Entire Load Range Research Articles

Zero-voltage Zero-current Transition Network for Dual Phase Interleaved Converter

In this article, a zero-voltage zero-current transition scheme suitable for a family of dual-phase interleaved converters is proposed. The transition network consists of an auxiliary transformer, a switch, and a clamp diode. This network uses a low component count structure, and yet achieves effective soft-transitions (zero-voltage turn-ON as well as zero-current turn-OFF) for the main switches. It facilitates zero-current turn-OFF of all the diodes along with zero-current turn-ON of the auxiliary switch. Additionally, the auxiliary transformer self-adjusts the current in the auxiliary network depending upon the loading conditions and thus the reactive energy during the soft-switching is low for the entire range of loads. A detailed theoretical analysis is presented by considering a high step-up dual-phase interleaved boost converter as an example. The feasibility of the proposed soft-switching scheme is implemented on the same and its effectiveness is demonstrated through experimental results which are obtained on a 400-W converter prototype.

Design and Implementation of 150 W AC/DC LED Driver with Unity Power Factor, Low THD, and Dimming Capability

This paper presents the implementation of a two-stage light-emitting diode (LED) driver based on commercial integrated circuits (IC). The presented LED driver circuit topology, which is designed to drive a 150 W LED module, consists of two stages: AC-DC power factor correction (PFC) stage and DC/DC power converter stage. The implementation of the PFC stage uses IC NCP1608, which uses the critical conduction mode to guarantee a unity input power factor with a wide range of input voltages. The DC/DC power converter with soft-switching characteristics for the entire load range uses IC FLS2100XS. Furthermore, the design of an electromagnetic interference (EMI) filter for the LED driver and the dimming control circuit are discussed in detail. The hardware prototype, an LED lighting system, with a rated power of 150 W/32 V from a nominal 220 V/50 Hz AC voltage supply was tested to show the effectiveness of the design. The presented LED driver was tested for street lighting, and the experimental results show that the power factor (PF) was higher than 0.97, the total harmonics distortion (THD) was lower than 7%, and the efficiency was 91.7% at full load. The results prove that the performance of the presented LED driver complies with the standards: IEC61000-3-2 and CIRSP 15:2009.

Enhanced Dual-Active-Bridge DC–DC Converter for Balancing Bipolar Voltage Level of DC Distribution System

Conventional dual-active-bridge (DAB) dc–dc converters have a limited structure to balance the bipolar voltage level of the bipolar dc distribution system. Therefore, to regulate the bipolar voltage level, additional voltage balancers are needed for the DAB converters, which eventually requires more devices resulting in low power conversion efficiency and low power density. This article proposes an enhanced DAB dc–dc converter that can balance the bipolar voltage level without the additional voltage balancers. The bipolar voltage level can be tightly regulated under entire unbalanced load condition and even when there is no-load at one side of the dc poles. Besides, its zero-voltage-switching capability can be extended to cover the entire load range, including the no-load condition. Furthermore, the proposed converter can be operated by using a simple single phase-shift modulation. Therefore, its control algorithm can be easily implemented in digital controllers. Finally, the theoretical analysis and the effectiveness of the proposed DAB converter are validated by a 3-kW prototype converter.

An H5-Bridge-Based Asymmetric LLC Resonant Converter With an Ultrawide Output Voltage Range

