Walking is the basic locomotion pattern for bipedal *** walking pattern is widely generated using the linear inverted pendulum *** linear inverted pendulum motion of each support period can be designed as a walk primi...
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Walking is the basic locomotion pattern for bipedal *** walking pattern is widely generated using the linear inverted pendulum *** linear inverted pendulum motion of each support period can be designed as a walk primitive to be connected to form a walking trajectory.A novel method of integrating double support phase into the walk primitive was proposed in this *** methoddescribes the generation of walking patterns using walk primitives with double support,specifically for lateral plane including walking in place,walking for lateral,and walking initiation,and for sagittal plane including fixed step length walking,variable step length walking,and walking *** to walk primitives without double support phase,those with double support phase reduce the maximum speedrequired by the robot and eliminate the need to adjust foothold for achieving continuous *** performance of the proposed method is validated by simulations and experiments on Neubot,a position-controlled bipedrobot.
real-worldrobots will face a wide variety of complex environments when performing navigation or exploration tasks, especially in situations where the robots have never been seen before. Usually, robots need to establ...
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real-worldrobots will face a wide variety of complex environments when performing navigation or exploration tasks, especially in situations where the robots have never been seen before. Usually, robots need to establish local or global maps and then use path planning algorithms to determine theirroutes. However, in some environments, such as a wild grassy path or pavement on either side of a road, it is difficult forrobots to plan routes through navigation maps. To address this, we propose a robust framework forrobot navigation using contrastive learning called Contrastive Observation-Action in Latent (COAL) space. To extract features from the action space and observation space, respectively, COAL uses two different encoders. At the training stage, COAL does not require any data annotation and a mask approach is employed to keep features with significant differences away from each other in latent space. Similar to multimodal contrastive learning, we maximize bidirectional mutual information to align the features of observations and action sequences in latent space, which can enhance the generalization of the model. At the deployment stage, robots only need the current image as observation to complete exploration tasks. The most suitable action sequence is selected from the sampleddata for generating control signals. We evaluate the robustness of COAL in both simulation andreal environments. Only 41 min of unlabeled training data is required to allow COAL to explore environments that have never been seen before, even at night. Compared with state-of-the-art methods, COAL has the strongest robustness and generalization ability. More importantly, the robustness of COAL is further improved by augmenting our training data using other open-source data sets, which indicates that our framework has great potential to extract deep features of observations and action sequences. Our code and trained models are available at .
With photovoltaic(PV)sources becoming more prevalent in the energy generation mix,transitioning grid-connected PV systems from grid-following(GFL)mode to gridforming(GFM)mode becomes essential for offering self-synchr...
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With photovoltaic(PV)sources becoming more prevalent in the energy generation mix,transitioning grid-connected PV systems from grid-following(GFL)mode to gridforming(GFM)mode becomes essential for offering self-synchronization and active support *** numerous GFM methods have been proposed,the potential of dC voltage control malfunction during the provision of the primary and inertia support in a GFM PV system remains insufficiently *** fill the gap,some main GFM methods have been integrated into PV systems featuring detaileddC source *** conduct a comparative analysis of their performance in active support anddC voltage *** GFM methods such as virtual synchronous machine(VSM)face a significant risk of dC voltage failure in situations like alterations in solarradiation,leading to PV system tripping and jeopardizing local system *** the case of dC GFM methods such as matching control(MC),the active support falls short due to the absence of an accurate anddispatchable droop *** address the issue,a matching synchronous machine(MSM)control method is developed to provide dispatchable active support and enhance the dC voltage dynamics by integrating the MC and VSM control *** active support capability of the PV systems with the proposed method is quantified analytically and verified by numerical simulations and field tests.
Thunderstorm detection based on the Atmospheric Electric Field(AEF)has evolved from time-domain models to space-domain *** is especially important to evaluate anddetermine the particularly Weather Attribute(WA),which...
