Improving Non-English-Majored College Students' Writing Skills: Combining a Know-Want-Learn Plus Model of Meta-Cognitive Writing Strategy Instruction and Internet-Based Language Laboratory Support

Abstract This paper reviewed a one-term experiment on integrating internet-based language laboratory (IBLL) in teaching writings kills with the know-want-learn (KWL) plus model to second-year nonEnglish-majored college students from Yangtze University. Subjects in this study consisted of 92 non-English-majored college students in the control group (CG) and 91 non-English-majored college students in the experimental group (EG). The results showed that 1) compared with a teacher-dominated approach for CG, internet-based language laboratory with KWL plus model of meta-cognitive writing strategy instruction for EG did a better job in enhancing students' writing skills; 2) there were significant differences between males in CG and EG, and females in CG and EG; 3) students in EG held the positive response for the combined instruction

Analysis of Inertia Characteristics of Direct-Drive Permanent-Magnet Synchronous Generator in Micro-Grid

Micro-grid has received extensive attention as an effective way to absorb new energy. Compared to large power systems, the micro-grid system consisting of power electronics is relatively weak due to the lack of support for synchronous machines. In this paper, the direct-drive wind turbine (WT) is connected to the low-inertia micro-grid as the research background. Based on the virtual inertia control of the WT, the inertia source and the physical mechanism of the WT connected to the micro-grid system are studied. The inertia characteristics of the rotor of the WT on the electromechanical time-scale, the DC side capacitor on the DC voltage time-scale, and the simulated grid under the droop control are analyzed. The research results show that under the control of the system, the inertia of the system is derived from the WT, DC capacitor, and the micro-grid simulated by droop control converter. The equivalent inertia of each link is determined by the control parameters, steady-state operating point, and structural parameters. The resulting inertia characteristics will have frequency domain characteristics under control. Finally, the correctness of the system inertia analysis conclusion is verified by simulation and experiment

Modeling and Mechanism Investigation of Inertia and Damping Issues for Grid-Tied PV Generation Systems with Droop Control

Inertia effect and damping capacity, which are the basic characteristics of traditional power systems, are critical to grid frequency stability. However, the inertia and damping characteristics of grid-tied photovoltaic generation systems (GPVGS), which may affect the frequency stability of the grid with high proportional GPVGS, are not yet clear. Therefore, this paper takes the GPVGS based on droop control as the research object. Focusing on the DC voltage control (DVC) timescale dynamics, the mathematical model of the GPVGS is firstly established. Secondly, the electrical torque analysis method is used to analyze the influence law of inertia, damping and synchronization characteristics from the physical mechanism perspective. The research finds that the equivalent inertia, damping and synchronization coefficient of the system are determined by the control parameters, structural parameters and steady-state operating point parameters. Changing the control parameters is the simplest and most flexible way to influence the inertia, damping and synchronization ability of the system. The system inertia is influenced by the DC voltage outer loop proportional coefficient Kp and enhanced with the increase of Kp. The damping characteristic of the system is affected by the droop coefficient Dp and weakened with the increase of Dp. The synchronization effect is only controlled by DC voltage outer loop integral coefficient Ki and enhanced with the increase of Ki. In addition, the system dynamic is also affected by the structural parameters such as line impedance X, DC bus capacitance C, and steady-state operating point parameters such as the AC or DC bus voltage level of the system and steady-state operating power (power angle). Finally, the correctness of the above analysis are verified by the simulation and experimental results