Mode Disturbance Research Articles

Prescribed performance based sliding mode path-following control of UVMS with flexible joints using extended state observer based sliding mode disturbance observer

The accuracy and stability of an underwater vehicle manipulator system (UVMS) are essential for performing underwater tasks. However, exogenous disturbance and unmodeled dynamics will lead to poor UVMS performance in terms of degraded transient behavior and large steady-state errors. In this paper, the path following problem with prescribed performance of a UVMS with flexible joints is addressed. First, a terminal sliding mode control scheme with prescribed performance is presented along with a novel extended state observer (ESO) based sliding mode disturbance observer (SMDO). The proposed controller simplifies the parameter tuning process by ensuring the predefined system behaviors of interest right after the design. Subsequently, a path following scheme is designed for the UVMS such that the position of both base vehicle and robot arms can converge to the specified path in 3-D space. Finally, numerical simulations and comparisons are conducted to show the effectiveness of the proposed method in terms of trajectory tracking in the presence of environmental disturbances and modeling uncertainties.

Research on Vibration Suppression of the Long Flexible Arm Based on Three Tilt Sensors

In this research, a new method based on the equivalence of modal characteristics, differential flatness (DF), and active disturbance rejection control (ADRC) is proposed for the stabilization control of the long flexible arm (LFA). There are two major problems in the system of the LFA. The first problem is that the LFA is very prone to the multiple-mode coupling, while the control systems need as few sensors as possible. Another problem is that the structure of the LFA in practice is often complex and subject to various disturbances. Therefore, in this paper, the equivalent multirigid body dynamic model of a LFA is derived from the modal information of the equivalent rigid body model of the prototype. Then, the output values of the three tilt sensors are synthesized into an output based on the DF method. Finally, the effectiveness of the proposed method is verified through physical experiments. Compared with PID, the proposed method has shorter settling time. The LFA can be restored within 7 seconds under the ADRC, while it needs 90 seconds or more to calm down without the control.

Experimental validation of disturbance observer-based adaptive terminal sliding mode control subject to control input limitations for SISO and MIMO systems

Nowadays, advances in different fields of technology have increased demands for reliable controllers. Uncertainty, disturbances, and limitations in control inputs are inevitable with most systems. Hence, considering them in designing a practical controller seems indispensable to any system. We propose an adaptive, robust, and finite time control technique for both multi-input multi-output (MIMO) and single-input single-output (SISO) systems. In the design of the proposed control technique, due to the undeniable existence of disturbances and control input limitations, their effects are fully taken to account. On the basis of a finite time sliding mode strategy, controllers and disturbance observers are designed. Then, the stability and finite time convergence of the proposed control scheme and disturbance observer are proven via the Lyapunov stability theory. Eventually, to investigate the performance of the proposed method in real-world applications, a hardware-in-the-loop (HIL) test is carried out for the proposed control scheme. Through numerical simulation and the results of the HIL test, the high-effective performance of the proposed controller for uncertain chaotic systems was demonstrated. Moreover, the results of the HIL test showed that by implementing continuous functions in the design of the controller, chattering, which has detrimental effects on systems, will be reduced in practical applications. Numerical simulations and the results of the HIL test bench for the modified controller clearly confirmed the effective performance of the offered control technique for practical systems. Thereby applying the proposed control technique for complex nonlinear systems subject to control input limitations, disturbances, and time-varying uncertainties will be useful.

Effect of an adverse pressure gradient on hypersonic wall pressure fluctuations

Measurements based on a plate-perpendicular fin model were conducted to investigate the effect of an adverse pressure gradient on hypersonic wall pressure fluctuations. The leading edge diameter of the perpendicular fin is designed to be 25 mm with a height of 200 mm. A linear sensor-array was used to measure the wall pressure fluctuation, and a numerical computation was carried out to validate the measurement. Wall pressure fluctuations were discussed in terms of two aspects: the time–frequency domain and spatial correlation. The flow types on the plate could be estimated by the sound pressure level distribution, and the dominant flow type that substantially contributes to the wall pressure fluctuations could be determined. The spatial correlation of wall pressure fluctuations was analyzed using the phase array technique, and two disturbance modes could be identified from the wavenumber map obtained using the beamforming algorithm. The investigation results revealed that the change in the unit Reynolds number caused by the variation in the inflow dynamic pressure leads to the change in the flow type and the distribution of wall pressure fluctuations. The small-scale vortices within the hypersonic laminar flow lead to the difference in the signs of the convective mode wavenumber and that generated by hypersonic turbulence.

