Quasi-resonant Mode Research Articles

Quasinormal modes of acoustic black hole

In this paper the electromagnetic and massive scalar perturbations of the Schwarzschild acoustic black hole are studied and their characteristic oscillation frequencies, so-called quasinormal modes are calculated. It has been shown that the odd- and even-parity electromagnetic perturbations are isospectral. We have shown that small value of a tuning parameter (ξ<2) of the acoustic black hole decreases the frequency and damping rate of perturbations. A quasi-resonance modes of the massive scalar perturbations that corresponds to possible maximum value of mass of the scalar field to generate the quasinormal modes have been determined. The mass of the scalar field makes the perturbations longer-lived. The time-domain analysis of the perturbations have shown that the acoustic black hole is stable against electromagnetic and scalar perturbations.

An Analytical Model of Dynamic Power Losses in eGaN HEMT Power Devices.

In this work, we present an analytical model of dynamic power losses for enhancement-mode AlGaN/GaN high-electron-mobility transistor power devices (eGaN HEMTs). To build this new model, the dynamic on-resistance (Rdson) is first accurately extracted via our extraction circuit based on a double-diode isolation (DDI) method using a high operating frequency of up to 1 MHz and a large drain voltage of up to 600 V; thus, the unique problem of an increase in the dynamic Rdson is presented. Then, the impact of the current operation mode on the on/off transition time is evaluated via a dual-pulse-current-mode test (DPCT), including a discontinuous conduction mode (DCM) and a continuous conduction mode (CCM); thus, the transition time is revised for different current modes. Afterward, the discrepancy between the drain current and the real channel current is qualitative investigated using an external shunt capacitance (ESC) method; thus, the losses due to device parasitic capacitance are also taken into account. After these improvements, the dynamic model will be more compatible for eGaN HEMTs. Finally, the dynamic power losses calculated via this model are found to be in good agreement with the experimental results. Based on this model, we propose a superior solution with a quasi-resonant mode (QRM) to achieve lossless switching and accelerated switching speeds.

A Dual-Mode Control Scheme to Improve Light Load Efficiency for Active-Clamp Flyback Converter

A novel dual-mode control scheme is proposed in this paper that permits the active-clamp flyback (ACF) converter to operate in both the quasi-resonant (QR) mode under light load and the active-clamp mode under medium or heavy load. The mode transition is performed based on the external dual-mode control circuit. In addition, the proposed converter incorporates a new QR mode valley switching (VS) control circuit that reduces switching loss in the main switch by achieving VS. Under medium to full load, the proposed converter becomes an ACF converter designed to achieve zero-voltage switching (ZVS), which reduces switching losses in both power switches. The proposed dual-mode control ACF converter has the following advantages: (1) compared with conventional ACF converters, the proposed ACF converters minimize switching losses by combining VS and ZVS; (2) under light load conditions, the frequency-limiting QR control mechanism is used to avoid disadvantageous switching losses caused by high switching frequencies. The 65 W ACF converter prototype with a DC 155 V input and a DC 19 V/3.42 A output under 65 kHz switching frequency was implemented. The experimental results demonstrate the feasibility of the proposed control scheme. The efficiency of the proposed converter reached 79% at a load of 3.5 W, which is 11% higher than the conventional ACF converter.

Stability and phase transition of rotating Kaluza\u2013Klein black holes

In this paper, we investigate the thermodynamics and phase transitions of a four-dimensional rotating Kaluza–Klein black hole solution in the presence of Maxwell electrodynamics. Calculating the conserved and thermodynamic quantities shows that the first law of thermodynamics is satisfied. To find the stable black hole’s criteria, we check the stability in the canonical ensemble by analyzing the behavior of the heat capacity. We also consider a massive scalar perturbation minimally coupled to the background geometry of the four-dimensional static Kaluza–Klein black hole and investigate the quasinormal modes by employing the Wentzel–Kramers–Brillouin (WKB) approximation. The anomalous decay rate of the quasinormal modes spectrum is investigated by using the sixth-order WKB formula and quasi-resonance modes of the black hole are studied with averaging of Padé approximations as well.

Study of Forward and Backward Modes in Double-Sided Dielectric-Filled Corrugated Waveguides.