To extend the output voltage range of the conventional LLC topology, a small magnetizing inductance and a large frequency modulation window are required. Both would jeopardize the system performances. To resolve this issue, this article proposes a novel H5-bridge-based asymmetric LLC resonant converter. By configuring the switch pattern of the H5-bridge, two asymmetric LLC resonant tanks could operate in idle, half-bridge, hybrid-bridge, and full-bridge modes. Correspondingly, six operation modes with scaled voltage gains are obtained. Hence, an ultrawide output voltage range is achieved with moderate magnetizing inductance and simplified design of resonant parameters. The switching frequency range is squeezed close to the resonant frequency, which is beneficial for control implementation and circulating current suppression. Furthermore, two resonant tanks facilitate an easier zero-voltage switching (ZVS) of the primary-side MOSFETs and alleviate the current and voltage stresses. The conduction loss is further reduced due to the power-sharing effect between resonant tanks. To achieve a minimized frequency window, the optimized design of two resonant tanks is analyzed. To verify this concept, a 1-kW-rated prototype with 390 V input and 80–450 V output is designed and tested. Primary-side MOSFETs’ ZVS are achieved over the entire load range. The designed prototype achieves 97.05% peak efficiency and good efficiency performance over the ultrawide output voltage range.

A Two-Switch, Isolated, Three-Phase AC–DC Converter

A new, three-phase, single-stage, isolated ac–dc converter (rectifier) that employs only two switches and achieves less than 5% total harmonic distortion of the three-phase input currents and provides a tightly regulated, isolated, output voltage is introduced. The rectifier features zero-voltage-switching of both switches over the entire input and load range without any additional soft-switching circuitry. The rectifier is derived by combining the three-phase, power-factor-correction, discontinuous-current-mode boost rectifier that is also known as Taipei rectifier with the conventional LLC resonant half-bridge converter. The introduced rectifier requires single feedback loop with frequency control to regulate the output voltage. The evaluation was performed on a 1-kW prototype operating with a three-phase line-voltage range from 180 to 264 $V_{\text{L}-\text{L}}$ and delivering a tightly-regulated, isolated, output voltage of 54 V. The measured efficiency of the prototype at nominal line voltage V IN = 208 VL-L is above 95% from 90% of full load down to 50% of full load. The maximum voltage stress is approximately 430 V.

Investigation of Zero Voltage Switching Capability for Bidirectional Series Resonant Converter Using Phase-Shift Modulation

A series resonant converter (SRC) using a phase-shift modulation (PSM) was invented to implement the bidirectional power flow. However, it has a narrow zero voltage switching (ZVS) range, which reduces the power conversion efficiency for the light load condition. In this paper, the ZVS condition of the SRC is analyzed according to the power flow directions. From this analysis, the SRC using an extended PSM and single PSM is proposed to obtain the soft switching for the entire load range. The analysis of ZVS condition and performance of proposed control algorithm are verified using simulation and experimental results with a 500-W prototype converter.

Experimental study of moment sharing in multi-joist timber-concrete composite floors from zero load up to failure

The critical T-sections of multi-joist timber-concrete composite (TCC) floors must be designed at ultimate for support shear force and midspan moment, both of which are influenced by transverse sharing, but to different extents. Prior experimental work has investigated only support reaction sharing and only up to serviceability loads. The present experimental study builds on that status quo by quantifying also moment sharing, via strain gauge layouts at quarter-span and midspan, along with reaction sharing via load cells at the supports of a multi-joist TCC specimen, over the entire load range up to failure. Use of steel mesh connectors bonded into hardwood laminated veneer lumber joists, and near geometric resemblance to a real building TCC floor recently built in London, were novel features of the specimen. The results show that midspan moment and reaction sharing both vary nonlinearly with load, but in distinctly different ways from each other (with up to almost 20% difference observed between them), in the progression between the uncracked, cracked and connection ductility regimes. In this approach reliable assessment of moment sharing depends on the quality of the recorded strains. Accordingly, the strain data were shown to be of high quality by converting these data to internal stress resultants that were then found to satisfy longitudinal equilibrium. It is concluded that this strain gauge layout is useful for future work aimed at building a database of transverse sharing of moments in TCCs.

