Full Load Range Research Articles

A Fully Integrated Low-Dropout Regulator with Improved Load Regulation and Transient Responses.

A fully integrated low-dropout (LDO) regulator with improved load regulation and transient responses in 40 nm technology is presented in this paper. Combining adjustable threshold push–pull stage (ATPS) and master–slave power transistors topology, the proposed LDO maintains a three-stage structure within the full load range. The proposed structure ensures the steady-state performance of LDO and achieves 0.017 mV/mA load regulation. The ATPS consumes little quiescent current at light load current condition, and the turn-on threshold of the ATPS can be adjusted by a current source. Once the value of current source is set, the turn-on threshold is also determined. A benefit of the proposed structure is that the LDO can be stable from 0 to 100 mA load current with a maximum 100 pF parasitic load capacitance and a 0.7 pF compensation capacitor. It also shows good figure of merit (FOM) without an extra transient enhanced circuit. For the maximum 100 mA load transient with 100 ns edge time, the undershoot and overshoot are less than 33 mV. The dropout voltage of the regulator is 200 mV with input voltage of 1.1 V. The total current consumption of the LDO was 24.6 μA at no load.

A Hybrid Extended Phase Shift Modulation Strategy for DAB Converter With DC Blocking Capacitor to Extend ZVS Range and Reduce RMS Current

This article is aimed at enlarging the zero-voltage switching (ZVS) range and reducing current stress for the dual-active-bridge (DAB) converter with dc blocking capacitors (DCBCs). A hybrid extended phase shift modulation strategy (HEPSMS) is proposed, which makes the converter switch between the full-bridge mode and the half-bridge mode to obtain multivoltage matching operation points. Thus, the root mean square (rms) current and the burden of achieving full load range ZVS are reduced. In addition, the voltage–second of the leakage inductor is controlled to achieve equivalent voltage matching under wide voltage output, thereby simplifying the control law and achieving full load range ZVS under a wide voltage range. The operation principle, ZVS range, and rms current are analyzed and compared with the conventional modulation method. Finally, a 1-kW experimental prototype with a 200-V input and a 100–400-V output was built to verify the feasibility and effectiveness of the proposed method.

A fast transient response current-feedback low-dropout regulator with dynamic current-enhancement technique

This paper proposed a dynamic current-enhancement technique based on AC coupling network and feedforward compensation capacitor for current-feedback low-dropout regulators (LDOs). Compared with traditional reported current-feedback LDOs, this design exhibits wider input voltage range, greater load capacity and fast transient response, yet no extra power consumption is introduced. Moreover, a complete stability analysis under full load range is given in this paper. The proposed LDO is fabricated in SMIC 0.18μm CMOS process. The input voltage range is 0.8–2.2 V and the maximum load current is 50 mA. The experiment results indicate that the overshoot and undershoot are 76 mV and 141 mV respectively when the load current is varied from 0 to 50 mA within 300 ns under the load of 100 pF load capacitor.

Application of DC-DC Converter in Sensor and MEMS Device Integration and Packaging

DC-DC (direct current controlled direct current) converter is the core control circuit in the field of power electronics technology. Based on the theory of sensors and MEMS (microelectromechanical systems), this paper constructs a DC-DC converter device integration and packaging model and proposes an enhanced current equalization technology with offset correction function suitable for two-phase DC-DC converters. Aiming at the generation mechanism of the output ripple of the two-phase DC-DC converter, the model adopts the ripple elimination technology based on the interleaved synchronous clock and the self-calibration interleaved time generator, so that each phase of the converter is accurately staggered within the full-load range, and the problem of output ripple amplitude is solved. During the simulation process, a high-performance two-phase DC-DC converter chip is designed and implemented, which includes an adaptive on-time control logic based on ripple feedback, a self-calibrating zero-current turn-off circuit, and a robust power switch transistor drive logic. The experimental results show that the full-load current of the chip reaches 6A, the peak efficiency is 91%, the phase-to-phase current error is <0.6%, and the output ripple is <9 mV. In the 90.265 V AC input, 0-10 W load range, the output voltage error is less than 0.96%, when the load is switched between no-load and full-load, and the system response speed is less than 200 ps, which effectively improves the overall performance of the DC-DC converter.

