Adaptive admittance tracking control for interactive robot with prescribed performance

An adaptive control approach is presented in this paper for tracking desired trajectories in interactive manipulators. The controller design incorporates prescribed performance functions (PPFs) to improve dynamic performance. Notably, the performance of the output error is confined in an envelope characterized by exponential convergence, leading to convergence to zero. This feature ensures a prompt response from admittance control and establishes a reliable safety framework for interactions. Simulation results provide practical insights,demonstrating the viability of the control scheme proposed in this paper.

Variable Admittance Control of High Compatibility Exoskeleton Based on Human-Robotic Interaction Force

The wearable exoskeleton system is a typical strongly coupled human-robotic system.Human-robotic is the environment for each other.The two support each other and compete with each other.Achieving high human-robotic compatibility is the most critical technology for wearable systems.Full structural compatibility can improve the intrinsic safety of the exoskeleton,and precise intention understanding and motion control can improve the comfort of the exoskeleton.This paper first designs a physiologically functional bionic lower limb exoskeleton based on the study of bone and joint functional anatomy and analyzes the drive mapping model of the dual closedloop four-link knee joint.Secondly,an exoskeleton dual closed-loop controller composed of a position inner loop and a force outer loop is designed.The inner loop of the controller adopts the PID control algorithm,and the outer loop adopts the adaptive admittance control algorithm based on human-robot interaction force(HRI).The controller can adaptively adjust the admittance parameters according to the HRI to respond to dynamic changes in the mechanical and physical parameters of the human-robot system,thereby improving control compliance and the wearing comfort of the exoskeleton system.Finally,we built a joint simulation experiment platform based on SolidWorks/Simulink to conduct virtual prototype simulation experiments and recruited volunteers to wear rehabilitation exoskeletons to conduct related control experiments.Experimental results show that the designed physiologically functional bionic exoskeleton and adaptive admittance controller can significantly improve the accuracy of human-robotic joint motion tracking,effectively reducing human-machine interaction forces and improving the comfort and safety of the wearer.This paper proposes a dual-closed loop four-link knee joint exoskeleton and a variable admittance control method based on HRI,which provides a new method for the design and control of exoskeletons with high compatibility.

Sound propagation in inhomogeneous waveguides with sound-speed profiles using the multimodal admittance method

The multimodal admittance method and its improvement are presented to deal with various aspects in underwater acoustics,mostly for the sound propagation in inhomogeneous waveguides with sound-speed profiles,arbitrary-shaped liquid-like scatterers,and range-dependent environments.In all cases,the propagation problem governed by the Helmholtz equation is transformed into initial value problems of two coupled first-order evolution equations with respect to the modal components of field quantities(sound pressure and its derivative),by projecting the Helmholtz equation on a constructed orthogonal and complete local basis.The admittance matrix,which is the modal representation of Direchlet-to-Neumann operator,is introduced to compute the first-order evolution equations with no numerical instability caused by evanescent modes.The fourth-order Magnus scheme is used for the numerical integration of differential equations in the numerical implementation.The numerical experiments of sound field in underwater inhomogeneous waveguides generated by point sources are performed.Besides,the numerical results computed by simulation software COMSOL Multiphysics are given to validate the correction of the multimodal admittance method.It is shown that the multimodal admittance method is an efficient and stable numerical method to solve the wave propagation problem in inhomogeneous underwater waveguides with sound-speed profiles,liquid-like scatterers,and range-dependent environments.The extension of the method to more complicated waveguides such as horizontally stratified waveguides is available.

Three-dimensional admittance analysis of lithospheric elastic thickness over the Louisville Ridge

Using bathymetry and altimetric gravity anomalies, a 1°×9 1° lithospheric effective elastic thickness（Te） model over the Louisville Ridge and its adjacent regions is calculated using the moving window admittance technique. For comparison, three bathymetry models are used： general bathymetric charts of the oceans, SIO V15.1,and BAT_VGG. The results show that BAT_VGG is more suitable for calculating T e than the other two models. T e along the Louisville Ridge was re-evaluated. The southeast of the ridge has a medium Te of 10–20 km, while Te increases dramatically seaward of the Tonga-Kermadec trench as a result of the collision of the Pacific and IndoAustralian plates.

