Light Load Conditions Research Articles

Decoupled Dual-PWM Control for Naturally Commutated Current-Fed Dual-Active-Bridge DC/DC Converter

The naturally commutated current-fed dual-active-bridge (CF-DAB) dc/dc converter is a suitable solution for the distributed generation system with low input current ripple and convenient current control. However, the efficiency under light load conditions is still a challenging issue with existing modulation schemes. In this article, a decoupled dual-pulse width modulation (PWM) control strategy is proposed to enhance the efficiency within a wide load range. The proposed modulation adjusts turn-on moments of secondary-side switches flexibly and charges the leakage inductor properly based on the instantaneous input current. The peak leakage inductor current, primary-side rms current, and the corresponding losses are reduced effectively compared to existing methods. Meanwhile, the proposed modulation strategy avoids the interactions between the primary-side duty cycle and the secondary-side duty cycle so as to decouple the voltage conversion ratio with leakage inductance and load conditions and simplify the control-loop design. The design process, power loss analysis, and implementation of the proposed modulation strategy are presented in detail. The impacts of deviations in parameters of input inductor and leakage inductor are also analyzed. Based on parameter estimation, a specific compensation loop without an additional current sensor is proposed to further improve the stability of the closed-loop control for the converter. The experimental results are given to verify the theoretical analysis and validity of the proposed modulation.

Load Test and Variable Speed Control of a 50-kW-Class Fully Superconducting Induction/Synchronous Motor for Transportation Equipment

This paper reports the design, fabrication, and test results of a 50-kW-class fully superconducting induction/synchronous motor for transportation equipment. Its maximum speed is 1800 rpm, and both rotor and stator windings were fabricated using Bismuth strontium calcium copper oxide tapes. The so-called ring-winding structure was used for the stator windings to improve the critical current of the stator windings in the core. The fabricated motor was immersed in liquid nitrogen and tested using a commercial pulse width modulation inverter. We successfully carried out a 3-kW load test at a synchronous speed of 1800 rpm. Furthermore, a variable speed test under light load conditions was also completed.

Operation of Current-fed Dual Active Bridge DC-DC Converters for Microgrid

Dual Active Bridge (DAB) is an isolated bidirectional DC-DC converter, which comprises two full bridge converters linked through a high frequency transformer. It has low stresses and permits high frequency performance because of the soft-switching. All the switches in the converter achieves the turn ON & OFF during Zero Voltage Switching (ZVS) and Zero Current Switching (ZCS) to minimize switching loss. Generally, DAB is classified as two types, namely, voltage-fed and current-fed variants. At light load conditions, soft-switching is not realized in case of voltage-fed DAB topologies. The application of current-fed DAB converters is to reduce the losses at the time of switching under light load conditions and improves the efficiency. This paper describes the various topologies of voltage-fed and current-fed DAB used for different applications in microgrid and fuel cell energy generation system by using the simulation. The performance of voltage-fed and current-fed DAB with snubber-less converters are also demonstrated and their effectiveness are validated.

Analysis and Suppression of the Circulating Current Influence in the Input-Series Auxiliary Power Supply for High-Input-Voltage Applications

The input-series converters based on transformer integration have the advantages of active input voltage sharing (IVS) and simplicity of the whole system, which are suitable for the high-input voltage multiple-output applications. However, due to the parameters error in each series module, the circulating current occurs among the series modules during the active IVS process. Aiming at this type input-series two-transistor flyback converter, the mechanism and influence of the circulating current in each series module are analyzed. On this basis, according to the characteristics of the peak current mode control scheme adopted in this converter, a suppression strategy is proposed, by which influence of the circulating current on the operational stability of the converter under the light load conditions can be eliminated. Finally, based on the simulating results, the experimental study has been done on a 60-W experimental prototype composed of three series modules, and the theoretical analysis and the proposed suppression strategy have been verified by the experimental results.