Photovoltaic Energy Storage System Based on Bidirectional LLC Resonant Converter Control Technology

Bidirectional DC/DC converters are widely adopted in new energy power generation systems. Because of the low conversion efficiency and non-isolation for conventional, bidirectional DC/DC converters in the photovoltaic energy storage complementary system, this paper proposes a bidirectional isolation LLC converter topology, with compensating inductance for the energy storage system; it has excellent characteristics, such as wide input voltage range and soft switching in full-load range. First, an AC equivalent model based on the fundamental wave equivalent method is established to derive the voltage gain. Meanwhile, a small signal model is also built to design a reasonably closed-looped controller. Finally, the improved bidirectional LLC resonant converter is applied to the photovoltaic energy storage complementary system. The correctness and feasibility for the bidirectional LLC converter topology under the proposed charging and discharging control strategy of the DC bus are verified by simulation and experimental results.

A Full Load Range ZVS Isolated Three-Level DC/DC Converter with Active Commutation Auxiliary Circuit Suitable for Electric Vehicle Charging Application

The isolated three-level DC/DC converter (ITLDC) can be used to charge electric vehicles. During the constant current charging stage, the ITLDC can be designed to realize nature zero voltage switching (ZVS). However, during the constant voltage charging stage, the charging current is small; thus, nature ZVS cannot be realized. This paper presents an active commutation auxiliary circuit (ACAC) for the ITLDC to realize the full load range ZVS. With the proposed ACACs, all the main switches achieve zero-voltage turn-on and quasi zero-voltage turn-off, and the auxiliary switches realize zero current turn-on and zero-voltage turn-off; thus, the efficiency will be high. The auxiliary currents generated by the ACACs are controllable. During the constant current charging stage, the ITLDC realizes nature ZVS and the auxiliary currents are controlled to zero; thus, the ACACs do not result in high current stress or bring in additional losses, and the efficiency will be high. During the constant voltage charging stage, the charging current decreases with charging time and the charging current is too small to realize nature ZVS. Thus, the ITLDC can work with the proposed ACACs and the auxiliary currents can be controlled within a suitable value to realize ZVS. With the proposed ACACs, the ITLDC can realize ZVS during the whole charging process; thus, the efficiency will be high. The structure and operating principle of the ITLDC with ACACs are introduced and the performance of the proposed TLDC is experimentally verified on a 1.5 kW prototype converter.

Parallel Server Systems with Cancel-on-Completion Redundancy

We consider a parallel server system with so-called cancel-on-completion redundancy. There are n servers and multiple job classes j. An arriving class j job consists of dj components placed on a randomly selected subset of servers; the job service is complete as soon as kj components out of dj (with [Formula: see text]) complete their service, at which point the unfinished service of all remaining [Formula: see text] components is canceled. The system is in general non-work-conserving in the sense that the average amount of new workload added to the system by an arriving class j job is not defined a priori—it depends on the system state at the time of arrival. This poses the main challenge for the system analysis. For the system with a fixed number of servers n, our main results include: the stability properties; the property that the stationary distributions of the relative server workloads remain tight uniformly in the system load. We also consider the mean-field asymptotic regime when [Formula: see text] while each job class arrival rate per server remains constant. The main question we address here is: under which conditions the steady-state asymptotic independence (SSAI) of server workloads holds and, in particular, when the SSAI for the full range of loads (SSAI-FRL) holds. (Informally, SSAI-FRL means that SSAI holds for any system load less than one.) We obtain sufficient conditions for SSAI and SSAI-FRL. In particular, we prove that SSAI-FRL holds in the important special case when job components of each class j are independent and identically distributed with an increasing-hazard-rate distribution.

A Weighted Efficiency Enhancement Method for Coupled Inductor Filter-Based H-Bridge Inverters

This article presents a weighted efficiency enhancement (WEE) method for H-bridge inverters based on coupled inductor filter (CIF). The proposed WEE method includes coupled inductor optimization design and switching frequency optimization (SFO) strategy. First, all the energy losses of the H-bridge inverter are elaborated in detail, and the energy loss analysis model of the inverter is constructed based on the dominant energy losses. By installing a CIF on the ac side of the inverter and reasonably selecting the switching frequency, zero-voltage switching (ZVS) is realized for all switches. In addition, an IEEI-type coupled inductor structure and the efficiency-oriented coupled inductor optimization design principle are presented. Then, an SFO strategy is proposed to minimize the total loss of the inverter under full range of loads. Compared with the inverter without the WEE method, the inverter with the WEE method significantly improves the weighted efficiency. Finally, a laboratory prototype is built to verify the validity of the proposed WEE method.

