Passivity Theory Research Articles

Teleoperation of wheeled mobile robots subject to longitudinal slipping and lateral sliding by time-domain passivity controller

Wheeled mobile robot (WMR)-based exploration on soft terrains has created new difficulties for its tele-control system. A critical problem is that wheel-terrain contact areas may induce both longitudinal slipping and lateral sliding. In this paper, a new approach for tele-driving a WMR that addresses the difficulties simultaneously induced by both longitudinal slipping and lateral sliding is presented. In the augmented coordination between the master and slave site, the translational and angular velocities of the slave WMR were modified by the wheel sliding angle. Moreover, they were separately coordinated with the positions of the master haptic interface. To improve the command-tracking performance with the augmented coordination, the teleoperator was designed with feedforward of the sliding angle. To compensate for the non-passivity induced by longitudinal slipping and lateral sliding, a time-domain passivity controller also is proposed. The stability and transparency of the proposed approach were analyzed based on the passivity theory. Numerical experiments validate that this proposed approach can effectively improve the teleoperation performance of human operators for the WMR on soft terrains.

Dissipativity analysis of negative resistance circuits

This paper deals with the analysis of nonlinear circuits that interconnect passive elements (capacitors, inductors, and resistors) with nonlinear resistors exhibiting a range of negative resistance. Active elements are necessary to design physical circuits that switch and oscillate. We generalize the classical passivity theory of circuit analysis to develop a port interconnection theory for such non-equilibrium behaviors. The approach closely mimics the classical methodology of (incremental) dissipativity theory, but with dissipation inequalities that combine signed storage functions and signed supply rates to account for the port interconnection of passive and active elements.

A Scalable Control Design for Grid-Forming Inverters in Microgrids

Microgrids are increasingly recognized as a key technology for the integration of distributed energy resources into the power network, allowing local clusters of load and distributed energy resources to operate autonomously. However, microgrid operation brings new challenges, especially in islanded operation as frequency and voltage control are no longer provided by large rotating machines. Instead, the power converters in the microgrid must coordinate to regulate the frequency and voltage and ensure stability. We consider the problem of designing controllers to achieve these objectives. Using passivity theory to derive decentralized stability conditions for the microgrid, we propose a control design method for grid-forming inverters. For the analysis we use higher-order models for the inverters and also advanced dynamic models for the lines with an arbitrarily large number of states. By satisfying the decentralized condition formulated, plug-and-play operation can be achieved with guaranteed stability, and performance can also be improved by incorporating this condition as a constraint in corresponding optimization problems formulated. In addition, our control design can improve the power sharing properties of the microgrid compared to previous non-droop approaches. Finally, realistic simulations confirm that the controller design improves the stability and performance of the power network.

Electrophysiological frequency domain analysis of driver passive fatigue under automated driving conditions

With the continuous improvement of automated vehicles, researchers have found that automated driving is more likely to cause passive fatigue. To explore the impact of automation and scenario complexity on the passive fatigue of a driver, we collected electroencephalography (EEG), detection-response task (DRT) performance, and the subjective report scores of 48 drivers. We found that in automated driving under monotonic conditions, after 40 min, the alpha power of the driver’s EEG indicators increased significantly, the accuracy of the detection reaction task decreased, and the reaction time became slower. The receiver characteristic curve was used to calculate the critical threshold of the alpha power during passive fatigue. The determination of the threshold further clarifies the occurrence time and physiological characteristics of passive fatigue and improves the passive fatigue theory.

Passivity-based stability analysis of parallel single-phase inverters with hybrid reference frame control considering PLL effect

The passivity-based stability criterion (PBSC) is an effective tool to analyze the interactive stability issues between the multi-parallel inverters and the grid. However, when using the passivity theory to evaluate the interactive stability, the influences of grid synchronization and multisampling on the passivity of inverter output admittance are overlooked in previous studies. To fill this gap, the impact factors in the grid-connected control, such as multisampling, capacitor current feedback active damping (CCF-AD) and various phase-locked loops (PLLs), on the passivity of inverter output admittance is investigated in this paper. Moreover, the stability of the interconnected system in the inductive and capacitive grid scenarios are also assessed. Since the effective control delay are determined by the multisampling coefficient, the passivity of inverter output admittance in the high-frequency range is mainly affected by multisampling and CCF-AD, whereas the passivity in the low-frequency range is related to the bandwidth of PLLs. In case of an identical PLL bandwidth, the non-passive region of admittance when using SOGI-PLL appears in a lower frequency band, and thus the non-passive region is the smallest in comparison, which provides stronger robustness. Finally, simulation studies and experimental results are presented to verify the effectiveness of the theoretical analysis.

