scholarly journals Low-load Efficiency Improvement of a Three-Phase Bidirectional Isolated DC-DC Converter (3P-BIDC) Via Enhanced Switching Strategy

2018 ◽  
Vol 7 (4.35) ◽  
pp. 932 ◽  
Author(s):  
N. S. Mohd Sharifuddin ◽  
N. M. L. Tana ◽  
H. Akagi
Keyword(s):  
Phase Shift ◽  
Load Condition ◽  
Mode Switching ◽  
Switching Strategy ◽  
Burst Mode ◽  
Modulation Technique ◽  
Three Phase ◽  
Low Load ◽  
Low Efficiency ◽  
Load Conditions

This paper presents the system design, operation and enhanced switching strategy of a three-phase bidirectional isolated dc-dc converter (3P-BIDC). The paper discusses the operating modes of the 3P-BIDC using phase-shift modulation (PSM), with analysis on its soft-switching characteristics. The phase-shift modulation is the simplest modulation technique that can be applied to the 3P-BIDC. However, it comes with the consequences of low efficiency performance in the low-load conditions. Therefore, this paper investigates the improvement in efficiency of the 3P-BIDC during low-load condition using an enhanced switching strategy combining burst-mode switching and phase-shift modulation. The model of a 700-V, 100-kW, 20-kHz 3P-BIDC and the enhanced switching strategy are verified via simulation using PSCAD. The simulation results shows that the combination of burst-mode and phase-shift modulation technique improves the efficiency of the 3P-BIDC at low-load conditions.  

scholarly journals Evaluation of a Three-Phase Bidirectional Isolated DC-DC Converter with Varying Transformer Configurations Using Phase-Shift Modulation and Burst-Mode Switching

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2836
Author(s):  
Nuraina Syahira Mohd Sharifuddin ◽  
Nadia M. L. Tan ◽  
Hirofumi Akagi
Keyword(s):  
Phase Shift ◽  
Voltage Drop ◽  
Load Condition ◽  
Mode Switching ◽  
Power Transfer ◽  
Burst Mode ◽  
Light Load ◽  
Three Phase ◽  
Efficiency Performance ◽  
Intermittent Switching

This paper presents the performance of a three-phase bidirectional isolated DC-DC converter (3P-BIDC) in wye-wye (Yy), wye-delta (Yd), delta-wye (Dy), and delta-delta (Dd) transformer configurations, using enhanced switching strategy that combines phase-shift modulation and burst-mode switching. A simulation verification using PSCAD is carried out to study the feasibility and compare the efficiency performance of the 3P-BIDC with each transformer configuration, using intermittent switching, which combines the conventional phase-shift modulation (PSM) and burst-mode switching, in the light load condition. The model is tested with continuous switching that employs the conventional PSM from medium to high loads (greater than 0.3 p.u.) and with intermittent switching at light load (less than 0.3 p.u), in different transformer configurations. In all tests, the DC-link voltages are equal to the transformer turns ratio of 1:1. This paper also presents the power loss estimation in continuous and intermittent switching to verify the modelled losses in the 3P-BIDC in the Yy transformer configuration. The 3P-BIDC is modelled by taking into account the effects that on-state voltage drop in the insulated-gate bipolar transistor (IGBTs) and diodes, snubber capacitors, and three-phase transformer copper winding resistances will have on the conduction and switching losses, and copper losses in the 3P-BIDC. The intermitting switching improves the efficiency of the DC-DC converter with Yy, Yd, Dy, and Dd connections in light-load operation. The 3P-BIDC has the best efficiency performance using Yy and Dd transformer configurations for all power transfer conditions in continuous and intermittent switching. Moreover, the highest efficiency of 99.6% is achieved at the light power transfer of 0.29 p.u. in Yy and Dd transformer configurations. However, the theoretical current stress in the 3P-BIDC with a Dd transformer configuration is high. Operation of the converter with Dy transformer configuration is less favorable due to the efficiency achievements of lower than 95%, despite burst-mode switching being applied.

