Direct Current Generation Research Articles

Effects of Using 24 watt Twisted Fluorescent Lamp, 13 watt Led Bulb and 30 watt Led T8 on Inverter Current, Photovoltaic Panel and Charging Current of Solar System

An alternative to the use of solar systems is an electricity saving activity that can provide a profit if the load used is in accordance with the level of capacity of the system. Load selection in solar systems is very important in ensuring the stability of the system itself. Energy from sunlight is the main source of direct current power generation but it is subject to the capabilities of the Maximum Power Point Tracking (MPPT) solar charger controller used. The selection of the appropriate load will provide good efficiency as well as more efficient energy savings. In this paper,13Watt LED bulb, 24Watt Twisted fluorescent lamp and 30Watt T8 LED lamp are tested in an experimental study to see the effect of their use on the inverter current, the current flowing through the photovoltaic panel and the current used to charge a battery in the solar system. These data will be used to make comparisons with the energy savings generated by this solar system to provide longer time to use. The brightness of the lamp is also compared using digital Lux meters. The results of this study have shown that the use of 13Watt LEDs is more economical in terms of direct current (Dc) power and contributes to brighter lighting than the 24Watt twisted fluorescent lamp and 30Watt T8 LED lamp used.

Disturbance Rejection and Control Design of MVDC Converter with Evaluation of Power Loss and Efficiency Comparison of SiC and Si Based Power Devices

With direct current (DC) power generation from renewable sources, as well as the current relocation of loads from alternating current (AC) to DC, medium-voltage DC (MVDC) should fill gaps in the areas of distribution and transmission, thereby improving energy efficiency. The MVDC system is a platform that interconnects electric power generation renewables (solar, wind) with loads such as data centers, industrial facilities and electric vehicle (EV) charging stations (also using MVDC technology). DC–DC power converters are part of the rising technology for interconnecting future DC grids, providing good controllability, reliability and bi-directional power flow. The contribution of this work is a novel and efficient multi-port DC–DC converter topology having interconnections between two converters, three-level neutral point clamping (NPC) on the high-voltage (HV) side and two converters on the low-voltage (LV) side, providing two nominal low voltages of 400 V (constant) and 500 V (variable), respectively. The design of this new and effective control strategy on the LV side has taken into condition load disturbances, fluctuations and voltage dips. A double-closed-loop control topology is suggested, where an outside voltage control loop (in which the capacitance energies are analyzed as variable, and the inside current loop is decoupled without the precise value of boost inductance) is used. The simulation results show the effectiveness of the proposed control system. In the second part of this study, wide-bandgap SiC and Si devices are compared by using comprehensive mathematical modeling and LT-spice software. Improving power loss efficiency and overall cost comparisons are also discussed.

The Inverse Relationship between Metal-Enhanced Fluorescence and Fluorophore-Induced Plasmonic Current

In this work we investigate the relationship between metal-enhanced fluorescence (MEF) and fluorophore-induced plasmonic current (PC). This is accomplished through measurements of both radiative emission (MEF) and direct electrical current generation between discrete metal nanoparticles upon fluorophore excitation (PC). We have conducted these measurements on silver and gold nanoparticle island films, over a range of nanoparticle sizes and spacing in the films. We have observed an inverse relationship in the magnitude of MEF with PC, where larger and more closely spaced metal nanoparticles are found to result in increased PC and subsequently a decreased MEF. We attribute this effect to the relatively high capacitance and low charging energy of large and closely spaced particles, providing an outlet for plasmon relaxation in the form of electron flow and electrical current generation. These results are significant as they open potential for controlling for and the optimization of both MEF and PC.

Rectification in Chiral Carbon Nanotubes with Hot Electron Injection

The novel effect of direct current generation by carbon nanotubes with hot electron injection which may arise due to an electromagnetic radiation with commensurate frequencies has been theoretically investigated using the semiclassical Boltzmann kinetic equation with relaxation time assumed constant. The nonlinearity of the current voltage characteristics and the chiral effects have been considered. We note that the direct current is a result of the strong nonprabolicity of the energy of the carbon nanotubes for the case where it Bloch oscillates. It is shown that the novel expression for the direct current generation strongly and significantly dependence on the hot electron injection rate, which leads to strong oscillatory behavior and the shift of the regions of absolute negative conductivity from low to higher dimensionless amplitude β values with increasing injection rate. We predict that carbon nanotubes with hot electron injection may be useful for generation of direct current.

