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Triet Hung Ho,Kyoung Kwan Ahn 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8
A newly assisted hydraulic circuit is proposed for a hydraulic transformer to improve energy saving potential of the system. The use of three directional controlled valves with the designed controller forces the transformer and the cylinder work in proper conditions, which contributes to improve energy utilization of the system. A model of hydraulic transformer including energy losses of the pump/motor is used to estimate energy consumption in different situations. A switching method based on desired load is also designed to select a feasible operating mode of the system. Simulation results indicate that saving energy is significantly improved by the proposed circuit.
Triet Nguyen-Van 제어·로봇·시스템학회 2018 International Journal of Control, Automation, and Vol.16 No.2
A new observer based sampled-data feedback control is proposed for a class of scalar nonlinear affine systems, where the control distribution is constant, in the presence of noise. The discrete-time states are estimated by a nonlinear state observer, and used for designing the sampled-data control. The discrete-time model used for controller and state observer design is derived using continualizated discretization method. This discretization method is based on the new concept of continualization of discrete-time models, and is applicable to any system whose Jacobian matrix is defined. In this work, it is shown that for the system without the presence of noise, the proposed sampled-data control preserves the equilibria and dynamics of the desired system, while the conventional control, which is based on forward difference method, does not. Simulations are carried out for the scalar Riccati system with the presence of noise to demonstrate the better performances of the proposed method not only in sampled-data control design, but also in system states estimation than the conventional method for both high and low sampling frequencies.
Speed Control of a Hydraulic Pressure Coupling Drive Using an Adaptive Fuzzy Sliding-Mode Control
Ho, Triet Hung,Ahn, Kyoung Kwan IEEE 2012 IEEE/ASME transactions on mechatronics Vol.17 No.5
<P>In this paper, an adaptive fuzzy sliding-mode control (AFSMC) was proposed for speed control of a hydraulic pressure coupling drive. The AFSMC combined a direct adaptive fuzzy scheme and a fuzzy sliding scheme in a new structure to reduce the tracking error and the chattering of the control effort. The input nonlinearity of the secondary unit, the input dead zone, was taken into account during the speed controller synthesis and analysis of the stability of the closed-loop system. The stability of a system was proven from Lyapunov's sense. Experiments were performed with different controllers, the AFSMC, the traditional sliding-mode control, and the PID controllers, and under different operating conditions. Then, the experimental results were brought into comparison to evaluate the effectiveness of the AFSMC controller from the viewpoints of stability, performance, and robustness of the closed-loop system.</P>
Ho Triet Hung,Kyoung Kwan 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10
A hydraulic cylinder drive using a hydraulic transformer, which is considered as secondary controlled unit, is studied here. Using hydraulic transformer for driving a hydraulic cylinder should avoid energy loss via controlled valves and get benefit from recovery of the load potential. Position control, an important issue of the cylinder control is investigated in this paper. To obtain robust position control in spite of external load disturbance and variation of parameters in the system, a two degree of freedom robust controller based on disturbance observer is designed. he controller includes a mixed ?- sensitivity H∞ controller and a high order disturbance observer. Weights for controller synthesis and filter in the disturbance observer are fixed in their structure but vary in values of the coefficients. Genetic algorithm is used to tune parameters of the weights and time constants of the filter. In this manner, a controller with its structure based on robust analysis and parameters depended on performance of nominal plant is design. Simulation results indicate that the system guarantees the robustness with external load disturbance, variation in parameters and sensor noise.
Minh Triet, Nguyen,Thai Duy, Le,Hwang, Byeong-Ung,Hanif, Adeela,Siddiqui, Saqib,Park, Kyung-Ho,Cho, Chu-Young,Lee, Nae-Eung American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.36
<P>A Schottky diode based on a heterojunction of three-dimensional (3D) nanohybrid materials, formed by hybridizing reduced graphene oxide (RGO) with epitaxial vertical zinc oxide nanorods (ZnO NRs) and Al0.27GaN0.73(similar to 25 nm)/GaN is presented as a new class of high-performance chemical sensors. The RGO nanosheet layer coated on the ZnO NRs enables the formation of a direct Schottky contact with the AlGaN layer. The sensing results of the Schottky diode with respect to NO2, SO2, and HCHO gases exhibit high sensitivity (0.88-1.88 ppm(-1)), fast response (similar to 2 min), and good reproducibility down concentration levels at room temperature. The sensing mechanism of the Schottky diode can be explained by modulation of the reverse saturation current due to the change in thermionic emission carrier transport caused by ultrasensitive changes in the Schottky barrier of a van der Waals heterostructure between RGO and AlGaN layers upon interaction with gas molecules. Advances in the design of a Schottky diode gas sensor based on the heterojunction of high-mobility two-dimensional electron gas channel and highly responsive 3D-engineered sensing nanomaterials have potential not only for the enhancement of sensitivity and selectivity but also for improving operation capability at room temperature.</P>
Ho, Triet Hung,Ahn, Kyoung-Kwan 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.5
A new hydraulic closed-loop hydrostatic transmission (HST) energy-saving system is proposed in this paper. The system improves the efficiency of the primary power source. Furthermore, the system is energy regenerative, highly efficient even under partial load conditions. It can work in either a flow or pressure coupling configuration, allowing it to avoid the disadvantages of each configuration. A hydraulic accumulator, the key component of the energy regenerative modality, can be decoupled from or coupled to the HST circuit to improve the efficiency of the system in low-speed, high-torque situations. The accumulator is used in a novel way to recover the kinetic energy without reversion of fluid flow. Both variable displacement hydraulic pump /motors are used when the system operates in the flow coupling configuration so as to enable it to meet the difficult requirements of some industrial and mobile applications. Modeling and a simulation were undertaken with regard to testing the primary energy sources in the two configurations and recovering the energy potential of the system. The results indicated that the low efficiency of traditional HSTs under partial load conditions can be improved by utilizing the pressure coupling configuration. The round-trip efficiency of the system in the energy recovery testing varied from 32% to 66% when the losses of the load were taken into account.