Fault-tolerant control for the multi-quadrotors cooperative transportation under suspension failures

This paper focuses on the fault-tolerant control of the multi-quadrotors cooperative payload transportation under suspension failures. A dynamic load reassignment and control strategy is proposed for the cooperative quadrotors by incorporating the high-order sliding mode disturbance observer into a dynamic surface control-based backstepping design. The dynamics of the cable-suspended payload transportation with multiple quadrotors are formulated. The unmeasurable suspension cable tensions, which will greatly impact the quadrotors' dynamics and stability, are respectively viewed as one part of the lumped disturbance and estimated by the super-twisting sliding mode-based finite-time disturbance observers. With the estimated disturbance compensation, the dynamic surface control laws are established for the cooperative quadrotors. Moreover, to guarantee the fault-tolerant control under suspension cable broken, a dynamic load assignment strategy is proposed to stably recover the cooperative load transportation. Finally, the stability of tethered quadrotors' flight control systems is analyzed. The simulation results show the effectiveness of the proposed algorithm under suspension failures.

Active vibration control for GyroWheel based on sliding mode observer and adaptive feedforward compensator

This article proposes an active vibration control method for the GyroWheel to ensure the attitude stability precision of the spacecraft. The method includes sliding mode disturbance observer and adaptive feedforward compensator. First, considering the disturbance torque caused by rotor imbalance, the dynamic equation adopting complex coefficients is derived with synchronous disturbances. To reduce the influence of model parameter perturbation, a finite time sliding mode observer is designed to estimate the rotor imbalance owing to its robustness. An integrator for the switching term is introduced in the sliding manifold, which attenuates the chattering phenomenon. Then, the observed unbalanced torque is utilized to generate the reference compensation tilting angle, which is fedforward to the command value to offset the synchronous frequency current. A variable step size seeking algorithm is adopted to tune the feedforward compensator gain adaptively. Finally, both numerical simulations and experiments have verified the effectiveness of the active vibration control scheme, achieving clean vibration torque.

A Robust Deadbeat Predictive Controller With Delay Compensation Based on Composite Sliding-Mode Observer for PMSMs

This article proposes an improved deadbeat predictive controller for permanent-magnet synchronous motor drive systems. It can eliminate the influence of the parameter mismatch of inductance, resistance, and flux linkage. First, the performance of the conventional predictive current method is investigated to analyze sensitivities of the electric parameters. Then, a composite sliding-mode disturbance observer (SMDO) based on the stator current and lumped disturbance is proposed, which can simultaneously estimate the future current value and lumped disturbance caused by the parameter mismatch of inductance, resistance, and flux linkage. Based on the discrete-time SMDO, currents are estimated and used to replace the sampled values to compensate one-step delay caused by the calculation and sampling delay. Both simulation and experimental performances of the proposed method have been validated and compared with the conventional control methods under different conditions. The comparison results show the superiority of the proposed predictive current control method based on the composite SMDO.

Study of a Gas Disturbance Mode Content Based on the Measurement of Atmospheric Parameters at the Heights of the Mesosphere and Lower Thermosphere

The main result of this work is the estimation of the entropy mode accompanying a wave disturbance, observed at the atmosphere heights range of 90–120 km. The study is the direct continuation and development of recent results on diagnosis of the acoustic wave with the separation on direction of propagation. The estimation of the entropy mode contribution relies upon the measurements of the three dynamic variables (the temperature, density, and vertical velocity perturbations) of the neutral atmosphere measured by the method of the resonant scattering of radio waves on the artificial periodic irregularities of the ionospheric plasma. The measurement of the atmosphere dynamic parameters was carried out on the SURA heating facility. The mathematical foundation of the mode separation algorithm is based on the dynamic projection operators technique. The operators are constructed via the eigenvectors of the coordinate evolution operator of the transformed system of balance equations of the hydro-thermodynamics.

