Rated Load Conditions Research Articles

A Flyback Converter with a Simple Passive Circuit for Improving Power Efficiency

This paper proposes an effective method to improve the power efficiency of the flyback converter in the continuous conduction mode (CCM). The proposed converter uses a simple passive circuit to reduce the switching power losses. The current through the output diode can be shifted to a new branch where one diode, one inductor, and one auxiliary winding of the transformer are included. The output diode current can be reduced to zero for the zero-current switching of the output diode. The additional inductor is used to control the changing rate of the additional diode current to reduce the reverse-recovery current. Keeping the simplicity of the passive method, the proposed converter improves the power efficiency compared to the conventional converter. The circuit configuration and the operation principle are described. The design considerations are presented, including the simulation verification. The experimental results for a 45 W prototype are discussed to evaluate the performance of the proposed converter. The proposed converter has achieved a power efficiency of 93.5% for the rated load condition, improving the power efficiency. The applications of the proposed converter are also discussed for the future research directions.

Studies on fuels and engine attributes powered by bio-diesel and bio-oil derived from stone apple seed (Aegle marmelos) for bioenergy

Biofuel is an alternative fuel for diesel engines which is necessary to reduce exhaust emissions and helps to balance the depletion of fossil fuels. This study details the synthesis of bio-diesel and bio-oil from stone apple seeds ( Aegle marmelos) through transesterification, direct oxygenate additive, and pyrolysis processes. The diesel engine is powered by the resulting stone apple methyl ester bio-diesel/diesel and bio-oil/diesel mixtures. In a test engine rig, the effectiveness and emission uniqueness of test fuel mixes were examined at various engine loads (EL = 3 kg–12 kg) and compression ratios (CR = 16–17.5) while maintaining a steady speed of 1500 r/min. Furthermore, engine performance and emissions for bio-diesel and bio-oil are measured and compared. The oxides of nitrogen (NOx) emission by bio-diesel and bio-oil opus were higher than neat diesel (FD). Also, carbon monoxide (CO) and hydrocarbon (HC) emissions were measured to be lower. The improvements of BTE by 4.87% and decrement of CO by 18.8%, HC by 13.26% were observed with the trans-esterified bio-diesel/diesel opus compared to diesel at a higher CR and rated load conditions. The engine analysis responses revealed that the FBD blend showed enhanced performance and lower emissions except NOx compared to diesel fuel. Hence, trans-esterified bio-diesel is a greater diesel alternative than FBDE and FBO.

Design and analysis of soft-switching isolated step-up/down DC–DC converter for fuel cell vehicles and EV battery charging applications

ABSTRACT With the increasing adoption of non-conventional energy sources, there is a significant demand for DC energy conversion systems as they play a crucial role in integrating power sources and loads that operate at different voltage levels. In this paper, a novel DC–DC converter topology is presented, which can efficiently perform Buck-boost operation with minimal duty cycle operation, making it an attractive option for DC energy conversion applications. Furthermore, its switching voltage stress is less than the voltage present at the output, allowing the use of low power rated devices. Additionally, the topology contains isolation between the load and source, which prevents circulating currents and protects the source from load harmonics. The proposed converter has the ability to achieve soft switching without using any extra circuitry. Moreover, the presented converter is evaluated against recently developed topologies in terms of active/passive components, gain, efficiency, and switching stress. Closed-loop analysis is done for the proposed converter using small-signal modeling. The converter is tested by subjecting it to a sudden step change at the input voltage from 20 V to 40 V in boost condition while maintaining a constant output voltage of 240 V. Additionally, load disturbances are introduced to assess the system’s robustness in closed-loop operation. In the laboratory, A 100-W prototype of the presented converter is built, which gives an efficiency of 95% at the rated load condition.