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Thunderstorm detection based on the Atmospheric Electric Field(AEF)has evolved from time-domain models to space-domain *** is especially important to evaluate anddetermine the particularly Weather Attribute(WA),which is directly related to the detection reliability and *** this paper,a strategy is proposed to integrate three currently competitive WA's evaluation ***,a conventional evaluation method based on AEF statistical indicators is *** evaluation approaches include competing AEF-based predicted value intervals,and AEF classification based on fuzzy *** AEF attributes contribute to a more accurate AEF classification to different *** resulting dynamic weighting applied to these attributes improves the classification *** evaluation method is applied to evaluate the WA of a particular AEF,to obtain the corresponding evaluation *** integration in the proposed strategy takes the form of a score *** cumulative score levels correspond to different final WA *** imaging is performed to visualize thunderstorm activities using those AEFs already evaluated to exhibit thunderstorm *** results confirm that the proposed strategy effectively andreliably images thunderstorms,with a 100%accuracy of WA *** is the first study to design an integrated thunderstorm detection strategy from a new perspective of WA evaluation,which provides promising solutions for a more reliable and flexible thunderstorm detection.
deep reinforcement learning forresource allocation has been investigated extensively owing to its ability of handling model-free and end-to-end problems. However, its slow convergence and high time complexity during ...
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deep reinforcement learning forresource allocation has been investigated extensively owing to its ability of handling model-free and end-to-end problems. However, its slow convergence and high time complexity during online training hinder its practical use in dynamic wireless systems. To reduce the training complexity, we resort to graph reinforcement learning for leveraging two kinds of relational priors inherent in many wireless communication problems: topology information and permutation properties. To harness the two priors, we first conceive a method to convert the state matrix into a state graph,and then propose a graph deep deterministic policy gradient(ddPG) algorithm with the desired permutation property. To demonstrate how to apply the proposed methods, we consider a representative problem of using reinforcement learning, predictive power allocation, which minimizes the energy consumption while ensuring the quality-of-service of each userrequesting video streaming. We derive the time complexity required by training the proposed graph ddPG algorithm and fully-connected neural network-basedddPG algorithm in each time step. Simulations show that the graph ddPG algorithm converges much faster and needs much lower time and space complexity than existing ddPG algorithms to achieve the same learning performance.
A new analytical model for geometric size and forming force prediction in incremental flanging(IF)is presented in this *** complex deformation characteristics of IF are considered in the modeling process,which can acc...
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A new analytical model for geometric size and forming force prediction in incremental flanging(IF)is presented in this *** complex deformation characteristics of IF are considered in the modeling process,which can accurately describe the strain and stress states in *** on strain analysis,the model can predict the material thickness distribution and neck height after *** considering contact area,strain characteristics,material thickness changes,and friction,the model can predict specific moments and corresponding values of maximum axial forming force and maximum horizontal forming force during *** addition,an IF experiment involving different tool diameters,flanging diameters,and opening hole diameters is *** the basis of the experimental strain paths,the strain characteristics of different deformation zones are studied,and the stable strain ratio is quantitatively described through two dimensionless parameters:relative tool diameter andrelative hole ***,the changing of material thickness and forming force in IF,and the variation of minimum material thickness,neck height,maximum axial forming force,and maximum horizontal forming force with flanging parameters are studied,and the reliability of the analytical model is verified in this ***,the influence of the horizontal forming force on the tool design and the fluctuation of the forming force are explained.
In this paper,a distributed Event-Triggered(ET)collision avoidance coordinated control for Quadrotor Unmanned Aerial Vehicles(QUAVs)is proposed based on Virtual Tubes(VTs)with flexible boundaries in the presence of un...
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In this paper,a distributed Event-Triggered(ET)collision avoidance coordinated control for Quadrotor Unmanned Aerial Vehicles(QUAVs)is proposed based on Virtual Tubes(VTs)with flexible boundaries in the presence of unknown external ***,VTs are constructed for each QUAV,and the QUAV is restricted into the corresponding VT by the artificial potential field,which is distributed around the boundary of the ***,the collisions between QUAVs are ***,the boundaries of the VTs are flexible by the modification signals,which are generated by the self-regulating auxiliary systems,to make the repulsive force smaller and give more buffer space for QUAVs without ***,a novel ET mechanism is designed by introducing the concept of prediction to the traditional fixed threshold ET ***,a disturbance observer is proposed to deal with the adverse effects of the unknown external *** this basis,a distributed ET collision avoidance coordinated controller is ***,the proposed controller is quantized by the hysteresis uniform quantizer and then sent to the actuator only at the ET *** boundedness of the closed-loop signals is verified by the Lyapunov ***,simulation and experimental results are performed to demonstrate the superiority of the proposed control method.
With good adaptability to weak power grids,the grid-forming inverter becomes the foundation of future power grids with high-proportion renewable ***,the virtual synchronous generator(VSG)control is recognized as the m...