Direct current contact-mode triboelectric nanogenerators via systematic phase shifting

The intermittency and discontinuous nature of power generation in Triboelectric Nanogenerators (TENGs) are arguably their most significant drawback, despite the promise demonstrated in low-power electronics. Herein, we introduce a novel technology to overcome this issue, in which, built-in systematic phase shifting of multiple poles is used to design a pseudo direct-current TENG. Unlike previous attempts of constructing near direct-current TENGs that base on the segmentation of electrodes of a sliding mode TENG, this technology introduces a new method that depends on planned excitation of constituent TENG units at different time intervals to obtain the necessary phase shifts, achieved by their structural design that contains an asymmetric spatial arrangement. Therefore, the direct current generation for TENG, which was previously limited to the sliding mode TENG units, are expanded to contact-mode TENGs. The technology allows for continuous and smooth operation of the driven loads and paves the way for a new dawn in energy scavenging from mechanical sources. We use the distance-dependent electric field (DDEF) platform to design the systematic phase shifting technology, which is experimentally demonstrated via a free-standing mode TENG (FSTENG) based design, to power a number of prototype devices. The resultant power output of the TENG indicates a crest factor close to 1.1 at relatively low frequencies, the best reported values for TENGs with contact-mode basic units, to date. This work provides a highly awaited solution to overcome the intermittency and sporadic nature of TENG outputs, thus, promoting the field towards powering next generation autonomous and mobile electronics.

Improved super‐twisting sliding mode control of a stand‐alone DFIG‐DC system with harmonic current suppression

This study presents an improved super-twisting sliding mode (SSM) approach to a stand-alone doubly fed induction generator (DFIG) for direct current (DC) generation system. By taking the uncertainties into consideration, an improved SSM regulator based on an extended state observer (ESO) is proposed to enhance the robustness of DC-voltage regulation. Moreover, a novel sinusoidal rotor current calculation method is proposed to generate sinusoidal reference of rotor current. A resonant-based ESO (R-ESO) SSM approach is proposed to regulate rotor current. By applying the R-ESO to estimate the model-related part of DFIG, the tracking performance with respect to a sinusoidal reference is improved. Then, the suppression ability to fifth and seventh harmonic currents are enhanced. Finally, both simulations and experiments on a 6-kW DFIG-DC system are provided to show the effectiveness of DC-voltage regulation and harmonic current suppression of the proposed approach.

Direct-current flexible piezoelectric nanogenerators based on two-dimensional ZnO nanosheet

Direct current (DC) power generation of piezoelectric nanogenerator (PNG) is promising for the realization of future self-powered electronics. Wurtzite structured two-dimensional (2-D) piezoelectric zinc oxide (ZnO) nanosheets can convert mechanical energy into electrical energy, and it produce DC output power. In this present work, we report DC power generation of PNGs based on the 2-D ZnO nanosheets. The growth condition has been optimized for the power generation, and effects of the surface morphologies and orientations have been investigated. The optimized PNGs produced voltage, current density and power density of up to 0.9 V, 16.5 μA cm−2 and 600 nW cm−2, respectively, for over 4000 cycles upon 4 kgf of force.

Direct current triboelectric cell by sliding an n-type semiconductor on a p-type semiconductor

Triboelectric generators are a type of devices for harvesting mechanical energy by utilizing triboelectric and electrostatic induction effects. When two materials of different electron affinities are brought into contact, electrons transfer across the contacted surfaces owing to triboelectrification. When the two materials are slid against each other with a variation of the contacting surface area, an alternating current is electrostatically induced in the external circuit. In this paper, a novel electric generator, called triboelectric cell, based on sliding friction between n- and p-type doped semiconductors without changing the contacting area is reported. A direct current is generated in the direction of the built-in electric field in the dynamic p-n junction across the contacted surfaces, flowing from the p-semiconductor through the external circuit to the n-semiconductor. The generated currents and voltages are studied through sliding speeds, accelerations, contacting forces, operation temperatures and the geometries of the top electrode. The direct current generation can be attributed to electron-hole pairs generated at the two sliding surfaces, which are then swept out the dynamic junction by the built-in electric field.

Sensorless PMSM Drive Implementation by Introduction of Maximum Efficiency Characteristics in Reference Current Generation

This paper presents the efficiency improvement in a speed closed-loop controlled permanent magnet synchronous machine (PMSM) sensorless drive. The drive efficiency can be improved by minimizing the inverter and the PMSM losses. These can be influenced by proper selection of DC-bus voltage and switching frequency of the inverter. The direct (d-) and quadrature (q-) axis current references generation methods, discussed in this paper, further improve the efficiency of the drive. Besides zero d-axis current reference control, the maximum torque per ampere (MTPA) characteristic is normally applied to generate the d- and q-axis current references in vector controlled PMSM drives. It assures control with maximum torque per unit of current but cannot assure maximum efficiency. In order to improve efficiency of the PMSM drive, this paper proposes the generation of d- and q-axis current references based on maximum efficiency (ME) characteristic. In the case study, the MTPA and ME characteristics are theoretically evaluated and determined experimentally by measurements on discussed PMSM drive. The obtained characteristics are applied for the d- and q-axis current references generation in the speed closed-loop vector controlled PMSM drive. The measured drive efficiency clearly shows that the use of ME characteristic instead of MTPA characteristic or zero d-axis current in the current references generation improves the efficiency of PMSM drive realizations with position sensor and without it—sensorless control.