An analytical design and analysis of a high gain switched inductor voltage multiplier cell power converter

The proposed modified higher gain boost converter employs switched Inductor and multiplier cell-based voltage boosting techniques, as the paper represents. This converter is modelled to enhance the static gain and efficiency. As the designed topology has an incessant source current at its input side, it is ideal for solar PV applications. With a power capacity of 100 W, the proposed topology is designed to work on 24 V source input and 200 V load/output voltage. The load voltage is maintained by a PI controller, which achieves the highest efficiency of 92% under rated load conditions. The converter’s transient performance with the controller is investigated under various situations, including supply voltage variation, reference voltage variation, and load power variation. Finally, the designed converter’s experimental model is created to evaluate the simulated and conceptual results.

A design study on MVAr class superconductor synchronous condenser with no-insulation HTS field coil

With the expansion of distributed power systems and renewable energy worldwide, the use of synchronous condensers (SC) has been gradually increasing to maintain the power quality of an electric grid. Because SC generates fewer harmonics and has the advantage of strengthening system inertia, it is considered as a primary option in Korea over other options such as Static Var Compensator (SVC) and STATic synchronous COMpensator (STATCOM). If superconductor synchronous condenser (SSC) is applied instead of SC, it brings more advantages: (1) it can minimize the adverse impact on the power system due to lower synchronous reactance, and (2) the higher power density can lead to many advantages in a limited area of substation. With these backgrounds, we report a design study on 40 MVAr SSC with no-insulation high-temperature superconductor (NI-HTS) field coil. Firstly, design criteria and procedures for electromagnetic design were set. Secondly, with the design procedure, the electromagnetic design having the minimum HTS conductor usage was obtained among the designs satisfying design criteria. Based on the final design, key characteristics of SSC including no-load voltage, the maximum flux density under the rated-load condition, V-curve characteristic, synchronous reactance, zero sequence reactance, negative sequence reactance, critical current, and NI-HTS characteristics were calculated by using finite element method. Lastly, the design comparison between SSC and SC was presented.

Experimental and Numerical Investigation of Cavitation Assessment for Runner Blades in a Francis Turbine

Cavitation in hydro turbines causes component deterioration that requires continuous and costly maintenance in the hydroelectric power generation stations. The Tarbela Dam Hydel Project (TDHP) in Pakistan is facing a cavitation problem in the Francis Turbine components, such as the runner and draft tube. Simulation work has been performed to examine and quantify the cavitation rate as a function of the suction head (SH) and flow velocity (FV) by utilizing a homogeneous cavitation model. The result shows that pressure fluctuation is maximum for overcrowded conditions and minimum for rated load conditions. Moreover, a higher cavitation rate is found for the part and overcrowded conditions compared to the rated load condition. Additionally, the cavitation rate becomes 50% higher when the SH increases from 5.54 to 12.34 m. Moreover, SEM results have verified the CFD results that higher FV and SH enhance the cavitation rate. Furthermore, the numerical work is validated by simplified hydrofoil geometry. The computational fluid dynamics results presented a good arrangement with the experimental data.

Alternative Performance Indices-Based Control Technique for a Unity Power Factor Three-Phase Rectifier

The implementation of a unity power factor (UPF) three-phase rectifier has the potential to enhance the power factor (PF). However, the PF and total harmonic distortion (THD) experience degradation in low-output regions due to the utilization of a “critical input inductor” under rated load conditions. In this study, an analysis of the operation principle of a UPF three-phase rectifier is conducted and a reference compensation current technique based on alternative performance indices is proposed. The optimal control algorithm is utilized to calculate the single harmonic phase delay of each phase and determine the compensator gain, taking into account factors such as the single harmonic distortion limit, THD limit, PF, and active power consumption. The output of the current compensator serves as the desired current source, which in turn drives the bidirectional switches. The simulation and experimental results demonstrate that the proposed control technique can significantly mitigate power supply current distortion, and the input power factor has been effectively improved within a wider load range.

