28-07-2011, 03:44 PM
Abstract
In this paper, the mathematical model of
STATCOM based on space vector theory is presented. The
voltage equations are transformed into the synchronous rotating
reference frame (dq-axis). The relationship between STATCOM
parameters and stability, transient and steady state
performances are determined. Stability investigation with Routh-
Hurwitz criterion indicates that the STATCOM is a stable
system and the numerical values of resistors, inductors and
capacitors in the STATCOM equivalent circuit have no effect on
stability. Steady state analysis reveals that the size of dc capacitor
does not affect STATCOM steady state performance. The
dynamic performances in terms of varying parameters are
displayed in the forms of both root locus plot and Bode plot.
The behavior of STATCOM for voltage regulation was
simulated with ATP-EMTP. The case study was made on a 230
kV radial system. With simple PI controllers and Modulus
Optimum design criterion, the voltage response to 3% step
change of the reference showed approximately 5% overshoot and
the settling time was within three cycles.
Index Terms--ATP-EMTP, FACTS, Modulus Optimal, Space
Vector, STATCOM, Voltage Regulation
I. INTRODUCTION
HE STATCOM, which is a short name for Static
Synchronous Compensator, is a second generation
FACTS or Flexible AC Transmission System device. It is
classified as a shunt compensator.
Basic STATCOM circuit (Fig. 1) consists of a voltage
source converter (VSC) and a dc storage capacitor. The VSC
converts ac voltages ( VA,VB,VC) to dc voltage level on the dc
side (UDC). The capacitor voltage can be adjusted by
controlling the phase angle difference between line voltage
(U) and VSC voltage (V). If the phase angle of line voltage
(U) is taken as a reference, the phase angle of VSC voltage
(V) is the same as the firing angle (δ) of VSC. Thus, if the
firing angles are slightly advanced, the dc voltage (Udc)
decreases and reactive power flows into STATCOM.
Conversely, if the firing angles are slightly delayed, the dc
voltage increases and STATCOM supplies reactive power to
the bus. By controlling the firing angles of VSC, the reactive
power can be generated from or absorbed by STATCOM and
the voltage regulation can be achieved.
Nitus Voraphonpiput is with Power System Analysis Department, Control
and Protection System Division, Electricity Generating Authority of Thailand,
Nonthaburi, Thailand 11130 (e-mail: nitus.v[at]egat.co.th).
Somchai Chatratana is with the National Science and Technology
Development Agency, Thailand (e-mail: somchaich[at]nstda.or.th).
Fig. 1. Basic circuit of STATCOM
II. STATCOM DYNAMIC ANALYSIS
An example radial system with STACOM is shown in Fig.
2a. Rd is included to represent small losses in the switching
devices of VSC. R and L represent the equivalent circuit of
the tie-transformer between bus U and V.
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