Coupled-Inductor-Based Dual Active Bridge Converter With Soft Switching Capability and Low Component Count

A coupled-inductor-based dual active bridge (DAB) converter with soft switching capability and low component count is proposed in this article. Under wide-input voltage range application, it only utilizes four active switches to achieve voltage regulation and can behave like the current-fed DAB (CF-DAB) converter. In addition, three magnetic components, including the input dc inductor, the transformer, and the leakage inductor, can all be integrated into one coupled inductor, thus reducing the magnetic component count. With the coupled-inductor structure, the voltage of the half bridge capacitor at the output side can be automatically changed according to different duty cycle. Consequently, the voltage matching at the two ports of the equivalent leakage inductor will always be satisfied by controlling the input capacitor voltage with the adopted pulsewidth modulation (PWM). Based on the detailed analysis of the working modes, power transfer characteristics, and zero-voltage switching (ZVS) conditions, full load range ZVS can be mathematically obtained, which shows that the full load range ZVS capability is an intrinsic feature of the proposed converter and is not related to the converter inductance values. Furthermore, the magnetic integration and parameter design are analyzed in detail. Finally, experimental results are provided to demonstrate the effectiveness of the proposed solution.

Thermal and flow calculations of platen superheater in large scale CFB boiler

Circulating Fluidized Bed (CFB) boilers are desirable technology to utilize solid fuels, operate within a wide load range, and promote the high flexibility in burning a wide range of coal and other solid fuels, keeping high efficiency and low gaseous pollution. The paper presents thermal and flow modeling results of steam superheater operated in the large-scale coal-fired CFB boiler, both in steady and transient states. The mathematical model of the superheater wall was developed using Control Volume-based Finite Element Method. The heat transfer coefficient as the sum of radiative and convective heat transfer coefficients was considered in the presented approach to modeling thermal processes in a circulating fluidized bed. The overall heat transfer coefficient was computed for the analyzed type of the boiler at full load and steady-state conditions using available measuring data and results obtained using Computational Fluid Dynamics (CFD) modeling. Depending on the modeling approach adopted in the CFD model, the heat transfer coefficient at full boiler load varies between 159.96 and 189.63 W/(m2·K). In the analyzed period of boiler start-up, results of steam outlet temperature (455 °C–485 °C), heat transfer coefficients on the flue-gas side (100 W/(m2∙K) and 120 W/(m2∙K)), and heat transfer coefficients on the steam-side (925–2008 W/(m2∙K)) vary with time. The methods presented in the paper can be applied to modeling transient flow and thermal processes in superheaters with complicated flow arrangements. The advantage of the proposed method is a short computing time compared to detailed and complex 3D models. The developed model of the superheater with the transfer coefficient determination methods can be used to perform calculations in the full range of boiler load, both during steady and transient boiler operation.

Three Winding Coupled Inductor-Based Dual Active Bridge DC-DC Converter With Full Load Range ZVS Under Wide Voltage Range

In this article, a three winding coupled inductor-based dual active bridge (TWCI DAB) dc-dc converter is proposed. Similar to the current-fed DAB converter, the proposed TWCI DAB has small input current ripple and wide input voltage range. In addition, the zero-voltage switching (ZVS) of all switches in the full load range under wide input voltage variation can be realized. With the magnetic integration structure, the size of the total magnetics can be reduced, and the efficiency is also increased compared with the discrete magnetic case. To better analyze the working principle of the three winding coupled inductor, a general analysis method based on magnetic reluctance model is first introduced to obtain the expressions of high frequency current. Furthermore, ZVS analysis and inductor design to obtain low inductor root mean square (rms) current and full load range ZVS based on the ZVS conditions, maximum power transfer and rms current are presented. Finally, the validity of the proposed topology and design are verified by experimental results from a 1-kW laboratory prototype.

A Coupled-Inductor-Based Soft-Switching Noninverting Buck–Boost Converter With Reduced Auxiliary Component Count

This letter proposes a coupled-inductor-based soft-switching noninverting buck–boost converter (NIBBC) with reduced auxiliary component count. Instead of using multiple auxiliary passive components to achieve soft switching, the proposed coupled-inductor-based NIBBC uses the coupled inductor as the main inductor, and the auxiliary current generated by the magnetic coupling effect is used to obtain the soft switching for all switches. With simple pulsewidth modulation under fixed frequency, full-load range zero-voltage switching can be obtained under a wide voltage range. Unlike the conventional method utilizing the coupled inductor only to generate nonactive power, the coupled inductor of the proposed converter also takes participant in the power transmission. Besides, the added diode can achieve zero current turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> that avoids the diode recovery issue. The operating principle, the soft switching, and the parameter designs are analyzed in this letter. Finally, experimental results have verified the effectiveness of the proposed solution.

Clinical Validation of a Rapid Variant-Proof RT-RPA Assay for the Detection of SARS-CoV-2.