Scaled-up Direct-Current Generation in MoS2 Multilayer-Based Moving Heterojunctions.

Techniques for scaling-up the direct-current (dc) triboelectricity generation in MoS2 multilayer-based Schottky nanocontacts are vital for exploiting the nanoscale phenomenon for real-world applications of energy harvesting and sensing. Here, we show that scaling-up the dc output can be realized by using various MoS2 multilayer-based heterojunctions including metal/semiconductor (MS), metal/insulator (tens of nanometers)/semiconductor (MIS), and semiconductor/insulator (a few nanometers)/semiconductor (SIS) moving structures. It is shown that the tribo-excited energetic charge carriers can overcome the interfacial potential barrier by different mechanisms, such as thermionic emission, defect conduction, and quantum tunneling in the case of MS, MIS, and SIS moving structures. By tailoring the interface structure, it is possible to trigger electrical conduction resulting in optimized power output. We also show that the band bending in the surface-charged region of MoS2 determines the direction of the dc power output. Our experimental results show that engineering the interface structure opens up new avenues for developing next-generation semiconductor-based mechanical energy conversion with high performance.

Interfacial friction-induced electronic excitation mechanism for tribo-tunneling current generation

Strong interfacial electronic excitation may be induced by Schottky sliding contact, giving rise to direct-current generation with high current density (J, on the order of 100 A m−2).

Expert assessments on the future of direct current in buildings

Increasing adoption of distributed generation, improving power electronics, and growing electronic loads in buildings have led researchers to propose increased use of direct current (DC) power distribution systems in buildings. As these systems have proven safe and reliable in other applications, they are now being considered for more widespread use in commercial and residential buildings. But nontechnical obstacles remain that have not been addressed in the technical engineering and economic analyses conducted thus far. In this paper, we report on an expert elicitation of 17 experts from industry, research organizations, and the implementation or operation of DC systems to better understand the biggest nontechnical challenges to deploying these systems more broadly. Because these challenges vary based on location, the focus of this study is on the United States of America.Results show that the two biggest barriers are industry professionals unfamiliar with DC and small markets for DC devices and components. To address these, experts proposed developing training programs for engineers and electricians, and developing pilot projects to prove the benefits of DC in niche applications where DC power distribution holds a clear advantage over AC Experts also identified lasting and inherent benefits of DC that make these systems better suited to serve future building loads. These include their ability to interface with distributed generation and onsite DC generation sources such as solar photovoltaics, as well as their ability to communicate and supply power over a single distribution line. Finally, experts identified research priorities to make a better case for what appears to be a promising technological solution to safely and reliably powering future buildings.

Power Generation from a Radiative Thermal Source Using a Large-Area Infrared Rectenna

Electrical power generation from a moderate temperature thermal source by means of direct conversion of infrared radiation is important and highly desirable for energy harvesting from waste heat and micropower applications. Here, we demonstrate direct rectified power generation from an unbiased large-area nanoantenna-coupled tunnel diode rectifier, called a rectenna. Using a vacuum radiometric measurement technique with irradiation from a temperature-stabilized thermal source, a generated power density of 8 nW/cm$^2$ is observed at a source temperature of 450C for the unbiased rectenna across an optimized load resistance. The optimized load resistance for the peak power generation for each temperature coincides with the tunnel diode resistance at zero bias and corresponds to the impedance matching condition for a rectifying antenna. Current voltage measurements of a thermally illuminated large-area rectenna show current zero crossing shifts into the second quadrant indicating rectification. Photon-assisted tunneling in the unbiased rectenna is modeled as the mechanism for the large short-circuit photocurrents observed where the photon energy serves as an effective bias across the tunnel junction. The measured current and voltage across the load resistor as a function of the thermal source temperature represents direct current electrical power generation.

Direct-current triboelectricity generation by a sliding Schottky nanocontact on MoS2 multilayers.

The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting 1-3 . A conventional triboelectric nanogenerator converts frictional energy into electricity by producing alternating current (a.c.) triboelectricity. However, this approach is limited by low current density and the need for rectification 2 . Here, we show that continuous direct-current (d.c.) with a maximum density of 106 A m-2 can be directly generated by a sliding Schottky nanocontact without the application of an external voltage. We demonstrate this by sliding a conductive-atomic force microscope tip on a thin film of molybdenum disulfide (MoS2). Finite element simulation reveals that the anomalously high current density can be attributed to the non-equilibrium carrier transport phenomenon enhanced by the strong local electrical field (105-106 V m-2) at the conductive nanoscale tip 4 . We hypothesize that the charge transport may be induced by electronic excitation under friction, and the nanoscale current-voltage spectra analysis indicates that the rectifying Schottky barrier at the tip-sample interface plays a critical role in efficient d.c. energy harvesting. This concept is scalable when combined with microfabricated or contact surface modified electrodes, which makes it promising for efficient d.c. triboelectricity generation.

