Variable Duty Cycle Research Articles

An Open-Loop Start-up Method for LLC Resonant Converter with Fixed Frequency and Variable Duty Cycle

An open-loop start-up method with fixed frequency and variable duty cycle for LLC resonant converter is proposed in this paper. The start-up method adopts pulse width modulation (PWM) technology to control LLC resonant converter with fixed switching frequency and variable duty cycle. Compared with conventional start-up method that uses a relative high switching frequency to start-up the converter with closed control loop, the proposed start-up method can reduce the start-up frequency, then the switching loss and driving loss during the start-up process can be reduced. Moreover, the proposed method can fast start-up the converter with low device`s electrical stress. Because high start-up frequency is no need for the proposed start-up method, then the hardware cost of driving chip can be decreased. The theory and the logic of the proposed start-up method is detailed analysed in this paper. The correctness and effectiveness of the proposed start-up method are verified by the built simulation results.

Tailoring the chemical composition and microstructure of CrxN deposited by HiPIMS through duty-cycle modifications

The development of homogeneous, dense, and smooth hard coatings is a challenging task, and that is why the high power impulse magnetron sputtering (HiPIMS) method has been proposed to tailor and control the microstructure through the modification of the duty cycle. HiPIMS offers extensive possibilities to obtain good quality films with fine and dense morphology. In this work, the synthesis of Cr x N coatings by HiPIMS with the variation of duty cycle (τ = 2.7% and 12%), substrate bias voltages (V b = −150 and − 250 V), and gas ratio ( f N 2/ Ar = 0.2 and 0.4) was evaluated. The influence of these processing conditions on the chemical composition, microstructure, and adhesion of HiPIMS Cr x N was investigated. A significant increment of the deposition rate and the chromium content in the Cr x N coatings is observed at τ = 12%; meanwhile, at τ = 2.7%, films showed high nitrogen content. The crystalline phases like α-Cr + h-Cr 2 N, h-Cr 2 N, and h-Cr 2 N + c-CrN were identified in the as-deposited films. The Cr-rich coatings presented faceted columns with cauliflower-like surface morphology , while the growth of the h-Cr 2 N phase caused a grain size refinement and a denser microstructure. The surface morphology of the h-Cr 2 N coatings changed from pyramidal to stacked pyramids with the reduction of the duty cycle. The transformation of the h-Cr 2 N to c-CrN leads to highly dense columnar microstructures with a fine granular morphology and a smooth surface. The duty cycle strategies can be applied to develop a particular microstructure with specific chemical composition and crystallographic phases, resulting in an alternative method to produce graded or multilayer systems. The duty cycle reduction increases the interfacial adhesion strength of the coatings. • Duty cycle modifies composition, phases, microstructure, and morphology. • Higher duty cycle enhances target current and coating deposition rates. • Duty cycle strategy is a good option to deposit graded or multilayer systems.

A grid interface current control strategy for DC microgrids

In this paper, a grid interface current control strategy is presented for a DC microgrid, which aims to reduce the disturbance from PV generation and the load variation to the main grid without a grid interface converter. The grid interface current is directly controlled by a battery DC-DC converter within the DC microgrid. Based on a comprehensive analysis of the battery DC-DC converter and interface current control, the control system has been mathematically modelled. This enabled two transfer functions to be derived that reflect the dynamic response of the inductor current to the duty cycle variation (inner loop), and the dynamic response of the grid interface current to the inductor current variation (outer loop). Experimental study has been done to assess the effectiveness of the proposed control strategy. The experimental results indicate that the proposed control strategy has a good performance to control the grid interface current without an interface converter, regardless the variations of both PV and the load conditions.

Duty cycle variation methods for Bragg gratings: comparative study and optimal design

An analysis of spectral response apodization by duty cycle methods for grating-assisted optical filters is presented. The study is performed for the case of codirectional couplers, Bragg reflectors, and mirrors. The modeling results show that the supersymmetric duty cycle (SDC) modulation method, initially considered for parity–time symmetric gratings in Lupu et al. [IEEE J. Sel. Top. Quantum Electron. 22, 35 (2016)10.1109/JSTQE.2016.2542791IJSQEN1077-260X], performs better than the other methods. An analytical approach to the transfer matrix of the modulated grating explains the better performance of the SDC method.