The COVID-19 pandemic has unveiled a pressing need to expand the diagnostic landscape to permit high-volume testing in peak demand. Rapid nucleic acid testing based on isothermal amplification is a viable alternative to real-time reverse transcription polymerase chain reaction (RT-PCR) and can help close this gap. With the emergence of SARS-CoV-2 variants of concern, clinical validation of rapid molecular tests needs to demonstrate their ability to detect known variants, an essential requirement for a robust pan-SARS-CoV-2 assay. To date, there has been no clinical validation of reverse transcription recombinase polymerase amplification (RT-RPA) assays for SARS-CoV-2 variants. We performed a clinical validation of a one-pot multi-gene RT-RPA assay with the E and RdRP genes of SARS-CoV-2 as targets. The assay was validated with 91 nasopharyngeal samples, with a full range of viral loads, collected at University College London Hospitals. Moreover, the assay was tested with previously sequenced clinical samples, including eleven lineages of SARS-CoV-2. The rapid (20 min) RT-RPA assay showed high sensitivity and specificity, equal to 96% and 97%, respectively, compared to gold standard real-time RT-PCR. The assay did not show cross-reactivity with the panel of respiratory pathogens tested. We also report on a semi-quantitative analysis of the RT-RPA results with correlation to viral load equivalents. Furthermore, the assay could detect all eleven SARS-CoV-2 lineages tested, including four variants of concern (Alpha, Beta, Delta, and Omicron). This variant-proof SARS-CoV-2 assay offers a significantly faster and simpler alternative to RT-PCR, delivering sensitive and specific results with clinical samples.

Decoupled EPS Control Utilizing Magnetizing Current to Achieve Full Load Range ZVS for Dual Active Bridge Converters

A decoupled extended phase shift control is proposed to decrease the control complexity and achieve full load range zero voltage switching (ZVS) for dual active bridge (DAB) dc–dc converters. In the proposed solution, full load range ZVS is achieved by adding an extra small fixed duty cycle and utilizing the magnetizing current. In addition, the two control variables are decoupled, since the control of the duty cycle is only determined by the voltage conversion ratio and is independent of the phase shift angle, which avoids the detection of operation mode and switching of control laws. The ZVS model considering junction capacitors and magnetizing inductance, ZVS region under full load range, and derivation of control law are analyzed in detail. Finally, the effectiveness of the proposed solution is experimentally verified on a 500-W, 250kHz GaN-based prototype.

Stress state failure analysis of thin-walled GLARE composite members subjected to axial loading in the post-buckling range

The paper investigated the load-carrying capacity and the participation of stress components in the failure analysis of top-hat-shaped composite columns subjected to uniform compression. GLARE members were axially compressed in laboratory tests employing a static testing unit. Failure tests were monitored in the full load range using the digital image correlation (DIC) system, which enabled visualization of full-field displacements and strains. Simultaneously, FEM numerical simulations were carried out to estimate the load-carrying capacity of the top-hat-shaped sections based on the nominal stress state in both the non-degraded and degraded composite models. In the latter, the material property degradation method (MPDG) allowed a progressive lowering of the material stiffness based on the presumed damage variables. Failure initiation in composite plies was monitored in FE simulations based on Hashin and Puck failure criteria. Stress state analysis was performed to investigate the participation of stress tensor components in the failure function of selected failure criteria. This enabled the identification of critical stresses contributing to aluminum plastic deformation and intra-laminar failure mechanisms that led to the composite fracture. The results of the numerical simulations were found to be in high agreement with the experimental evidence.

Power-Estimation-Based Synchronous Rectification Solution for Bidirectional DAB-LLC Converter

An LLC-DAB bidirectional converter with reduced switch count as a DC-DC transformer (DCX) is proposed in this paper. It can achieve voltage regulation, full load range zero voltage switching (ZVS) for eight main switches and wide load range ZVS for four auxiliary switches, with consideration of the switch junction capacitors under different power direction. A part portion of total power is transferred through an auxiliary DAB circuit to achieve voltage regulation and bidirectional power conversion. The main power is transferred through LLC circuit with an easy PWM scheme achieving high conversion efficiency. Different from the existing LLC-DAB DCX structure, the two secondary side transformer outputs are in parallel, and connected to the same full-bridge circuit. In this way, the auxiliary DAB circuit can not only adjust the output voltage, but also can inject current into the secondary side to help achieving ZVS of switches without synchronous rectifier (SR) circuit. The converter operation principle is analyzed under different power directions, and ZVS is analyzed with the consideration of all the switch junction capacitors. Based on the analysis, the design consideration is introduced. Finally, a 2-kW prototype with 750V input and 400V output is built up to verify the effectiveness of the proposed solution.

