Large Feedback Gain Research Articles

Distributed-observer-based adaptive fault tolerant formation maneuver for autonomous surface vehicles under stochastic cyber-attack

This paper investigates the distributed adaptive fault-tolerant formation maneuver control strategy for multiple autonomous surface vehicles (ASVs) systems subject to stochastic cyber-attack and actuator failures. Existing works have provided solutions against continuous attacks on communication channels while ignoring the increasingly prevalent intermittent attacks. Compared to the former, the latter are more challenging to detect, having been insufficiently described and addressed. Motivated by this observation, this article is concerned with the stochastic intermittent injection attacks, which are modeled as stochastic impulsive sequences, characterized by stochastic injection instant and intensity, leading to unpredictable changes in the state information transmitted by the neighbors. Taking this dilemma into consideration, a novel distributed observer is proposed, capable of effectively observing the target formation even in the presence of stochastic intermittent injection attacks. Meanwhile, a large feedback gain is incorporated into the observer to reduce the impact of attacks on system stability. A linear sliding manifold, together with the adaptive algorithm, is utilized to construct a fault tolerant control architecture for each follower ASV without employing model parameters which can confront the embarrassing scenario of actuator failures. Eventually, theoretical deduction and numerical simulations are conducted to confirm the feasibility of the proposed collaborative control scheme.

Distributed observer for LTI systems under stochastic impulsive sequential attacks

In this paper, we consider the distributed state estimation problem of continuous-time linear time-invariant (LTI) systems, where communication channels are attacked by stochastic impulsive sequences. In a networked system, the communication channel between an agent and its neighbor is vulnerable to being attacked. Continuous attacks have been widely studied so far, but with the development of attack techniques, intermittent attacks have been emerging, which are more difficult to be identified and detected, and have not been well portrayed and studied. Therefore, this paper investigates a random intermittent injection attack, which leads to abrupt and random changes of the state information transmitted by the neighbors. First, this attack is modeled as a stochastic impulsive sequential attack, where both its impulsive time and impulsive intensity are random. Then a distributed observer under stochastic impulsive sequential attack is proposed. Since the impulsive attack destroys the stability of the system, in order to attenuate the impact of the impulsive attack, a large feedback gain is necessary. By using the graph theory, matrix theory and stochastic analysis, sufficient conditions for the existence of the distributed observer in the sense of mean square and in the sense of almost sure are presented, respectively. Finally, the effectiveness of the proposed distributed observer is verified by numerical simulations.

Almost Sure Stability of Nonlinear Systems Under Random and Impulsive Sequential Attacks

This article is concerned with the stability problem for a class of Lipschitz-type nonlinear systems in networked environments, which are suffered from random and impulsive deception attacks. The attack is modeled as a randomly destabilizing impulsive sequence, whose impulsive instants and impulsive gains are both random with only the expectations available. Almost sure stability is ensured based on Doob's Martingale Convergence Theorem. Sufficient conditions are derived for the solution of the nonlinear system to be almost surely stable. An example is given to verify the effectiveness of the theoretical results. It is shown that the random attack will be able to destroy the stability, therefore, a large feedback gain may be necessary.

Wide Input and Load Integral Gain Changeable Digital Control DC-DC Converter

The aim of this paper is to present an integral gain changeable digital control dc-dc converter with wide input and load regulation characteristics. Since the green energy depends on the environment, wide input regulation characteristics are necessary in dc-dc converters. Additionally, dc-dc converters have an issue that the output voltage of dc-dc converters is increased in the light load condition. When the large feedback gain is used to realize wide regulation characteristics, the stability becomes worse. The proposed method can address all of them using a simple integral gain changeable method. The integral gain is changed quickly by the load current value. The integral changeable function uses a single approximate function which is designed by the stabilization range of output voltage based on the integral control. The proposed method has great regulation characteristics against both of the input voltage and load. Furthermore, it has a superior transient response to the conventional integral gain fixed method. Simulated and experimental results are provided to confirm the effectivity of proposed method.

Consensus of third-order nonlinear multi-agent systems

This paper considers the consensus problem of third-order nonlinear multi-agent systems with a fixed communication topology. A consensus protocol is proposed for solving such a problem. By a transformation, the consensus problem is converted to a stability problem, then sufficient consensus criteria are obtained by proposing a novel Lyapunov function. It is shown that consensus can be achieved for a sufficiently large feedback gain, provided that certain quadratic inequalities with respect to two parameters are satisfied. Finally, the effectiveness of the theoretical results is demonstrated through an example.