Psychological Acceptability Weighted Priority Scheduling: A Case Study of Animal Hospital

A solution to the patient scheduling problem for a case study animal hospital called Mix+Factor scheduling is proposed in this work. Mix scheduling is based on the weighted sum of patient arrival order, the job type and the priority. The priority is based on the veterinarian opinion on the treatment type. Factor is an additional function based on the psychological acceptability of the patient owners in allowing some later jobs to be moved ahead in the waiting queue. The experimental results are conducted on three synthesis workloads to create a light-load, normal-load and high-load conditions. The synthesis workloads are created according to the mixture of jobs at the case study animal hospital. The results show that the Mix+Factor algorithm provides similar or better average waiting time performance in comparison with the currently used algorithms, namely First-Come-First-Served. In addition, Mix+Factor can also provide a better scheduling in order to reduce the waiting time for specific patients such as violence animals or patients with appointments. A study on potential benefit of opening an extra treatment room shows that an extra treatment room can significantly reduce the waiting time and better serve the specific patients than that of the currently used algorithm.

Multi-Resonance-Core-Based Dickson Resonant Switched-Capacitor Converters With Wide Regulation

The Cuk dual resonance core (DRC) realizes overlapped dual resonance to regulate its output voltage. However, the DRC configuration was only applied to the Fibonacci switched-capacitor converter (SCC), series–parallel SCC, and voltage doubler. In this paper, the Cuk DRC is modified and then is extended to the Dickson SCC to form a multi-resonance-core-based (MRC) Dickson resonant switched-capacitor converter. All charging and discharging loops achieve soft charging, and so the inherent capacitor charge sharing loss and the high current transient spikes are eliminated. The modular configuration makes the MRC Dickson easy to be extended to a higher voltage level. The on -time fixed frequency modulation is adopted, all transistors being turned on with zero-current-switching (ZCS) operation and all diodes being turned off with ZCS operation. Most importantly, the conversion ratio of the MRC Dickson can be regulated continuously, widely, and efficiently even at light load condition, which is a huge advantage over the traditional Dickson SCC with limited control headroom. A comprehensive analysis of the operation principle, voltage-gain curve, component stress analysis, and output characteristic is provided. The converter operation principle and regulation capability were verified by both simulation and experiment.

Weightlifting load effect on intra-limb coordination of lower extremity during pull phase in snatch: Vector coding approach

ABSTRACT This study examined the weightlifting load effects on the lower extremity coordination pattern during a snatch pull movement. Twenty male elite weightlifters performed snatch trials in each of the three load conditions [light (30%), medium (65%) and heavy (90%) of their maximum weightlifting capacities]. Kinematic data for the transition, second pull and take-off phases of a snatch were collected at 200 Hz using an eight-camera motion capture system. Angle-angle plots and coupling angles were calculated for further analyses. The results indicate that participants utilised knee flexion control-strategy in light and medium load conditions during the transition phase, but not for in-phase strategy in heavy load condition. In the second pull phase, participants utilised concurrent ankle dorsiflexion and knee extension, followed by hip extension strategy. The heavy load condition exhibited the distinct coordination strategies before knee extension. In the take-off phase, light and medium load conditions appeared to use thigh-phase strategy (right ankle-knee: p = 0.788, left: p = 0.035, right knee-hip: p = 0.012, left: p = 0.017, right ankle-hip: p = 0.029, left: p = 0.011). This suggests that the heavy load condition requires the use of two-joint coordination patterns (in-phase or anti-phase) as compared to the other lighter load conditions.

Three Phase Current-Fed Semi Dual Active Bridge DC–DC Converter With Hybrid Operating Mode Control

A high-frequency isolated unidirectional three phase (3p) current-fed (CF) semi-dual active bridge (SDAB) dc–dc converter is proposed for unidirectional power-flow applications suitable for wide input and load variations with small input current ripple, such as for fuel stacks and photovoltaic (PV) array. A hybrid operating mode control was proposed to handle the operating stability throughout full load range especially the light load conditions by which, dual-pulsewidth modulation (PWM) and phase shifted control with fixed clamping voltage was implemented over certain kind of load while varying clamping voltage using only dual-PWM (D-PWM) control was used under light-load conditions. The ideal power transferred expressions are derived based on the analysis of power transmission characteristics. The ideal rms expressions of the leakage inductor current are ideally derived for leakage inductance value optimization or minimizing the loss; and the ideal soft-switching conditions based on charges have been given. A 2-kW 3p-CF-SDAB prototype using SiC mosfet s has been built to verify the validity the proposed control strategy. With the proposed control, the steady-state performance throughout full load of range is pretty well. Seamless transition can be obtained between the two operating modes and the dynamic performance is good. The conversion efficiency is high and the loss distribution is given.