Arduino Controller Based 3-Switch Isolated DC-DC Boost Converter for PV and Battery Application

This paper discusses a Arduino controlled 3-switch Isolated DC-DC Boost converter for PV and battery application. The presented converter has vital benefits such as a switch reduction, snubber circuit elimination with an additional diode, a capacitor; obtain the same primary and secondary voltage waveforms of the transformer with duty cycle variation. The MATLAB Simulink model of the presented converter for 95W PV system has been developed for 20V dc input. The hypothetical forecasts and the performance of the PV based presented converter has been effectively confirmed with the aid of simulation results. The experimental setup of the presented converter for 100W PV module has been successfully implemented using Arduino Uno microcontroller to confirm the simulation outcomes.

Interposed pulsed power system for fast separation of radioactive beams

This paper presents the novel design of an interposed pulsed power system, developed to drive a fast-switching magnet with a large multi-mH load inductance, and high field amplitude (> 1 T). This modulator can produce variable flat-top pulses from 1 to 30 ms with rise and fall times of less than 0.5 ms at a variable duty cycle of 3–91% into a heavily inductive load. The system employs a novel over-voltage topology to overcome the inherent inductance and achieve the fast rise and fall times, switching to a precision DC supply to efficiently maintain the flattop without requiring many-kV voltage. We present a power source design consideration, including the results of computer modeling as well as the first experimental results of a modulator scaled test model will also be presented.

Imperfections of Scalar Approximation in Calibration of Computer-Generated Holograms for Optical Surface Measurements

Computer-generated hologram (CGH) null correctors are used as accuracy standards for interferometric measurements of optical surfaces and optical systems. Diffractive optics calibrators (DOCs) have been developed to evaluate the phase tolerance of CGHs based on scalar approximation by measuring variations in duty cycle and etching depth. However, if the grating period of a CGH < 5λ, the scalar approximation is not accurate for phase analysis and reconstruction. In this study, the measurement errors of DOCs with small-period CGHs were investigated and experimentally verified. Results show that the imperfections of scalar approximation in CGHs cannot be ignored and the development of rigorous evaluation methods to improve the measurement accuracy of CGHs is of great practical significance.

A Search for Rapid Mid-infrared Variability in Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxies

Abstract Fermi-LAT’s detection of γ-rays from narrow-line Seyfert 1 galaxies (NLS1s) has received increasing attention. Understanding these γ-NLS1s is of interest because they have some properties similar to blazars, which are known to show rapid and large-amplitude variability. Based on the largest sample of γ-NLS1s (25 sources), we carried out a systematic search for rapid mid-infrared (MIR, 3.4 and 4.6 μm) variability using the multiepoch data of the Wide-field Infrared Survey Explorer (WISE). We also compared a few variability properties between γ-NLS1s and γ-ray blazars. Our main results are as follows. (1) Thirteen γ-NLS1s showed significant (>3σ) rapid variability in at least one of the two MIR bands. The MIR emission of these sources is dominated by the synchrotron emission of relativistic electrons in the jet. (2) The γ-NLS1s with flat radio spectra are more variable than those not detected in γ-rays. (3) The γ-NLS1s tend to show smaller amplitude of variability as well as lower duty cycle relative to γ-ray blazars. (4) The γ-NLS1s tend to show a trend of bluer-when-brighter on both intraday and long timescales, similar to γ-ray blazars. (5) The γ-NLS1s that are more variable on long timescales have larger amplitudes of variability and higher duty cycles on intraday timescales. (6) In the majority of cases, the γ-NLS1s fall in the WISE Gamma-ray Blazar Strip (WGS). However, we noted migrations outside of the WGS due to significant variability.

Incorporation of P5+ and P3− from phosphate precursor in TiO2:P coatings produced by PEO: XPS and DFT study