Evaluation of uncertainties in pressure fluctuations measurement on low-head Francis turbine model during part-load operation

The Francis turbines are often operated at the part load (PL) conditions to meet the electricity demand while maintaining system stability. During PL operations, the turbine experiences flow instabilities and vortex formation in the draft tube, leading to potential damage to the turbine. This experimental study focused on measuring pressure fluctuations in a model low-head Francis turbine at PL operation, i.e. 70% of rated load condition. Eight pressure sensors were installed at various locations to measure the pressure fluctuations. In-situ calibrations were performed for various measuring instruments used in testing, such as flow meters, pressure transducers, torque transducers, and speed sensors. The uncertainty evaluation for hydraulic turbine efficiency and pressure fluctuations in the draft tube cone was carried out at the PL operations. Quantifying the uncertainty for both Type A and Type B was conducted. The maximum estimated uncertainty for measuring hydraulic turbine model efficiency is ±0.272% and for pressure fluctuations during PL operation is ±1.358%.

Flow-induced vibration analysis in a pump-turbine runner under transient operating conditions

The dynamic characteristics of the pumped storage unit (pump-turbine runner) make it highly susceptible to vibrations. Previous studies seldom addressed the clearance variation due to runner vibration, largely because of two challenges: the integration of the moving grid with the clearance and governing equations, and the intricacy of factoring in the entire shaft system's influence on vibration. By employing user-defined functions (UDF), kinematic equations for the pump-turbine runner's rotation and translation were formulated and integrated with computational fluid dynamics results. This paper introduces a computational method to simulate clearance-induced vibration displacement. The study examines the impact of clearance vibration displacement on the pump-turbine's transient flow field and runner vibrations under various operating conditions. Notably, deviations from the rated load condition led to an expansion-contraction trajectory of the runner axis, culminating in chaotic behaviour in the "S" characteristic zone. The correlation between runner vibrations and pressure fluctuations strengthened with the clearance displacement model, especially in narrow labyrinth seal clearances. Simulations also provided a refined estimation of the secondary rotational speed increase during load rejection. The method's reliability is confirmed through field test data comparison, offering a fresh perspective to identify the vibration characteristics of the pump-turbine runner.

Power Decoupling Control of Electrolytic Capacitor-Less Dual-Inverter to Reduce Interharmonic Currents Under Periodic Load Fluctuation

This study proposes a control method for an electrolytic capacitor-less dual-inverter with an aim to reduce the interharmonic currents. Owing to the low-energy buffer of the electrolytic capacitor-less inverter, load fluctuations superimpose harmonic currents on the input current. The proposed control method facilitates output power pulsation control of main inverter, which is a constant frequency regardless of load fluctuations. The experimental results exhibit a reduction in the interharmonic currents at 20 and 80 Hz by 68 and 72 %, respectively. Moreover, the power factor is improved by 11 pt., and total harmonic distortion (THD) of the input current is reduced by 26 pt. under rated load conditions. Therefore, the proposed control method can effectively reduce the interharmonic currents and improve the power factor and THD of the input current.

A novel step-up/step-down DC-DC converter based on flyback and SEPIC topologies with improved voltage gain

A novel step-up/step-down DC-DC converter with improved voltage gain characteristics is suggested in this paper. The proposed converter combines flyback and single-ended primary inductance converter (SEPIC) converters. The voltage control loop design is simplified due to the use of only a single controlled switch. It has been discussed how switch duty cycle affects voltage gain. This relationship demonstrates that the proposed converter voltage gain is improved compared with flyback and SEPIC converters. However, compared to flyback and SEPIC converters, it has a higher voltage gain at any given duty cycle. The proposed converter operation is thoroughly discussed, the associated equations are derived, and its parameters are expertly designed. Moreover, it is designed to supply a DC load of 2.5 kW, 500 V, and 5 A. The proposed converter efficiency exceeds 84% under rated load conditions. Additionally, it is also presented as an adapter for electric vehicles. The waveforms associated with the simulation of the converter across the universal line voltage of 110-260 Vrms are shown. At both line voltages, the total harmonics distortions (THDs) of the line current are 17.12% and 27.26%, respectively. MATLAB/Simulink is utilized for validation in order to validate the topology for different applications.

