H∞ control of an active suspension system

An H_∞ controller for an active suspension system is designed, which has taken the performance of ride comfort and the system robustness into account. Simulation results show that a concentrated weighting of the car body acceleration output, for the frequency where human being are most sensitive to vibration, has been executed by introducing the frequency dependent weighing function, thus the suspension acceleration frequency response characteristic can be improved. It is also pointed out that the designed controller is effective in the system robustness against the fluctuation of parameter of system. Project supported by the Natural Science Foundation of Hunan Province Synopsis of the first author Liu Shaojun, professor, born on Nov. 14, 1955, majoring in automation and mechanical engineering.     

A physically based algorithm for land surface emissivity retrieval from combined mid-infrared and thermal infrared data

This work is concerned with the problem ofL ₂ gain disturbance attenuation for nonlinear systems and nonlinear robust control for power systems. In terms of the recurrence design approach proposed, the nonnegative solution of dissipative inequality and the storage function of nonlinearH _∞ control for a generator excitation system are acquired. From this storage function, the excitation controller is constructed. Moreover, simulation results manifest the effectiveness of this design method.     

State space methods for decentralized H∞ control

This paper presents state space methods for decentralized H_∞ control, which contain two respects: a parametrization approach and an iterative algorithm. For large scale systems withN subsystems, decentralized H_∞ controllers can be derived by a parametrization result for centralized H_∞ controllers and designed by an iterative algorithm with structured constraint to the controllers. Project supported by the National Natural Science Foundation of China Synopsis of the first author Wu Min, professor, born in July, 1963, research interests are in robust control, digital control systems theory, nolinear control systems and industrial process contnol.     

Decentralized H∞ state feedback control for large-scaleinterconnected uncertain systems with multiple delays

Decentralized H∞ control was studied for a class of interconnected uncertain systems with multiple delays in the state and control and time varying but norm-bounded parametric uncertainties. A sufficient condition which makes the closed-loop system decentralized asymptotically stable with H∞ performance was derived based on Lyapunov stability theorem. This condition is expressed as the solvability problem of linear matrix inequalities. The method overcomes the limitations of the existing algebraic Riccati equation method. Finally, a numerical example was given to demonstrate the design procedure for the decentralized H∞ state feedback controller.     

Delay-independent decentralized H ∞ control for multi-channel discrete-time systems with uncertainties

A robust decentralized H∞ control problem was considered for uncertain multi-channel discrete-time systems with time-delay. The uncertainties were assumed to be time-invariant, norm-bounded, and exist in the system, the time-delay and the output matrices. Dynamic output feedback was focused on. A sufficient condition for the multi-channel uncertain discrete time-delay system to be robustly stabilizable with a specified disturbance attenuation level was derived based on the theorem of Lyapunov stability theory. By setting the Lyapunov matrix as block diagonal appropriately according to the desired order of the controller, the problem was reduced to a linear matrix inequality （LMI） which is sufficient to existence condition but much more tractable. An example was given to show the efficiency of this method.     

RobustH ∞ controller design for a class of uncertain systems

TheH ^∞ control problem for a class of systems with time-varying and nonlinear uncertainties is considcred. A new sufficient condition based on LMI is provided to judge their robust stability andL ₂-gain finiteness. Solvability conditions are presented for both state feedback and output feedback cases, which are all reduced to solutions of LMIs. The design procedure is also discussed via LMI approach. Project supported by the National Natural Science Foundation of China (Grant No. 59704004).     

Dynamic extending nonlinear H∞ control and its application to hydraulic turbine governor

There exists a large class of nonlinear systems with uncertainties, such as hydraulic turbine governors, whose robust control problem is hard to solve by means of the existing robust control approaches. For this class of systems, this work presents a dynamic extending H∞ controller via both differential geometry and H∞ theory. Furthermore, based on differential game theory, it has been verified that the proposed control strategy has robustness in the sense that the disturbance can be attenuated effectively because the L2-gain from the disturbance input to the regulation output signal could be reduced to any given level. Thirdly, a robust control strategy for hydraulic turbine governor is designed according to the proposed extending H∞ control method, and has been developed into a real control equipment. Finally the field experiments are carried out which show clearly that the developed control equipment can enhance transient stability of power systems more effectively than the conventional controller.     