An Improved Adaptive Passive Coordinated Control for Generator Excitation and STATCOM

An improved adaptive backstepping passive coordinated control strategy is proposed to deal with the uncertainty of damping coefficient and mechanical power and external disturbance on the system stability. A nonlinear coordinated controller of generator excitation and STATCOM (static synchronous compensator) is designed to improve its adaptability. The adaptive estimation laws of damping coefficient and mechanical power are designed by using I&I (immersion and invariance) adaptive control to improve the adaptive ability of the controller. Based on the backstepping recursive method, the control law of STATCOM is designed and combines the passivity theory, thus acquiring the control law of generator excitation. In the backstepping design, the derivative of the virtual control input and external disturbance are considered to be uncertain, and the nonlinear damping algorithm is introduced to reduce the “calculation explosion.” Simulation results show that the designed controller improves the stability of the power system and shows strong adaptability and robustness.

Role of acceptor concentration-dependent FRET behind luminescence tuning in polymer capped ZnO for application in hybrid LEDs

Surface modification of the ZnO nanoparticles using polymer can be an important way to tune their optoelectronic properties. On capping the ZnO nanoparticles (NPs) using the polymer polyvinylpyrrolidone (PVP), a synchronous change in the photoluminescence emission has been observed from different defect states with different formation energies, which raises doubts about the decade-old proposed theory of passivation of defect states upon surface capping. The doubt has been confirmed by X-ray photoelectron spectroscopy (XPS) of the samples. Blue shifting of the band edge absorption on polymer capping has been attributed to a change in exciton dynamics due to the tuning of band alignment on surface modification. Polymer concentration-dependent tunability for emission from defect states has been explored using two new photophysical process – acceptor (PVP)-concentration-dependent Förster resonance energy transfer (FRET), and generation of superoxide (O2-) charge-transfer states. Surface capping has been found to improve spectral purity at the cost of a decrease in quantum efficiency. Therefore, to design a very bright hybrid light-emitting layer using polymer capped ZnO, we must consider the emission and absorption spectral overlap between the ZnO nanoparticles and the polymer, FRET, exciton diffusion and balling efficiency of the polymer.

Voltage regulation of buck converter with constant power load: An adaptive power shaping control

In this paper, the problem of voltage regulation of DC–DC buck converter with unknown constant power load (CPL) and input voltage is addressed. A power shaping controller (PSC) based on the passivity theory is proposed to stabilize this system. In addition, borrowing immersion & invariance (I&I) technique, an observer can be designed to estimate CPL and input voltage simultaneously. By combining PSC with I&I observer, an adaptive control scheme is achieved. Besides, the estimate of the domain of attraction is given to rigorously guarantee the convergence property by virtue of the invariant set theory. Then, the locally asymptotic stability of the closed-loop system is established. Finally, the simulation and experimental results show the effectiveness of the proposed control method.

A framework of analytical methods for horizontal behaviours of monopiles under V-H-M loads in sand

The piles of offshore wind turbines are always subjected to multidirectional loads. The vertical and lateral behaviours of piles are designed separately in practice. However, many studies have shown that the vertical load has a substantial influence on the lateral behaviours of piles. The influence of the vertical load on the lateral behaviours of monopiles can be divided into three aspects: (1) the influence of the friction stress on the ultimate resistance p u of the p-y curve, (2) the P-Δ effect, and (3) the M R effect induced by the uneven distribution of vertical skin friction. Based on the passive wedge theory and the influence of the ultimate soil resistance per unit length p u caused by the vertical loads, the corrected p-y curve for sand is obtained. Considering the P-Δ effect and MR effect, an analytical method for monopiles under combined loads, including the lateral load, vertical load and moment, in sand is proposed based on the elastic-foundation beam theory coupled with p-y curves. The method is verified by analysing several existing cases. The capability of the proposed method to reasonably calculate the responses of monopiles under multidirectional loads in sand has been verified.

Novel Passive Controller Design for Enhancing Boost Converter Stability in DC Microgrid Applications

Boost converters have nonminimum phase (NMP) characteristics, which makes the stable closed-loop control design difficult. Based on the passive theory, this article proposes to add a feedforward loop in the conventional double-loop closed loop to compensate for the NMP effect. Therefore, the potential instability caused by NMP can be avoided. Such compensation is especially useful for dc microgrid applications where boost converters are widely used as interface converters. Two types of feedforward gain are discussed and compared. The gain of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> with a high-pass filter is used eventually for integrating with conventional droop control because it does not change the low-frequency quiescent operation point. The stability of the proposed controller is analyzed through loop gain on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$s$ </tex-math></inline-formula> plane. Besides, how the output impedance of the converter is shaped by the passive controller is analyzed. The experimental results validate the effectiveness of the proposed passive controller.