Reproduction of pressure field in ultrasonic‐measurement‐integrated simulation of blood flow

Ultrasonic-measurement-integrated (UMI) simulation of blood flow is used to analyze the velocity and pressure fields by applying feedback signals of artificial body forces based on differences of Doppler velocities between ultrasonic measurement and numerical simulation. Previous studies have revealed that UMI simulation accurately reproduces the velocity field of a target blood flow, but that the reproducibility of the pressure field is not necessarily satisfactory. In the present study, the reproduction of the pressure field by UMI simulation was investigated. The effect of feedback on the pressure field was first examined by theoretical analysis, and a pressure compensation method was devised. When the divergence of the feedback force vector was not zero, it influenced the pressure field in the UMI simulation while improving the computational accuracy of the velocity field. Hence, the correct pressure was estimated by adding pressure compensation to remove the deteriorating effect of the feedback. A numerical experiment was conducted dealing with the reproduction of a synthetic three-dimensional steady flow in a thoracic aneurysm to validate results of the theoretical analysis and the proposed pressure compensation method. The ability of the UMI simulation to reproduce the pressure field deteriorated with a large feedback gain. However, by properly compensating the effects of the feedback signals on the pressure, the error in the pressure field was reduced, exhibiting improvement of the computational accuracy. It is thus concluded that the UMI simulation with pressure compensation allows for the reproduction of both velocity and pressure fields of blood flow.

Tubuloglomerular Feedback-Mediated Dynamics in Three Coupled Nephrons

A model of three coupled nephrons branching from a common cortical radial artery is developed to further understand the effects of equal and unequal coupling on tubuloglomerular feedback. The integral model of Pitman et al. (2002), which describes the fluid flow up the thick ascending limb of a single, short-looped nephron of the mammalian kidney, is extended to a system of three nephrons through a model of coupling proposed by Pitman et al. (2004). Analysis of the system, verified by numerical results, indicates that stable limit-cycle oscillations emerge for sufficiently large feedback gain magnitude and time delay through a Hopf bifurcation, similar to the single nephron model, yet generally at lower values. Previous work has demonstrated that coupling induces oscillations at lower values of gain, relative to uncoupled nephrons. The current analysis extends this earlier finding by showing that asymmetric coupling among nephrons further increases the likelihood of the model nephron system being in an oscillatory state.

Temperature feedback control for improving the stability of a semiconductor-metal-oxide (SMO) gas sensor

Stability is a major concern of semiconductor-metal-oxide (SMO) gas sensors in practical applications, as they may cause false alarm problems. Ambient temperature is a major factor affecting the SMO gas sensor's stability. In this paper, we use a novel way to improve temperature stability of SMO (tin oxide) gas sensors by applying a temperature feedback control circuits which are compatible with our microelectromechanical systems sensor fabrication. A built-in platinum temperature sensor can precisely detect the sensor's working temperature. It provides feedback information to compensate the microheater's current to maintain the sensor's working temperature constant, regardless of ambient temperature change. Test results showed that, with this approach, significant improvement of stability has been achieved compared to SMO gas sensors without temperature compensation under the same ambient variation. The algorithm is realized through a hardware circuit, whose advantages include real time, large feedback gain, and low cost.

Feedback-mediated dynamics in two coupled nephrons

Previously, we developed a dynamic model for the tubuloglomerular feedback (TGF) system in a single, short-looped nephron of the mammalian kidney. In that model, a semi-linear hyperbolic partial differential equation was used to represent two fundamental processes of solute transport in the nephron’s thick ascending limb (TAL): chloride advection by fluid flow along the TAL lumen and transepithelial chloride transport from the lumen to the interstitium. An empirical function and a time delay were used to relate glomerular filtration rate to the chloride concentration at the macula densa of the TAL. Analysis of the model equations indicated that stable limit-cycle oscillations (LCO) in nephron fluid flow and chloride concentration can emerge for sufficiently large feedback gain magnitude and time delay. In this study, the single-nephron model was extended to two nephrons, which were coupled through their filtration rates. Explicit analytical conditions were obtained for bifurcation loci corresponding to two special cases: (1) identical time delays but differing feedback gains, and (2) identical gains but differing delays. Similar to the case of a single nephron, our analysis indicates that stable LCO can emerge in coupled nephrons for sufficiently large gains and delays. However, these LCO may emerge at lower values of the feedback gain, relative to a single (i.e., uncoupled) nephron, or at shorter delays, provided the delays are sufficiently close. These results suggest that, in vivo, if two nephrons are sufficiently similar, then coupling will tend to increase the likelihood of LCO.

Interaction of active and passive vibration control of laminated composite beams with piezoceramic sensors/actuators

The interaction between active and passive vibration control characteristics was investigated numerically and verified experimentally for carbon/epoxy laminated composite beams with a collocated piezoceramic sensor and actuator. The finite element method was used for the analysis of dynamic characteristics of the laminated composite beams. Damping and stiffness of adhesive and piezoceramic layers were taken into account in the finite element modeling. The optimal control theory was applied for the analysis of control characteristics of the beam. Experiments on the active vibration control of the laminated composite beams were carried out using velocity feedback control. The effect of varying the stacking sequence of the laminated composite beam on the active and passive damping properties was studied. The finite element analysis was verified by comparing the experimental results in terms of active and passive damping ratios (ζ) and modal dampings (2ζω) as well as fundamental frequency. When the gain in velocity feedback control is small, the active control follows the trend of the passive control, but provides additional effects due to the active control. For a large feedback gain, the active control is dominant over the passive control. Active control is more effective in the structure with higher bending stiffness than in the structure with lower bending stiffness when the feedback gain is large.

Application of equivalent control method to the systems with large feedback gain

Differential equations of slow motion in the systems with a large feedback gain are obtained using the equivalent control method developed for the analysis of sliding mode in systems with discontinuous controls [1].