A new method of computing multi-component E -pH diagrams

Aqueous E-pH Diagram is an essential tool for analyzing hydrometallurgical and corrosion processes. Due to the requirements for environmental protection and energy saving in recent years, waste water processing and hydrometallurgical process of concentrate have been greatly developed. The construction of E-pH diagrams has turned to multi-component systems. However, there are some limits in plotting such diagrams. There is only one diagram for one multi-component system, which can not reflect the truth of the aqueous reaction. In the paper, a new computation method is proposed to construct E-pH diagrams. Component activity term is used to determine the boundary of stable areas. For the multi-component systems, different atom ratios of elements have been taken into account. M-S-H₂O system is chosen to study since it is of importance in metallurgical solution. Compared with conventional methods, the algorithm is simple and conforms to real conditions. Synopsis of the first author Zhang Chuanfu, professor, born in Feb. 1945. Research division mainly includes three aspects: 1) New methods and fundamental theory on nonferrous metallurgy; 2) Mathematical modelling and computer simulation in metallurgical engineering; 3) Metallurgical resources environment engineering.     

Synthesis of γ-Al2O3 nanoparticles by chemical precipitation method

Highly pure active γ-Al₂O₃ nanoparticles were synthesized from aluminum nitrate and ammonium carbonate with a little surfactant by chemical precipitation method. The factors affecting the synthesis process were studied. The properties of γ-Al₂O₃ nanoparticles were characterized by DTA, XRD, BET, TEM, laser granularity analysis and impurity content analysis. The results show that the amorphous precursor Al(OH)₃ sols are produced by using 0.1 mol/L Al(NO₃)₃ · 9H₂O and 0.16 mol/L (NH₄)₂CO₃ · H₂O reaction solutions, according to the volume ratio 1.33, adding 0.024% (volume fraction) surfactant PEG600, and reacting at 40 °C, 1 000 r/min stirring rate for 15 min. Then, after stabilizing for 24 h, the precursors were extracted and filtrated by vacuum, washed thoroughly with deionized water and dehydrated ethanol, dried in vacuum at 80°C for 8 h, final calcined at 800 °C for 1 h in the air, and high purity active γ-Al₂O₃ nanoparticles can be prepared with cubic in crystal system, O _H ⁷ -FD3M in space group, about 9 nm in crystal grain size, about 20 nm in particle size and uniform size distribution, 131. 35 m²/g in BET specific surface area, 7 – 11 nm in pore diameter, and not lower than 99.93% in purity. Foundation item: Project(03JJY3015) supported by the Natural Science Foundation of Hunan Province     

A new processing method for the <Emphasis Type="Italic">AE</Emphasis> index

In this paper, we introduce an effective processing method to acquire the time derivative of the AE index as a coefficient. Using this coefficient, the AE index can be divided into the four stages: quiet, ascending, descending and active stages. The statistical results show that the ascending and descending stages of the AE index are dominant and occupy two thirds of the whole period. An analysis of the relationship between the occurrence frequencies of the Dst index and AE index in solar cycle 23 shows that the monthly variation of the occurrence frequencies of the ascending stage of AE is closely related to the decrease of the Dst index. Supported by the National Natural Science Foundation of China (Grant Nos. 40704031, 40536030)     

Synthesis and coloring properties of Cd（S1-xSex） pigments by precipitate-hydrothermal method

Cd（S1-xSex） pigments （red to yellow） were synthesized by precipitate-hydrothermal method. The structure, morphology and hue of the powder were characterized by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDAX） and CIE chromaticity. The optimum synthesis conditions were obtained and reaction mechanism was further analyzed as well. The results show that molar ratio of S to Se, pH value and hydrothermal reaction conditions have great effects on the hues of the pigments. Pigments with vivid hues are obtained under the conditions that pH value is about 13.0, hydrothermal reaction condition is at 140 ℃ for 4 h or at 160 ℃ for 6 h. The reaction mechanism is that Se^2- of Cd（S1-xSex） substitutes S^2- of CdS and then forms a continuous solid solution.     

Single crystal β-Ga2O3: Cr grown by floating zone technique and its optical properties

β-Ga2O3 Cr single crystals were grown by floating zone technique. Absorption spectra and fluorescence spectra were measured at room temperature. The values of field splitting parameter Dq and Racah parameter B were obtained by the peak values of absorption spectra. The value 10Dq/B=23.14 manifests that in -Ga2O3 crystals Cr3 ions are influenced by low energy crystal field. After high temperature annealing in air, the Cr3 intrinsic emission was enhanced and the green luminescence disappeared. The strong and broad 691 nm emission was obtained at 420 nm excitation due to the electron transition occurred from 4T2 to 4A2. The studies manifest that the β-Ga2O3 crystals have the potential application for tunable laser.