Multimode Control Strategy for SiC mosfets Based Semi-Dual Active Bridge DC–DC Converter

In order to meet the full load range operation requirement for a semi-dual active bridge (semi-DAB) dc–dc converter working as a battery charger, a multimode control strategy was presented. Under heavy load, it works with single phase-shifted control. Under light load, it works with pulsewidth modulation (PWM) and variable switching frequency. Under very light load conditions, it works with PWM and constant switching frequency mode. Light load conversion efficiency can be improved significantly by using the proposed multimode control strategy. Detailed loss breakdown is analyzed and compared with different switching frequencies under light load conditions. The implementation of the control strategy was given and a seamless transition can be obtained among three operating modes according to the load power. The effectiveness of the control strategy was validated by the experimental results of a 1.6-kW hardware prototype.

Effects of Secondary Leakage Inductance on the LLC Resonant Converter

It is quite often to utilize the transformer leakage inductance in the resonant tank of the LLC resonant converter to allow for a drastic reduction in the converter cost, weight, size, and volume. The effects of the secondary leakage inductance on the operation of the LLC resonant converter are not well discussed in the relevant literature, and it is the purpose of this paper to give an insight into these effects. The contribution of this paper lies in the following: first, highlighting that it is not always an accurate assumption to consider that the values of the primary and secondary leakage inductance are identical, specifically in asymmetric magnetic core structures. Second, it has been disclosed that the well-known coupling factor ( k 12) cannot properly express the unequalized leakage inductance distribution in the proposed asymmetric transformer. Therefore, the authors bring the primary coupling factor ( k 1) and secondary coupling factor ( k 2) into practice to appropriately express the unequalized leakage distribution on the primary and secondary windings, which can be controlled by the allocation of the relevant winding with respect to the air gap, utilizing the noise absorber, and changing the distance between the winding. Several transformer prototypes had been built and experimentally tested to validate these hypotheses. Third, it has been observed that the transformer voltage gain and efficiency can be improved when the transformer leakage inductance is concentrated on the secondary side to avoid the voltage drop inflicted by the relatively large value of the magnetizing current $(i_{m})$ , especially at the light load condition. Fourth, it has been reported that in a transformer structure with a concentrated value of leakage on the secondary side would decrease the resonant tank input impedance, vertically widen the voltage–gain curve of the converter, and eventually increase the frequency control bandwidth with respect to the load variation. Transformer prototypes had been constructed and tested in a 390 V/12 V–220 W LLC resonant converter to evaluate the proposed analysis.

Self-Oscillating Pulsewidth Modulation for Inductive Power Transfer Systems

This paper presents a new self-oscillating tuning loop for inductive power transfer (IPT) systems using a combination of phase shift and pulsewidth modulations (PS-PWMs). Self-oscillating methods are the uncertainty-tolerant solution for power and frequency control of resonant converters. However, constant duty-cycle operation affects their effectiveness with extra dc-link current ripples and losses. In this paper, PS-PWM is achieved by instant phase displacement controlling between the two legs of the inverter, which guarantees zero voltage switching (ZVS) for transients and light-load conditions. The presented solution simultaneously integrates PWM and PS switching methods with a fast dynamic response even under nonlinear conditions, e.g., battery loads, and sudden load changes. In the presented work, an optically controlled phase shifter is proposed, which has a simple structure and smoother phase regulation in comparison with digital potentiometers. Moreover, this paper analyzes the behavior of the proposed method in bifurcation condition and shows the reliability and stable operating area of the system. To show the feasibility of the presented switching technique, a prototype is implemented based on series–series (SS)-compensated topology and investigated for different operating frequencies and loads.

Decoupled Stator Resistance Estimation for Speed-Sensorless Induction Motor Drives Considering Speed and Load Torque Variations

There are many adaptive full-order observer (AFO)-based simultaneous speed and stator resistance estimation techniques for speed-sensorless induction motor (IM) drives. However, they still need to be improved since the stator resistance estimator is sensitive to speed and load torque variations, especially under low-speed and light-load conditions. In response to this problem, an improved “phase-shift”-based compensation method is proposed for the stator resistance estimation in this paper. Compared with the existing methods, the proposed stator resistance estimation approach is decoupled with the speed estimator by adopting an operating-point-tracking compensation coefficient. Accordingly, the robustness of the stator resistance estimation is guaranteed to speed and load torque variations. The neglected estimated rotor flux error is first introduced for the proposed stator resistance estimator to distinguish the stator resistance error component. Then the sensitivity analysis of the proposed compensation coefficient against parameters variations is carried out. Furthermore, the stability of the speed estimator and the stator resistance estimator is guaranteed owing to the proposed method. The experimental results highlight the effectiveness of the proposed method for improving the accuracy and the stability of the stator resistance estimator under different speeds and load torque conditions.

