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High performance robust force control of hydraulic load simulator with constant but unknown hydraulic parameters is considered. Incontrast to the linear control based on hydraulic linearization equations, hydraulic inherent nonlinear properties and uncertainties makethe conventional feedback proportional-integral-derivative (PID) control not yield to high performance requirements. Furthermore, thehydraulic system may be subjected to non-smooth and discontinuous nonlinearities due to the directional change of valve opening. In thispaper, based on a nonlinear system model of hydraulic load simulator, a discontinuous projection-based nonlinear adaptive robust backsteppingcontroller is developed with servo valve dynamics. The proposed controller constructs a novel stable adaptive controller andadaptation laws with additional pressure dynamic related unknown parameters, which can compensate for the system nonlinearities anduncertain parameters, meanwhile a well-designed robust controller is also synthesized to dominate the model uncertainties coming fromboth parametric uncertainties and uncertain nonlinearities including unmodeled and ignored system dynamics. The controller theoreticallyguarantee a prescribed transient performance and final tracking accuracy in presence of both parametric uncertainties and uncertainnonlinearities; while achieving asymptotic output tracking in the absence of unstructured uncertainties. The implementation issues arealso discussed for controller simplification. Some comparative results are obtained to verify the high-performance nature of the proposedcontroller.
Creep properties of soft interlayers are key factors associated with the long-term stability of geological bodies. An experimental and theoretical study on the ring shear creep properties of soft interlayers collected from Esheng, Sichuan province, China are performed in this study. Ring shear creep tests of soft interlayers, which are remolded into over-consolidated samples having various water contents and the same initial dry density, are performed in laboratory, to analyze the creep deformation characteristics of samples in detail. The calculated long-term shear strength of samples is close to residual strength. By substituting the dashpot with a new unsteady fractal dashpot, a novel unsteady fractal derivative creep (UFDC) model, which can be defined in series with an improved Maxwell model and an improved viscoplastic model, is proposed based on theory of fractal derivative. The new model can efficiently explain the soft interlayers creep deformation. The results indicate that most model parameters are sensitive to the shear stress. However, at the accelerated creep stage, the fractional order of the second dashpot in the UFDC model has little effect on the fitting of experimental data.
This study proposes a novel five-level three-phase hybrid-clamped converter composed of only six switches and one flying capacitor (FC) per phase. The capacitor-voltage-drift phenomenon of the converter under the classical sinusoidal pulse width modulation (SPWM) strategy is comprehensively analyzed. The average current, which flows into the FC, is a function of power factor and modulation index and does not remain at zero. Thus, a specific modulation strategy based on space vector modulation (SVM) is developed to balance the voltage of DC-link and FCs by injecting a common-mode voltage. This strategy applies the five-segment method to synthesize the voltage vector, such that switching losses are reduced while optional vector sequences are increased. The best vector sequence is then selected on the basis of the minimized cost function to suppress the divergence of the capacitor voltage. This study further proposes a startup method that charges the DC-link and FCs without any additional circuits. Simulation and experimental results verify the validity of the proposed converter, modulation strategy, and precharge method.
The poor energy efficiency is a big issue in the conventional electro-hydraulic proportional valve controlled fast forging system due tothe huge throttling losses and overflow losses. Aimed to address this problem, a new compound control strategy of displacement anddual-pressure was proposed in this study. Firstly, the mathematic model of the main components was built, and the compound controlstrategy was designed depending on the different working conditions. Then, the overall control system was integrated for both downstrokestage and return-stroke stage. The proposed control strategy was tested and evaluated in a 0.6 MN fast forging press. Results indicatedthat the input energy was reduced by 50% and energy loss decreased dramatically while control performance is good. Results alsoshow that control performance and energy saving is significantly affected by the variation of △p and pb. Overall, the proposed new controlstrategy could be used for the fast forging press with high energy efficiency.
