Robust Finite-Time Control Algorithm Based on Dynamic Sliding Mode for Satellite Attitude Maneuver

Robust finite-time control algorithms for satellite attitude maneuvers are proposed in this paper. The standard sliding mode is modified, hence the inherent robustness could be maintained, and this fixed sliding mode is modified to dynamic, therefore the finite-time stability could be achieved. First, the finite -time sliding mode based on attitude quaternion is proposed and the loose finite-time stability is achieved by enlarging the sliding mode parameter. In order to get the strict finite-time stability, a sliding mode based on the Euler axis is then given. The fixed norm property of the Euler axis is used, and a sliding mode parameter without singularity issue is achieved. System performance near the equilibrium point is largely improved by the proposed sliding modes. The singularity issue of finite-time control is solved by the property of rotation around a fixed axis. System finite-time stability and robustness are analyzed by the Lyapunov method. The superiority of proposed controllers and system robustness to some typical perturbations such as disturbance torque, model uncertainty and actuator error are demonstrated by simulation results.

Finite-Time Controller for Flexible Satellite Attitude Fast and Large-Angle Maneuver

In order to deal with the fast, large-angle attitude maneuver with flexible appendages, a finite-time attitude controller is proposed in this paper. The finite-time sliding mode is constructed by implementing the dynamic sliding mode method; the sliding mode parameter is constructed to be time-varying; hence, the system could have a better convergence rate. The updated law of the sliding mode parameter is designed, and the performance of the standard sliding mode is largely improved; meanwhile, the inherent robustness could be maintained. In order to ensure the system’s state could converge along the proposed sliding mode, a finite-time controller is designed, and an auxiliary term is designed to deal with the torque caused by flexible vibration; hence, the vibration caused by flexible appendages could be suppressed. System stability is analyzed by the Lyapunov method, and the superiority of the proposed controller is demonstrated by numerical simulation.

Dynamic Sliding Mode Controller with Variable Structure for Fast Satellite Attitude Maneuver

In order to deal with the low convergence rate of the standard sliding mode in satellite attitude control, a novel variable structure sliding mode is constructed in this paper by designing the update law of the sliding mode parameter. By implementing this method, the advantage such as simple structure and strong robustness of the standard sliding mode are maintained and the system convergence rate is largely improved. The fixed sliding mode parameter is modified, and the update law is designed. When the system state is away from the sliding mode surface, the parameter is fixed, and when the system state approaches the sliding mode surface, the parameter begins to update. The constraint on control torque and angular velocity is taken into consideration, and the constraint on control parameters is given to ensure that the system state do not exceed its upper bound. System stability is proved by the Lyapunov stability theorem, and the superiority of the proposed controller is demonstrated by numerical simulation.

Acoustics Source Identification of Diesel Engines Based on Variational Mode Decomposition, Fast Independent Component Analysis, and Hilbert Transformation

Diesel engines are widely used in railway systems, particularly in freight trains. Despite their high efficiency in energy conversion, they usually generate high levels of acoustics pollution during operation. In order to mitigate this problem, a series of active/passive acoustics control methods are used to reduce noise. Most of these methods are only effective if the prior knowledge of sources is given. In other words, it is essential to recognize the acoustics source. Variational mode decomposition (VMD) is a signal processing method that enhances the signal corrupted by background noise. However, the decomposed results of VMD depend on their mode parameter and penalty parameter. Therefore, an evaluation method based on system modal parameters (natural frequency and damping ratio) is proposed to select the mode parameter, and the penalty parameter can be selected from the power spectra of signals. In order to increase the accuracy of decomposition for diesel engines and find out the sources of acoustics, a method combining VMD, fast independent component analysis, and Hilbert transformation (VMD-FastICA-HT) is proposed for the separation and identification of different sources for diesel engines. The optimization results indicate that when the penalty parameter value is 1.5 to 16 times the maximum signal amplitude, better decomposition results can be achieved. Therefore, the separated independent acoustics are more accurate in source identification. Furthermore, both simulation data and in situ operational data of diesel engines for vehicles are used to validate the effectiveness of the proposed method.

Calculated studies of the vibrational properties of the mode parameter of the electric power system containing asynchronous turbogenerators by their frequency characteristics

The article presents the results of a study of the oscillatory properties of the operating parameter of electric power systems during joint operation of synchronous and asynchronous turbine generators at the station and the influence of the proportional ratios of their powers on the oscillatory properties based on their amplitudefrequency characteristics.

Спиновые флуктуации и концентрационные магнитные переходы в киральных геликоидальных ферромагнетиках Fe-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-Si

The fluctuation theory is applied to the study of concentration transformations in chiral helicoidal ferromagnetic quasi-binary unordered Fe1-xCoxSi alloys with Dzyaloshinsky-Moriya interaction. The ground state is described on the basis of the LDA + U + SO approximations used in ab initio calculations with additional allowance for concentration fluctuations associated with the difference in the potentials of the intra-atomic Hubbard interaction at the sites occupied by iron and cobalt. Solutions of the obtained equations of the magnetic state for the phases of the long-range and short-range orders with the right and left magnetic chirality are considered. The concentration dependences of the parameters of the intermode interaction are investigated, and the regions of the compositions in which magnetic phase transitions of the first kind induced by thermal fluctuations take place, accompanied by the appearance of fluctuations of the spin helix. It is shown that the transition with a change of the sign of magnetic chirality is accompanied by the appearance of a minimum in the concentration dependence of the mode-mode parameter and the appearance of quantum helicoidal ferromagnetism with a noticeable increase in zero spin fluctuations.

Design and Analysis of a Sliding Mode Parameter Limit Regulating System for Turbo Fan Engine

In this paper, a sliding mode (SM) parameter limit regulating system is designed to regulate the fuel flow rate to the turbofan engine. Firstly, a linear engine model is identified using a general engine dynamic nonlinear model. Then based on the one Lyapunov function, one SM parameter limit regulating system is designed mainly including regulators design, selector design and integrator design. After that the feedback gains and coefficient sets (switching gain and boundary thickness for every regulator) of the SM regulators are optimized and chosen. Finally, the global asymptotical stability of the regulating system is demonstrated. The simulation results also show that SM parameter limit regulator functions all the time during engine transient state control process, and the design SM parameter limit regulating system ensures that the target steady speed state or limit steady state can be attained in finite time interval without exceeding critical parameter limits.