Unsteady Flow Features and Vibration Stresses of an Actual Size Steam Turbine Last Stage in Various Low Load Conditions

2013 ◽  
Author(s):  
Naoki Shibukawa ◽  
Yoshifumi Iwasaki ◽  
Mitsunori Watanabe
Keyword(s):  
Steam Turbine ◽  
Pressure Fluctuation ◽  
Load Condition ◽  
Test Facility ◽  
Stress Increase ◽  
Unsteady Pressure ◽  
Low Load ◽  
Vibration Stress ◽  
Last Stage ◽  
Load Conditions

Experimental investigations with a six stage real scale low pressure steam turbine operated at a very low load conditions are presented in this paper. Although the tested 35 inch last stage blades are circumferentially coupled at both tip and mid span with an intention to reduce the vibration stress, still its increase was observed at extremely low load condition. The pressure fluctuations were measured by several silicon diaphragm sensors which were mounted on both inner and outer casings of the stator inlet, exit and blade exit position. The measurement of the vibration stress was performed by strain gauges on several blades. The power spectra of unsteady pressures were precisely investigated considering both their location and steam flow condition. And the results implied that huge reverse flow and re-circulation started in the same location as a blade-to-blade CFD predicted. In terms of the correlation between vibration stress and the flow feature, the pressure fluctuation around the blade tip produces dominant effects on the vibration stress. The unsteady pressure frequency were also investigated and compared with those of the blade resonance and rotational speed. Basic trends observed in the results are similar to what other researchers reported, and on top of that, the continuous trends of pressure fluctuation and blade vibration stress were systematically investigated. Even the wall pressure, not the pressure on blade surface, showed the effective fluctuations which excited the several nodes of natural frequencies of the last stage blade. A series of FFT of fluid force by a full annulus quasi-steady CFD simulation seems to predict dominant mode of the excitation which account for the behavior of vibration stresses. The mechanism of the rapid stress increase was examined by considering CFD results and measured unsteady pressure data together. As the test facility takes a responsibility as an independent power producer, the tests were conducted in real plant operations which include multi stage effects, inlet distortions, Reynolds Number effect and so on. The obtained data and the particular indicator of vibration stress increase can be used as a part of design tool validation with neither aerodynamic nor mechanical corrections.

SI/HCCI Mode Switching Optimization in a Gasoline Direct Injection Engine Employing Dual Univalve System

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Yintong Liu ◽  
Liguang Li ◽  
Haifeng Lu ◽  
Stephan Schmitt ◽  
Jun Deng ◽  
...  
Keyword(s):  
High Efficiency ◽  
Direct Injection ◽  
Load Condition ◽  
Gasoline Direct Injection ◽  
Mode Switching ◽  
Nox Emissions ◽  
Combustion Mode ◽  
Timing Control ◽  
Main Challenge ◽  
Low Load

Homogeneous charge compression ignition (HCCI) is a feasible combustion mode meeting future stringent emissions regulations, and has high efficiency and low NOX and particle emissions. As the narrow working condition range is the main challenge limiting the industrialization of HCCI, combustion mode switching between SI and HCCI is necessary when employing HCCI in mass production engines. Based on a modified production gasoline direct injection (GDI) engine equipped with dual UniValve system (a fully continuously variable valvetrain system), SI/HCCI mode switching under low load condition is investigated. According to the results, combustion mode switching from SI to HCCI is more complicated than from HCCI to SI. As HCCI requires strict boundary conditions for reliable and repeatable fuel auto-ignition, abnormal combustion easily appears in transition cycle, especially when combustion switches from SI to HCCI. Timing control strategies can optimize the combustion of transition cycles. With the optimization of timing control, the mode switching from SI to HCCI can be completed with only two transition cycles of late combustion, and abnormal combustion can be avoided during the mode switching from HCCI to SI. Under the low load condition, the indicated efficiency reaches 39% and specific NOX emissions drop down to around 1 mg/L/s when the combustion mode is switched to HCCI mode. Compared to SI mode, the indicated efficiency is increased by 10% and the specific NOX emissions are reduced by around 85%.

scholarly journals Current optimal control method for three-phase dual active bridge converter in light load conditions

2021 ◽  
Vol 300 ◽  
pp. 01009
Author(s):  
Xiaobin Mu ◽  
Xiang Wang ◽  
Fengjiao Dai
Keyword(s):  
Control Method ◽  
Storage System ◽  
Time Domain Analysis ◽  
Energy Storage System ◽  
Current Control ◽  
Dual Active Bridge ◽  
Light Load ◽  
Three Phase ◽  
Low Efficiency ◽  
Load Conditions

Three-phase dual active bridge converter has many performance advantages, and is widely used in electric vehicle charging, battery energy storage system, power electronic transformer, and other energy conversion occasions. However, in the traditional control method, it has the problem of low efficiency under light load conditions. In this paper, firstly, the power and current expressions of the converter under light load conditions are solved by time-domain analysis, and an optimal current control method under light load conditions is proposed. This control method can simultaneously realize the minimum inductance current stress and RMS. Finally, the effectiveness of this method is verified by experiments.