Performance and emission characteristics of conventional diesel combustion/partially premixed charge compression ignition combustion mode switching of biodiesel-fueled engine

In this experimental study, a production grade engine was modified to operate in two combustion modes, namely conventional diesel combustion (CDC) and premixed charge compression ignition (PCCI) combustion, depending on the engine load. For mode switching, an open electronic control unit was programmed to operate the engine in PCCI combustion mode up to medium engine loads and then automatically switching it to CDC mode at higher engine loads, by varying the fuel injection parameters and the exhaust gas recirculation rate. For performance and emission characterization in the entire load range (idling-to-full load) of the test engine, a test cycle of 300 s was used, which included CDC mode, PCCI combustion mode, and transition between these two modes. Results showed that both mineral diesel and B20 (20% biodiesel blended with mineral diesel, v/v) fueled PCCI combustion resulted in significantly lower NOx and particulate emissions compared to baseline CDC. Relatively lower exhaust gas temperature in PCCI combustion mode led to slightly inferior engine performance and higher concentration of unregulated emission species such as SO2, HCHO, and so on. B20-fueled engine resulted in relatively lower unregulated emission species and particulates compared to the mineral diesel–fueled engine in both the combustion modes. In CDC mode, contributions of accumulation mode particles were significantly higher compared to nucleation mode particles. Relatively lower emission of aromatic compounds in PCCI combustion mode compared to CDC mode was another important finding of this study; however, B20-fueled engines resulted in slightly higher emissions of aromatic compounds.

Soft-Switched High Step-Up Quasi-Z-Source DC–DC Converter

A soft-switched nonisolated high step-up dc–dc converter based on the quasi-impedance-source structure is presented in this paper. In the proposed converter, a technique similar to the synchronous rectifier is applied such that the diode of the impedance network is replaced with an active switch. In this way, not only is conduction loss associated with the diode reduced but also zero-voltage-switching characteristics for power switches are provided. Also, output diodes of the proposed converter are switched under zero-voltage-zero-current-switching condition which extremely reduces their switching and reverse-recovery losses. It is shown that by correct design of the components, soft-switching performance is retained for all the semiconductor devices over the entire range of output load. All these factors together with simplicity of the proposed structure result in high efficiency over a wide range of output power. Moreover, the proposed converter benefits from continuous input current and a shared ground between input and output. Operating principles of the proposed converter along with its steady-state analysis are presented. Also, experimental results obtained from a laboratory prototype for 48 to 350 V voltage conversion and 100 W nominal power are provided to validate the feasibility of the proposed converter.

On the capabilities and limitations of predictive, multi-zone combustion models for hydrogen-diesel dual fuel operation

Compared with traditional hydrocarbon fuels, hydrogen provides a high-energy content and carbon-free source of energy rendering it an attractive option for internal combustion engines. Co-combusting hydrogen with other fuels offers significant advantages with respect to thermal efficiency and carbon emissions.This study seeks to investigate the potential and limitations of multi-zone combustion models implemented in the GT-Power software package to predict dual fuel operation of a hydrogen-diesel common rail compression ignition engine. Numerical results for in-cylinder pressure and heat release rate were compared with experimental data. A single cylinder dual-fuel model was used with hydrogen being injected upstream of the intake manifold. During the simulations low (20 kW), medium (40 kW) and high (60 kW) load conditions were tested with and without exhaust gas recirculation (EGR) and at a constant engine speed of 1500 rpm. Both single and double diesel injection strategies were examined with hydrogen energy share ratio being varied from 0 to 57% and 0–42 respectively. This corresponds to a range in hydrogen air-equivalence ratios of approximately 0–0.29.The results show that for the single-injection strategy, the model captures in-cylinder pressure and heat release rate with good accuracy across the entire load and hydrogen share ratio range. However, it appears that for high hydrogen content in the charge mixture and equivalence ratios beyond the lean flammability limit, the model struggles to accurately predict hydrogen entrainment leading to underestimated peak cylinder pressures and heat release rates. For double-injection cases the model shows good agreement for hydrogen share ratios up to 26%. However, for higher energy share ratios the issue of erroneous hydrogen entrainment into the spray becomes more accentuated leading to significant under-prediction of heat release rate and in-cylinder pressure.