This work studies the propagation characteristics of a rectangular waveguide with aligned/misaligned double-sided dielectric-filled metallic corrugations. Two modes are found to propagate in the proposed double-sided configuration below the hollow-waveguide cutoff frequency: a quasi-resonant mode and a backward mode. This is in contrast to the single-sided configuration, which only allows for backward propagation. Moreover, the double-sided configuration can be of interest for waveguide miniaturization on account of the broader band of its backward mode. The width of the stopband between the quasi-resonant and backward modes can be controlled by the misalignment of the top and bottom corrugations, being null for the glide-symmetric case. The previous study is complemented with numerical results showing the impact of the height of the corrugations, as well as the filling dielectric permittivity, on the bandwidth and location of the appearing negative-effective-permeability band. The multi-modal transmission-matrix method has also been employed to estimate the rejection level and material losses in the structure and to determine which port modes are associated with the quasi-resonant and backward modes. Finally, it is shown that glide symmetry can advantageously be used to reduce the dispersion and broadens the operating band of the modes.

Stability and quasinormal modes of black holes in conformal Weyl gravity

In this paper, we first investigate the thermal stability of black holes in conformal Weyl gravity with a comparison with the Schwarzschild black holes. Then, we consider a minimally coupled massive scalar perturbation and calculate the quasinormal modes in asymptotically dS spacetime by employing the sixth order WKB approximation and asymptotic iteration method. The deviations from those of the Schwarzschild-dS solutions are obtained and the possibility of the presence of quasi-resonance modes for Weyl black hole solutions is investigated. Finally, we consider a massless scalar perturbation in the background of asymptotically AdS solutions and calculate the quasinormal modes by using the pseudospectral method. The effects of the free parameter of the theory on the quasinormal modes are studied and deviations from those of the Schwarzschild-AdS black holes are investigated. The imaginary part of quasinormal frequencies in AdS spacetime is the time scale of a thermal state (in the conformal field theory) to approach thermal equilibrium.

Quasi-normal modes and stability of Einstein\u2013Born\u2013Infeld black holes in de Sitter space

We study gravitational perturbations of electrically charged black holes in (3+1)-dimensional Einstein–Born–Infeld gravity with a positive cosmological constant. For the axial perturbations, we obtain a set of decoupled Schrödinger-type equations, whose formal expressions, in terms of metric functions, are the same as those without cosmological constant, corresponding to the Regge–Wheeler equation in the proper limit. We compute the quasi-normal modes (QNMs) of the decoupled perturbations using the Schutz–Iyer–Will’s WKB method. We discuss the stability of the charged black holes by investigating the dependence of quasi-normal frequencies on the parameters of the theory, correcting some errors in the literature. It is found that all the axial perturbations are stable for the cases where the WKB method applies. There are cases where the conventional WKB method does not apply, like the three-turning-points problem, so that a more generalized formalism is necessary for studying their QNMs and stabilities. We find that, for the degenerate horizons with the “point-like” horizons at the origin, the QNMs are quite long-lived, close to the quasi-resonance modes, in addition to the “frozen” QNMs for the Nariai-type horizons and the usual (short-lived) QNMs for the extremal black hole horizons. This is a genuine effect of the branch which does not have the general relativity limit. We also study the exact solution near the (charged) Nariai limit and find good agreements even far beyond the limit for the imaginary frequency parts.

A Dual Active Clamp DC–DC Converter With High Voltage Gain

In this article, a novel dual active clamp converter with high voltage gain is proposed for dc-dc applications. The active clamps' switches turn on and off under zero-current switching (ZCS). In addition, the main switch turns on under ZCS condition, as well. Therefore, switching losses are significantly reduced. The converter is also capable of operating under quasi-resonance (QR) mode. In this mode, switching losses are reduced further by lowering the voltage and current, at which the main switch turns off. In comparison with the conventional interleaved converter, the voltage gain of the proposed converter is almost the same, but the number of semiconductors and switching loss are significantly reduced. The switching frequency of the active clamps' switches is half of the main switching frequency. The operation principles of the proposed converter are studied in both pulsewidth modulation and QR modes, and the advantages are investigated. A 200-W prototype is implemented to validate the desired functionality of the converter, and experimental results are compared in both modes.