The study of the incorporation of P ions in TiO2 coatings was carried out in this work using Plasma Electrolytic Oxidation (PEO) technique, which was analyzed using XPS and compared with simulations using DFT. The synthesis was carried out using the PEO technique making variations of the useful duty cycle between 10 and 50%. The solution used is composed of Na3PO4 and NaOH, with a process duration of 7 min. The TiO2/P coatings were characterized by XPS with high resolution spectra and analyzed by deconvolution of the spectra. The XPS results showed the incorporation into the crystal lattice of P ions in the form of phosphate ions [(PO4)3−] and phosphide ions (P3−). Density functional theory (DFT) calculations were carried out to demonstrate the formation of various structural defects in titanium dioxide systems. The results show the coexistence of TiO2, TiO2/PO4 and TiO2/P. In this case, the reduction of phosphorus from P5+ to P3− favors the generation of titanium phosphide (TiP) that occurs as a consequence of the high temperature generated in discharge channels (ton). Single and multiple P substitutions formation energies are presented showing that all the substitutions studied are energetically favorable. The single replacement of the P atom in TiO2 sites were calculated showing that the replacement of P at the Ti site is energetically preferred over the replacement of P at the O site with replacement energies of 0.47 eV and 1.42 eV respectively. Along the same lines, a narrowing of the band gap and a shift to the left of the states were observed in all the calculations presented due to the presence of P in the general structure. Finally, the calculation of various substitutions of P in TiO2 with the amount of P replaced in the experimental observations showed an accumulation of electron density in the energy gap attributed mainly to the orbitals of the substituted P.

A Case Study: Influence of Circuit Impedance on the Performance of Class-E2 Resonant Power Converter for Capacitive Wireless Power Transfer

The evolution of power electronics led to rapid development in wireless charging technology; as a result, a single active switch topology was introduced. The present market utilizes inductive wireless power transfer (IPT); because of the disadvantages of cost, size, and safety concerns, research on wireless power transfer was diverted towards capacitive wireless power transfer (CPT). This paper studies the optimal impedance tracking of the capacitive wireless power transfer system for maximum power transfer. Compared to prior methods developed for maximum power point tracking in power control, this paper proposes a new approach by means of finding impedance characteristics of the CPT system for a certain range of frequencies. Considering the drone battery as an application, a single active switch Class-E2 resonant converter with circular coupling plates is utilized. Impedance characteristics are identified with the help of equations related to the input and resonant impedance. The impedance tracking is laid out for various resonant inductors, and the difference in current peak is observed for each case. Simulations verify and provide additional information on the reactive type. Additionally, hardware tests provide the variation of input current and output voltage for a range of frequencies from 70 kHz to 300 kHz. Efficiency at the optimal impedance points for a resonant inductor with 50 μH and 100 μH are tested and analyzed. It is noted that the efficiency for a resonant inductor with 50 μH is 8% higher compared to the CPT with a 100 μH resonant inductor. Further hardware tests were performed to investigate the impact of frequency and duty cycle variation. Zero-voltage-switching (ZVS) limits have been discussed with respect to both frequency and duty cycle.

Fast switching magnet for heavy ion beam separation

This paper presents the design for a switching magnet capable of deflecting 6.5 MeV/u heavy-ion beams with mass-to-charge ratio of 7 by 10 degrees. This magnet can produce variable flat-top pulses from 1 to 30 ms with rise and fall times of less than 0.5 ms at a variable duty cycle of 3–91% into a heavily inductive load. The magnet has a laminated, iron dominated, H-shaped core. Directly-cooled copper pancake coils energize the magnet. We present the magnet design considerations, including the results of extensive computer modeling. We also present the conceptual engineering design and the studies of magnet yoke fabrication.

Influence of pulsed-substrate bias duty cycle on the microstructure and defects of cathodic arc-deposited Ti1-xAlxN coatings

The influence of pulsed substrate bias duty cycle on the growth, microstructure, and defects of Ti 1-x Al x N coatings grown by cathodic arc deposition was investigated. Ti 1-x Al x N coatings of varying compositions (x = 0.56, 0.38, 0.23) were deposited on cemented carbide substrates with 10, 25, 50, and 95% duty cycles of −50 V pulsed-bias under 10 Pa of pure N 2 gas. Coatings grown at low duty cycles (10 and 25%) showed strongly textured, under-dense coatings with facetted columns and low amount of lattice defects. Applying higher duty cycles (50 and 95%) produced coatings that have denser microstructures, less preferred orientation, increasing compressive stresses and increased lattice defect densities. Our study elucidates how duty cycle variation not only changes the overall average energy supplied at the growth front but also kinetically influences the coating growth and thus microstructure and defect structure. • Ti 1-x Al x N coatings were grown on WC-Co substrates with 10, 25, 50, and 95% duty cycles of -50 V pulsed-substrate bias. • Duty cycle variation significantly and systematically affected their growth, microstructure, and crystallographic defects. • Low duty cycle conditions produced textured, under-dense coatings with facetted columns and low amount of lattice defects. • Higher duty cycles produced coatings that have denser microstructures, less texture, compressive stresses and increased lattice defects. • Duty cycle change was a powerful tool to achieve arc coatings with low defect density, high crystal quality and low stress.

