Search

Pulse train control technique is realized through the output voltage regulation of switching dc-dc converter by adjusting the control pulse combination of high-power and low-power control pulses in a control pulse repetition cycle. Once the circuit parameters are determined, the control pulse combination is fixed. The control pulse combination directly affects the steady-state performances of pulse train (PT) controller. In this paper, the control pulse combination of PT control technique is studied by using the continued fraction technique. A one-dimensional normal form of discrete-time map of PT controlled buck converter operating in discontinuous conduction mode is also established in which the steady state performances, such as parameter evaluation of multi-periodicities and output voltage ripple of PT controlled DCM buck converter, are analyzed. The simulation result, experimental result, and the results in the literature are in accordance with the theoretical analysis. This investigation is helpful to obtain a deeper understanding of PT control technique.

After dimension reduction, two boundary voltages of V2 controlled buck converter are deduced under different operation mode, based on which, its equivalent one-dimensional discrete-time model is established and complex nonlinear bifurcation behaviors are emphatically studied. Two boundary conditions under which shift between stable period-one state and subharmonic oscillation state and shift between continuous conduction mode (CCM) and discontinuous conduction mode (DCM) take place are derived by analyzing stability and operation mode. The research results show that in V2 controlled buck converter period-doubling bifurcation and border-collision bifurcation can occur with varying circuit parameters and the converter has different bifurcation routes at different circuit parameters. Simulation and experiment platforms are implemented and the corresponding results verify the validity of equivalent discrete-time model and theoretical analysis.

The two inductor current boundaries are derived, and segmented smooth iteration mapping model of current controlled quadratic boost converter is established based on the detailed description of switching states. The comparative analyses of the nonlinear bifurcation behaviors are performed with input inductor current and the storage inductor current as current feedback respectively. Two boundary conditions for the transition from stable period-one state to sub-harmonic oscillation state and for the transition from discontinuous conduction mode to continuous conduction mode are derived by analyzing stability and operation mode. The operation-state regions corresponding to circuit parameter regions are estimated by utilizing the parameter-space maps. An experimental circuit is built and the results show that both different bifurcation routes and operation mode transition phenomenon are changed with parameter variation, the current controlled quadratic boost converter exhibits complicated dynamical behaviors. The experimental results verify the correctness of the theoretical analysis.

In this paper, the ZnO nanorod arrays (NRAs) with a diameter of 50nm and a length of 250 nm were synthesized by chemical bath deposition method. Two devices with structures of ITO (indium tin oxides)/ZnO/poly-(3-hexylthiophene) (P3HT)/Au and ITO/ZnO@ZnS/P3HT/Au were fabricated and their performances were tested and evaluated separately. The I-V curves were measured for discussion of the threshold voltage, series resistance, reverse leakage current, and rectification ratio. Results show that the device with modified ZnO shows a decline in the threshold voltage, series resistance and reverse leakage current, but has an enhanced rectification ratio. The effect of ZnS coating on the improvement of conductive properties of the device could be attributed to the suppression of the non-radiative recombination of surface defects as shown by means of photoluminescence spectrum.

By introducing ramp compensation current into the feedback control circuit of current controlled switching DC-DC converter it can not only effectively extend the stable operation range of the switching DC-DC converter to realize chaotic stability control, but also shift its operation mode from discontinuous conduction mode to continuous conduction mode to realize operation mode shift. Taking current-controlled buck-boost converter as example by establishing the two-dimensional discrete-time model and the corresponding Jacobian matrix of current-controlled buck-boost converter with ramp compensation and two inductor current borders, the dynamical mechanism of ramp compensation for switching DC-DC converter is investigated. By analyzing the conditions of the instability and border collision bifurcation, the effects of the ramp compensation on the stable period oscillation and operation mode shift of switching DC-DC converter are discussed, and the corresponding stability boundary and mode shift boundary are obtained. Finally, an experimental circuit is built and the results are observed, from which the physical significance of the ramp compensation for chaotic stability control and operation mode shift of switching DC-DC converter is illustrated and the correctness of theoretical analysis is verified.

A dynamical model is proposed and the corresponding characteristic aligns are derived for voltage-mode bi-frequency controlled switching converter operating in discontinuous conduction mode. According to the dynamical model, the border-collision bifurcation and multi-period behaviors, such as period-2, period-3, period-4, and so on, are studied using bifurcation diagrams as the circuit parameters are varied. It is found that the converter behaves along the bifurcation route of period-1, multi-period, and period-1, and the change of period state is induced by border-collision bifurcation. Based on the characteristic equation, the converter stability is investigated by the Lyapunov exponent. It is shown that Lyapunov exponent is always smaller than zero with the variation of circuit parameters and the converter operates in stable period state all the time. Also, it is validated that period-3 behavior of voltage-mode bi-frequency controlled switching converter does not predicate its inevitable chaos. Time-domain waveforms, phase portraits, and frequency spectra of voltage-mode bi-frequency controlled switching converter are analyzed by circuit simulation, which validates the feasibility of dynamical model and the correctness of theoretical analysis. Simulation results are verified by experiments in this paper.