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With good adaptability to weak power grids,the grid-forming inverter becomes the foundation of future power grids with high-proportion renewable ***,the virtual synchronous generator(VSG)control is recognized as the mainstream control strategy for grid-forming *** permanent magnet synchronous generator(PMSG)based wind generation systems connected to power grid via VSG-controlled grid-forming inverters,some novel impacts on the low-frequency oscillations(LFOs)emerge in power *** first impact involves the negative/positive damping effect on *** this paper,the small-signal torque model of VSG-controlled PMSGbased wind generation systems is established based on the damping torque analysis method,revealing the influence mechanism of machine-side dynamics on LFOs and proving the necessity of the double-mass model for accurate stability *** second impact is the resonance effect between torsional oscillation and ***,this paper uses the open-loop resonance analysis method to study the resonance mechanism and to predict the root ***,a damping enhancement strategy is proposed to weaken and eliminate the negative damping effect of machine-side dynamics on LFOs and the resonance effect between torsional oscillation and ***,the analysis result is validated through a case study involving the connection of the VSG-controlled PMSG-based wind generation system to the IEEE 39-bus AC grid,supporting the industrial application and stable operation of VSG-controlled PMSGbased wind generation systems.
Grid-following voltage source converter(GFLVSC)and grid-forming voltage source converter(GFM-VSC)have different dynamic characteristics for active power-frequency andreactive power-voltage supports of the power *** p...
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Grid-following voltage source converter(GFLVSC)and grid-forming voltage source converter(GFM-VSC)have different dynamic characteristics for active power-frequency andreactive power-voltage supports of the power *** paper aims to clarify andrecognize the difference between gridfollowing(GFL)and grid-forming(GFM)frequency-voltage support more intuitively and ***,the phasor model considering circuit constraints is established based on the port circuit equations of the *** is revealed that the voltage and active power linearly correspond to the horizontal and vertical axes in the phasor space referenced to the grid voltage ***,based on topological homology,GFL and GFM controls are transformed and mapped into different *** topological similarity of the characteristic curves for GFL and GFM controls is the essential cause of their *** on the above model,it is indicated that GFL-VSC and GFM-VSC possess uniformity with regard to active powerresponse,type of coupling,and phasor *** differ in synchronization,power coupling mechanisms,dynamics,and active power-voltage operation domain in the quasi-steady *** studies are undertaken on GFL-VSC and GFM-VSC integrated into a four-machine two-area *** results verify that the dynamic uniformity anddifference of GFL-VSC and GFM-VSC are intuitively and comprehensively revealed.
The expandable graphite(EG)modified TiO_(2) nanocomposites were prepared by the high shearmethod using the TiO_(2) nanoparticles(NPs)and EG as precursors,in which the amount of EG doped in TiO_(2) was 10 wt.%.Followed...
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The expandable graphite(EG)modified TiO_(2) nanocomposites were prepared by the high shearmethod using the TiO_(2) nanoparticles(NPs)and EG as precursors,in which the amount of EG doped in TiO_(2) was 10 wt.%.Followed by the impregnation method,adjusting the pH of the solution to 10,and using the electrostatic adsorption to achieve spatial confinement,the Pt elementswere mainly distributed on the exposed TiO_(2),thus generating the Pt/10EG-TiO_(2)-10 *** best CO oxidation activity with the excellent resistance to H_(2)O and SO_(2) was obtained over the Pt/10EG-TiO_(2)-10 catalyst:CO conversion after 36 hr of the reaction was ca.85%under the harsh condition of 10 vol.%H_(2)O and 100 ppm SO_(2) at a high gaseous hourly space velocity(GHSV)of 400,000 hr−*** properties of the catalystswere characterized by various *** results showed that the electrostatic adsorption,which riveted the Pt elements mainly on the exposed TiO_(2) of the support surface,reduced the dispersion of Pt NPs on EG and achieved the effective dispersion of Pt NPs,hence significantly improving CO oxidation activity over the Pt/10EG-TiO_(2)-10 *** 10 wt.%EG doped in TiO_(2) caused the TiO_(2) support to form a more hydrophobic surface,which reduced the adsorption of H_(2)O and SO_(2) on the catalyst,greatly inhibiteddeposition of the TiOSO_(4) and formation of the PtSO4 species as well as suppressed the oxidation of SO_(2),thus resulting in an improvement in the resistance to H_(2)O and SO_(2) of the Pt/10EG-TiO_(2)-10 catalyst.
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