Design and implementation of a PC-Based subharmonin wave analyzer

Salman Majid Salman Al-Rawi
Dr. Manal J. Al-Kindi
Dr. M. T. Lazim

Abstract : The aim of this thesis is to design an effective and easy-to-handle system to analyze signals that contain subharmonic frequency components in its spectrum using a micro-computer based system. Subharmonic generation is widely occurring for low frequency bands especially at power frequencies, 50 Hz or 60 Hz, when these signals are used in energy processing. One of the famous techniques is called integral-cycle control or Amplitude Modulation of power signal. The study of the analytical properties of the integral-cycle waveforms can help an optimized analyzing algorithm that will be designed depending on these properties. It is suggested to use a system which consists of personal computer sound card used for signal sampling and acquisition, and a MATLAB program used to control the data acquisition process and an effective mathematical analysis to resolve the signal into its spectral components. Such a system can be realized easily because MATLAB contains the special functions and instructions used for the above purpose. It is found that the use of the computer sound card as a signal input port, causes distortion of the signal (and hence its spectrum) because of the sound card built-in band pass filter which attenuates the low frequency components of the signal. So, an approximated equation to the inverse of the filter characteristics is found. This correction of distortion is done based on a comparison of a number of theoretically obtained spectrums derived by previous researchers in this field. The degree of accuracy of the practically estimated spectrums is found to be 87.88 .