Showing papers by "Kang-Zhi Liu published in 2022"

A High Performance Thermal Expansion Offset Composite Cathode for it - Sofcs

Abstract: The introduction of negative thermal expansion (NTE) materials into cathodes with large thermal expansion coefficient (TEC) can not only reduce the mismatch of thermal expansion behavior between solid oxide fuel...

柴达木盆地新生代地层年代框架与沉积-构造演化

Abstract:

The Qaidam Basin hosts thick Cenozoic strata with an uninterrupted depositional time frame from early Cenozoic to the Quaternary, where remarkable number of mammalian fossils were discovered. These properties of the Cenozoic strata provide a unique chance to establish the basin-wide chronological framework by using palaeomagnetistratigraphy and biostratigraphy. Armed with the chronological framework, the sedimentary evolution and structural deformation of the Qaidam Basin and its adjacent region can be reconstructed to reveal the deformational processes and dynamic mechanism of the Tibetan Plateau expansion during the Cenozoic. According to the previous studies, the Cenozoic strata preserved in the Qaidam Basin, have been subdivided into seven primary progressively younger stratigraphic units: The Lulehe, Xia Ganchaigou, Shang Ganchaigou, Xia Youshashan, Shang Youshashan, Shizigou, and Qigequan formations. Despite the long study history of the Qaidam Basin, they are still controversial questions of basin-wide Cenozoic stratigraphic unit correlations and the time of formation of the Qaidam Basin. On the basis of the field observations, this paper summarizes relatively long magnetostratigraphic sections (thickness ≥ 4500 m), such as the Huatugou, Lulehe, Honggou, Dahonggou, and Huaitoutala magnetostratigraphies in the Qaidam Basin from the west to east. The magnetostratigraphies/refined magnetostratigraphies dated the Lulehe Fm. to span from 31 to 23.7 Ma, Xia Ganchaigou Fm. from 23.7 to 17 Ma, Shang Ganchaigou Fm. from ca. 17 to ca. 12 Ma, Xia Youshashan Fm. from ca. 12 to ca. 10 Ma, Shang Youshashan Fm. from ca. 10 to ca. 7 Ma, and Shizigou Fm. is younger than ca. 7 Ma. Our interpretations suggest that the westernmost portion of the Qaidam Basin is probably formed in the Eocene, and the middle part of the basin began to accumulate sediments since the Oligocene (ca. 31–26 Ma). In the eastern part of the Qaidam Basin, Cenozoic subsidence was likely to initiate during the early to middle Miocene (ca. 16 Ma). Although onset of the Qaidam Basin expanded between Eocene and early Miocene from the west to east, significant portion of the basin seems to subsided after the Oligocene. This phenomenon indicates that the most profound episode of the tectonic deformation around the Qaidam Basin has occurred since the Oligocene. In the Qaidam Basin, the sediment accumulation rates over the basin had increased significantly during the middle Miocene (ca. 15 Ma). We rule out climate changes to drive the rapid middle-Miocene erosion and accumulation rates because of stepwise aridification of the northeastern Tibetan Plateau during the Neogene time interval. Thus, the increased accumulation rates imply direct relation to upward growth of the mountain ranges around the Qaidam Basin. There is abundant evidence demonstrates occurrences of the Oligocene (ca. 30 Ma) and middle-Miocene (10–15 Ma) stages of crustal shortening in many localities in and around the Tibetan Plateau, suggesting that both stages the deformation in ca. 30 and 10–15 Ma are synchronous and large-scale tectonic activation events. The regional synchronicity of plateau-wide deformational phases indicates significant changes in the dynamics of the plateau growths during the Oligocene and middle-Miocene. We suggest that ca. 30 and 10–15 Ma upward and outward growths of the Tibetan Plateau are likely to be driven by removal of mantel lithosphere beneath different portions of the Tibetan Plateau. Following the continuous convergence between the Indian and Eurasian continents, the lithosphere of the Tibetan Plateau was thickened. Removal of thickened, dense lithosphere could cause the uplift of the Tibetan Plateau, and then applied exert compressive stresses to the relatively lower relief region to trigger pulsed outward growth of the plateau to its recent margins.

