No abstract

Abstract-In this paper, a modified direct torque control (DTC) for permanent magnet synchronous machine is proposed, which enables important torque and flux ripple reduction by using voltage vectors with variable amplitude and angle. Conventional DTC presents some drawbacks, including large torque ripple, variable switching frequency and acoustic noise. The reason lies in that t h e switching table is composed of a limited number of discrete voltage vectors with fixed amplitude and position. Moreover, the selected vector will work during the whole sampling period, a n d hence their effects on torque and flux may usually be too large or too small. In the proposed DTC, the amplitudes of torque and flux errors are differentiated and they are employed to regulate the amplitude and position of the output voltage vectors on-line, which would finally be synthesized by space vector modulation (SVM). Two simple formulas are developed to derive the amplitude and position of the commanding voltage vectors from the errors of torque and flux. Conventional switching table and hysteresis controllers are eliminated and fixed switching frequency is obtained with the help of SVM. Stator flux is estimated from an improved voltage model, which is based on a low-pass filter with compensations of the amplitude and phase. The proposed DTC exhibits excellent dynamic performance and significant torque ripple reduction at steady state, which are validated by the presented simulation and experimental results.

No abstract

Single-sided linear induction motors (SLIMs) have lately been applied in transportation system traction drives, especially in the intermediate speed range. They have merits such as the ability to exert thrust on the secondary without mechanical contact, high acceleration or deceleration, less wheel wear, small turning circle radius and flexible road line. The theory of operation for these machines can be directly derived from rotary induction motors, but several issues involving the transversal edge and the longitudinal end effects, and half-filled slots at the primary ends, need to be investigated. In this paper, a T model equivalent circuit is proposed which is based on onedimensional magnetic equations of the air-gap, where half-filled slots are considered by an equivalent pole number. Then, it deduces two-axis equivalent circuits to study the SLIM dynamic performance. The theoretical analyses have been validated by experimental results on SLIM prototypes.

Hard carbon (HC) is one of the most promising anode materials for sodium-ion batteries (SIBs) due to its suitable potential and high reversible capacity. At the same time, the correlation between carbon local structure and sodium-ion storage behavior is not clearly understood. In this paper, the two series of HC materials with perfect spherical morphology and tailored microstructures were designed and successfully produced using resorcinol formaldehyde (RF) resin as precursor. Via hydrothermal self-assembly and controlled pyrolysis, RF is a flexible precursor for high-purity carbon with a wide range of local-structure variation. Using these processes, one series of five representative RF-based HC nanospheres with varying degrees of graphitization were obtained from an RF precursor at different carbonization temperatures. The other series of HC materials with various microscopic carbon layer lengths and shapes was achieved by carbonizing five RF precursors with different cross-linking degrees at a single carbonization condition (1300 °C and 2 h). On the basis of the microstructures, unique electrochemical characteristics, and atomic pair distribution function (PDF) analyses, we proposed a new model of “three-phase” structural for HC materials and found triregion Na-ion storage behavior: chemi-/physisorption, intercalation between carbon layers, and pore-filling, derived from the HC phases, respectively. These results enable new understanding and insight into the sodium storage mechanism in HC materials and improve the potential for carbon-based SIB anodes.

No abstract

No abstract

High valence Mo-doped Na3−5xV2−xMox(PO4)3/C (0 < x < 0.04) has been investigated to promote Na ion diffusion.