This paper presents a new approach to alleviate the harmonics and to enhance the power factor of the ASD （adjustable speed drive）. A conventional ASD with 2-level PWM （pulse width modulation） inverters generate hi...This paper presents a new approach to alleviate the harmonics and to enhance the power factor of the ASD （adjustable speed drive）. A conventional ASD with 2-level PWM （pulse width modulation） inverters generate high dv/dt and high frequency common mode voltages which are harmful for the drive applications. It reduces the motor bearings life and conducted EMI （electro magnetic interference） deteriorates the insulation. In this paper, a diode clamped multilevel （3-level） inverter is used to perform dual task. It generates HF （high frequency） current to be injected at the input of the three-phase front-end rectifier thereby improving the harmonic spectra and the power factor. It also drives the induction motor. The salient feature of this paper is that it does not require separate converters for improving power factor and to drive induction motor. Furthermore, inverter switches operate with ZVS （zero voltage switching）, thus reducing the switching losses substantially, The voltage stress of the switches also has been reduced to half of the conventional 2-level converter. The inverter is operated with SPWM （sinusoidal pulse width modulation） technique. The simulation results for a prototype of 2.2 kW are presented.展开更多
张洪年(2000)考察Cantonese Made Easy(CME)1888和1907两版中的变调现象,发现十数年间,粤语高平变调和高升变调的使用都有相当的增长,特别是高平变调的增长更为显著。本文旨在探讨下面两个问题:(1)CME两书中所反映的增长是否单一现象;(2...张洪年(2000)考察Cantonese Made Easy(CME)1888和1907两版中的变调现象,发现十数年间,粤语高平变调和高升变调的使用都有相当的增长,特别是高平变调的增长更为显著。本文旨在探讨下面两个问题:(1)CME两书中所反映的增长是否单一现象;(2)CME两书之前和之后的变调现象又是怎样。考察的结果印证了张文的观察。此外,根据我们对早期材料的考察,我们推测变调应该在1870年代以前就已产生。假设早期材料所反映的变调增长速度保持不变,我们推测高平变调的扩散比高升变调早结束。这个假设得到早期材料中变调的使用和现代粤语调查结果的支持。展开更多
文摘This paper presents a new approach to alleviate the harmonics and to enhance the power factor of the ASD （adjustable speed drive）. A conventional ASD with 2-level PWM （pulse width modulation） inverters generate high dv/dt and high frequency common mode voltages which are harmful for the drive applications. It reduces the motor bearings life and conducted EMI （electro magnetic interference） deteriorates the insulation. In this paper, a diode clamped multilevel （3-level） inverter is used to perform dual task. It generates HF （high frequency） current to be injected at the input of the three-phase front-end rectifier thereby improving the harmonic spectra and the power factor. It also drives the induction motor. The salient feature of this paper is that it does not require separate converters for improving power factor and to drive induction motor. Furthermore, inverter switches operate with ZVS （zero voltage switching）, thus reducing the switching losses substantially, The voltage stress of the switches also has been reduced to half of the conventional 2-level converter. The inverter is operated with SPWM （sinusoidal pulse width modulation） technique. The simulation results for a prototype of 2.2 kW are presented.
基金香港科技大学研究项目“Cantonese tones at the turns of the 19^th and 20^th centuries：Acoustic and statistical analyses”(DAG06/07.HSS02)的资助
文摘张洪年(2000)考察Cantonese Made Easy(CME)1888和1907两版中的变调现象,发现十数年间,粤语高平变调和高升变调的使用都有相当的增长,特别是高平变调的增长更为显著。本文旨在探讨下面两个问题:(1)CME两书中所反映的增长是否单一现象;(2)CME两书之前和之后的变调现象又是怎样。考察的结果印证了张文的观察。此外,根据我们对早期材料的考察,我们推测变调应该在1870年代以前就已产生。假设早期材料所反映的变调增长速度保持不变,我们推测高平变调的扩散比高升变调早结束。这个假设得到早期材料中变调的使用和现代粤语调查结果的支持。