Design Methodology of Tightly Regulated Dual-Output LLC Resonant Converter Using PFM-APWM Hybrid Control Method

A dual-output LLC resonant converter using pulse frequency modulation (PFM) and asymmetrical pulse width modulation (APWM) can achieve tight output voltage regulation, high power density, and high cost-effectiveness. However, an improper resonant tank design cannot achieve tight cross regulation of the dual-output channels at the worst-case load conditions. In addition, proper magnetizing inductance is required to achieve zero voltage switching (ZVS) of the power MOSFETs in the LLC resonant converter. In this paper, voltage gain of modulation methods and steady state operations are analyzed to implement the hybrid control method. In addition, the operation of the hybrid control algorithm is analyzed to achieve tight cross regulation performance. From this analysis, the design methodology of the resonant tank and the magnetizing inductance are proposed to compensate the output error of both outputs and to achieve ZVS over the entire load range. The cross regulation performance is verified with simulation and experimental results using a 190 W prototype converter.

Experimental Investigation of Performance, Emission and Combustion Characteristics of a Common-Rail Diesel Engine Fuelled with Bioethanol as a Fuel Additive in Coconut Oil Biodiesel Blends

In the present study, the effects of adding of bioethanol as a fuel additive to a coconut biodiesel-diesel fuel blend on engine performance, exhaust emissions, and combustion characteristics were studied in a medium-duty, high-pressure common-rail turbocharged four-cylinder diesel engine under different torque conditions. The test fuels used were fossil diesel fuels, B20 (20% biodiesel blend), B20E5 (20% biodiesel + 5% bioethanol blend), and B20E10 (20% biodiesel + 10% bioethanol blend). The experimental results demonstrated that there was an improvement in the brake specific energy consumption (BSEC) and brake thermal efficiency (BTE) of the blends at the expense of brake specific fuel consumption (BSFC) for each bioethanol blend. An increment in nitrogen oxide (NOx) across the entire load range, except at low load conditions, was found with a higher percentage of the bioethanol blend. Also, it was found that simultaneous smoke and carbon monoxide (CO) emission reduction from the baseline levels of petroleum diesel fuel is attainable by utilizing all types of fuel blends. In terms of combustion characteristics, the utilization of bioethanol blended fuels presented a rise in the peak in-cylinder pressure and peak heat release rate (HRR) at a low engine load, especially for the B20E10 blend. Furthermore, the B20E10 showed shorter combustion duration, which reduced by an average of 1.375 °CA compared to the corresponding baseline diesel. This study therefore showed that the B20E10 blend exhibited great improvements in the diesel engine, thus demonstrating that bioethanol is a feasible fuel additive for coconut biodiesel-diesel blends.

Analysis and Comparison of Push–Pull Class-E Inverters With Magnetic Integration for Megahertz Wireless Power Transfer

This paper presents the circuit design and magnetic integration of push–pull class-E inverters for wireless power transfer (WPT) up to megahertz. The design criterion for achieving zero-voltage switching (ZVS) of a class-E inverter with coupled windings is derived mathematically. The approaches of magnetic integration for push–pull class-E inverters are analyzed and compared. Then, a new magnetic structure with hybrid magnetic materials is proposed to build the integrated inductors with either coupled windings or uncoupled windings. A 3-MHz WPT system is built to verify the analysis. The detailed comparison of the class-E inverters with magnetic integration is presented in terms of switch voltage, efficiency, harmonic currents, and thermal distribution. In the optimized design example, the switches keep ZVS over the entire load range without using any closed-loop control. The system efficiency reaches 87.1% at 350-W output power.