Цифровая схема коммутации силовых ключей источников питания в квазирезонансном режиме

Цифровая схема коммутации силовых ключей источников питания в квазирезонансном режиме

Quasinormal modes of Dirac field in 2 + 1 dimensional gravitational wave background

In this study, we investigate the solutions of the massive and massless Dirac equation, at first, in the 2+1 dimensional gravitational wave background and then in the background with the presence of a constant magnetic field. In both situations, using the solutions obtained in terms of the confluent Heun functions, we calculate the quasinormal modes (QNMs) and discuss the stability conditions of the background. Comparing the quality factors derived from the QNMs in the existence of Dirac field mass and constant magnetic field with together, we see that the magnetic field plays a very important role in reducing the number of the gravitational wave oscillations because of its damping or screening effect, but there is no magnetic field effect on the proper oscillations of the gravitational wave. In addition, we acquire quasi-resonance modes (QRMs) for the massive test field in the absence of magnetic field and massless Dirac field in the presence of magnetic field from these QNMs. In both situations, the gravitational wave (GW) background becomes a good oscillator because the quality factor is very high. Moreover, we discuss the gravitational redshift for the wave background. Finally, we see that the obtained the GW frequencies and redshift values in the context of the study are compatible with the observational data.

Vectorial and spinorial perturbations in Galileon black holes: Quasinormal modes, quasiresonant modes, and stability

In this work we have considered a model that includes the interaction of gravity and matter fields with Galilean invariance (the so-called derivative coupling) as well as some corresponding black hole type solutions. Quasinormal perturbations of two kinds of matter fields have been computed by different methods. The effect of the derivative coupling in the quasinormal spectrum has been analyzed and evaluated.

A Highly Integrated Series–Parallel Switched-Capacitor Converter With 12 V Input and Quasi-Resonant Voltage-Mode Regulation

This paper presents an integrated circuit (IC) implementation of a hybrid switched capacitor converter based on a modified series-parallel architecture. The converter operates in a quasi-resonant mode to regulate a nominal 3.7 V output from a 12 V supply. The design uses zero-current detection and nested 1-b regulation to autotune the zero-current switching state, simplify the design of a digital voltage-mode control scheme, and achieve partial zero-voltage switching. The modified architecture is able to operate with single-voltage rated devices without degrading the voltage times current product of the converter. This paper discusses details of level shifting, gate driving, and bootstrapping for an all n-channel powertrain, including a precharge circuit, to facilitate safe startup. The converter IC was designed in 180-nm bulk CMOS with a 5 V option for power devices. It was tested in a flip-chip assembly with a 36 nH 0402 inductor to deliver up to 4.6 W at 87.5% efficiency at a power density of 0.23 W/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

New breed of solid-state transformer mainly combing hybrid cascaded multilevel converter with resonant DC-DC converters

This paper proposes a new breed of solid-state transformer (SST) distribution tail system mainly based on hybrid cascaded multilevel converter and resonant DC-DC converters between medium-voltage distribution and low-voltage customer side. The proposed SST topology mainly combines per-phase cascaded H-bridge converters based on the DC transformers (DCTs) with the square-wave two-level VSC based on the assembled DCT together. The proposed system can offer the operational flexibility for active and reactive power control for medium-voltage side based on the simplified single-stage control system structure concept thanks to the characteristics of the resonant DC-DC converters working under the quasi-resonant mode. Additionally, compared to the existing SST systems, it offers better features such as smaller space volume, simpler control system, lower unit cost, etc. To illustrate the feasibility of the proposed SST distribution tail system, this paper assesses its dynamic performance during steady-state and network alterations, including its response to medium-voltage ac-side unbalance.

Energy-efficient operation modes of a frequency converter with a series-parallel resonant circuit under power stabilization at a variable load

An analysis of the power characteristics for a frequency converter is performed for matching with a varying load by means of a series-parallel resonant circuit. It is shown that a change in the active component of the load does not always lead to a proportional change in the input resistance of the resonance circuit, with at certain frequencies the resonant circuit even exhibiting a constant input resistance under a change in the load within a considerable range; that is, it has the properties of parametric output-power stabilization. At these frequencies, a large reactive component appears in the input impedance of the circuit, which does not allow one to obtain an operation mode close to a resonance one or achieve an acceptable energy-conversion efficiency. The frequency characteristics of the circuit have been studied under conditions of an extreme approach of its resonant frequencies. It is found that, in this case, owing to the distortions of the phase-frequency characteristic, one can obtain a quasi-resonant operation mode of the converter over the entire range of the load resistance. It is shown that the proposed method for the tuning of resonance circuit allows one, under a twofold change in the load, to achieve parametric stabilization of the output power with energy parameters of cosϕ > 0.94 at extreme points of the range of resistance variation. The obtained results are confirmed by simulation and physical experiment.

