A generalization of the PWM (pulse width modulation) subharmonic method for controlling single-phase or three-phase multilevel voltage source inverters (VSIs) is considered. Three multilevel PWM techniques for VSI inverters are presented. An analytical expression of the spectral components of the output waveforms covering all the operating conditions is derived. The analysis is based on an extension of Bennet's method. The improvements in harmonic spectrum are pointed out, and several examples are presented which prove the validity of the multilevel modulation. Improvements in the harmonic contents were achieved due to the increased number of levels. >

A new multilevel PWM method: a theoretical analysis

The study was carried out to assess the determinants of household food security among rural households in Sekyere-Afram Plains District of Ghana Data were collected from 100 randomly selected households through the use of structured questionnaires Analytical techniques employed included descriptive statistics to analyze the characteristics of respondent households, and logistic regression model to examine the determinants of food security among the households surveyed Among the variables considered in the model, household size, farm size, off-farm income, credit access, and marital status were found to significantly influence household food security Consistent with a priori expectation, larger households were found to be food insecure compared with households with smaller sizes, ceteris paribus Also, consistent with findings from previous empirical studies, farm size, off-farm income and credit access were found to have significant positive effect on household food security The study, therefore, recommended improved access to credit for rural households and diversification of household economic activities to include off-farm income generating businesses to improve food security at the household level

Determinants of household food security in the sekyere-afram plains district of ghana

The analysis and test results are given for an experimental single-phase controlled-current PWM (pulse-width-modulated) rectifier that operates at unity power factor with near sinusoidal current waveform and that has power reversal capability. The twice-line-frequency AC power is identified as a source of voltage harmonics in the DC link. The harmonics enter into the voltage regulation feedback loop to distort the AC current waveform. These undesirable harmonics can be removed by a low-pass filter. It is noted that the overall design must address the possibility of instability due to the low-pass filter in the feedback path. >

A single-phase controlled-current PWM rectifier

A pulsewidth modulation (PWM) control technique suitable for fully controlled three-phase ac/dc converters is analyzed, which gives sinusoidal input currents and ideally smoothed dc voltage. The technique allows four-quadrant operation and full-range control of the input power factor. An extension to a simplified converter scheme, capable of one-quadrant operation, is also considered. Operation of the converter is analyzed under both ideal and actual conditions. Control implementation and design criteria are discussed and experimental results are reported.

Three-Phase AC/DC PWM Converter with Sinusoidal AC Currents and Minimum Filter Requirements

Fossil fuels and other conventional energy sources used to generate electricity are finite. Therefore, alternative energy sources should be pursued to meet present and future energy demands. The photovoltaic (PV) is a promising renewable energy source, especially for the remote areas. The PV is a DC power source that needs to be converted into usable AC power using an inverter. However, its nonlinearity and output fluctuation pose challenges in the design of PV based inverter. In this paper, a PV inverter controller system with the fundamentals of a fuzzy logic controller (FLC) and its applications and execution are reviewed. The different fuzzy controllers, inverter control algorithms, and switching techniques are studied. The findings indicate that the fuzzy logic controls have been gaining attention in the area of power control engineering, especially in inverter controller design for PV applications and generation. The FLC has a flexible and intelligent design, expedient user interface, easy computation and learning system, and combinations of different control algorithms. The FLC is also verifiable for completeness, redundancy, and consistency. However, finding the boundaries of membership functions and other rules of FLC requires manual tuning, long computation time, and considerable effort. This paper comprehensively reviews the FLC-based inverter control system to minimize PV output fluctuations, which cause inverter issues related to output harmonics, power factor, switching schemes, losses, and system implementation. The inverter system and its control strategy for future PV applications and generation require further research and development. Consequently, this review focuses on many factors and challenges and provides recommendations for designing capable and efficient inverter control systems for converting PV power to usable AC power. All the highlighted insights of this review will hopefully lead to increased efforts toward the development of the advanced inverter control systems for PV applications for AC loads and the utility grid.

http://dspace.uniten.edu.my/jspui/bitstream/123456789/13353/1/Fuzzy%20logic%20inverter%20controller%20in%20photovoltaic%20applications%20Issues%20and%20recommendations.pdf

Fuzzy Logic Inverter Controller in Photovoltaic Applications: Issues and Recommendations

Various resonant circuits are reviewed and compared in order to unify the different design methods that are available for low-loss snubbers. Two passive resonant snubbers are described in detail, with some design guidelines for selecting all the snubber components. This is supplemented by experimental results obtained when utilizing these two snubbers to protect a power Darlington transistor module. >

A summary of resonant snubber circuits for transistors and GTOs

Improved power factor converter structures (IPCS) suitable for medium to high power applications are categorized by their input characteristics. The interaction of an IPCS with the supply network is reviewed in terms of utility imposed reactive and harmonic compensation requirements. The reduction in capacitive VA requirements for reactive compensation can be offset under certain circumstances by substantially larger filter capacitors. Consequently, the choice of an IPCS for a given application is not universal but depends on customer needs, utility requirements, and economic considerations.

Considerations on the Application of Improved Power Factor Converter Structures

A new method for calculation of speed-torque transfer functions is presented. It is applicable to any electrical machine described by a set of linear equations. By predicting the form of the transfer function as well as the nature of its zeroes, the method yields a considerable insight into speed-load interaction and can be used in the design of motor drives.

The Speed-Torque Transfer Function of Electric Drives

A novel methodology which is convenient for the design of optimal sliding-mode control for an asynchronous machine drive is developed. A suitable model of the induction machine control system, incorporating the counter-EMF (electromotive force) under field orientation, is presented. Analytic solutions for the optimal switching vector C, and the feedback matrix, L in unit-vector sliding-mode control are obtained. The optimal synthesis is directly related to the desired system specifications in the time domain without the necessity of solving the Riccati equation or complicated matrix equations. This greatly simplifies the conventional complicated design procedure and improves the design quality. Simulation and experimental results verify the optimal design. >

http://ieeexplore.ieee.org/iel5/726/952/00025083.pdf

Optimal sliding mode control of asynchronous machine speed with state feedback

The specifications of a highly flexible controller for a three-phase McMurray inverter are defined and the construction of a suitable controller is described. The controller is capable of operation in either the six step or pulsewidth modulation mode and incorporates safe start-up and shut-down procedures. The operation of the controller is illustrated by a series of inverter and controller oscillograms.

A McMurray Inverter Controller

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