Research on Voltage-Chopping and Energy-Saving Controlling Technology for Three-Phase AC Asynchronous Motor

2012 ◽  
Vol 433-440 ◽  
pp. 1033-1037 ◽  
Author(s):  
Dian Sheng Sun
Keyword(s):  
Energy Saving ◽  
Power Factor ◽  
Supply Voltage ◽  
Asynchronous Motor ◽  
Voltage Regulator ◽  
Basic Principles ◽  
Three Phase ◽  
Low Load ◽  
Energy Saving Technology ◽  
Low Efficiency

This work discusses the basic principles of Voltage-Chopping and energy-saving technology for the three-phase AC asynchronous motor running in the low load conditions causing the low power factor and low efficiency. On this basis, Developed chopping control and energy saving controller for three-phase AC asynchronous motor .By real-time detection of power factor and other parameters，the energy-saving controller using PWM chopped-controlled voltage regulator means regulating the motor supply voltage to achieve the purpose of energy saving.

scholarly journals Effective elimination of harmonics on the part of chosen dc bus in dual active type converter

2018 ◽  
Vol 7 (2.25) ◽  
pp. 53
Author(s):  
N Janaki ◽  
Dr R.Krishna Kumar
Keyword(s):  
Phase Shift ◽  
Square Wave ◽  
Active Type ◽  
Modulation Technique ◽  
Three Phase ◽  
Bridge Type ◽  
Dc Bus ◽  
Wave Control

In order to manage the flow of power in the dual bridge type converter, a modulation technique called phase shifted square wave is employed. As an outcome, increased range of ripples in current is resulted, and that further provokes the vibration in inductance and capacitance circuit. Due to this effect, there exists uncertainty in the value of current and voltage, failure of operating components and stress in the filter. To miti-gate the above ill effects, three level modulation can be done using three phase shift square wave control angles. These three angles now elimi-nate the harmonics in chosen DC link and the harmonic eliminating procedure is justified and simulated.  

scholarly journals Thermal System Simulation Study of Wide-Load Out-Of-Stock Technical Transformation to Reduce SCR Inlet Flue Gas Temperature of 300MW Subcritical Boiler

2021 ◽  
Author(s):  
Tao Qin ◽  
Jun Rong ◽  
Guang Yang ◽  
Yankai Wang ◽  
Yi Han ◽  
...  
Keyword(s):  
Flue Gas ◽  
System Simulation ◽  
Load Condition ◽  
Optimal Solution ◽  
Inlet Temperature ◽  
Thermal System ◽  
Gas Temperature ◽  
Low Load ◽  
Thermal Calculations ◽  
Load Conditions

During the operation of a 300MW subcritical boiler of a power plant, there is a low temperature of the SCR inlet flue gas under medium and low load conditions. In order to effectively solve the problem of low SCR inlet temperature under low load conditions, and improve the adaptability of the coal type. Three kinds of wide load denitration technology reform schemes are proposed. With the boiler thermal system simulation software BESS, the thermal calculations of the three transformation schemes were carried out. The results show that: the Scheme C is the optimal solution. After the transformation, the temperature of the SCR inlet flue gas increased by 21°C under the ultra-low load condition, and the exhaust gas temperature increased by about 7°C. At the same time, the possible impacts of the reform of the Scheme C and the key issues that need to be paid attention to during the transformation process are evaluated and discussed.

Influence of Wetness on Efficiency of the Full Scale Size Low Pressure Turbines

2012 ◽  
Author(s):  
Tomohiko Tsukuda ◽  
Hiroyuki Kawagishi ◽  
Naoki Shibukawa ◽  
Tadayuki Hashidate ◽  
Koichi Goto ◽  
...  
Keyword(s):  
Load Condition ◽  
Low Pressure ◽  
Test Results ◽  
Absolute Value ◽  
Low Pressure Turbine ◽  
Scale Size ◽  
Low Load ◽  
Lp Turbine ◽  
Stage Efficiency ◽  
Load Conditions

Efficiencies of 60Hz full size test turbines were measured in various wet steam conditions to reveal the wetness impact on the performance. We changed the wetness and stage load conditions independently under the condition of constant steam mass flow rate in the low pressure turbine. The test results told that the stage efficiency decreases with the increasing of wetness as many studies showed, furthermore, the stage efficiency decreases more in smaller load conditions than in the design point. In addition, blade length effects were examined by comparing two types of LP turbine to be found that the longer case got more deficits at the same wetness. Some theoretical evaluations were tried and a combination of some simple loss models explained the tendencies above, qualitatively. The evaluation showed that absolute value of mechanical wet loss such as braking loss remained unchanged regardless of load conditions, so in low load condition, ratio of mechanical loss to stage load increased, resulting decrease of stage efficiency. It also showed that increasing wet loss at the longer blade was mainly because higher circumferential velocity caused larger mechanical wet loss such as braking loss.

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