Passivity of Lotka–Volterra and quasi-polynomial systems

This study approaches the stability analysis and controller design of Lotka–Volterra and quasi-polynomial systems from the perspective of passivity theory. The passivity based approach requires to extend the autonomous system model with a suitable input structure. The condition of passivity for Lotka–Volterra systems is less strict than the classic asymptotic stability criterion. It is shown that each Lotka–Volterra system is feedback equivalent to a passive system and a passifying state feedback controller is proposed. The passivity based approach enables the design of novel state feedback controllers to Lotka–Volterra systems. The asymptotic stability can be achieved by applying an additional diagonal state feedback having arbitrarily small gains. This result was further explored to achieve rate disturbance attenuation in controlled Lotka–Volterra systems. By exploiting the dynamical similarities between the Lotka–Volterra and quasi-polynomial systems, it was shown that the passivity related results, developed for Lotka–Volterra systems, are also valid for a large class of quasi-polynomial systems. The methods and tools developed have been illustrated through simulation case studies.

A percolation theory for designing corrosion-resistant alloys.

Iron-chromium and nickel-chromium binary alloys containing sufficient quantities of chromium serve as the prototypical corrosion-resistant metals owing to the presence of a nanometre-thick protective passive oxide film1-8. Should this film be compromised by a scratch or abrasive wear, it reforms with little accompanying metal dissolution, a key criterion for good passive behaviour. This is a principal reason that stainless steels and other chromium-containing alloys are used in critical applications ranging from biomedical implants to nuclear reactor components9,10. Unravelling the compositional dependence of this electrochemical behaviour is a long-standing unanswered question in corrosion science. Herein, we develop a percolation theory of alloy passivation based on two-dimensional to three-dimensional crossover effects that accounts for selective dissolution and the quantity of metal dissolved during the initial stage of passive film formation. We validate this theory both experimentally and by kinetic Monte Carlo simulation. Our results reveal a path forward for the design of corrosion-resistant metallic alloys.

Passivity-Based Decentralized Control for Discrete-Time Large-Scale Systems

Passivity theory has recently contributed to developing decentralized control schemes for large-scale systems. Many decentralized passivity-based control schemes are designed in continuous-time. It is well-known, however, that the passivity properties of continuous-time systems may be lost under discretization. In this letter, we present a novel stabilizing decentralized control scheme by ensuring passivity for discrete-time systems directly and thus avoiding the issue of passivity preservation. The controller is synthesized by locally solving a semidefinite program offline for each subsystem in a decentralized fashion. This program comprises local conditions ensuring that the corresponding subsystem is locally passive. Passivity is ensured with respect to a local virtual output which is different from the local actual output. The program also comprises local conditions ensuring that the local passivity of all subsystems implies the asymptotic stability of the whole system. The performance of the proposed controller is evaluated on a case study in DC microgrids.

The use of passive cable theory to increase the threshold of nociceptors in people with chronic pain

Background Chronic pain is one of the disorders that cost any society high expenses. The major mechanisms responsible for the conversion of pain from acute to chronic are still unclear. One major mechanism of these mechanisms is the hypersensitivity of nociceptors to any noxious stimulus. Treatment approaches for chronic pain have not targeted the abnormal function of nociceptors or achieved long-time relief of pain yet. Objectives To outline the effectiveness of passive cable theory to decrease the hypersensitivity of nociceptors in patients with chronic pain and renormalize the abnormal hypersensitivity of nociceptors. Major Findings applying the concept of the passive cable theory in the treatment of chronic pain would decrease the hypersensitivity of nociceptors and produce a decrease in chronic pain levels. This could occur through increasing the passive background leakage of ions in the opposite direction against their major flow direction. During the major flow of ions through the cell membrane occurs with any noxious stimulus, a background passive leakage of the same ions occurs in the opposite direction. This leakage helps in increasing the postsynaptic potentials and prolongs their decay phase. In turn, this decreases the hyperexcitability of the central nervous system, which commonly occurs in chronic pain. Both decreases in the peripheral and central sensitization would decrease the depletion of β-arrestin-2, which leads to a decrease in the descending painful mechanism. Conclusion The use of passive cable theory would be a useful intervention to decrease the hypersensitivity of peripheral nociceptors and hyper-excitability of the central nervous system, which are common mechanisms of persisted chronic pain. This helps to renormalize the abnormal mechanism commonly occur in chronic pain and would cause a prolonged decrease in chronic pain.

The secondary passivity: Merleau-Ponty at the limit of phenomenology

This paper considers the move from passivity to a generative passivity in Merleau-Ponty’s ontology. In The Visible and the Invisible Merleau-Ponty calls this generative passivity a “secondary passivity” and in his passivity lectures he describes it as “passivity without passivism.” The paper argues that this secondary passivity must be understood in terms of an ecart within the phenomena. That is, in terms of a separation and distance which is matrixed and configured within what appears. This is the basis for Merleau-Ponty’s statement in his passivity lectures that “the touchstone of a theory of passivity,” is a “notion of oneiric symbolism,” and why for him passivity is intimately connected to a “primordial symbol.” If the symbolic is so associated with passivity, the symbolic also does not concern origins but is both the ontological limit and divergence in phenomena. This association forces Merleau-Ponty to consider what it means for phenomenological reflection retrace its steps back to an initial event of expression and even whether phenomenology is ultimately served by description. Finally, this paper considers Merleau-Ponty’s attitude toward the literary usages of language as a means of doing a phenomenology of the secondary passivity.

