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College English teaching evaluation is an important step to improve the quality of teaching and to promote students' development and assessment of teachers' performance, which is characterized by many factors and multidimensional structure. The current college English teaching evaluation method faces such problems: fuzzy evaluation criteria, subjective judgment and the difficulty to quantify evaluation results. Based on cloud theory, this article will explore college English teaching evaluation, and establish a comprehensive evaluation model based on cloud gravity center by using weight deviation to measure the quality of teaching. This article will also build an inter-relationship mapping between qualitative and quantitative evaluation, which supports the whole process of comprehensive evaluation with the combination of qualitative and quantitative indexes. Finally this article gives an example of specific application of this method.

Aiming at the simulation of the three-phase inverter and SVPWM, the paper introduces their principles. A new method to build SVPWM simulation block in MATLAB/Simulink is proposed. The on-voltage-drop of the power devices is taken into account; the switch and diode are modeled as the connection in series of a resistance and a voltage source in simulation. The simulation and experiment results verify the correctness of simulation models, and show that the on-voltage-drop of the power devices has effects on the phase current and phase/line voltage, especially when the inverter works at a light load state.