Cycloconverter performs the power converting function in a single stage without any intermediate d.c link i.e the cycloconverter can produce adjustable voltage, adjustable frequency ac power from an ac source of fixed voltage and frequency. The production of harmonics in the output of a cycloconverter as a result of the process of voltage synthesis is unavoidable. The direct process of frequency changing makes the harmonics as a function of both the input and output frequencies. As a result the cycloconverter input current and output voltage waveform contain harmonics, non-standard harmonics and sub-harmonics. The harmonic spectrum of cycloconverter input and output waveform depends upon its control strategy, pulse number and structure. In this paper the comparative frequency spectrum analysis of two major cycloconverter structures i.e circulating current (CC) and non circulating current cycloconverter (NCC) are made using FFT and DWT. Hence it establishes the acceptability of wavelet transform in detecting the harmonics in the input and output voltage and current waveform. Further using the power quality indices a comparison in performance of NCC and CC are made.The analysis are performed in MATLAB/SIMULINK environment.

1. R.F.Chu and J. J. Burns, “Impact of cycloconverter harmonics,” IEEE Trans.Ind, Appl., vol.22, no.4, pp.417-435, May/June 1989.
2. W. Timpe, “Cycloconverter drives for mill rolling mills ,” IEEE Trans.Ind, Appl., vol.1A-18, pp.400-404, Jul./Aug. 1982.
3. C. P. LeMone, M. Ehara and L. Nehl, “AC adjustable speed application for the cement industry,” in Proc. IEEE Cement Industry Technical Conf. Salt lake city, UT, 1986, pp. 335-362.
4. G.T.Heydt,Power quality engineering, IEEE Power Engineering Review, pp 5-7, sep 2001
5. Heydt et al, “Power Quality Indices for aperiodic voltage and current’’,IEEE Trans Power Delivery,vol-15,no.2, pp-784, Apr 2000.
6. L. Gyugyi and B. R. Pelly, “Static Power Frequency Changers, Theory, Performance and Applications,” NewYork, Wiley, 1976.
7. Milad Basirifar, Abbas Shoulaie, “A comparative study of Circulating Current Free and Circulating Current Cycloconverters”, 2010, IEEE conferences.
8. W.A. Wikinson, M.D. Cox, “Discrete wavelet analysis of power system transients’’, IEEE Transactions on Power Systems, Vol. 11, No. 4, November 1996
9. Surya Santoso, Edward J. Powers and W. Mack Grady, Peter Hofmann, “Power quality assessment via Wavelet transform analysis’’, IEEE Transactions on Power Delivery, Vol. 11, No. 2, April 1996.
10. V.L.Pham and K.P.Wong, “Wavelet-transform-based algorithm for harmonic analysis of power system waveforms’’ IEE Proc. Gener-Transm. Disirib. Vol. 146, No.3, May I999.
11. Wang Jianze Ji Yanchao, Wang Fei Ran Qiwen, “New method for transient harmonics measurement Based on Wavelet Transform’’, IEEE, 1998.
12. E.Y. Hamid, R. Mardiana and Z.4 Kawasaki, “Method for RMS and power measurements based on the wavelet Packet transform’’, IEE Proc Meus Techno1 I Vol 149, No 2, March 2002.

circulating current cycloconverter(CC) non circulating current cycloconverter(NCC) harmonics power quality indices fast fourier transform(FFT) discrete wavelet transform(DWT)