Adel Ahmed

New High Voltage Gain Dual-boost DC-DC Converter for Photovoltaic Power Systems

Abstract This article presents a new circuit topology of a high-voltage step-up boost DC-DC converter for photovoltaic power systems. The converter boosts the low-output voltage of the solar cell to the required voltage for the load. The proposed circuit has various advantages compared to the conventional boost converters, namely a higher boost rate with low duty cycle, lower voltage stress on components, and higher efficiency. The equations of a dual-boost converter are analyzed, highlighting the advantages of the new DC/DC converter circuit topology. The operation principle is explained using the operating intervals equivalent circuits and operation waveforms. Then, mathematical and theoretical analyses of continuous and discontinuous conduction modes of the converter are presented. Losses and thus efficiency of the proposed converter are calculated using MATLAB (The MathWorks, Natick, Massachusetts, USA). Calculations are used to compare the efficiency of the proposed topology with others available in the literature regarding the benefits of decreasing cost and complexity. A photovoltaic system simulation model is developed using PSIM (Powersim Inc., Woburn, Massachusetts, USA) to validate the proposed converter. The proposed high voltage gain boost converter has been implemented for a 100-W load and tested to verify the principle of operation.

Effect of the dielectric barrier on discharges in non-uniform electric fields

This paper is aimed at calculating the electric field in the point-to-plane electrode system with the plate covered with a dielectric layer. With charge accumulation on the dielectric surface by corona discharge, the field in the dielectric is increased at the expense of a decrease in the gas gap. The charge accumulation on the dielectric surface proceeds to the maximum possible value when the normal component of the surface field vanishes. With the dielectric layer fully-charged, the percentage decrease of the field in the gas gap is maximum at the dielectric surface and declines along the gap axis to vanish at the point tip. The percentage decrease of the field becomes more pronounced with the increase of the diameter of the dielectric layer. The effect of inter-electrode spacing and the dielectric layer thickness on the field distribution is investigated. An accurate method of charge simulation was used for field calculation irrespective of the thickness of the dielectric layer and the gap geometry. With ion flow along the flux lines from the stressed point to the ground plane, the field enhancement factor increases and the volume charge density decreases along the flux lines. The voltages of the ion flow threshold and corona quenching are calculated and compared with previous measurements. The method of calculation is extended to calculate how high the surface potential of the charged dielectric needs to be to trigger a micro-spark in the electrostatic discharges from grounded point electrodes.

Harmonic Mitigation, Maximum Power Point Tracking, and Dynamic Performance of Variable-speed Grid-connected Wind Turbine

Abstract This article presents a method for harmonic mitigation and maximum power point tracking for a variable-speed grid-connected 20-kW wind turbine. The wind energy conversion system consists of a permanent magnet synchronous generator driven by variable-speed 20-kW wind turbine. The output of the permanent magnet synchronous generator is connected to a single-switch three-phase boost rectifier to generate DC voltage, which feeds a current-controlled inverter to interface the system with the electric utility. The single-switch three-phase boost rectifier is an active power factor correction technique to maintain the power factor at the permanent magnet synchronous generator side to nearly unity and mitigate the permanent magnet synchronous generator current harmonics. To mitigate inverter output current and voltage harmonics, an LCL filter has been used. A complete analysis of the harmonic content has been done everywhere in the system. The results show that the proposed maximum power point tracking control strategy succeeded to track the maximum wind power irrespective of the wind speed. This strategy in presence of an LCL filter achieved harmonic mitigation at the permanent magnet synchronous generator and inverter output sides. The dynamic response of the wind energy conversion system is tested under a three-phase fault condition. For comparison purposes, an active power filter is designed and checked against the single-switch three-phase boost rectifier for harmonic mitigation at the permanent magnet synchronous generator side.

Electric field distortion caused by asymmetric pollution on insulator surfaces

The pollution on the surface of an insulator is asymmetric, although insulators, in general, are axisymmetric. The distortion of fields on the surface of an asymmetrically polluted axisymmetric insulator is computed in this paper. The surface charge simulation method (SCSM) has been used with cylindrical, conical and toroidal surface elements. The volume resistivity of the insulation also has been taken into consideration, using complex permittivity for the insulating material.

NO removal using dielectric barrier discharges in a multirod reactor stressed by AC and pulsed high voltages

This paper is aimed at investigating the nitric oxide (NO) removal using dielectric barrier discharges (DBD) in a multi-rod reactor stressed by ac and pulse high voltages. The effects of various parameters (the voltage amplitude, frequency, gas flow rate, use of the γ-alumina pellets and the voltage type) on the discharge power and NO removal rate have been studied experimentally in the multi-rod DBD reactor. When the reactor was filled with γ-alumina pellets, improvement in NO removal rate was observed. The pulse voltage gives higher NO removal rate in comparison with ac voltage at the same energy density. Records of the discharge photograph and the emission intensity have been made at varying voltage amplitude, frequency, and gas flow rate. The records confirm the dependency of the discharge power on these parameters.