A Coordinated Control Method for Integrated System of Wind Farm and Hydrogen Production: Kinetic Energy and Virtual Discharge Controls

Abstract: This paper proposes a novel coordinated control method of wind farms (WFs) and hydrogen production systems (HPSs). In a grid-connected system where the WF and the HPS are connected to the grid, the WF can supply the power to the grid, producing hydrogen in the HPS. Moreover, the output fluctuation of the WF can be mitigated when the HPS produces hydrogen from the output surplus. The purpose of the grid-connected system is to smooth the WF output fluctuation sufficiently, produce hydrogen constantly, and maintain a high capacity factor in the HPS. The proposed coordinated control achieves the mitigation of the WF output and the high capacity factor in the HPS. The key ideas are 1) utilizing the kinetic energy of wind generators and 2) virtual discharge of the HPS. The fluctuation components of the WF output are compensated by both the WF and the HPS. The proposed coordinated controller enables us to produce hydrogen constantly in the HPS with a low-rated power. The advantage of the proposed coordinated control is verified by a comparative analysis with conventional methods through simulations using real wind data.

Optimal control input for discrete-time networked control systems with data dropout

Abstract: These days, networked control systems (NCSs) in which data is transmitted via communication have been actively studied for many potential applications. In an NCS, data dropout degrades control performance depending on network conditions. For an NCS with data dropout, the authors propose a model-predictive-control-based input optimisation, representing data dropout as both a Bernoulli model and a finite-order Markov chain. Using the proposed NCS data dropout model, the authors derive an optimal input that provides the estimated error between the expected state of the plant and a given reference. The proposed control problem is formulated as its equivalent quadratic programming, as executed at each online sampling. The authors also demonstrate simulations and experiments to show the effectiveness of the proposed method.

Optimal Hydrogen Production and High Efficient Output Smoothing in Wind Farm

Abstract: This paper proposes a novel optimal control method for integrated systems of Wind farms (WFs) and hydrogen production systems (HPSs). Green hydrogen production via renewable power generation (RPG), such as wind power generation, is a promising technology to overcome environmental problems. RPG has the potential to become more widespread if we can produce hydrogen in an HPS using the output fluctuation and the output surplus of RPG, which cause power outages due to supply-demand imbalances. The proposed optimal control maximizes the capacity factor of HPS while producing hydrogen constantly and satisfying the technical requirement related to the output fluctuation of the WF. The proposed control is also easy to implement and needs no WF output forecast. We demonstrate the effectiveness of the proposed optimal control through simulated comparative analysis with conventional methods.

Decentralized resolution of finite-state, non-convex, and aggregative optimal control problems

Abstract: —A general class of large-scale, nonconvex, and non- smooth optimization problems is introduced. It has the form of a multi-agent problem, where the agents interact through an aggregative term. A convex relaxation of the problem is provided together with an estimate of the relaxation gap. A numerical method, called stochastic Frank-Wolfe algorithm, is presented. The method allows to find approximate solutions of the original problem in a decomposed fashion. The convergence of the method is guaranteed from a theoretical point of view. An aggregative deterministic optimal control problem is formulated, with discrete state-space and discrete time. It is shown that the stochastic Frank-Wolfe algorithm can be applied to the optimal control problem; in particular, it amounts to solve at each iteration a series of small-scale optimal control problems, corresponding to each agent. These sub-problems are solved by dynamic programming. Numerical results are presented, for a toy model of the charging management of a battery fleet.