Single-phase-to-ground fault protection based on zero-sequence current ratio coefficient for low-resistance grounding distribution network

Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to their high settings of the action value when a high-impedance grounding fault occurs.In this study,the relationship between the zero-sequence currents of each feeder and the neutral branch was analyzed.Then,a grounding protection method was proposed on the basis of the zero-sequence current ratio coefficient.It is defined as the ratio of the zero-sequence current of the feeder to that of the neutral branch.Nonetheless,both zero-sequence voltage and zero-sequence current are affected by the transition resistance,The influence of transition resistance can be eliminated by calculating this coefficient.Therefore,a method based on the zero-sequence current ratio coefficient was proposed considering the significant difference between the faulty feeder and healthy feeder.Furthermore,unbalanced current can be prevented by setting the starting current.PSCAD simulation results reveal that the proposed method shows high reliability and sensitivity when a high-resistance grounding fault occurs.

Zero-sequence Current Suppressing Strategy for Dual Three-phase Permanent Magnet Synchronous Machines Connected with Single Neutral Point

Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.

Determination of interface states and their time constant for Au/SnO_2 /n-Si (MOS) capacitors using admittance measurements

The frequency dependence of admittance measurements （capacitance–voltage （C–V ） and conductance–voltage （G/ω–V ）） of Au/SnO2 /n-Si （MOS） capacitors was investigated by taking into account the effects of the interface states （N ss ） and series resistance （Rs ） at room temperature. Admittance measurements were carried out in frequency and bias voltage ranges of 1 kHz–1 MHz and （ 5V）–（＋9V）, respectively. The values of N ss and R s were determined by using a conductance method and estimating from the admittance measurements of the MOS capacitors. At low frequencies, the interface states can follow the AC signal and yield excess capacitance and conductance. In addition, the parallel conductance （G p /ω） versus log（f） curves at various voltages include a peak due to the presence of interface states. It is observed that the N ss and their time constant （τ） range from 1.23 ×10 12 eV-1 ·cm-2 to 1.47 ×10 12 eV-1 ·cm-2 and from 7.29 ×10-5 s to 1.81 ×10-5s, respectively.

Input Admittance and Current Distribution of Infinitely Long Circular Cylindrical Antenna Driven at Center

In this paper, by change of integration path in complex spectrum domain and by defining input admittance as the ratio of complex radiated power to amplitude of square of voltage across the gap, new expressions of admittance (valid for all frequencies ) of infinitely long cylindrical antenna with and without conducting ground are obtained. Meanwhile corresponding formulas of current distribution are derived in detail. Some numerical computations are also given.

Electric admittance analysis of quartz crystal resonator in thickness-shear mode induced by array of surface viscoelastic micro-beams

The electric admittance of a compound system composed of a thickness-shear mode （TSM） quartz crystal resonator （QCR） and an array of surface viscoelastic micro-beams （MBs） is studied. The governing equations of the MBs are derived from the Timoshenko-beam theory in consideration of shear deformation. The electrical admittance is described directly in terms of the physical properties of the surface epoxy resin （SU-8） MBs from an electrically forced vibration analysis. It is found that both the inertia effect and the constraint effect of the MBs produce competitive influence on the resonant frequency and admittance of the compound QCR system. By further comparing the numerical results calculated from the Timoshenko-beam model with those from the Euler-beam model, the shear deformation is found to lead to some deviation of an admittance spectrum. The deviations are revealed to be evident around the admittance peak（s） and reach the maximum when a natural frequency of the MBs is identical to the fundamental frequency of the QCR. Besides, a higher order vibration mode of the MBs corresponds to a larger deviation at the resonance.

Game Analysis of Rational FRS on Market Admittance

The dynamic signaling game-model is employed to study countermeasures of Q, U and C for supply-demand on financial market. As the game result, the mixed equilibrium of Q and U exists naturally without FRS. It is concluded that FRS on market admittance is objective demand of financial market, also the rational management behavior of government FRSI. And in addition to the empirical criteria, the FRS agreements between FRSI and financial-institutions should be considered as one of advanced FRS techniques. These must cover:① the regulation conformed status investigation with sufficient frequency,② corresponding punitive measures with sufficient strength. Thus the information can be delivered FRSI have ensured only qualified and regulation-conformed financial-institutions could be allowed to enter. That could safeguard the steadiness of the financial market.

