This document discusses a synchronous link converter var compensator (SLCVC). The SLCVC uses selective harmonic elimination techniques to eliminate the 5th, 7th, and 11th harmonics. The main compensator controls the fundamental component of compensator current by controlling the DC link voltage. An auxiliary converter provides online elimination of higher order harmonics generated by the main compensator. Simulation studies were carried out to evaluate the compensator's performance. Experimental testing verified the control strategy by operating the SLCVC as a load compensator and changing the reference DC link voltage. The SLCVC provided superior performance through effective combination of high power low frequency and low power high frequency switching devices.

1. Synchronous link converter var
compensator
By Humayun Liaqat
12063122-071
University of Gujrat (Pakistan)

2. Introduction
• The traditional methods of reactive volt-ampere
compensation consisting of switched capacitor or
fixed capacitor and phase controlled reactor coupled
with passive filters are increasingly being replaced by
new approaches utilizing the concept of Synchronous
Link Converters.

3. Introduction
• several ter- minologies such as ‘Var
Generators’
• 1) ‘Advanced Static Var Generators
• 2), Synchronous Solid State Var
Compensators
• 3) ‘PWM Inverter Var Compensator’

4. Operating Principle
• The main converter is operated with selective harmonic
elimination technique, so as to eliminate 5th, 7th, and
11th harmonics. Hence the switching frequency of the
main compensator devices is 450Hz. The switching
instants are fixed and the fundamental component of the
compensator current is controlled by controlling the
magnitude of dc link voltage rather than controlling the
modulation index. The auxiliary converter is operated in
current controlled mode and provides on line elimination
of the higher order harmonics generated by the main
compensator

6. CONTROL STRUCTURE
• Var supplied by the compensator is proportional to
the magnitude of the dc link voltage. The var
demand of the load obtained from the var calculator
is used to set the reference dc link voltage command.

8. SIMULATION STUDIES
• Detailed simulation studies are carried out to predict
the performance of the proposed compensator. A
dedicated computer program is developed for the
purpose and simulation results are presented. The
value of the dc link capacitance is 400pF and the
hysteresis window height is kept 1.0 Amp. The values
of the two inductors are L, = 20mH; Lo = 12mH.

10. PROPOSED SLCVC AS VAR GENERATOR
• The control strategy discussed in the previous section
maintains a sinusoidal current by controlling +h,e
auxiliary converter switching. As a result, the load
non- linearities if present also get compensated by
the auxiliary compensator. Therefore, when the
source is supplying a nonlinear load, auxiliary
compensator has to compensate load harmonics in
addition to the harmonics generated by the main
compensator.

11. Experimental Verification
• The proposed control strategy is experimentally
verified by operating the SLCVC as a load
compensator. Dur- ing testing, the load current of
each phase is maintained at (0.5 i j6.O)Amp and the
reference dc link voltage is changed from 150V to
18OV. Figures 12 and 13 depict the compensator
performance for this condition.

13. CONCLUSIONS
• A simplified control scheme of a high power low
distortion SLCVC is proposed. Superior performance
characteristics are obtained by effectively combining
high power low frequency and low power high
frequency switching devices. Detailed simulation
studies are carried out to demonstrate the
effectiveness of the scheme.

14. REFERENCES
1. V. R. Kanetkar, M. S. Dawande, and G. K. Dubey.
"Recent Advances in Synchronous Link Converters."
IETE Baok Seties, Power Eiectmnies end Drives
edited by G. K. Dubey and C. R. Kasarbada, IETS ,
1994
2. Laszlo Gyugi, "Reactive Power Generation and
Control by Thyristor Circuits." IEEE Ilnns. Ind. Appl. ,
vol. IA-15, DO. 5, pp 521-532, Sept. /Ocl. 1979.

15. 3. C. W. Edwards, K. E. Mattern, E. J. Stacey, P. R.
Nannen, and J. Cubernick. "Advanced Static Var
Generator Employing GTO Thyristors." IEEE fins. Power
Delivery. vol. PWRD-3, no. 4, pp 1622-1627. Oct. 1988.
4. G. Joos. L. T. Moran, and P. D. Ziogas, '"Perfixmance
Analysis of a PWM Inverter VAR Compensator," IEEE
%na. Power Electmmcs. , vol. PE-6, no. 3, pp 380-391.
Jul. 1991.