On the definition and effect of optimum gear microgeometry modifications for the gearbox of an offshore 10‐MW wind turbine

AbstractThis work develops an optimization algorithm for the definition of gear microgeometry modifications (MGM) on a gearbox belonging to an offshore 10‐MW wind turbine. Subsequently, the impact of the gear microgeometry on the performance of gears and bearings is quantified: First, under rated load conditions and, second, accounting for the environmental conditions to estimate the long‐term damage. To fulfil this task, a high‐fidelity numerical model of the drivetrain is used, which meets the design requirements of the Technical University of Denmark (DTU) 10‐MW reference offshore wind turbine. The optimization achieves a uniform distribution of the contact stress along the tooth flank, shifts its maximum value to the central position, and eliminates edge contact. These enhancements increase the gear safety factors. Nevertheless, the most significant improvement concerns planetary bearings, for which optimum gear MGM achieve a homogeneous share of the load among bearings. Moreover, deviations of the microgeometry with respect to the defined optimum are also addressed. In gears, lead slope deviations are counteracted by crowning modifications to restrain the increase of the load offset. Concerning planetary bearings, slope deviations can be beneficial or detrimental depending on whether they overload downwind or upwind planetary bearings, respectively. Finally, accumulated damage to planetary bearings after 20 years of service is assessed. Before MGM, results predict a premature failure of planetary bearings, while optimum MGM extend their predicted life above 20 years by achieving a reduction of the maximum accumulated fatigue damage by a factor of 4.4.

A New Cuk-Based DC-DC Converter with Improved Efficiency and Lower Rated Voltage of Coupling Capacitor

DC-DC converters play a crucial role in recent and advanced applications, enabling efficient power conversion and management for renewable energy systems, electric vehicles, portable devices, and advanced communication systems. In line with this, the objective of this paper is to introduce a new DC-DC configuration based on the Cuk converter named as Mahafzah converter, which utilizes a coupling capacitor with a lower rated voltage. The paper aims to demonstrate the effectiveness of the proposed converter in terms of improved efficiency, reduced size, and reduced semiconductor device currents compared to the conventional Cuk converter. The proposed configuration comprises the same components as the Cuk converter, but in a different arrangement, without any additional elements. The main advantage of the proposed converter is using a coupling capacitor with a much lower rated voltage than the Cuk converter, resulting in a smaller capacitor size, reduced printed circuit board (PCB) size, and manufacturing cost. Additionally, the proposed converter reduces the currents of the semiconductor devices compared to those in the Cuk converter. To demonstrate its effectiveness, the converter is operated under continuous current mode (CCM) with a constant duty cycle and switching frequency. The study provides an in-depth discussion of the various operating modes by making use of equations relating to currents, voltages, duty cycles, and voltage gains. It also provides detailed illustrations of the limits between CCM and discontinuous current mode (DCM). The effectiveness of the proposed converter is demonstrated through a design example with operating parameters of 1 kW, 200 V/−300 V, and 20 kHz. Additionally, a low voltage–low power prototype (12/−18 V, 3.24 W, 20 kHz) is established to verify the operation of the proposed converter. Simulation and experimental verification of the proposed configuration achieved the desired results to improve efficiency and reduce the rate. The results clearly indicate that the efficiency of the proposed converter surpasses that of the conventional Cuk converter under identical operating conditions, reaching approximately 88% at rated load conditions.