Using an Off-the-Shelf Lock-In Detector for Admittance Spectroscopy in the Study of Plants

We report on the development of an electrical characterization admittance spectroscopy equipment and method based on an off-the-shelf lock-in detector that is cheap and yet highly sensitive. It is concluded that a contacted constant-pressure electrode configuration is preferable. It was further determined that the temperature does not have great impact in the measured values, but relative humidity of air can be important, especially in the constant-gap electrode configuration. In-situ measurements are difficult since the coupling of the plant with the environment is of high importance. Another aspect is the cables;they are important in that they have to be terminated by their characteristic impedance (50 Ω?in our case) to avoid reflections that introduce artificial attenuation and phase shifts in the signal. We introduce a fingerprint plot type to be able to distinguish between various plants and other specimens, and can actually detect the aqueous state of a plant.

VDTA Based Electronically Tunable Voltage-Mode and Trans-Admittance Biquad Filter

In this paper, a biquad filter configuration based on two voltage differencing transconductance amplifiers (VDTAs) as newly active elements and only two capacitors as passive elements is proposed which can realize voltage-mode low pass (LP), band pass (BP), high pass (HP), band reject (BR) and all pass (AP) filtering responses using three voltage inputs. Simultaneously, the same configuration can also be used to obtain LP, BP and HP filtering responses in transadmittance-mode. The proposed biquad is capable of providing electronic control of quality factor independent of pole frequency through single transconductance parameter (biasing current). It also offers the advantage of low active and passive sensitivity. To support the theoretical analysis, the PSPICE simulation of the proposed circuit is done using 0.18 μm CMOS technology from TSMC.

Computing of Mutual Admittance between Two Circumferential Slots on Cylindrical Waveguide

This paper studies radiation from circumferential slots on cylindrical waveguide by Poynting’s vector method. It can help us to find mutual admittance between two circumferential slots in an antenna array. The main advantage of Poynting’s vector method is its accurate convergence to compute mutual admittance between two circumferential slots. The importance of this matter will be more salient while we want to compare it with other mutual admittances and also use it to optimize an antenna array.

Least Squares Hermitian Problem of Matrix Equation (<i>AXB</i>, <i>CXD</i>) = (<i>E</i>, <i>F</i>) Associated with Indeterminate Admittance Matrices

For A&#8712;Cm&#935;n, if the sum of the elements in each row and the sum of the elements in each column are both equal to 0, then A is called an indeterminate admittance matrix. If A is an indeterminate admittance matrix and a Hermitian matrix, then A is called a Hermitian indeterminate admittance matrix. In this paper, we provide two methods to study the least squares Hermitian indeterminate admittance problem of complex matrix equation (AXB,CXD)=(E,F), and give the explicit expressions of least squares Hermitian indeterminate admittance solution with the least norm in each method. We mainly adopt the Moore-Penrose generalized inverse and Kronecker product in Method I and a matrix-vector product in Method II, respectively.

Protection of Zero-Sequence Power Variation in Mountain Wind Farm Collector Lines Based on Multi-Mode Grounding

The arc-suppression coil(ASC)in parallel low resistance(LR)multi-mode grounding is adopted in the mountain wind farm to cope with the phenomenon that is misoperation or refusal of zero-sequence protection in LR grounding wind farm.If the fault disappears before LR is put into the system,it is judged as an instantaneous fault;while the fault does not disappear after LR is put into the system,it is judged as a permanent fault;the single-phase grounding fault(SLG)protection criterion based on zerosequence power variation is proposed to identify the instantaneous-permanent fault.Firstly,the distribution characteristic of zero-sequence voltage(ZSV)and zero-sequence current(ZSC)are analyzed after SLGfault occurs in multi-mode grounding.Then,according to the characteristics that zero-sequence power variation of non-fault collector line is small,while the zero-sequence power variation of fault collector line can reflect the active power component of fault resistance,the protection criterion based on zero-sequence power variation is constructed.The theoretical analysis and simulation results show that the protection criterion can distinguish the property of fault only by using the single terminal information,which has high reliability.