A Current-Mode Delay-Based Hysteretic Buck Regulator With Enhanced Efficiency at Ultra-Light Loads for Low-Power Microcontrollers

A current-mode buck regulator with delay-based hysteretic control for microcontroller applications is proposed. Unlike conventional hysteretic buck regulators with accurate explicit hysteretic bands, the proposed design relies only on the inherent delay of a low-speed single-threshold comparator to realize the hysteretic band, and can be seamlessly used across all loads in continuous conduction mode and discontinuous conduction mode without modifying the controller's parameters. Moreover, without additional adaptation circuits or frequency regulation loops, the proposed delay-based hysteretic operation does not increase variations in the switching frequency with process and temperature, and results in even less variations in the switching frequency with the input and output voltages when compared to corresponding designs with accurate explicit hysteretic bands. The simplicity of the design reduces silicon area and quiescent current significantly, which in turns enables achieving high efficiency at both heavy and light load conditions as strictly required by low-power microcontrollers. The regulator is designed in a 65 nm digital CMOS technology. It occupies 0.18 mm2 and supports a wide range of input voltages (1.8–4.2 V), output voltages (0.9–1.5 V), and load current (up to 300 mA). Measurement results show that the proposed regulator achieves 95% peak efficiency, while achieving between 62% and 87% efficiency at 10-μA load across all operating conditions.

An Isolated Multilevel Quasi-Resonant Multiphase Single-Stage Topology for 380-V VRM Applications

In order to increase the efficiency of modern microprocessor power supplies used in data centers, 380-V dc power distribution systems have been attracting attention due to their high efficiency and high reliability. This paper presents an innovative single-stage approach for 380-V voltage regulator modules (VRMs) based on a quasi-resonant multilevel topology constant on -time operation. The proposed topology inherently integrates the multiphase approach, providing fast phase shedding and flat high-efficiency curves even at light-load conditions. This is a unique advantage, which is not possible to establish in the two-stage approach, which is very important in server architectures, and where high efficiency is required even at light-load conditions. This paper analyzes the circuit topology and proposes a control architecture for fast transient response, including current-sharing capabilities. The digital controller has been implemented in 0.16- $\mu$ m lithography together with a digital pulsewidth modulation with a 195-ps resolution and a 40-MS/s 7-bit analog-to-digital converter. Experimental results show an efficiency of 93% for a 120-A 380–1.8-V VRM power supply.

COMPARISON OF BORED PILE AXIAL BEARING CAPACITY BASED ON VESIC’S METHOD (1970), STANDARD PENETRATION TEST (SPT), AND LOADING TEST IN THE PROJECT OF ELEVATED TOLL ROAD JAKARTA – CIKAMPEK STA.9+500 – STA.47+000

As a foundation under the structure can be generally divided into two types, namely the foundation deep and shallow foundation. Selection of the type of foundation depends on the type of structure including the construction load on whether light or heavy loads and also depending on the soil type. For the construction of a light load and soil conditions quite well, usually worn shallow foundation, but the construction of a heavy load is usually the type of deep foundation is the right choice. In general, the more complex the deep foundation of a shallow foundation. To this writer tried to concentrate on planning the foundation of this thesis in which bored pile (Bored Pile Foundations). Bored Pile foundation is a foundation built by drilling the ground first, then filled with steel reinforcement and cast. Bored pile used when soil solid base which has a carrying capacity of it lies very deep, which is approximately 15 m as well as the state of the soil around the many stands a large building and rise to the feared could lead to cracks in the existing building effect vibrations caused by staking activity when administered pile foundation. Carrying capacity of bored pile end bearing capacity is obtained than that obtained from pressure and friction pile tip bearing capacity obtained from carrying friction or adhesion force between the bored pile and the surrounding soil. K e yword :Bored Pile, Axial Bearing Capacity, SPT, Loading Test

Identification of failure modes of a PEEK-steel gear pair under lubrication

An experimental investigation is conducted to identify the failure modes of the lubricated PEEK gears under different loading conditions through the enclosed power flow test rig, supplemented with the measurements on wear, vibration and the surface micro-topography. The FZG C type gear pair is selected while the mating driving gear is chosen with the material of C45. Experimental results reveal that the pitting-induced tooth breakage occurs under light and moderate loading conditions, while the tooth root breakage dominates under heavy duty loading conditions. The measurement of the wear and the tooth surface micro-topography help to identify that the micro-pits near the pitch line lead to the final tooth breakage under moderate loading conditions. Meanwhile, the insufficiency of the bending strength under heavy loading conditions is the cause of the tooth root fracture.