Effects of tip air injection on the aerodynamic stability of an axial flow compressor with total pressure distortion

The compressor is a critical component that determines the aerodynamic stability of an aero-engine. Total pressure inlet distortion decreases the thrust and shrinks the stability margin, thus inducing severe performance degradation or even flameout. Generally, tip air injection is used to reduce the adverse influence of total pressure inlet distortion on the aerodynamic stability. In the present work, an experimental investigation on the effects of tip air injection on the stability of a two-stage low-speed axial compressor with total pressure inlet distortion was carried out. A flat baffle generated the total pressure distortion at the inlet of the compressor. The stall margin of the compressor was reduced significantly by the total pressure distortion. When the dimensionless insertion depth of the flat baffle was 0.45, the stall margin decreased to 11.4%. Under the total pressure inlet distortion, tip air injection effectively improved the distortion resistance capability of the compressor. The circumferential layout of the nozzle played a critical role in the stability expansion effect of tip air injection under the inlet flow condition of the total pressure distortion. The modal wave disturbance was likely to occur in the distortion-affected region (the low-pressure region and the mixing region). Tip air injection did not inhibit the generation of the modal wave but restrained the development of the modal wave into the stall cell. It improved the low-speed compressor’s tolerance to the modal wave and allowed a higher amplitude modal wave to occur.

Connectivity‐maintained and specified‐time vehicle platoon control systems with disturbance observer

AbstractIn this article, the connectivity‐maintained platoon control problem for networked vehicles with external disturbance is considered. By modeling each vehicle as a nonlinear triple integral system, a specified‐time sliding model disturbance observer and a specified‐time controller are presented to ensure the convergence of the platoon system. The predetermined performance method is applied to maintain the connectivity of vehicles in the platoon, which enables flexibility in the communication connectivity between vehicles. The specified time sliding mode disturbance observer is proposed to estimate the external disturbance within the predefined time and it is proved to be uniformly ultimate boundedness stable by using the time transformation method. A dynamic gain controller with the time constraint is proposed to achieve the stable platoon with connectivity maintained for each vehicle. The proposed approach can simultaneously guarantee the specified‐time convergence and connectivity maintenance without depending on any system parameters. The effective of the proposed controller is proved by the Lyapunov function. Finally, comparative simulation results are obtained to verify the effectiveness of the proposed protocols.

Electro-hydraulic position servo system based on sliding mode active disturbance rejection compound control

This study proposes a compound control method based on sliding mode and active disturbance rejection control to address the difficulty of controlling the cutting head for boom-type roadheader with parameter changes and uncertain disturbances. The fastest discrete tracking differentiator and extended state observer based on the traditional active disturbance rejection control are designed. Additionally, the controller of the sliding mode and active disturbance rejection control is constructed. Theoretical analysis indicates that the proposed controller ensures asymptotic stability, despite the existing uncertain disturbances. Moreover, a system based on AMESim and MATLAB/Simulink Co-simulation model is developed to further verify the performance of proposed algorithm. Compared with traditional active disturbance rejection control, proportional-integral-derivative(PID) and sliding mode control, co-simulation results demonstrate that the sliding mode active disturbance rejection compound control improves the tracking accuracy and robustness of the position servo system.

Wavelet probability distribution mapping for detection and correction of dynamic data injection attacks in WAMS

The dependency of synchrophasor technology on shared/dedicated communication networks for data transfer and the lack of security specifications in C37.118 standard makes phasor measurements susceptible to data manipulation attacks. More critically, a false data injection attack could influence both accuracy of state estimates and the evaluation of system dynamics. Typically, false data sequences are modeled as multi-constraint non-linear optimization with random, step, or ramp type distribution. However, a carefully designed attack that mimics the dynamic response of a natural disturbance can hugely impact trends-based applications of synchrophasor-based disturbance monitoring and mode metering. This work designs a multi-channel/multi-sample dynamic injection attack in phasor trends to closely mimic natural disturbances aiming at trends-based applications. Also, the work proposes an un-supervised wavelet probability mapping method for the detection and correction of dynamic false data sequences. The proposed method identifies the attack sequences from disturbances using relative wavelet energy measure and replaces the corrupted sub-sequences with coherent un-corrupted trends using a kernel density estimation-based mode mapping method. The efficacy of the proposed method is validated for simulated injection cases in IEEE-118 bus system using DigSILENT/PowerFactory and real phasor data for the Eastern region of the India grid. The results show that the proposed method exhibits high detection accuracy and low correction error for different categories of dynamic false data cases under real system conditions.