Emphasis on switch selection and its switching loss comparison for on‐board electric vehicle charger

A DC/DC converter plays a vital role in on-board electric vehicle (EV) charger. Among the many converter topologies, the phase-shifted full-bridge DC/DC converter (PSFBDC) is widely used. For improved efficiency, PSFBDC is embedded with passive auxiliary networks resulting in several unique configurations for achieving soft-switching in entire load range. The architecture of the chosen DC/DC converter configuration should comply with the society of automotive engineers (SAE) standards. Although, the conduction loss of the converter can be minimised by choosing a proper topology configuration and proper switching of the configuration, the selection of appropriate for PSFBDC plays an important role in enhancing the overall efficiency. An optimistic method for the selection of switch configuration satisfying the reduced power loss and cost-effective aspects is presented. For demonstrating the proposed method, a 1 kW 100 kHz system with commercially available switches IRFP460, IXFN64N60P, and IPP65R045C7 is chosen and the obtained results are presented.

A Five-Switch Bridge Based Reconfigurable LLC Converter for Deeply Depleted PEV Charging Applications

This letter presents a reconfigurable dual LLC converter based on a five-switch bridge to charge the deeply depleted plug-in electric vehicle onboard battery packs. Due to the reconfiguration of the primary-side switch network, two resonant tanks could operate in integrated half-bridge, half-bridge, hybrid-bridge, and full-bridge modes. Thus, four operation modes are derived, with their normalized voltage gains scaled to 1:2:3:4, respectively. Those four modes enable a squeezed switching frequency span, which is close to the resonant frequency. Therefore, the efficiency performance over an ultra-wide output voltage range can be optimized. Zero-voltage-switching can be realized in all power mosfet s over the entire load range. The operating principles, voltage gains analysis are briefed. A 1.1-kW-rated prototype converting the 390-V input to 100–420 V output, is designed and tested to validate the proof of concept. A total of 97.64% of peak efficiency and good efficiency over the full charging range is reported.

Compact Single-Stage Micro-Inverter with Advanced Control Schemes for Photovoltaic Systems

This paper proposes a grid-connected single-stage micro-inverter with low cost, small size, and high efficiency to drive a 320 W class photovoltaic panel. This micro-inverter has a new and advanced topology that consists of an interleaved boost converter, a full-bridge converter, and a voltage doubler. Variable switching frequency and advanced burst control schemes were devised and implemented. A 320 W prototype micro-inverter was very compact and slim with 60-mm width, 310-mm length, and 30-mm height. In evaluations, the proposed micro-inverter achieved CEC weighted efficiency of 95.55%, MPPT efficiency >95% over the entire load range, and THD 2.65% at the rated power. The proposed micro-inverter is well suited for photovoltaic micro-inverter applications that require low cost, small size, high efficiency, and low noise.

Experimental investigation of iso-butanol/diesel reactivity controlled compression ignition combustion in a non-road diesel engine

As non-road engine emission control programs are developed largely in number of countries around the world, adopting a high efficiency and low emission combustion techniques has become essential. Flexible fuel operation using in-cylinder blending technique is a primary option for using higher octane fuel in a non-road diesel engine to mitigate emissions and fossil fuel dependency. In the present study, iso-butanol/diesel dual fuel reactivity controlled compression ignition concept is preferred considering the benefits of iso-butanol over other alcohol fuels and better combustion control over other low temperature combustion concepts. An experimental investigation is performed on a suitably modified single cylinder non-road diesel engine for the entire load range (0–100% engine full load) focusing on the effect of operating parameters (iso-butanol mass fraction, diesel injection timing, diesel injection pressure, diesel mass in split injection, and intake air temperature) on the dual fuel combustion, performance and emission characteristics. The reactivity controlled compression ignition combustion is analyzed at each load condition and the best operating points are selected based on brake thermal efficiency and emissions. The results indicated that increase in iso-butanol mass fraction with advanced start of injection of direct injected diesel fuel showed a 99% reduction in oxides of nitrogen and a 91% reduction in smoke emissions with 4.5% increase in brake thermal efficiency. Further the drawback in dual fuel combustion, hydrocarbon emission is reduced by 65% with an increase of intake air temperature from 303 K to 338 K. Also, both hydrocarbon and carbon monoxide emissions are reduced with increase in diesel injection pressure and mass of diesel fuel injected in first injection due to the enhanced mixture formation.