The Novel Quasi-Resonant Flyback Converter With Autoregulated Structure for Parallel/Serial Input

In this paper, a novel quasi-resonant flyback converter that mainly comprises two modules of flyback converters is proposed. A relay is connected in series to the input terminals of two transformers, and the transformer input structure is adjusted according to the input voltage to improve the conversion efficiency. In addition, a novel frequency-limiting quasi-resonant control strategy for solving the limitations of the conventional quasi-resonant control strategies is proposed, wherein the switching frequency is increased under light load conditions. Here, the current-mode pulsewidth modulation IC is used as the core controller. The operating principle and design parameters of the converter are analyzed and discussed in detail. The experimental results prove the feasibility of the proposed circuit.

A Novel Hybrid Mode Control for a Phase-Shift Full-Bridge Converter Featuring High Efficiency Over a Full-Load Range

A novel hybrid mode control technique for a phase-shift full-bridge (PSFB) converter is proposed in this paper. The proposed method can improve power efficiency under both the light-load and heavy-load conditions. The basic concept of the proposed control technique is to decrease the turns ratio to reduce the circulating current, hence resulting in lower circulating losses. However, the output voltage under heavy load may not be stabilized using phase-shift control if smaller turns ratio is utilized. Therefore, the proposed technique employs asymmetrical pulsewidth modulation to achieve higher output voltage. To further improve the efficiency, an adaptive dead-time control method, which determines the dead-time value according to the load level, is also proposed. To validate the correctness and effectiveness of the proposed method, a 480-W PSFB converter is constructed and experiments are carried out accordingly. Comparing with a conventional PSFB converter, the efficiency of the proposed method can be improved up to 3.2%, 1.3%, and 0.6% under light-load, 30% load, and full-load conditions, respectively.

Performance investigation of a novel expander coupling organic Rankine cycle: Variable expansion ratio rotary vane expander for variable working conditions

Organic Rankine cycle (ORC) waste heat recovery (WHR) has been proven to be a promising method for low-grade energy reutilization. However, the working conditions can move far from the nominal conditions when the heat source energy varies. This paper presents an investigation of a novel expander for ORC, the variable expansion ratio rotary vane expander (VERRVE), adjusting its expansion ratio (ER) by regulating the outlet opening angle according to variable working conditions. A VERRVE with an adjustable ER range of 1.55–3.02 was first designed. Second, the VERRVE was modeled by GT-SUITE, and its performance at various ERs was investigated. Compared to inlet temperature, the inlet working fluid pressure is the more sensitive influencing factor. Third, this expander was applied to automotive ESC working conditions. An inlet mass flow rate controller was added to ensure that the inlet heat matched the engine exhaust. For the light load condition a50, the influence of the ER is more remarkable. When the ER decreases from 3.02 to 1.83, the output power and exergy efficiency increase by 61.81% and 56.09%, respectively. VERRVE introduces variable ER into ORCs, which is especially recommended for application to ORC WHR systems with variable heat sources.

Investigation of voltage stress on a single switch boost-fly-back integrated high gain converter with light load condition

Abstract In this paper, investigation of voltage stress on a single switch Boost-Fly-back integrated (SSBFI) DC-DC converter is carried out for light load condition. During this condition, reverse recovery occurs on the switches of the converter enabling resonance condition on the parasitic elements of the devices causing an increased device voltage stress. An appropriate snubber parameter design is a prerequisite to save the devices from the affect of such stress. A proper snubber design can be achieved with a detailed realization of the parasitic elements and suitably evaluated through a complex and tedious analysis. However, an indirect method using maximum voltage stress analysis can also be a suitable alternative for proper snubber design. A detailed study is carried out in this regard mainly focusing on power electronic device voltage stress in steady state under variation of load condition. The theoretical analysis is validated through a laboratory prototype with a capacity of 50 W.