ~ 40%)
Size of reactive
components
Bigger
Small
Loss
Bigger
Very small
Response
Slow
Very fast)
Generally, STATCOM is more effective and more
rapid compensator than SVC regarding to V-I
characteristic, V-Q characteristic, transient stability and
response time.[1] Many researches about the analysis and
design method of STATCOM system had been already
done at reference [2][3].
In this paper, basic principle of STATCOM operation
and the functions of each component are explained.
Prototype 30kVA STATCOM system is practically
designed according to reference [2] to develop a costeffective and compact compensator. Its basic operating
characteristics are verified by the simulation
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2 PRINCIPLE OF STATCOM OPERATION
A. System configuration
Fig. 1(a) shows the basic configuration of STATCOM
system.
AC M AIN S
Vs
Is
I inv 1
Link
reactor
(L1)
V inv 1
DC
Capacitor
(C1)
IL
Voltage Source Inverter
(with or without independently
regulated dc source)
LO A D
As we know at equ. (1), there are two different
methods of controlling the inverter output voltage to
generate the leading or lagging reactive power from VSI.
One is to change the dc capacitor voltage indirectly by
controlling the phase angle between inverter output
voltage and source voltage of utility mains. STATCOM
without independently regulated dc source can be
controlled by this method.
The other is to control the modulation index of the
inverter switching pattern directly while dc capacitor
voltage is separately regulated well by another controller.
STATCOM with independently regulated dc source can
be controlled by this method.
To achieve more fast dynamic response of reactive
power compensation while dc capacitor voltage is
regulated well, modulation index control for the required
reactive power generation and phase angle control for the
regulation of dc capacitor voltage can be done at the same
time.[4]
(a) Configuration
Is
3 DESIGN OF STATCOM
A. Design specification
L1
Vs
Design specification of 30kVA prototype STATCOM
is shown in Table II.
TABLE II. DESIGN SPECIFICATION
Item
Specification
V in v 1
if V in v 1 > V s , I s = lead in g cu r r e n t
if V in v 1 < V s , I s = lag g in g c u r r e nt
(b) Single phase equivalent circuit
Fig. 1. STATCOM system based on VSI
STATCOM based on VSI (voltage source inverter) is
a synchronous voltage source connected to the utility
mains in parallel through a link reactor(L1) as shown in
Fig. 1(a).
Switching device can be GTO for high voltage, high
power application or can be IGBT for low voltage, low
power application. It is necessary to note that the size of
dc capacitor in STATCOM is considerably smaller than
the general ac capacitor for direct power factor
compensation.
30kVA
Rated input voltage
380/220V
Rated input frequency
60Hz
Total harmonic distortion of ac
input current
Less than 5%
B. Design results
Prototype 30kVA STATCOM system is designed to
develop a cost-effective and compact compensator.
Inductance and power rating of link reactor (L1) can
be calculated by equ. (2) and equ. (3). Dc capacitor can be
selected by equ. (4) and equ. (5)
Design results are summarized in Table III.
4⋅
B. Injection and absorb of reactive power
X L1 =
As explained in Fig.1(b), inverter output voltage
should be controlled to inject or absorb the reactive
current on STACOM. Inverter output voltage of VSI can
be generally expressed by equ. (1).
Vinv _ peak = MI ⋅ Vdc
Output power rating
∞

1  n +1
⋅  2 ⋅ ∑ (−1) j +1 cos(k ⋅ α j ) − 1
4 
 j =1

∑k
k =5
π ⋅ MI ⋅ THDi − 4 ⋅
∞
1
∑
4
k =5 k
2
(2)
 n +1

⋅  2 ⋅ ∑ ( −1) j +1 cos(k ⋅ α j ) − 1
 j =1

2
where, k : harmonic order
αj
: j th angle of switching pattern.
(1)
2
where, Vinv _ peak : inverter output voltage(peak) [V],
MI : modulation index of switching pattern,
Vdc : dc capacitor voltage [V]
2
2 ⋅ Rf ⋅ Vdc
X C1 =
3⋅
1402
(
S L1 = X L1 ⋅ I s 1 + THDi
∞
1
2
⋅ (Ak −1 + Ak +1 )
2
k
k =6 ,12
∑
)
(3)
(4)
Ak =
respectively. Vsa is phase voltage of ac mains, Isa is
phase current of ac mains and Ic is input current of dc
capacitor
It is verified in Fig. 3 that that STATCOM is being
operated as a capacitor load or inductive load depend -ing
on the operation mode (leading compensation or lagging
compensation)
4  n +1

⋅  2 ⋅ ∑ ( −1) j +1 cos(k ⋅ α j ) − 1 (5)
k ⋅ π  k =1

where, Rf : ripple factor of dc capacitor.
k : harmonic order (=6, 12….)
Ak : Fourier coefficient of the switching pattern.
TABLE III. DESIGN RESULTS
Item
Specification
Link reactor
4.851 [mH], 3.8kVA
dc capacitor
102 uF
Peak current
Peak reverse
767.8[V]
blocking voltage
Modulation index (MI)
αj
Isa
64.9 [A]
of switching device
Switching pattern (
Vsa
)
Ic
1.12
4.4, 10.8, 14.1, 21.1, 23.4,
31.6, 33.0 , 42.3, 43.1, 65.0,
66.3, [Deg]
(a) Lagging compensation mode
4 MODEL AND SIMULATION
A. Simulation model
Isa
STATCOM system without indepe
ndently regulated dc source is modeled for simulation
as Fig. 2 and reactive power is generated by the phase
angle control.
Vsa
Ic
(b) Leading compensation mode
Fig. 3. Simulation results
5 CONCLUSION
In this paper, basic principle of STATCOM operation
and the functions of each component are explained.
30kVA STATCOM system is practically designed and the
basic operating characteristics are verified by the
simulation.
(a) Voltage source converter
REFERENCES
[1] N. G. Hingorani and L. Gyugyi,, "Understanding FACTS”, IEEE
(b) dc voltage controller and reactive power controller
Fig.. 2. Simulation model of 30kVA STATCOM
B. Simulation results
Lagging and leading compensation of the designed
STATCOM system are shown in Fig. 3(a) and Fig. 3(b)
Press, 1999.
[2] Luis T. Moran, Phoivos D. Ziogas and Geza Joos, “Analysis and
Design of a Three-Phase Synchronous Solid-state Var
Compensator”, IEEE Trans. Ind. Appl., vol. 25, no.4 , pp. 598-608,
July/Aug., 1989.
[3] Hassan Ali Kojori, Shashi B. Dewan and J. Douglas Lavers, “A
Large-Scale PWM Solid-State Synchronous Condenser”, IEEE
Trans. on Ind. Appl., vol. 28, no. 1, Jan./Feb., 1992.
[4] Guk C. Cho, Nam S. Choi, Chun T. Rim and Gyu H. Cho,
“Modeling, Analysis and Control of Static VAR Compensator
Using Three-Level Inverter”, IEEE Ind. Appl. Society Annual
Meeting, pp. 837-843, 1992.
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