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.
1. Fast Fourier transformation
2. Gate-turn off thyristor
5. Total harmonic distortion
6. Voltage source converter
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.
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 . 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.
 Colin D. Schauder, “Advanced Static VAR Compensator Control System,” U.S. Patent 5 329 221, Jul. 12, 1994.
 Derek A. Paice, “Optimized 18-Pulse Type AC/DC, or DC/AC Converter System,” U.S. Patent 5 124 904, Jun. 23, 1992.
 Kenneth Lipman, “Harmonic Reduction for Multi-Bridge Converters,” U.S. Patent 4 975 822, Dec. 4, 1990.
 K.K. Sen, “Statcom - Static Synchronous Compensator: Theory, Modeling, And Applications,” IEEE PES WM, 1999,Vol. 2, pp. 1177 –1183.
 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.