ABSTRACT:
A
multi-pulse GTO based voltage source converter (VSC) topology together with a
fundamental frequency switching mode of gate control is a mature technology being
widely used in static synchronous compensators (STATCOMs). The present practice
in utility/industry is to employ a high number of pulses in the STATCOM,
preferably a 48-pulse along with matching components of magnetics for dynamic
reactive power compensation, voltage regulation, etc. in electrical networks.
With an increase in the pulse order, need of power electronic devices and
inter-facing magnetic apparatus increases multi-fold to achieve a desired
operating performance. In this paper, a competitive topology with a fewer
number of devices and reduced magnetics is evolved to develop an 18-pulse,
2-level + 100MVAR STATCOM in which a GTO-VSC device is operated at fundamental
frequency switching gate control. The inter-facing magnetics topology is conceptualized
in two stages and with this harmonics distortion in the network is minimized to
permissible IEEE-519 standard limits. This compensator is modeled, designed and
simulated by a Sim Power Systems tool box in MATLAB platform and is tested for
voltage regulation and power factor correction in power systems. The operating
characteristics corresponding to steady state and dynamic operating conditions
show an acceptable performance.
KEYWORDS:
1. Fast
Fourier transformation
2. Gate-turn
off thyristor
3. Magnetic
4. STATCOM
5. Total
harmonic distortion
6. Voltage
source converter
SOFTWARE: MATLAB/SIMULINK
MATLAB MODEL:
Fig.
1 MATLAB model of ±100MVAR 18-pulse STATCOM
EXPECTED SIMULATION RESULTS:
Fig.
2 Three phase instantaneous voltage(va , vb, vc) and current (ia, ib, ic) with
75MW 0.85pf lagging load when V* sets at 1.0pu, 1.03pu and 0.97pu
Fig.
3 Operating characteristics in voltage regulation mode for 70MW, 0.85pf(lag)
load
Fig.
4 Voltage(va) spectrum in capacitive mode
Fig.
5. Voltage spectrum (va) in inductive mode.
Fig.
6. Current (ia) spectrum in capacitive mode.
Fig.
7. Current spectrum (ia) in inductive mode.
Fig.
8 Operating characteristics for unity power factor (upf) Correction in var
control mode for 75MW, 0.85pf(lag) load
Fig.
9. Voltage harmonics(va) spectrum for upf correction.
Fig.
10 Current harmonics(ia) spectrum for upf correction
Fig.
11 Operating characteristics following 10% load injection at the instant of
0.24s in voltage regulation mode on 70MW, 0.85pf(lag) load
Fig.
12 Voltage harmonics (va) spectrum after load variation
Fig.
13. Current harmonics (ia) spectrum after load variation.
Fig.
14 Operating characteristics in var control mode for incremental Load variation
of 10% at the instant of 0.24s on an initial load of 70MW, 0.85pf(lag)
Fig.
15 Voltage harmonics (va) spectrum after the load injection
Fig.
16. Current harmonics (ia) spectrum after the load injection.
CONCLUSION:
A
new 18-pulse, 2-level GTO-VSC based STATCOM with a rating of + 100MVAR, 132kV
was modeled by employing three fundamental 6-pulse VSCs operated at fundamental
frequency gate switching in MATLAB platform using a Sim Power Systems tool box.
The inter-facing magnetics have evolved in two stage sinter- phase transformers
(stage-I) and phase shifter (stage-II), and with this topology together with
standard PI-controllers, harmonics distortion in the network has been greatly
minimized to permissible IEEE-519 standard operating limits [9]. The
compensator was employed for voltage regulation, power factor correction and
also tested for dynamic load variation in the network. It was observed from the
various operating performance characteristics which emerged from the simulation
results that the model satisfies the network requirements both during steady
state and dynamic operating conditions. The controller has provided necessary
damping to settle rapidly steady states for smooth operation of the system
within a couple of cycles. The proposed GTO-VSC based 18-pulse STATCOM seems to
provide an optimized model of competitive performance in multi-pulse topology.
REFERENCES:
[1]
Colin D. Schauder, “Advanced Static VAR Compensator Control System,” U.S.
Patent 5 329 221, Jul. 12, 1994.
[2]
Derek A. Paice, “Optimized 18-Pulse Type AC/DC, or DC/AC Converter System,”
U.S. Patent 5 124 904, Jun. 23, 1992.
[3]
Kenneth Lipman, “Harmonic Reduction for Multi-Bridge Converters,” U.S. Patent 4
975 822, Dec. 4, 1990.
[4]
K.K. Sen, “Statcom - Static Synchronous Compensator: Theory, Modeling, And
Applications,” IEEE PES WM, 1999,Vol. 2, pp. 1177 –1183.
[5]
Guk C. Cho, Gu H. Jung, Nam S. Choi, et al. “Analysis and controller design of
static VAR compensator using three-level GTO inverter,” IEEE Transactions Power
Electronics, Vol.11, No.1, Jan 1996, pp. 57 –65.