Extension of Zero Voltage Switching Capability for CLLC Resonant Converter

TheCLLC resonant converter has been widely used to obtaina high power conversion efficiency with sinusoidal current waveforms and a soft switching capability. However, it has a limited voltage gain range according to the input voltage variation. The current-fed structure canbe one solution to extend the voltage gain range for the wide input voltage variation, butit has a limited zero voltage switching (ZVS) range. In this paper, the current-fed CLLC resonant converter with additional inductance is proposed to extend the ZVS range. The operational principle is analyzed to design the additional inductance for obtaining the extended ZVS range. The design methodology of the additional inductance is proposed to maximize the ZVS capability for the entire load range. The performance of the proposed method is verified with a 20 W prototype converter.

Load-Velocity Relationship in National Paralympic Powerlifters: A Case Study.

To examine the relationships between different loading intensities and movement velocities in the bench-press exercise (BP) in Paralympic powerlifters. A total of 17 national Paralympic powerlifters performed maximum dynamic strength tests to determine their BP 1-repetition maximum (1RM) in a Smith-machine device. A linear position transducer was used to measure movement velocity over a comprehensive range of loads. Linear-regression analysis was performed to establish the relationships between the different bar velocities and the distinct percentages of 1RM. Overall, the correlations between bar velocities and %1RM were strong over the entire range of loads (R2 .80-.91), but the precision of the predictive equations (expressed as mean differences [%] between actual and predicted 1RM values) were higher at heavier loading intensities (∼20% for loads ≤70% 1RM and ∼5% for loads ≥70% 1RM). In addition, it seems that these very strong athletes (eg,1RM relative in the BP = 2.22 [0.36]kg·kg-1, for male participants) perform BP 1RM assessments at lower velocities than those previously reported in the literature. The load-velocity relationship was strong and consistent in Paralympic powerlifters, especially at higher loads (≥70% 1RM). Therefore, Paralympic coaches can use the predictive equations and the reference values provided here to determine and monitor the BP loading intensity in national Paralympic powerlifters.

Properties of Beam-to-Column Joint in Steel-Concrete Composite Frame Unpropped or Partly Propped During Slab Execution

The issues of load-bearing capacity and stiffness of end-plate beam-to-column composite joints under monotonic or cyclic bending moment loading have been discussed in numerous publications. Publicly available descriptions of various computational models and reports from experimental research concern joints with structure not changing in their entire load range. However, it is difficult to find the results of experimental tests or theoretical analyses of the load-bearing capacity and rotational capacity of a beam-to-column joint in composite frame with a reinforced concrete slab or steel-concrete composite slab executed on not propped steel member. Meanwhile, there are structural solutions in which floor slabs are executed using permanent formwork and temporary formwork girders arranged between the girders of a steel frame before concreting, without vertical slab props or with a limited number of them. In such a structure with a variable static scheme, the results of the internal forces analysis in the ultimate limit state may be different from the results for a structure made with full support. These differences are related among other to different characteristics of seemingly the same joints. The aim of the work was therefore an attempt to assess the impact of technology of the structure execution on the load capacity and rotational capacity of the beam-column connection in the steel-concrete composite frame in the ultimate limit state. The examples of steel-concrete composite joints of frame made with full temporary support as well as without vertical slab props were analysed. A modified two-stage non-linear component method was used in the calculations. Load capacities of the basic components as well as their initial stiffness were adopted according to Eurocode 3 and Eurocode 4, while their ultimate deformation values in ULS were adopted according to the author’s own analysis or other available results. The rotational capacity of composite joints made at several levels of the steel joint’s effort during slab concreting was considered. It was assumed that during execution the steel beams are always protected against torsional buckling. Conclusions regarding the estimation of the load capacity and rigidity of the joint as well as its rotational capacity depending on the assembly method are presented.