Neutral Point Balancing for Three-Level Neutral Point Clamped Inverters Under Light Load Conditions

2018 ◽  
Author(s):  
Alexander Lange ◽  
Marco Zimmermann ◽  
Bernhard Piepenbreier
Keyword(s):  
Neutral Point ◽  
Light Load ◽  
Load Conditions

Power Electronic Traction Transformer: Efficiency Improvements Under Light-Load Conditions

2014 ◽  
Vol 29 (8) ◽  
pp. 3971-3981 ◽  
Author(s):  
Thomas Besselmann ◽  
Akos Mester ◽  
Drazen Dujic
Keyword(s):  
Power Electronic ◽  
Light Load ◽  
Load Conditions

scholarly journals Optimized Hip-Knee-Ankle Exoskeleton Assistance Reduces the Metabolic Cost of Walking With Worn Loads

2021 ◽  
Author(s):  
Gwendolyn M Bryan ◽  
Patrick Franks ◽  
Seungmoon Song ◽  
Ricardo Reyes ◽  
Meghan O’Donovan ◽  
...  
Keyword(s):  
Body Weight ◽  
Muscle Activity ◽  
Metabolic Cost ◽  
Load Carriage ◽  
Heavy Load ◽  
Human In The Loop ◽  
Light Load ◽  
Wide Range ◽  
Ankle Exoskeleton ◽  
Load Conditions

Abstract BackgroundLoad carriage is a typical activity in a wide range of professions, but prolonged load carriage is associated with increased fatigue and overuse injuries. Exoskeletons could improve the quality of life of these professionals by reducing metabolic cost to combat fatigue and reducing muscle activity to prevent injuries. Current exoskeletons have reduced the metabolic cost of loaded walking by up to 23% when assisting one or two joints. Greater metabolic reductions may be possible with optimized assistance of the entire leg. MethodsWe used human-in the-loop optimization to optimize hip-knee-ankle exoskeleton assistance with no additional load, a light load (15% of body weight), and a heavy load (30% of body weight) for three participants. All loads were applied through a weight vest with an attached waist belt. We measured metabolic cost, exoskeleton assistance, kinematics, and muscle activity. We performed one-tailed paired t-tests to determine significant reductions for metabolic cost and muscle activity, and we performed an analysis of variance (ANOVA) to determine significant changes across load conditions for metabolic cost and applied power. ResultsExoskeleton assistance reduced the metabolic cost of walking relative to walking in the device without assistance for all tested conditions. Exoskeleton assistance reduced the metabolic cost of walking by 47% with no load (p = 0.02), 35% with the light load (p = 0.03), and 43% with the heavy load (p = 0.02). The smaller metabolic reduction with the light load may be due to insufficient participant training or lack of optimizer convergence. The total applied positive power was similar for all tested conditions, and the positive knee power decreased slightly as load increased. Optimized torque timing parameters were consistent across participants and load conditions while optimized magnitude parameters varied. ConclusionsWhole-leg exoskeleton assistance can reduce the metabolic cost of walking while carrying a range of loads. The consistent optimized timing parameters suggest that metabolic cost reductions are sensitive to torque timing. The variable torque magnitude parameters could imply that torque magnitude should be customized to the individual, or that there is a range of useful torque magnitudes. Future work should test whether applying the load to the exoskeleton rather than the person's torso results in larger benefits.

Piston Bowl Geometry Effects on Gasoline Compression Ignition in a Heavy-Duty Diesel Engine

2020 ◽  
Author(s):  
Meng Tang ◽  
Yuanjiang Pei ◽  
Hengjie Guo ◽  
Yu Zhang ◽  
Roberto Torelli ◽  
...  
Keyword(s):  
Diesel Engine ◽  
Design Optimization ◽  
Software Package ◽  
Compression Ignition ◽  
Heavy Duty ◽  
Light Load ◽  
Heavy Duty Diesel Engine ◽  
Air Mixing ◽  
Heavy Duty Diesel ◽  
Load Conditions

Abstract A design optimization campaign was conducted to search for improved combustion profiles that enhance gasoline compression ignition in a heavy-duty diesel engine with a geometric compression ratio of 17.3. Three-dimensional computational fluid dynamics simulations were employed using the software package CONVERGE. A large-scale design of experiments (DoE) approach was used for the optimization. The main parameters explored include geometric features, injector specifications, and swirl motion. Both stepped-lip bowls and re-entrant bowls were included in the optimization effort in order to assess their respective performance implications. A total of 256 design candidates were prepared using the software package CAESES for automated and simultaneous geometry generation and combustion recipe perturbation. The design optimization was conducted for three engine load points representing light to medium load conditions. The design candidates were evaluated for fuel efficiency, emissions, fuel-air mixing characteristics, and global combustion behavior. Simulation results show that the optimum designs were all stepped-lip bowls, which exhibited better overall performance than re-entrant bowls due to improvements in fuel-air mixing, as well as reduced heat loss and emissions formation. Improvements in indicated specific fuel consumption of up to 3.2% were achieved while meeting engine-out NOx emission targets of 1–1.5 g/kW·hr. Re-entrant bowls performed worse compared to the baseline design, and significant performance variations occurred across the load points. Specifically, the re-entrant bowls were on par with the stepped-lip bowls under light load conditions, but significant deteriorations occurred under higher load conditions. As a final task, selected optimized designs were then evaluated under simulated full-load conditions.

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