Wind energy conversion system under asymmetrical voltage failures: Analysis and nonlinear control

AbstractThis work presents the analysis and proposes nonlinear controls of a wind energy conversion system (WECS) to pass through symmetrical and asymmetrical voltage failures. The WECS is equipped with a nonsalient pole permanent magnet synchronous generator (PMSG) and two full converters, synchronous generator side converter (SGSC) and grid side converter (GSC), joined by a direct current (DC) link. As a consequence of the strong disturbances considered, a general strategy based on grid voltage values changes control references at SGSC and GSC. This strategy uses two flags for indicating normal grid voltages, symmetrical faults, or asymmetrical ones. Then, while control laws deal with model uncertainties and fast disturbances due to wind gusts, the strategy changes references to surpass strong, probably unbalanced, grid voltages disturbances. To assure robust properties, controllers are designed via a conjunction of Lyapunov and passivity theories. The proposed controllers and the strategy are tested under realistic wind conditions, uncertain parameters, and strong voltage disturbances.

A Phase-Shaping Approach to the Control of Parametric Systems and Its Application

The robust performance design of parametric systems is a long-standing unsolved problem, even though its analysis has seen significant success. Most existing design methods usually treat the parameter uncertainty as other types, such as norm-bounded uncertainty, and apply the corresponding approach. However, such treatment inevitably broadens the range of uncertainty and brings about design conservatism consequentially. To overcome such difficulty and establish a less conservative performance design method for parametric systems, this article looks back at the passivity theory and put forward a phase-shaping approach. This approach is composed of a generalized Popov transformation and a phase-shaping method for the nominal system. The key idea is to transform an uncertain but positive parameter into a positive real function while shaping the phase of the nominal system via a meta-heuristic method. This design freedom of phase shaping makes it possible to achieve a higher performance. Furthermore, this method is applied to the control design of drivetrain system: a test bed for automobile drivetrains. Its superiority is validated experimentally on an industrial setup.

Control of Interlinking Converters in Hybrid AC/DC Grids: Network Stability and Scalability

Hybrid AC/DC networks are an effective solution for future power systems, due to their ability to combine advantages of both AC and DC networks. However, they bring new technological challenges, one key area being the control of such a network. The network, and especially the interlinking converter (ILC), must be controlled to ensure that the DC and AC subsystems coordinate to stabilize the network and allocate power appropriately. This is an area which has attracted considerable recent interest due to the non-triviality of the control design. One promising tool is passivity theory which allows the derivation of decentralized conditions through which the stability of the network can be guaranteed. This paper investigates the application of a passivity framework to AC/DC grids, using a typical lossless line assumption. By ensuring that an appropriately formulated passivity condition is satisfied by the AC and DC buses, and the interlinking converter, the stability of the interconnection can be guaranteed. We also discuss how the ILC controller may be designed to achieve an appropriate power allocation between AC and DC sources. Simulation results demonstrate that the proposed ILC control design regulates the frequency and voltages of the hybrid AC/DC network with a stable operation maintained.

Passivity Analysis of Replicator Dynamics and Its Variations

In this article, we focus on studying the passivity properties of different versions of replicator dynamics (RD). The RD represents a deterministic monotone nonlinear dynamic, which allows incorporation of the distribution of population types through a fitness function. We use tools for control theory, in particular, the passivity theory, to study the stability of the RD when it is in action with evolutionary games. The passivity theory allows us to identify the class of evolutionary games in which stability with RD is guaranteed. We show that several variations of the first order RD satisfy the standard loseless passivity property. In contrary, the second-order RD does not satisfy the standard passivity property; however, it satisfies a similar dissipativity property known as negative imaginary property.

Passivity based sliding mode control and synchronization of a perturbed uncertain unified chaotic system

The problem of passivity-based sliding mode control is considered, for the unified chaotic system having uncertainties and perturbations. Using a combination between sliding mode method and the passivity method, an appropriate switching surface for the uncertain and perturbed system is designed, and then through passivity theory, the stability of the system is ensured. The proposed design is applied in two control problems, the first one being the stabilization of the uncertain perturbed unified chaotic system and the second one is the synchronization between two unified chaotic systems, where only the slave system contains uncertainties and perturbations. Finally, the effectiveness of the proposed methods are illustrated through numerical simulations, and also through a microcontroller implementation.