Research on Temperature Distribution of Large Permanent Magnet Synchronous Direct Drive Wind Turbine

A wind turbine is a conversion mechanism that converts wind energy into electrical energy, but the conversion efficiency cannot reach 100%, so there is partial loss. These losses are converted into thermal energy, which in turn causes the wind turbine to heat up and affect generator performance. Therefore, the cooling and temperature field analysis of wind turbines is very important. In this paper, an electromagnetic analysis model is established by using the parameters of a 4 MW wind turbine; the losses of each part of the generator under rated load and three-phase short-circuit conditions are calculated, respectively; and the heat source is imported into the workbench fluent software to determine the cooling mode, so as to obtain the magnetic-thermal-flow field coupling model of permanent magnet synchronous direct drive wind turbine. The temperature distribution and temperature rise of the generator are obtained. Under the rated load condition, the overall maximum temperature rise of the wind turbine is 41.4 °C, about 180 mm near the fluid outlet side, which is as high as the winding temperature rises, because the winding is the main heating body. The maximum temperature rise of the rotor model and the permanent magnet model is about 36 °C. Under the three-phase short circuit condition, the temperature distribution of each component is similar to that under the rated load condition, and the temperature near the fluid inlet is low; the lowest is only 29.8 °C. The higher the temperature at the fluid’s outlet, but not close to it, the higher the temperature is when it is about 180 mm away from the fluid’s outlet side. The temperature difference in the same axial length is relatively large, with a maximum temperature difference of about 120 °C. The temperature distribution and temperature rise of the generator are independent of the operating conditions, which mainly affect the value. Additionally, through experimental verification, the minimum error under the rated load condition is 1.05%, the maximum error is 3.3%, and the average error is 2.30%. The minimum error under the three-phase short-circuit condition is 1.5%, the maximum error is 3.62%, and the average error is 2.26%. The difference with the engineering error range requirements is small, indicating the reasonable and effective effectiveness of this method. This study aims to provide a strong reference for analyzing the cooling and magnetic thermal flow field and a coupling analysis of direct drive wind turbines.

Study on combustion performance of microgas turbine combustor with different fuels

AbstractA low‐pollution single‐tube microgas turbine combustor using different gas fuels was studied. The combustion performance of two kinds of landfill gas and natural gas was tested in a single‐head combustor. The effects of fuel nozzle position, and the fuel distribution ratio between pilot and main combustion stage on pollutant emission were investigated under rated load condition. The flow field, temperature field, and pollutant generation characteristics with different fuel nozzle diameters and nozzle positions were analyzed by numerical simulation. The results show that: the combustor can form an obvious central recirculation zone, which is convenient for ignition and stable flame propagation; in the case of limited premixed length, the influence of fuel nozzle position on fuel–air mixing uniformity is less obvious than that of fuel nozzle diameter. The fuel–air mixing uniformity plays a decisive role in the temperature field and the generation of pollutants in the combustor. The combustor has good pollutant emission characteristics, and the NOx emission can be reduced to about 10 ppmv (15% O2 concentration) under the appropriate combination of fuel nozzle diameter and position, which provides a reference for the further optimization of low‐emission combustor.

양방향 경계모드 벅/부스트 컨버터의 디지털 제어기법

This paper presents the digital control techniques of a bidirectional CRM(critical-conduction mode) buck(boost) converter, a dead-time design method that optimizes ZVS(zero-voltage switching) and valley-switching operation, and a switching-frequency limitation that ensures stable converter operation. To verify the feasibility of the design, a Si-MOSFET-based bidirectional CRM buck(boost) converter is built with 260-430 V input, 160-240 V output, and 1.0 kW rated capacity. The bidirectional CRM converter achieves an efficiency of up to 99.6% at buck mode and 98.7% at boost mode under rated load conditions.