Passivity-Based Robust Controller Design for Load-Independent Voltage Source Inverters

Abstract: We propose a novel voltage controller design procedure for voltage source inverters (VSIs) with uncertain loads, focusing on the passivity of loads. VSIs have been widely used in many applications. A VSI must regulate the load voltage to its sinusoidal reference quickly and accurately without distortion. It is essential to design a voltage controller that takes into account various load conditions since it is rarely known in advance what types of loads are connected to the VSI. In particular, it is challenging to suppress the voltage harmonic distortion caused by a nonlinear load, such as a diode rectifier, while achieving fast-tracking and zero steady-state error. A controller designed by the proposed procedure guarantees robust stability of the VSI independent of the load type and value. Namely, no information about uncertainties of load is needed to stabilize the VSI. Moreover, the proposed procedure realizes zero-steady state error, fast-tracking, and low distortion. We demonstrate the effectiveness of the proposed controller through comparative analysis with the proportional resonant (PR) and conventional robust controllers via simulations and experiments.

Disturbance rejection of T–S fuzzy systems: a membership function-dependent EID method

Abstract: The disturbance rejection problem of T–S fuzzy systems is concerned. Since the T–S fuzzy system is characterised by its membership function, less conservative stabilisation conditions can be derived from membership function-dependent Lyapunov function which contributes to the improvement of disturbance rejection performance. Specifically, we utilise a configuration composed of a membership function-dependent state observer for the state estimation, a membership function-dependent equivalent-input-disturbance estimator for the estimation and compensation of disturbance and an internal model for the reference tracking. It is revealed that this membership function-dependent Lyapunov function naturally leads to control gains switching in accordance with the derivative signs of the normalised premise variables. The switching rules and the design conditions for all control gains are obtained explicitly. In particular, the free-weighting-matrix approach is used to lessen the conservatism in the stability condition. Moreover, a concrete procedure for the controller design including the switching rule is given. Finally, the developed method is tested via simulations. The advantage of the membership function-dependent equivalent-input-disturbance method is validated by comparing with conventional methods.

Error-Driven-Based Performance Analysis of Nonlinear Equivalent-Input-Disturbance Approaches*

Abstract: Disturbances are inevitable in control practice. Many methods have been reported for disturbance rejection. Among them, equivalent-input-disturbance (EID) approach is effective for both matched and mismatched disturbances. However, since the disturbances are usually unknown, conventional methods cannot be used to analyze the control performance of disturbance rejection, especially the dynamic performance. In this paper, by treating the Luenberger observer as the role of an ideal system, an auxiliary variable, i.e., the output error betwween the disturbed system and the ideal system, is introduced to aid the disturbance-rejection performance analysis of EID approaches. The relation between the control performance and the output error are revealed. Then, a nonlinear EID estimator is constructed to speed up the disturbance-rejection control. The finite-time dynamic performance and uniformly ultimately bounded steady-state performance are guaranteed. Further, a design algorithm is developed for the NEID-based closed-loop control system. Finally, by comparing with a conventional linear EID-based method, simulation results illustrate the validity and superiority of the developed method.

Inverse Polarity Resonant Switched-Capacitor Converter with ZVS Operation and Full-range Regulation

Abstract: A new full-range regulation method for inverse polarity resonant switched-capacitor converter is proposed under all load conditions. The converter with fixed on-time pulse frequency modulation is highlighted as an example to implement the proposed method, which features the benefits of full-range voltage regulation, ZVS turn-on for switches and ZCS turn-off for diodes. Experimental results are presented to support the proposed full-range regulation method.

Broadband light management in hydrogel glass for energy efficient windows

Abstract: Windows are critically important components in building envelopes that have a significant effect on the integral energy budget. For energy saving, here we propose a novel design of hydrogel-glass which consists of a layer of hydrogel and a layer of normal glass. Compared with traditional glass, the hydrogel-glass possesses a higher level of visible light transmission, stronger near-infrared light blocking, and higher mid-infrared thermal emittance. With these properties, hydrogel-glass based windows can enhance indoor illumination and reduce the temperature, reducing energy use for both lighting and cooling. Energy savings ranging from 2.37 to 10.45 MJ/m2 per year can be achieved for typical school buildings located in different cities around the world according to our simulations. With broadband light management covering the visible and thermal infrared regions of the spectrum, hydrogel-glass shows great potential for application in energy-saving windows.