Study on the lubrication of piston skirt-cylinder liner under the engine working conditions of different speeds and loads

The working condition (speed and load) of internal combustion engine is one of important factors affecting the lubrication performance of piston skirt-cylinder liner. In actual normal use, the working condition of internal combustion engine is constantly changed under different speeds and loads. However, the current lubrication performance of piston skirt-cylinder liner is analyzed generally under only one or several working conditions of internal combustion engine, in which the working conditions does not cover full range of different engine speeds and loads. In addition, it is generally assumed in current studies that the piston skirt is fully lubricated in all strokes of an engine working cycle. In this paper, a four-stroke internal combustion engine is taken as the research object, the lubrication performance of piston skirt-cylinder liner under full working condition range of internal combustion engine with different engine speeds and loads are analyzed, in which the lubrication status of piston skirt is determined by considering the actual lubricating oil transport. The results show that there are differences in the lubrication performance of piston skirt-cylinder liner under different working conditions of internal combustion engine. The rated working condition of internal combustion engine may not be the most unfavorable working condition to the lubrication performance of piston skirt. Therefore, it is necessary to analyze the lubrication performance of piston skirt under full working condition range of internal combustion engine with different speeds and loads when the piston assembly is designed.

Reordering of vertical vibration modes in an axially compressed beam on a Winkler foundation

This study reveals a special vibration characteristic of an axially compressed Timoshenko beam on a Winkler foundation, namely that the vibration configuration in the sequence of the natural frequencies may undergo a reordering in response to changes in certain parameters. New explicit analytical expressions of the natural frequencies are derived, which considers both the shear and rotatory inertia effects in the beam. The key independent dimensionless parameters that control the modal reordering phenomenon are then identified from the resulting frequency. By examining the vibration response of structures with various parameters over the full range of axial loads, it is observed that the frequencies of some initial low- and high-order vibration modes approach each other and then veer away, thus causing a reordering in the vibration modes. The fundamental reason for the occurrence of this phenomenon is also discussed in detail. Finally, the effect of the key structural parameters is investigated, it is shown that the structure having a greater slenderness ratio or a greater relative stiffness between the foundation and beam is more prone to experience a vibration modal reordering under axial pressure.

Comparison of different load-following control strategies of a sCO2 Brayton cycle under full load range

The supercritical CO2 Brayton cycle has been regarded as a promising next-generation power conversion system owing to its flexibility and high efficiency. Dynamic performance and control strategy are essential research topics when systems are subjected to various load demands. Inventory control has been proven as a very effective load control method and valve controls have the potential to meet wider load demands. While few studies have focused on the differences in efficiency and system performance under different control strategies. In this study, a dynamic model of recompression supercritical CO2 Brayton cycle is proposed, and its components are carefully validated. Moreover, an inventory and anti-surge coupled control strategy is proposed to achieve better control performance. Under the premise of considering system security, various control strategies meeting 0%–100% load range are compared. The primary objective of this study is to reveal the differences in efficiency and dynamic performance of various control strategies in the full load range, to provide a basis for the selection of control strategies in off-design conditions. The results demonstrate that inventory and anti-surge coupled control allow safe tracking loads as low as 0%, and it provided an absolute advantage in terms of efficiency compared to valve controls.

A Bidirectional Symmetrical C4LC-DCX Resonant Converter With Power Limitation Capability

To achieve the maximum efficiency of resonant converter under wide voltage conversion gain range, two stage conversion, which adopts the resonant converter operating at resonant frequency to work as a dc–dc transformer (DCX) in isolation stage, is a preferred solution. This article proposes a bidirectional C4LC resonant converter to work as a DCX. The structure of the topology is totally symmetrical, and two auxiliary inductors are used to achieve full load range zero-voltage-switching (ZVS) for all the power switches under bidirectional power flow. Unlike conventional ZVS analysis, the ZVS of the proposed converter is analyzed with considerations of all the switch junction capacitors and load. The clamping diodes are also combined in the topology which can help achieve natural power limitation in case of overload and limit the startup current. Even though four inductors and one transformer are illustrated in the topology, all these magnetic components can be simplified and manufactured with one external inductor and one conventional transformer. Meanwhile, the converter operates at a fixed frequency and adopts the synchronous pulsewidth modulation (PWM) modulation, which can achieve constant voltage gain and automatically change the power direction without synchronous rectifier (SR) current detection. Finally, the experimental results from a 1-kW prototype verify the effectiveness of the proposed converter.