Considering only about one third of the world's energy consumption is effectively utilized for functional uses, and the remaining is dissipated as waste heat, thermoelectric (TE) materials, which offer a direct and clean thermal-to-electric conversion pathway, have generated a tremendous worldwide interest. The last two decades have witnessed a remarkable development in TE materials. This Review summarizes the efforts devoted to the study of non-equilibrium synthesis of TE materials with multi-scale structures, their transport behavior, and areas of applications. Studies that work towards the ultimate goal of developing highly efficient TE materials possessing multi-scale architectures are highlighted, encompassing the optimization of TE performance via engineering the structures with different dimensional aspects spanning from the atomic and molecular scales, to nanometer sizes, and to the mesoscale. In consideration of the practical applications of high-performance TE materials, the non-equilibrium approaches offer a fast and controllable fabrication of multi-scale microstructures, and their scale up to industrial-size manufacturing is emphasized here. Finally, the design of two integrated power generating TE systems are described-a solar thermoelectric-photovoltaic hybrid system and a vehicle waste heat harvesting system-that represent perhaps the most important applications of thermoelectricity in the energy conversion area.
To overcome inferior rate capability and cycle stability of MnO-based materials as a lithium-ion battery anode associated with the pulverization and gradual aggregation during the conversion process, we constructed robust mesoporous N-doped carbon (N-C) protected MnO nanoparticles on reduced graphene oxide (rGO) (MnO@N-C/rGO) by a simple top-down incorporation strategy. Such dual carbon protection endows MnO@N-C/rGO with excellent structural stability and enhanced charge transfer kinetics. At 100 mA g, it exhibits superior rate capability as high as 864.7 mAh g, undergoing the deep charge/discharge for 70 cycles and outstanding cyclic stability (after 1300 cyclic tests at 2000 mA g; 425.0 mAh g remains, accompanying merely 0.004% capacity decay per cycle). This facile method provides a novel strategy for synthesis of porous electrodes by making use of highly insulating materials.
This paper presents a multi-rate fractional-order repetitive control (MRFORC) scheme for three-phase shunt active power filter (APF). The proposed APF control scheme includes an inner proportional-integral (PI) control loop with a sampling rate identical to switching frequency and an external plug-in RC loop with a reduced sampling rate. The MRFORC loop is implemented in dq-frame with interleaving for the reduction of computational burden in each control cycle. Moreover, in order to deal with the harmonics in the presence of wide grid frequency variations, FORC, which replaces the fractional-order elements with the Lagrange-interpolation based finite impulse response (FIR) filter, is adopted instead of the conventional RC. The synthesis, stability analysis and parameters tuning criteria of the MRFORC system are derived in detail. A step by step design example of the proposed controller is also given in the paper. Finally, experiments are performed to validate the feasibility and effectiveness of the proposed scheme.
This study presents finite control set model predictive control (FCS-MPC) methods to eliminate leakage current for a three-level T-type transformerless photovoltaic (PV) inverter without any modification on topology or any hardware changes. The proposed FCS-MPC methods are capable of eliminating the leakage current in the transformerless PV system by applying the defined candidate voltage vector (VV) combinations with only six medium and one zero VVs (6MV1Z) or three large and three small VVs, which generate constant common-mode voltage to perform the optimisation in every control period. With fewer VVs used for the optimisation, the computational burden can be significantly reduced. Furthermore, comparative analysis is performed to show that among these proposed methods, the 6MV1Z method can achieve satisfactory performances in both grid current tracking and neutral point potentials balance control even with less number of candidate VVs, which exhibits the FCS-MPC as an alternative control strategy to be used in the grid-connected transformerless PV system. Finally, experiments are performed to validate the analysis and the effectiveness of the proposed methods.
This paper proposes a novel model-based estimator for distributed electrochemical states of lithium-ion batteries. Through systematic simplifications of a high-order electrochemical-thermal coupled model consisting of partial differential-algebraic equations, a reduced-order battery model is obtained that features an equivalent circuit form and captures local state dynamics of interest inside the battery. Based on the physics-based equivalent circuit model, a constrained ensemble Kalman filter (EnKF) is pertinently designed to detect internal variables such as the local concentrations, overpotential, and molar flux. To address slow convergence issues due to weak observability of the battery model, the lithium ions mass conservation is judiciously considered as constraints in the estimation algorithm. The estimation performance is comprehensively examined under a wide operating range. It demonstrates that the proposed EnKFbased nonlinear estimator is able to accurately reproduce the physically-meaningful state variables at a low computational cost and is significantly superior to its prevalent benchmarks for online applications. Index Terms-Lithium-ion batteries, ensemble Kalman filter, physics-based equivalent circuit model, state estimation. I. INTRODUCTION D UE to the distinct advantages of high power and energy densities, low self-discharge rate, favorable modularity, and recent fast decline in cost, lithium-ion (Li-ion) batteries Manuscript
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