Robust fractional‐order super‐twisting sliding mode control to accurately regulate lithium‐battery / super‐capacitor hybrid energy storage system

One of the main challenges in front of the inventors and researchers to compensate the power quality problems is the existence of an efficient and reliable electric energy source for dynamic voltage restorer (DVR). Recent advances in the technologies of lithium-battery (LB) and super-capacitor (SC) have made them possible to be used as hybrid energy storage system (HESS) for DC-power supply of DVR. But then, a robust and efficient controller must be essentially designed to compensate the intricate correlation between system components, unknown nonlinearities, parameter uncertainties related to the HESS. Hence, fractional-order super-twisting sliding mode control (FOSTSMC) is proposed for LB/SC-HESS to smoothly and accurately smoothly track the current reference and control the DC-link voltage of the asymmetric half-cascaded multilevel inverter of DVR during different compensation conditions. As the primary controller, FOSTSMC has compensated the unknown nonlinear parts and parameter uncertainties related to LB/SC-HESS through the real-time disturbance estimation using sliding mode state and disturbance observer (SMSDO). Both the battery current and DC-link voltage due to the physical measurability are chosen to design the control scheme based on the proposed FOSTSMC. The proposed controller has been compared with the proportional integral derivative and the sliding mode control under different probable scenarios to evaluate and validate its observability and controllability. To better present the effects of FOSTSMC, AHCMLI, and HESS-based DVR, they have been quantified as follows: Three real-time stability benchmarks that is, overshoot, undershoot and settling time are respectively attained for FOSTSMC: 0.6, 0.4, and 0.03; for sliding mode control: 1.1, 0.7 and 0.019; for proportional integral derivative: 0.9, 2, and 0.117. That is to say, FOSTSMC can smoothly and accurately track the current reference and control the DC-link voltage during different compensation conditions as compared with other controllers. Asymmetric half-cascaded multilevel inverter can provide 33 steps with consideration of 12 unidirectional switches, whereas binary, trinary, and other multilevel structures can provide less than 27 steps with consideration of 12 switches. The quasi-AC voltage synthesizer-based DVR can completely and accurately compensate the voltage sag and swell with THD of 2.12 and 2.35, respectively. The THD of mal-compensation voltage sag and swell using the conventional DVR are respectively 11.57 and 13.86.

Optimal Adaptive Control and Backstepping Control Method with Sliding Mode Differentiator

In order to improve the success rate of space debris object capture, how to increase the resistance to interference in the space robot arm has become an issue of interest. In addition, since the space operation time is always limited, finite-time control has become another urgent requirement needed to be addressed. Considering external disturbances, two control methods are proposed in this paper to solve the control problem of space robot arm. Firstly, a linear sliding mode control method is proposed considering the model uncertainties and external disturbances. The robot arm can track the desired trajectory, while a trade-off between optimality and robustness of the solved system can be achieved. Then, in order to reduce conservativeness and relax restrictions on external disturbances, a novel backstepping control method based on a finite-time integral sliding mode disturbance observer is developed, which compensates for the effects of both model uncertainties and infinite energy-based disturbance inputs. Finally, simulation examples are given to illustrate the effectiveness of the proposed control method.

Fractional-order control with second-order sliding mode algorithm and disturbance estimation for vibration suppression of marine riser

Suppression of the vibration caused by environmental loads in marine risers is critical to prevent irreparable damages. This paper addresses this issue by proposing a novel boundary control for a flexible riser connected to a vessel at its top. In this regard, initially, a sliding mode observer (SMO)-based disturbance estimator is constructed to estimate the uncertainty of the vessel's dynamics. Next, using backstepping, a suitable virtual control along with the respective error dynamics are derived. A fractional-order error surface is defined to achieve Mittag-Leffler convergence for the control error variable. A second-order sliding mode (SOSM) control law is used to stabilize this error surface. The boundedness and ultimate boundedness of the riser's deflection under the proposed boundary control is shown by Lyapunov analysis. Comparative simulations demonstrate the robust vibration suppression performance of the proposed controller.