Er3+-doped 25BaO-(25-x)SiO2-xAl2O3-25B2O3 transparent glasses are prepared with x = 0, 12.5 and 25 by a solid-state reaction. The Er-related NIR luminescence intensity, which corresponds to the transition of 4I15/2-4I13/2, is obviously altered with different silicon/aluminum ratios. The Judd-Ofelt parameters of the Er3+ ions are adopted to explain the intensity change in the NIR fluorescence, and the Raman scattering intensity versus the amount of Al and/or Si components are discussed. The spectra of the three samples are quite similar in the peak positions, but different in intensity. The maximal phonon density of state for the samples is calculated from the Raman spectra and is correlated to the NIR luminescence efficiency.

Based on the power simulation software, the reason of the output voltage phase lagging behind the inductor current phase is analyzed qualitatively, and the mechanism to cause the pulse bursting phenomenon in fixed-off-time (FOT) controlled Buck converter is explained. The way to choose the equivalent series resistance (ESR) of output capacitor to eliminate these complex nonlinear phenomena is discussed. The critical ESR to ensure the state operation of FOT controlled Buck converter is obtained. The study results indicate that the ESR has a great effect on the operation state of FOT controlled Buck converter. When the ESR is smaller than the critical value, the output voltage phase lags behind the inductor current phase, resulting in the pulse bursting phenomenon; while when the ESR is larger than the critical value, the output voltage variation keeps in phase with the inductor current variation, the pulse bursting phenomenon disappearing. In addition, the describing function method is used to obtain the transfer function from the reference voltage to the output voltage. By using the Routh-Hurwitz criterion, it is indicated that the critical ESR is the condition of destabilizing FOT controlled Buck converter.

According to the charge variation of output capacitor in a switching cycle, the output voltage variation in a switching cycle can be obtained, from which an approximate discrete-time model of pulse train (PT) controlled buck converter operating in discontinuous conduction mode (DCM) is established. Based on the model, the border-collision bifurcations of the PT controlled DCM buck converter with the variations of the load resistance and the input voltage are studied. By constructing the corresponding iterative map curves, the stabilities of the fixed points, formed by the orbits of period-1, period-2, period-3 and so on, are analyzed, and the mechanisms of border-collision bifurcations of the converter under different operation states are revealed. The analysis results indicate that with the variation of parameters, the PT controlled DCM buck converter always operates in different periodic states, in which the change of the operation mode with periodic state is caused by the border-collision bifurcation and the lyapunov exponent is always less than zero. By using PSIM circuit simulation software, the time domain waveforms and phase portraits under different load resistances are obtained. Experimental results are provided to verify the correctnesses of theoretical analyses and circuit simulations and the feasibility of dynamical modelling.

In this paper, a practical equivalent circuit of an active flux-controlled memristor characterized by smooth piecewise-quadratic nonlinearity is designed and an experimental chaotic memristive circuit is implemented. The chaotic memristive circuit has an equilibrium set and its stability is dependent on the initial state of the memristor. The initial state-dependent and the circuit parameter-dependent dynamics of the chaotic memristive circuit are investigated via phase portraits, bifurcation diagrams and Lyapunov exponents. Both experimental and simulation results validate the proposed equivalent circuit realization of the active flux-controlled memristor.

KBr:Pr with a submicron rod structure is successfully synthesized by a solid-state reaction using absolute alcohol as the abrasive. X-ray diffraction, scanning electron microscopy, photoluminescence spectra and fluorescence decay curves are used to characterize the resulting materials. The influences of Pr3+ dopant concentration on the luminescence and lifetime are discussed. Furthermore, luminescent measurements show that KBr:Pr has a high emission intensity compared with other Pr-doped matrixes, which is related to the low phonon energy of KBr. The results suggest that the phonon energy of the host is important in determining the luminescent efficiency.

In this paper, the low-frequency oscillation phenomenon in a pulse train (PT) controlled buck converter operating in continuous conduction mode (CCM) is found and studied. The mechanism of this low-frequency oscillation phenomenon and the way to suppress it are studied. The time-domain simulation results and their corresponding phase portraits indicate that the equivalent series resistance (ESR) of the output filter capacitor has a critical effect on this low-frequency oscillation phenomenon. When the ESR is zero or small enough, such a low-frequency oscillation phenomenon appears in the PT controlled CCM buck converter because the output voltage can not be regulated timely. With the increase of ESR, the PT controlled CCM buck converter operates chaotically. The output voltage can be regulated timely and such a low-frequency oscillation phenomenon can be suppressed effectively. Experimental results are provided to verify the theoretical analyses and the simulations.

Peak current controlled buck converter with current source load shows the complex phenomenon of fast-scale and slow-scale subharmonic oscillations. Its piecewise smooth switching model and discrete iterative map model are established in this paper. According to its discrete iterative map model, the effects of circuit parameters on the nonlinear dynamic behaviors of buck converter are analyzed by numerical simulation. It is found that attractive regions of fast-scale and slow-scale subharmonic oscillations and dual tori phenomena exist in the bifurcation diagram and Poincaré mapping, respectively. Time-domain simulation waveforms and phase portraits of buck converter are obtained by Runge-Kutta algorithm using the piecewise smooth switching model. The research results indicate that n-type subharmonic oscillation constituted by subharmonic oscillation and frequency-reduced subharmonic oscillation exists in the inductor current, and sine-type subharmonic oscillation constituted by fast scale and low scale exists in the output voltage, respectively. Analysis and simulation results are verified by experimental results.