Zero-Sequence Current Suppression Strategy for Open-End Winding Permanent Magnet Synchronous Motor Based on Model Predictive Control

Compared with the traditional three-phase star connection winding,the open-end winding permanent magnet synchronous motor(OW-PMSM)system with a common direct current(DC)bus has a zero-sequence circuit,which makes the common-mode voltage and the back electromotive force(EMF)harmonic generated by the inverters produce the zero-sequence current in the zero-sequence circuit,and the zero-sequence current has great influence on the operation efficiency and stability of the motor control system.A zero-sequence current suppression strategy is presented based on model predictive current control for OW-PMSM.Through the mathematical model of OW-PMSM to establish the predictive model and the zero-sequence circuit model,the common-mode voltage under different voltage vector combinations is fully considered during vector selection and action time calculation.Then zero-sequence loop constraints are established,so as to suppress the zero-sequence current.In the end,the control strategy proposed in this paper is verified by simulation experiments.

Electromagnetic Zero-Sequence Harmonics Blocker： Modeling and Experimental Analysis

This paper reveals new contributions to the analysis and development of devices for harmonic distortion mitigation. Considering the sequential distribution of harmonic currents, zero-sequence components could be diminished using electromagnetic devices, particularly the eZSB （electromagnetic zero-sequence blocking）. One important characteristic of this device, which has received particular attention on this research, is its robustness and low cost of construction. Theoretical and experimental results related to the behavior of the electromagnetic blocking devices are presented. The results illustrate the consistence of the theoretical aspects related with the model in the frequency domain, as well as the performance of the blocking devices, reducing zero-sequence harmonic currents, mainly by the conjunct action of the eZSF （electromagnetic zero-sequence harmonic filter）, working as a impedance coupler. In this context, aiming the evaluation of the reliability of the results obtained through mathematical modeling, experimental tests have been carried out using a low-power prototype, highlighting particular aspects related to its function as a zero-sequence harmonic blocker.

Measurement and Analysis of Mechanical Admittance of Gun-Shoulder System

Lots of factors have influence on the firing accuracy of automatic weapon. During firing,the movement state of gun-shoulder system can be varied due to the impulsion of powder gases and the impact of moving parts,resulting in a gunpoint being deviated from initial value to decrease the firing accuracy of weapon. The development of intelligent controlling gun carriage for weapon system is necessary for reflect its automatic firing accuracy objectively. An electronic measuring system for measuring the receiving force and movement of gun-shoulder system under initiative state is built based on the characteristics of standing non-rest automatic weapon. The constitutes of measuring system and the correction method of shoulder receiving force are described,and the mechanical admittance function of gun-shoulder system is obtained using electronically measured data,the modal identification of admittance functions of gun-shoulder system is made by adopting the orthogonal component method,and the key difference between the passive state and initiative state of standing non-rest automatic weapon is discussed.

Topology and admittance estimation:Precision limits and algorithms

Distribution grid topology and admittance information are essential for system planning,operation,and protection.In many distribution grids,missing or inaccurate topology and admittance data call for efficient estimation methods.However,measurement data may be insufficient or contaminated with large noise,which will fundamentally limit the estimation accuracy.This work explores the theoretical precision limits of the topology and admittance estimation(TAE)problem with different measurement devices,noise levels,and numbers of measurements.On this basis,we propose a conservative progressive self-adaptive(CPS)algorithm to estimate the topology and admittance.The results on IEEE 33 and 141-bus systems validate that the proposed CPS method can approach the theoretical precision limits under various measurement settings.

Interaction analysis and enhanced design of grid-forming control with hybrid synchronization and virtual admittance loops

The hybrid power-and voltage-based synchronization control method has shown potential for enhancing the stability of grid-forming(GFM)inverters.However,its effectiveness may be compromised if other control loops are not properly designed.To address the control-loop interactions,this paper presents a design-oriented analysis method for multiloop-controlled GFM inverters.The method begins by identifying the dominant oscillation modes through modal analysis.The sensitivities of damping ratios to control parameters are then determined for the dominant modes,which allows for characterization of control-loop interactions.A co-design method of GFM control is next developed based on the sensitivity analysis.Lastly,simulations and experimental results are presented to confirm the effectiveness of the method.