Analysis of phonocardiogram (PCG) signals provides a non-invasive means to determine the abnormalities caused by cardiovascular system pathology. In general, time-frequency representation (TFR) methods are used to study the PCG signal because it is one of the non-stationary bio-signals. The continuous wavelet transform (CWT) is especially suitable for the analysis of non-stationary signals and to obtain the TFR, due to its high resolution, both in time and in frequency and has recently become a favourite tool. It decomposes a signal in terms of elementary contributions called wavelets, which are shifted and dilated copies of a fixed mother wavelet function, and yields a joint TFR. Although the basic characteristics of the wavelets are similar, each type of the wavelets produces a different TFR. In this study, eight real types of the most known wavelets are examined on typical PCG signals indicating heart abnormalities in order to determine the best wavelet to obtain a reliable TFR. For this purpose, the wavelet energy and frequency spectrum estimations based on the CWT and the spectra of the chosen wavelets were compared with the energy distribution and the autoregressive frequency spectra in order to determine the most suitable wavelet. The results show that Morlet wavelet is the most reliable wavelet for the time-frequency analysis of PCG signals.

No abstract

SUMMARYThis paper presents a fast and real-time space vector pulse width modulation (SVPWM) algorithm for multilevel inverters. A min.-max. method for selecting switching states is proposed for SVPWM algorithm. With the proposed method, the minimum switching commutation transition of between the triangles on the space vector diagram of the reference voltage vector is provided. The proposed SVPWM algorithm is also rather suitable for all values of linear modulation range and provides simplicity and applicability. Using this SVPWM algorithm, threephase voltages have been obtained from a five-level cascade inverter. These voltages are applied to a three-phase ac motor. The simulation results are verified by the experimental results.

No abstract

In this article, an integrated lab environment for the electrical engineering education is presented which includes hardware and software for the modeling, simulation and control of multilevel inverters. A five-level cascade inverter is designed and implemented which is an educational platform for the students to test different pulse width modulation (PWM) techniques and verify simulation results. The integrated environment is based on Matlab together with dSPACE. Sinusoidal PWM (SPWM) and Selected Harmonic Elimination PWM (SHEPWM) blocks are constructed in Matlab/Simulink and converted to C code using Matlab/Real-Time Workshop. C codes are sent to dSPACE's DS1103 digital signal processor (DSP) via dSPACE/Real-Time Interface software. Voltages with variable frequency and amplitude obtained from SPWM and SHEPWM techniques are applied to an induction motor. Simulation and experimental results are visualized on the designed graphical user interface (GUI). The GUI is developed using dSPACE's ControlDesk software. ß