Maximum power point tracking for variable speed grid connected small wind turbine

This paper presents a method for harmonic mitigation and maximum power point tracking (MPPT) for a variable speed-grid connected 20 kW wind turbine. The wind energy conversion systems consist of permanent magnet synchronous generator (PMSG) driven by variable-speed 20 kW wind turbine. The output of the PMSG is connected to a single switch three-phase boost rectifier to generate DC voltage which feeds a current controlled inverter to interface the system with the electric utility. The single switch three-phase boost rectifier is an active power factor correction technique to maintain the power factor at the PMSG side to nearly unity and mitigate the PMSG current harmonic. To mitigate inverter output current and voltage harmonics, an LCL filter has been used. A complete analysis of the harmonic content has been done everywhere in the system. The results show that the proposed MPPT control strategy succeeded to track the maximum wind power irrespective of the wind speed. This strategy in presence of LCL filter achieved harmonic mitigation at the PMSG and inverter output sides.

On the static behaviour of dielectric barrier discharges in uniform electric fields

This paper is aimed at calculating the electric field in a parallel-plate electrode system with one of the plates covered with a dielectric layer. With deposition of charge on the dielectric surface, the field in the gas gap is reduced with a subsequent shrinking of the discharge activity in the gap. The charge deposition on the dielectric surface proceeds to the maximum possible value when the normal component of the surface field vanishes. Not only the normal field component but also the field in all the gap vanishes at the maximum possible charge on the dielectric surface with a subsequent suppression of the gap micro-discharges. An accurate method of charge simulation was used for field calculation irrespective of the thickness of the dielectric layer and the value of the charge deposited on the dielectric surface. The threshold and suppression voltages of the gap micro-discharges are calculated based on a criterion for self-sustained discharge-activity in the gap. The calculated voltages are compared with those estimated before and those measured for different gap lengths.

A solar-wind hybrid power system for irrigation in Toshka area

This paper is aimed at calculating the power demand of a combined irrigation and domestic load in Toshka area, Toshka, Egypt. The pipe line system for irrigation is designed. An economic feasibility study has been made for hybrid PV-wind system to power this combined load. Sizing of the hybrid system components was investigated using MATLAB Code and HOMER Package. The energy cost values of the hybrid system agrees reasonably with published those before.

A numerical model using surface charges for the calculation of electric fields and leakage currents on polluted insulator surfaces

The pollution on the surface of an insulator is asymmetric though the insulators, in general, are axisymmetric. A pollution layer of wet or dry type has an enhancement effect on the distribution of the electric potential, field and leakage current on the surface of the high-voltage (HV) outdoor insulators. In the present work, a numerical method for the computation of the electric potential, field and surface leakage current on the surface of the polluted HV insulators is developed. The method is based on the surface charge simulation (SCSM) and discrete charge simulation techniques when the simulation charges are complex at a given frequency. The method takes into account surface as well as volume conductivities in addition to the effect of the dry band or wet pollution. Due to the conductivity of the insulation a complex permittivity of the insulating material has to be regarded. The surface pollution on the insulators, in general, is asymmetric and is simulated by small or big patches of dry band or wet pollution. Therefore, the field configuration has to be three-dimensional. Special emphasis is laid on the extreme local field variation at the boundary between dry and wet surface patches. As an example, the method is applied to a polluted cylindrical insulator supporting a HV electrode above the ground plane.

The barrier effect on the onset voltage of negative corona in air

This paper is aimed at calculating the onset voltage of negative corona in rod - plane gaps as influenced by the presence of a dielectric barrier located either parallel or normal to the gap axis. The effect of the barrier thickness, permittivity and location with respect to the stressed rod on the calculated onset voltage is investigated. The method of calculation is based on the criterion of self-recurring single electron avalanches developed in the gap when stressed negatively. The electric field values used for avalanche growth are evaluated using a combined technique based on boundary-element and discrete-charge simulations. In this technique, the surface charge on the rod is simulated by fictitious discrete charges while the surface charge on the faces of the barrier is simulated by surface charged boundary elements. The electric field assumes values higher than those in the absence of the barrier whatever the position of the barrier, parallel or normal to the gap axis. The smaller the distance between the barrier and the rod, the larger the thickness and the higher the relative permittivity of the barrier, the lower is the corona onset voltage.