Vector-Controlled Dual Stator Multiphase Induction Motor Drive for Energy-Efficient Operation of Electric Vehicles

ABSTRACT This paper proposes an Indirect Field Oriented Controlled Dual Stator Multiphase Induction Motor (IFOC-DSMIM) as a traction unit in an Electric Vehicle (EV) for the enhancement of its fuel economy and average loading capacity. The performance of the drive is studied by loading it under standard drive cycles that include free running, acceleration, and braking conditions using the MATLAB/Simulink environment. Its performance analysis is carried out to obtain efficiency curves under the three modes of excitation using a steady-state equivalent circuit approach. Studies on load sharing between the two stators, speed tracking and torque-producing capability of the drive are executed on its dynamic model and the simulation results are depicted. The average energy efficiency of the vehicle with the proposed DSMIM drive system is at least 10% higher than a Single Stator Multiphase Induction Motor (SSMIM) drive under different load percentages. Furthermore, under 75% of rated load conditions the energy efficiency is 20% higher. Thus, the proposed DSMIM configuration promises to provide a sizeable energy saving in the EV system, reducing the energy cost and increasing the driving range.

Design and Implementation of 3-kW Simmer and 30-kV DC Trigger Power Supply System for Driving Xenon Flash Lamps in Large-Area Processes

This article describes a 3-kW simmer and 30-kV dc trigger power supply system for driving xenon flash lamps in large-area processes. Simmer power supply is designed to output maximum of 3 kV for maintaining the lighting state of the lamp after having triggered and to supply low ripple current continuously for maintaining the ignited state. It is designed based on an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> resonant converter and design and implementation of the high-voltage transformer and output rectifier are presented. For igniting xenon lamps, dc trigger is designed to output a maximum of 30 kV auxiliary trigger voltage. The system that both power supplies is operated by one main inverter is presented. Through the resistive-load test, it is verified that the simmer outputs 600 V, 5 A under rated-load condition and 120 V, 1 A under light-load conditions. It is also verified that the simmer outputs 3 kV and the dc trigger outputs 30 kV under the no-load condition.Finally, the simmer and dc trigger power supply system is applied to lighting various xenon lamps from single lamp (306 mm, 8Φ) to three series lamps (400 mm, 26Φ). Required output voltages for stable driving various types of xenon lamps in the lighting mode are presented.

Magnet Eddy Current Loss and Thermal Analysis of a Dual-Permanent-Magnet-Excited Machines

This article investigates the eddy current loss mechanism of a dual-permanent-magnet-excited machines (DPMM). Based on the flux modulation effect, abundant harmonics are induced in the air gap of DPMM. The harmonics of air-gap flux density due to rotor permanent magnets (PMs), stator PMs, and armature reaction are investigated qualitatively and separately. Then, the orders, frequency, and rotation speed of the harmonics are deduced theoretically. The harmonics that contribute to the eddy current losses are deduced accordingly. Finally, the loss distribution of the proposed DPMM is estimated through simulation and the thermal field of the proposed motor is analyzed. A prototype is fabricated to validate the analysis. Temperature rise of both stator and rotor PMs under rated load condition is measured through experiment.

Performance Analysis and Optimization of Built-In Permanent Magnet and Salient-Pole Electromagnetic Hybrid Excitation Generators for Vehicles

To solve the problems of the low power density of pure electric excitation generator and nonadjustable magnetic field of pure permanent magnet (PM) generator, a salient-pole hybrid excitation generator (HEG) was proposed in this paper. The designed generator realized coexcitation of two magnetic fields by changing the shape of the pole shoes and embedding the combined-pole PM steels. Compared with other HEGs, it had the advantages of high power density, less excitation loss, and small volume. The paper deduced the analytical expressions of the main magnetic field and armature reaction magnetic field of the HEG and analyzed the armature reaction magnetic circuit, the main influencing parameters, and the influence law of each parameter on the generator output performance to complete the parameter matching of the whole machine. The prototype was trial manufactured and tested with the optimized parameters. The results show that the designed HEG has a low voltage regulation rate, good no-load characteristics, and regulation characteristics. It can ensure the regulated output voltage under rated load conditions and meet the application requirement.