Design features of negative feedback and power smoothing filter of the DC / DC converter with pulse loads for transmitter-receiver modules of active electronically scanned arrays

The fundamental difference of the voltage converter of the secondary power supply source for the transmitter-receiver modules of active electronically scanned arrays with impulse load and variable duty cycle from traditional voltage converters that constantly consume power from the primary network is shown. Methods for improving the quality of transient processes in voltage converter with constant power consumption during start-up by soft start are not applicable to improve the quality of transients in periodic current pulses caused by a pulsed load. Since any ripples, noises, instabilities in the power supply of the transmitter-receiver modules of active electronically scanned arrays operating in a linear mode lead to parasitic amplitude modulation of the emitted signal and to a deterioration in the quality of selection and target tracking, very strict requirements are imposed on the quality of the transmitter-receiver modules supply voltage (voltage ripple kп ≤ 0,5 %, the amount of overshoot of the output voltage sU ≤ 2 %, etc.). The article shows that such a quality of the output voltage with a pulsed load of the transmitter-receiver modules of active electronically scanned arrays can be obtained using a lower-type voltage converter, with a double-circuit negative feedback for the output voltage and current of the inductor, with a storage capacitor and with a power smoothing filter with the characteristics of Chebyshev and Butterworth. The work investigated the influence of the negative feedback depth on the output voltage and current of the smoothing filter choke, the value of the storage capacitor capacity, the type and parameters of the smoothing filter, and recommendations were given to select their optimal values, at which the required quality of the supply voltage for the transmitter-receiver modules of active electronically scanned arrays was ensured, taking into account the minimization of their dimensions.

Loss-coupled DFB nano-ridge laser monolithically grown on a standard 300-mm Si wafer.

We present a loss-coupled distributed feedback microlaser, monolithically grown on a standard 300-mm Si wafer using nano-ridge engineering. The cavity is formed by integrating a metallic grating on top of the nano-ridge. This allows forming a laser cavity without etching the III-V material, avoiding damaged interfaces and the associated carrier loss. Simulations, supported by experimental characterisation of the modal gain of the nano-ridge devices, predict an optimal duty cycle for the grating of ~0.4, providing a good trade-off between coupling strength and cavity loss for the lasing mode. The model was experimentally verified by characterising the lasing threshold and external efficiency of devices exhibiting gratings with varying duty cycle. The high modal gain and low threshold obtained prove the excellent quality of the epitaxial material. Furthermore, the low loss metal grating might provide a future route to electrical injection and efficient heat dissipation of these nanoscale devices.

A reliability assessment approach for a Hodgkin-Huxley neuron circuit

The performance of the Hodgkin-Huxley neuron circuits used in novel communication and computer systems depends on its capacitors. Thus, degradation of capacitors in neuron circuits may have significant impact on reliability of the neuron. In this paper, a simulation-based reliability assessment approach was developed for a Hodgkin-Huxley neuron circuit to consider the degradation of capacitors. SPICE simulation, neural information coding method, and degradation modelling of capacitors are integrated to assess impact of capacitors on the given neuron circuit. A MOS-based Hodgkin-Huxley neuron circuit is simulated to obtain output waveforms with degraded capacitors. It has been found that the output waveform of the selected neuron changes significantly with capacitors' degradation. In the total operation range of the neuron, degradation of capacitors may result in significant errors and loss of neural information. Capacitor's degradation elevates the duty ratio threshold for generating voltage spikes, and would lead to higher values of the inter-spike interval, regardless of variation of input period and duty cycle. However, by limitation of the input range and duty ration, information carried by S-Space code is transmitted correctly.

Investigation: Cutting Transport Mechanism in Inclined Well Section under Pulsed Drilling Fluid Action

Due to gravity, drilling cuttings are easily accumulated in an inclined well section, ultimately forming a cuttings bed, which places the drill pipe under strong friction torque. In severe cases, this can cause dragging, stuck drills, and broken drill tools. Because conventional drilling fluids are difficult to prevent the formation of cuttings in inclined well sections, a method of carrying cuttings with the pulsed drilling fluid to improve wellbore cleanness is proposed. Experiments and numerical simulations are conducted to investigate the effects of cuttings bed transport velocity, cuttings size, cuttings height, drill pipe rotation speed, cuttings bed mass, and roughness height. The optimal pulse parameters are determined per their respective impact on cuttings transport concerning varied periods, amplitudes, and duty cycles of the pulsed drilling fluid. Compared to cuttings transport under the conventional drilling fluid flow rate, the pulsed drilling fluid produces the turbulent dissipation rate, increases cuttings transport velocity, and thus improves the wellbore clearance rate.