The Influence of EMI Power Filter’s Layout on the Measurement of Mains Terminal Disturbance Voltage

In the first place, this article analyzes the principles of electro magnetic interference (EMI) power filter from the aspects of the differential mode and the common mode disturbance. Afterwards, the design requirements of key components in the EMI power filter and the layout principles of filter is investigated. Next, the influence of layout of EMI power filter on the measurement of mains terminal disturbance voltage has been studied experimentally by the lap quality of the filter onto the equipment under test, the distance between the input and output power line of filter, as well as the input cable length of EMI power filter. Finally, we draw the conclusion that the layout quality of power filter has important impact on the measurement of mains terminal disturbance voltage. It means that the related rules should be strictly abided by when the EMI power filter is used to restrain the conducted disturbance.

Hypersonic Boundary-Layer Receptivity over a Blunt Cone to Freestream Pulse Disturbances

Although receptivity plays a key role in the transition of hypersonic flows, most prior computational receptivity studies have neglected to study broadband frequency disturbance spectra. This work uses perfect gas linear stability theory (LST) and direct numerical simulation (DNS) to study the receptivity of flow over a 9.525 mm nose radius, 7 deg half-angle straight cone at Mach 10 using finite spherical and planar pulses to approximate disturbances with broadband frequency spectra. Freestream fast acoustic, slow acoustic, temperature, and vorticity pulses of both geometries were studied to investigate a wide range of forcing conditions. Unsteady DNS predicts second mode growth and agrees well with LST. DNS and LST data are used to extract second mode receptivity coefficients and phase spectra. For the finite pulses the strongest to weakest responses are for the fast acoustic, temperature, slow acoustic, and vorticity pulses, respectively. The planar disturbances show the strongest response for the slow acoustic, temperature, vorticity, and fast acoustic pulses in that order. Fast Fourier transform results show significant variation in the spectral disturbance response between disturbance types and geometries, and the planar fast acoustic pulse in particular is shown to much more readily excite modal disturbances other than the primary second mode.

Adaptive sliding mode disturbance observer–based funnel trajectory tracking control of quadrotor with external disturbances

This paper studies trajectory tracking control problem of quadrotor in the presence of external disturbances. A new control scheme integrating adaptive sliding mode disturbance observer (ASMDO) with backstepping funnel control is designed in both position loop and attitude loop. Adaptive sliding mode disturbance observer is utilized to estimate and compensate the external disturbances of quadrotor system, which relaxed the upper bound requirement in conventional sliding mode disturbance observer (SMDO) whilst adapting the gain of discontinuous term to a level as small as possible for consideration of chattering mitigation. The modified funnel function not only guarantees the dynamic quality in the tracking process but also avoids derivative operation of Euclidian norm of tracking error in the backstepping design. To guarantee stabilization of closed-loop system, Lyapunov stability criterion is utilized in the overall controller design process. Finally, the effectiveness and superiority of the proposed scheme are illustrated by simulation results.

On the Stability of Convection in a Non-Newtonian Vertical Fluid Layer in the Presence of Gold Nanoparticles: Drug Agent for Thermotherapy

We consider the effect of gold nanoparticles on the stability properties of convection in a vertical fluid layer saturated by a Jeffreys fluid. The vertical boundaries are rigid and hold at uniform but different temperatures. Brownian diffusion and thermophoresis effects are considered. Due to numerous applications in the biomedical industry, such a study is essential. The linear stability is investigated through the normal mode disturbances. The resulting stability problem is an eighth-order ordinary differential complex eigenvalue problem that is solved numerically using the Chebyshev collection method. Its solution provides the neutral stability curves, defining the threshold of linear instability, and the critical parameters at the onset of instability are determined for various values of control parameters. The results for Newtonian fluid and second-grade fluid are delineated as particular cases from the present study. It is shown that the Newtonian fluid has a more stabilizing effect than the second-grade and the Jeffreys fluids in the presence of gold nanoparticles and, Jeffreys fluid is the least stable.

Temperature Effect on the Fundamental Breakdown Mechanism of Mack Mode Disturbances in Hypersonic Boundary Layers

Temperature Effect on the Fundamental Breakdown Mechanism of Mack Mode Disturbances in Hypersonic Boundary Layers