Single‐stage QR AC–DC converter based on buck–boost and flyback circuits

In this study, a single-stage quasi-resonant (QR) AC–DC converter based on buck–boost and flyback circuits is proposed. The forestage buck–boost circuit works in discontinuous conduction mode to achieve a high-input power factor (PF), and the backstage flyback converter, working in QR mode, is responsible for energy transfer. The QR switch mode can improve the efficiency of the converter by decreasing the switch turn-on losses. The single-stage topology can reduce the cost and raise the reliability of the system. The detailed design process is described in this study, and a 50 W prototype was developed that has a maximum PF higher than 0.99 and a maximum efficiency of 90.91% in nominal working conditions.

Low permeability composite magnetic core transformer with high coupling coefficient and its application to PFM controlled quasi-resonant mode flyback-type DC-DC converter

Low permeability composite magnetic core transformer with high coupling coefficient and its application to PFM controlled quasi-resonant mode flyback-type DC-DC converter

Quasinormal modes of dilaton-de Sitter black holes: scalar perturbations

Dilaton black hole solutions in low energy string theory (well known as GMGHS black holes) have analogue black holes with a cosmological constant derived by Gao and Zhang. Here, we study quasi normal modes of this dilaton-de Sitter black hole under neutral scalar field perturbations. We have employed the sixth order WKB analysis to compute the quasi normal mode frequencies. A detailed study is done for the quasi normal mode frequencies by varying the parameters in the theory such as the mass, cosmological constant, dilaton charge and the spherical harmonic index. For the massive scalar field we observed that the usual quasi resonance modes that exists for asymptotically flat black holes do not exist for this particular black hole. We have approximated the scalar field potential of the near-extreme dilaton de Sitter black hole with the P$\ddot{o}$schl-Teller potential and have presented exact quasi normal frequencies.

A Novel Control Scheme of Quasi-Resonant Valley-Switching for High-Power-Factor AC-to-DC LED Drivers

This paper presents a novel control scheme of quasi-resonant (QR) mode and valley-switching for high-power-factor (PF) ac-to-dc light-emitting diode (LED) drivers. The proposed driver control scheme is based on a buck PF corrector converter, which is operated in QR valley-switching. The proposed control scheme can directly sense the QR valley signal from the current sensor, and it is definitely different from the conventional method which senses the QR valley signal from auxiliary winding. The cost and size of the driver circuit can be remarkably reduced when the proposed control scheme is adopted. Furthermore, the proposed circuit can provide not only high PF and low total harmonic distortion but also high conversion efficiency. Up to 0.99 PF and 91.5% efficiency are obtained from an 8-W (40-W replaced) LED bulb driver prototype.

Magnetic-Coupling Current-Balancing Cells based Input-parallel Output-parallel (IPOP) LLC Resonant Converter Modules for High-Frequency Isolation of DC Distribution Systems

The input-parallel output-parallel (IPOP) dc–dc converters are suitable for low-voltage and high-current applications, especially using high-frequency isolation instead of traditional line-frequency transformer for ac–dc converters in dc distribution. Compared to the existing closed-loop control for IPOP dc–dc converters, the magnetic-coupling current-balancing (MC-CB) cells based IPOP <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter modules are proposed in this paper, which can realize the IPOP system work under open-loop operating condition naturally. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> modules can be used as a high-frequency isolation dc transformer operating under the quasi-resonant mode, which can achieve zero-voltage switching (ZVS) for inverter side and zero-current switching (ZCS) for rectifier side ensuring high power density and high efficiency. The proposed MC-CB cells for IPOP <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> LLC</i> resonant converter modules can adaptively ensure both the input-current sharing (ICS) and the output-current sharing (OCS) among constituent modules to make the IPOP system operate stably. Additionally, the steady-state and dynamic-state current-sharing performance of MC-CB cells for the IPOP converter system are analyzed based on a magnetic model. In the end, a hardware prototype has been designed and tested. The experimental results have verified the validity and performance of the proposed MC-CB cells for the IPOP <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter modules.

Study on a Novel Single-Stage QR PFC Converter

A novel quasi-resonant single-stage single-switch PFC flyback converter is analyzed. By the additional winding, power factor correction can be achieved, and the topology can be simplified. The circuit can work in quasi-resonant mode, so the switching loss is reduced. By means of digital frequency reduction, the efficiency of the converter is improved further.