Energy Efficient MAC with VariableDuty Cycle for Wireless Sensor Networks

ABSTRACT WSN consists of many sensors, they need high throughput and network lifetime to get involved in communication. Duty Cycle is a key factor in sensor nodes to maintain sleep, active condition in the presence of overhearing, collisions of packets while data transmission between sensor nodes. The key challenge of sensor nodes is to attain high energy efficiency, throughput and low End-End Delay. This paper presents several of existing approaches for MAC protocol. They are (1) Synchronization between nodes (2) Mathematical Analysis (3) TDMA based MAC and (4) Cross-Layer Design. We proposed a new method for MAC protocol with variable duty cycle. Neighboring nodes follow same duty cycle and same active time. Far away nodes doesn’t maintain same duty cycle, hence their active time is not same. The duty cycle is maintained in synchronous way and adaptive manner among the nodes within the network. In this paper, a conventional MAC and proposed MAC are simulated using NS-2.35. Variable duty cycle approach in the proposed MAC with sleep and idle states for the nodes yields better throughput and energy efficiency with respect to other conventional technique. These results validate that the proposed variable DC-MAC is feasible for Wireless Sensor Network applications.

Current Limiting in Overload Conditions of an LLC-Converter-Based DC Transformer

The dc transformers based on an LLC converter operated in open loop near resonant frequency have several crucial advantages compared to other topologies. These advantages are the stiff voltage ratio with a natural power flow, the dc grid isolation via medium-frequency transformer, and the high efficiency due to the resonant converter nature. Despite these advantages, the open-loop operation does not provide any options to limit the transferred current during overload conditions in the dc grid. This is critical, since it prevents the grid from recognizing that either some local primary regulation or load shedding is required. This article proposes a closed-loop control method that utilizes variable duty cycles to limit the current once the overload situation is detected. An applicable control scheme is derived and implemented. Since the duty-cycle modulation increases the losses of the converter, an online thermal model is implemented to protect the dc transformer during the overload conditions. The proposed current-limiting mode with the thermal model are validated using an exemplary low-voltage dc transformer prototype, demonstrating the general feasibility and overall good performance.

Embedded processor system for controllable period-width multichannel pulse width modulation signals

This paper proposes a sophisticated embedded processor system configured on zynq-xc7z020 field programmable gate array (FPGA) device for generating four channels pulse width modulation signals with variable duty cycles and periods using embedded design techniques. The main advantages of the technique are the high ability to perform a simultaneous control on period and pulse width of the generated signals and a high system design adaptation to choose the number of input/output channels. Controlling the the period and the pulse width is achieved by injecting a digital signal to the designed system to manipulate embedded timers’ operation. Vivado design suite is used to develop the system hard ware in the integrated development environment where the processing unit and peripherals are instantiated and interconnected. A practical aplication program in C language is prepared to make the system act according to the target. The designed system can be used to drive multi-phase D.C to D.C convertors. The system performance is verified by using vivado logic analyzer and chipscope windows. The superiority of the proposed approach over other approaches is that it resulted in a multi-inputs/multi-outputs pulse width modulation system with high controllability on the pulse width and the period that ranges from 15 nsec to 60 sec.

Design of a Portable Photovoltaic I–V Curve Tracer Based on the DC–DC Converter Method

The I–V curve tracer is an instrument that captures the current–voltage characteristics of photovoltaic (PV) generators under real operating conditions. Such device can be used to evaluate their performance and identify faults or aging effects, but its high costs have prevented it from being widely used in the industry. This article thus proposes the design of a low-cost, portable I–V curve tracer based on the classic dc–dc Cuk converter for PV modules of up to 300 W. In order to obtain a compact device, some design techniques are proposed, including circuit reduction, high switching frequency operation, specification of the optimum load resistor power rating, and improved measurement distribution because of a nonlinear duty cycle variation. Experimental curves were compared with those acquired from commercial PV tracers to demonstrate its accuracy. In addition, the physical parameters of the well-known single-diode model have been extracted and compared with data provided by manufacturers to identify aging effects and module performance.