This work presents a digital graphic scanning (DGS) method, based on computer scanning graphics, to generate a grinding profile avoiding the difficulties appeared from the complex equations of the contact line. First the enveloping surface between the forming tool (rotor) profile and its corresponding cutting locus was developed, then based on Bresenham algorithm, the best possible pixels of the enveloping surface in the pixel matrix of screen were demonstrated using a specified color. Finally, the grinding profile data of the rotor (forming tool) were collected by scanning the pixel matrix of screen, capturing the coordinates of the indicated color of the best possible pixels. Comparing the analytical gearing envelope method and the DGS method, the feasibility of the DGS method was indicated. The DGS method was shown as a precise, rapid, efficient and stable computing tool to generate a grinding profile. In addition, such an approach can be applied in designing other similarly conjugated products such as gears, perpetual screws and milling cutters.
The metal surface topology contains abundant information related to the health states of the cutting tool as well as the cutting operation. In this paper, we attempt to adopt 2D digital images of the machined metal surface, acquired via non-contact photo-imaging techniques, as the monitoring media. A Wallis filter based dodging algorithm is applied to cure the uneven contrast phenomenon caused by imperfect lighting illumination. 3D digital models were derived and retrieved from the digital image using a wavelet enhanced Shape from shading (SFS) transform. The minimization based SFS is presented to retrieve the 3D digital surface from the milled workpiece. The dual tree complex wavelet transform is adopted to enhance SFS such that the interfering noise can be suppressed. In the end, quantitative surface roughness indicators are utilized to estimate the surface roughness numerically. A milling cutting experiment of aero-material of aluminum alloy 7075 was carried out to verify the effectiveness of the proposed approach. The comparison results demonstrate that the proposed approach was capable of retrieving 3D surfaces of high precision. With the approach, the digital image emerges as a promising vehicle for machining condition monitoring of CNC machines.
Electric load simulator (ELS) is an important equipment to exert aerodynamic load to actuation system according to flight condition. The key issue of ELS is how to eliminate the influence of extra torque caused by actuation system, parametric uncertainties and uncertain nonlinearities. In order to overcome these difficulties, this paper proposes a powerful model-based adaptive robust torque control (ARTC) algorithm which transfers external disturbance elimination problem to a performance-oriented problem under uncertainties and nonlinearities. A discontinuous projection-based online parameter adaptation is employed to reduce the effect of various parameter uncertainties. Instead of discontinuous friction model, a continuous friction model based on smooth shape function is applied for friction compensation. The estimated velocity of actuator is utilized in ARTC controller for eliminating extra torque. The backstepping design via adaptive robust control Lyapunov function is employed to construct ARTC control law for ELS. Extensive comparative results indicate that the proposed ARTC controller is effective to achieve a guaranteed transient as well as final tracking accuracy in the presence of both parametric uncertainties and uncertain nonlinearities.
Wide area protection (WAP) system is a control and protection system based on power grid information through network communication. WAP can determine fault location and clear fault selectively and quickly, then analysis the effect of power system stability after fault components disconnection and take appropriate control measures. WAP consists of master and slave station. With wide area information, WAP can solve the setting and matching difficulty of protective relaying, and can shorter the delay time of back-up protection. WAP also can improve the level of power system security and stability operation, and coordinate protective relaying and stability control. Obtain real-time wide area information reliably and accurately is the key point to build WAP. The reliability of network, synchronization accuracy, and the efficiency of communication protocols are key technologies of WAP. Full use of wide area information to get smarter, more reliable and more adaptable control strategy that coordinated protective relaying and stability control is the core contents of WAP. This paper summarizes the theory and engineering problems countered in the process of WAP research and application, and introduces the solutions or ideas. This paper brings out several urgent problems to be solved in order to promote WAP technology, and gives outlook of key issues in the implementation WAP at smart substation.
To improve our current understanding of tsunami-like solitary waves interacting with a row of vertical slotted piles on a sloping beach, a 3D numerical wave tank based on the CFD tool OpenFOAM® was developed in this study. The Navier-Stokes equations were employed to solve the two-phase incompressible flow, combining with an improved VOF method to track the free surface and a LES model to resolve the turbulence. The numerical model was firstly validated by our laboratory measurements of wave, flow and dynamic pressure around both a row of piles and a single pile on a slope subjected to solitary waves. Subsequently, a series of numerical experiments were conducted to analyze the breaking wave force in view of varying incident wave heights, offshore water depths, spaces between adjacent piles and beach slopes. Finally, a slamming coefficient was discussed to account for the breaking wave force impacting on the piles.