339,513 research outputs found
Control Strategies for Open-End Winding Drives Operating in the Flux-Weakening Region
This paper presents and compares control strategies for three-phase open-end winding drives operating in the flux-weakening region. A six-leg inverter with a single dc-link is associated with the machine in order to use a single energy source. With this topology, the zero-sequence circuit has to be considered since the zero-sequence current can circulate in the windings. Therefore, conventional over-modulation strategies are not appropriate when the machine enters in the flux-weakening region. A few solutions dealing with the zero-sequence circuit have been proposed in literature. They use a modified space vector modulation or a conventional modulation with additional voltage limitations. The paper describes the aforementioned strategies and then a new strategy is proposed. This new strategy takes into account the magnitudes and phase angles of the voltage harmonic components. This yields better voltage utilization in the dq frame. Furthermore, inverter saturation is avoided in the zero-sequence frame and therefore zero-sequence current control is maintained. Three methods are implemented on a test bed composed of a three-phase permanent-magnet synchronous machine, a six-leg inverter and a hybrid DSP/FPGA controller. Experimental results are presented and compared for all strategies. A performance analysis is conducted as regards the region of operation and the machine parameters.Projet SOFRACI/FU
Conventional Space-Vector Modulation Techniques versus the Single-Phase Modulator for Multilevel Converters
Space-vector modulation is a well-suited technique
to be applied to multilevel converters and is an important
research focus in the last 25 years. Recently, a single-phase
multilevel modulator has been introduced showing its conceptual
simplicity and its very low computational cost. In this paper,
some of the most conventional multilevel space-vector modulation
techniques have been chosen to compare their results with those
obtained with single-phase multilevel modulators. The obtained
results demonstrate that the single-phase multilevel modulators
applied to each phase are equivalent with the chosen wellknown
multilevel space-vector modulation techniques. In this
way, single-phase multilevel modulators can be applied to a
converter with any number of levels and phases avoiding the
use of conceptually and mathematically complex space-vector
modulation strategies. Analytical calculations and experimental
results are shown validating the proposed concepts
The effect of voluntary modulation of the sensory-motor rhythm during different mental tasks on H reflex
Objectives:
The aim of this study was to explore the possibility of the short-term modulation of the soleus H reflex through self-induced modulation of the sensory-motor rhythm (SMR) as measured by electroencephalography (EEG) at Cz.
Methods:
Sixteen healthy participants took part in one session of neuromodulation. Motor imagery and mental math were strategies for decreasing SMR, while neurofeedback was used to increase SMR. H reflex of the soleus muscle was elicited by stimulating tibial nerve when SMR reached a pre-defined threshold and was averaged over 5 trials.
Results:
Neurofeedback and mental math both resulted in the statistically significant increase of H reflex (p = 1.04·10− 6 and p = 5.47·10− 5 respectively) while motor imagery produced the inconsistent direction of H reflex modulation (p = 0.57). The average relative increase of H reflex amplitude was for neurofeedback 19.0 ± 5.4%, mental math 11.1 ± 3.6% and motor imagery 2.6 ± 1.0%. A significant negative correlation existed between SMR amplitude and H reflex for all tasks at Cz and C4.
Conclusions:
It is possible to achieve a short-term modulation of H reflex through short-term modulation of SMR. Various mental tasks dominantly facilitate H reflex irrespective of direction of SMR modulation.
Significance:
Improving understanding of the influence of sensory-motor cortex on the monosynaptic reflex through the self-induced modulation of cortical activity
Quasi-optimal grouping for broadcast systems with hierarchical modulation
Recently, we proposed to combine time sharing with hierarchical modulation to
increase the transmission rate of broadcast systems. Our proposal involves to
group the receivers in pairs in order to transmit with hierarchical modulation.
We introduced several grouping strategies but the optimal matching remained an
open question. In this letter, we show that the optimal grouping is the
solution of an assignment problem, for which efficient algorithms exist such as
the Hungarian method. Based on this algorithm, we study the performance of the
optimal grouping in terms of spectrum efficiency for a DVB-S2 system.Comment: Submitte
Gain tuning and fidelity in continuous variable quantum teleportation
The fidelity of continuous variable teleportation can be optimized by
changing the gain in the modulation of the output field. We discuss the gain
dependence of fidelity for coherent, vacuum and one photon inputs and propose
optimal gain tuning strategies for corresponding input selections.Comment: 23 pages, 10 figure
Efficiency Improvement of Fault-Tolerant Three-Level Power Converters
Fault-tolerant power converters play a critical role in the transportation electrification. However, fault-tolerant operation, high efficiency, and low cost usually result in design criteria that have conflicting constraints and goals. The majority of the fault-tolerant power converter topologies presented in the literature confirm these conflicts. In this paper, three types of fault-tolerant neutral-point clamped (NPC) converters are investigated. Various modulation strategies are explored to reduce the losses of the redundant phase leg. The simulation and experimental results show that the Switching Frequency Optimal Phase opposition Disposition modulation strategy is the most effective approach in minimizing the losses in the redundant phase leg
Traders' strategy with price feedbacks in financial market
We introduce an autoregressive-type model of prices in financial market
taking into account the self-modulation effect. We find that traders are mainly
using strategies with weighted feedbacks of past prices. These feedbacks are
responsible for the slow diffusion in short times, apparent trends and power
law distribution of price changes.Comment: 4 pages, 5 figures, submitted to Physica
The Impact of Channel Feedback on Opportunistic Relay Selection for Hybrid-ARQ in Wireless Networks
This paper presents a decentralized relay selection protocol for a dense
wireless network and describes channel feedback strategies that improve its
performance. The proposed selection protocol supports hybrid
automatic-repeat-request transmission where relays forward parity information
to the destination in the event of a decoding error. Channel feedback is
employed for refining the relay selection process and for selecting an
appropriate transmission mode in a proposed adaptive modulation transmission
framework. An approximation of the throughput of the proposed adaptive
modulation strategy is presented, and the dependence of the throughput on
system parameters such as the relay contention probability and the adaptive
modulation switching point is illustrated via maximization of this
approximation. Simulations show that the throughput of the proposed selection
strategy is comparable to that yielded by a centralized selection approach that
relies on geographic information.Comment: 30 pages, 9 figures, submitted to the IEEE Transactions on Vehicular
Technology, revised March 200
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