Five-level selective harmonic elimination PWM strategies and multicarrier phase-shifted sinusoidal PWM: A comparison

The multicarrier phase-shifted sinusoidal pulse-width modulation (MPS-SPWM) technique is well-known for its important advantage of offering an increased overall bandwidth as the number of carriers multiplied with their equal frequency directly controls the location of the dominant harmonics. In this paper, a five-level (line-to-neutral) multilevel selective harmonic elimination PWM (MSHE-PWM) strategy based on an equal number of switching transitions when compared against the previously mentioned technique is proposed. It is assumed that the four triangular carriers of the MPS-SPWM method have nine per unit frequency resulting in seventeen switching transitions for every quarter period. Requesting the same number of transitions from the MSHE-PWM allows the control of sixteen non-triplen harmonics. It is confirmed that the proposed MSHE-PWM offers significantly higher converter bandwidth along with higher modulation operating range. Selected results are presented to confirm the effectiveness of the proposed technique

Multiple sets of solutions for harmonic elimination PWM bipolar waveforms: Analysis and experimental verification

Multiple sets of solutions for the selective harmonic elimination pulse-width modulation method for inverter control exist. These sets present an independent solution to the same problem but further investigation reveals that certain sets may offer an improved overall harmonic performance. In this paper, a minimization method is discussed as a way to obtain these multiple sets of switching angles. A simple distortion harmonic factor that takes into account the first two most significant harmonics present in the generated waveform is considered in order to evaluate the performance of each set. The bipolar waveform is thoroughly analyzed and two cases are considered; single-phase patterns which eliminate all odd harmonics and three-phase counterparts which eliminate only the nontriplen odd harmonics from the line-to-neutral pattern but such harmonics are naturally eliminated from the line-to-line waveform. Experimental results support the theoretical considerations reported in the paper

Load matching in a direct-coupled photovoltaic system-application to Thevenin's equivalent loads

A methodology is developed for the assessment of load matching and further estimation of the optimum photovoltaic (PV) arrays arrangement over a prolonged period of time. The method calls for the calculation of the appropriate effectiveness factor defined as the ratio of the load energy over the maximum energy that can be produced by the PV array for a specific time period. The effectiveness factor depends on the PV array characteristics, the load characteristics, and the solar irradiance conditions. To produce realistic predictions for the effectiveness factor and the PV arrays arrangement with validity over long periods of time, the present statistical model describing irradiance employs a stochastic variation of solar radiation over a long period of time and not just a fixed diurnal variation as traditionally done in the past. Simulations are performed for the case of Thevenin's equivalent loads. In order to generalize the analysis, the simulation results are presented in a reduced form based on the values of the voltage and current corresponding to the maximum power of the PV array. The results are presented in multiple-curve comprehensive plots, which allow to determine the optimum photovoltaic array panel's arrangement without engaging sophisticated mathematical calculations

Wear of Cutting Tools Used in Milling Treatments

The usage of Computer Numerical Controlled Machines has been generalized over the last decades due to the increased demands for the production of mechanical parts with précised dimensions, higher production rates and products with better treated surface quality. It is well known that the duration of life of a cutting tool is one of the most important parameters during the cutting of metal parts, because it affects the cost of the manufacturing process substantially. Therefore, it is important to know accurately, the relation between the duration of life of the cutting tool and the conditions of the machinery such as cutting velocity, feed rate (fz), the depth of cut (radial and axial) etc. The purpose of this research is to conduct a proper number of cutting experiments in milling, measuring the wear of the cutting tools, in order to conclude in a mathematical model the wear cutting tool. This model can be implemented for the prediction of the cutting tool life, which is very important for the determination of the best cutting conditions. From the experimental diagrams we can come to conclusions for the course of the wear of the cutting tool in connection with the velocity of cutting, for the machinability of the materials used etc. The wear of the used cutting tools was determined by means of optical microscopy and stereoscopy.</jats:p

Estimation of total atmospheric pollution using global radiation data: introduction of a novel clear day selection methodology

This work investigates the possibility of determining the degree of atmospheric pollution over the small Greek city of Serres based solely on measurements of global solar radiation and some simple meteorological variables. Hourly data of solar irradiance on an horizontal plane are recorded simultaneously together with relative humidity and wind speed. Along with some traditional techniques for selecting the clear sky days of the period examined, the statistical coefficients of skewness and kurtosis of the daily distributions of hourly radiation data have been employed with reasonable success. Indeed, for the cloudless days of this study, the values of the above quantities are confined within narrow ranges which provide a criterion for their identification from the cloudy days. Comparison of global radiation data under clear sky conditions with reference values from a suitable theoretical model of literature, in combination with the results of a recent study for the nearby city of Thessaloniki, provides evidence that there is virtually no atmospheric pollution in Serres. Correlation of the observed deviations between measurements and predictions with recorded meteorological data lends further support to the above argument. (C) 1999 Elsevier Science Ltd. All rights reserved