Patch Antenna on a Solar Cell for Satellite Communications

The goal of this work was to use new patch antenna structures based on photovoltaic cells. The radiating patch element of a patch antenna was replaced by a solar cell. Direct Current (DC) generation remained the original feature of the solar cell, but additionally it was now able to receive and transmit electromagnetic waves. It is dedicated to harvesting the energy on the one hand and on the other hand to the RF transmission for telecommunications applications in isolated environments. We propose a square grid with four bus bars around the active area, for this geometry fingers are considered uniform and evenly spaced. A mathematical model which would serve the minimization of power losses of the cell and therefore the improvement in the conversion efficiency was studied. A simulation allowed analyzing the performance of the antenna, with a silicon material, and testing its parameters such as the reflection coefficient (S11), gain, directivity and radiated power. The performance analysis of the solar cell patch antenna was conducted using Advanced Design System (ADS) software. Simulation results for this antenna showed a resonance at a frequency of 14.88 GHz with an effective return loss of -14.77dB and a gain of 5.77dBi.

Patch Antenna based on a Photovoltaic Cell with a Dual resonance Frequency

The present work was to use photovoltaic solar cells in patch antenna structures. The radiating patch element of a patch antenna was replaced by a solar cell. Direct Current (DC) generation remained the original feature of the solar cell, but additionally it was now able to receive and transmit electromagnetic waves. Here, we used a new patch antenna structure based on a photovoltaic solar cell. It was then used to collect photo-generated current as well as Radio Frequency (RF) transmission. A mathematical model which would serve the minimization of power losses of the cell and therefore the improvement in the conversion efficiency was studied. A simulation allowed analysing the performance of the antenna, with a silicon material, and testing its parameters such as the reflection coefficient (S11), gain, directivity and radiated power. The performance analysis of the solar cell patch antenna was conducted using Advanced Design System (ADS) software. Simulation results for this antenna showed a dual resonance frequency of 5.77 GHz and of 6.18 GHz with an effective return loss of -38.22dB and a gain of 1.59dBi.

Generation of transverse direct current in a superlattice under a bichromatic high-frequency electric and constant magnetic fields

Direct-current generation in a semiconductor superlattice exposed to a high-frequency bichromatic electric field applied along its axis and to a constant magnetic field perpendicular to the surface, i.e., superlattice axis, is studied. In the first non-vanishing approximation in terms of the magnetic-field strength, an explicit expression for the current density in the case of the ratio of electric-field frequencies equal to two is derived.

Direct Current Generation in Carbon Nanotubes by Terahertz Field

We report on a theoretical investigation of a direct current generation in carbon nanotubes (CNTs) that are stimulated axially by terahertz (THz) field. We consider the kinetic approach based on the semiclassical Boltzmann’s transport equation with constant relaxation time approximation, together with the energy spectrum of an electron in the tight-binding approximation. Our results indicate that for strong THz-fields, there is simultaneous generation of DC current in the axial and circumferential directions of the CNTs, even at room temperature. We found that a THz-field can induce a negative conductivity in the CNTs that leads to the THz field induced DC current. For varying amplitude of the THz-field, the current density decreases rapidly and modulates around zero with interval of negative conductivity. The interval decreases with increasing the amplitude of the THz-field. We show that the THz-field can cause fast switching from a zero DC current to a finite DC current due to the quasi-ballistic transport, and that electron scattering is a necessary condition for switching.

Система генерирования электрической энергии постоянного тока на базе магнитоэлектрического генератора и активного выпрямителя

Система генерирования электрической энергии постоянного тока на базе магнитоэлектрического генератора и активного выпрямителя

Rectification due to harmonic mixing of two coherent electromagnetic waves with commensurate frequencies in carbon nanotubes

We report on a theoretical investigation of carbon nanotubes subjected to a pure alternating electric field consisting of two phase-shifted harmonic fields of frequencies ω1 = Ω and ω2 = 2Ω (harmonic mixing) without any direct current bias. We employed a tight-binding approximation for the description of the energy bands of the carbon nanotubes and the Boltzmann transport equation with constant relaxation time approximation. The results are compared to that of a superlattice under similar conditions. The results indicate a direct current generation by the carbon nanotubes due to the harmonic mixing. The described effect is in essence, due to the nonlinearity associated with the non-parabolicity of the electron energy band, which is greater in the carbon nanotubes than the superlattices. The strong effect observed in the carbon nanotubes is attributed to the stark components and the specific dispersion law inherent in hexagonal crystalline structure of the carbon nanotubes.