PMSM矢量控制下逆变器母线电流频谱分析

逆变器直流母线电流频谱的准确解析是对电磁干扰进行分析及母线电容选取的重要理论基础。针对永磁同步(PMSM)作为负载时逆变器直流母线电流频谱的数学表达和理论求解方法分析了相电压基波和高次谐波对应的等效阻抗。分析得出:非凸极PMSM各次谐波对应的视在电感相等并且恒定;凸极式PMSM的基波电流可以在直轴和交轴上进行相量分解,其对应电感为直轴和交轴电感,高次谐波对应的电感随着转子的位置变化。理论计算时可以通过忽略高次谐波或取平均电感的方法来进行近似。给出了母线电流频谱计算的方法与过程。仿真和实验都证明了本文给出的计算方法及公式的正确性和有效性。     

某纯电动汽车车内噪声试验分析与识别

纯电动汽车由于内部结构与内燃机汽车存在着明显的区别,其噪声源也有较大差异.文章利用振动噪声频谱分析仪所获得的实验数据,通过频谱分析法对某款纯电动汽车的不同工况下车身内多处测点进行频谱分析,同时结合纯电动汽车主要总成结构的频谱特性,识别出不同工况下的噪声源,并进一步分析了引起噪声的具体原因.这些成果对未来纯电动汽车开发、...     

火电机组工作与备用电源为两电网的厂用电切换

厂用工作电源和备用电源为不同电网时,电源间的相位角是随机变化的,其手动正常切换及事故切换都不能采用同一电网中的切换方式。通过分析厂用电母线电压衰减特点,并结合某电厂探索运用实例,总结出两电网的厂用电切换方式。     

蒙古族水文化的历史记忆及意义分析

蒙古民族长期生活在干旱少雨的蒙古高原上,从事着逐水草而居的游牧生活。由于游牧业对水的过分倚重,使得水在牧民生产、生活中影响深广,形成了许多关于水的独特文化。对蒙古族的水文化进行历史追溯,揭示其形成原因和影响,仍有很强的现实意义。     

气相色谱-质谱法测定水中三氯乙醛

建立吹扫捕集/气相色谱/质谱法测定饮用水源地水中三氯乙醛的方法.通过测定不加碱反应水中原有的三氯甲烷以及加碱以后水中的三氯甲烷含量,间接计算出水中三氯乙醛的含量.该方法检出限为0.1μg/L,回收率介于84％～110％之间,相对标准偏差为2.2％～4.8％,能够满足饮用水源地水中三氯乙醛的分析需要.     

一种12-bit 1MSPs SAR ADC的设计

设计了工作在5 V单电源电压下,典型采样速度为1 MSPs的12位低功耗逐次逼近型模数转换器。设计中D/A转换器采用了加电容分压器的电荷分布式结构,在扩展并行D/A转换器分辨率的同时大大节省了芯片面积,内置的3.3 V参考电压源采用自偏置的供电方式,提高了基准电压的精度,同时也降低了功耗。使用cadence spectre工具进行仿真,后仿结果表明,设计的D/A转换器、3.3 V基准源满足12 bit A/D转换的要求,逐次逼近A/D转换器可以正常工作。     

烟台移动污染源对大气环境质量影响分析

分析了烟台市机动车尾气污染对大气环境的影响.结合市区2条主要干线北马路和南大街的车流量、交通状况和机动车运行状况,分析主要污染物NOx和CO的排放情况;在对烟台市机动车保有量调查的基础上,利用MOBILE排放因子模型预测2010年烟台市机动车尾气排放量.结果表明:烟台市2010年VOC排放量约8.8万t、PM10排放量约1.58万t、NOx排放量约4.7万t,分别比2006年增加约40.9％、20.9％和58％,必须采取科学有效的措施治理和预防机动车尾气对大气环境的影响.     

松华坝水源保护区土地利用/土地覆被变化研究

以松华坝水源保护区为研究对象,通过解译Landsat TM遥感影像得到两期(1992年、2001年)1:10万土地利用图.基于GIS的叠加分析功能,建立了两个时期的土地利用类型转移矩阵.并结合DEM,定量研究了该区域近十年的土地利用/覆被的变化特征.研究结果表明:(1)该水源区土地利用类型以林地为主,其次是草地和耕地,...     

培养基中有机氮源对替考拉宁发酵的影响

替考拉宁是采用放线菌发酵生产的一种重要抗生素,发酵培养基中有机氮源的选择对替考拉宁的产量有较大影响,比较了培养基中分别添加豆饼粉、酵母粉及蛋白胨对替考拉宁发酵单位的影响,结果表明,2％酵母粉的效果最优,其效价比等量豆饼粉提高16％,比等量蛋白胨提高20％.     

Characteristics of strontium isotopes and their implications in the Qixing Cave of Guizhou,China

The strontium isotopic compositions (87Sr/86Sr) of samples including soils, bedrock, soil waters, drip waters and their corresponding speleothems in the Qixing Cave (QXC), Guizhou Province, China, were systemically measured and analyzed. The results indicate that there are significant Sr isotopic differences among samples. The mean 87Sr/86Sr ratios in drip water for the samples 1#, 4# and 9# were 0.709568, 0.709139 and 0.708761, respectively, which possibly result from different flow paths, residence times, and other hydrogeological processes in the unsaturated zone overlying QXC. Meanwhile, levels of 40.8%, 57.6% and 72.4% of Sr in drip waters for 1#, 4# and 9#, respectively, were derived from bedrock dissolution, which was calculated by the mixture model of the two end-members (soil and bedrock). There is, however, no positive correlation between the relative proportion from bedrock dissolution (δ13C value is 1.8‰) and drip water δ13CDIC values. The mean drip water δ13CDIC value in 1# is the heaviest (–4.5‰) with the lowest contribution rate of bedrock dissolution, whereas the value in 9# is the lightest (–9.3‰) with the highest contribution rate of bedrock dissolution. The proportion from host rock dissolution in 4# is higher than that in 1# and lower than that in 9#, while its mean drip water δ13CDIC value (–8.6‰) is higher than that of 9# and lower than that for 1#. This suggests that the prior calcite precipitation (PCP) processes in the unsaturated zone overlying the cave are responsible for the δ13CDIC value differences between different drip waters, and not bedrock dissolution. Furthermore, this study also demonstrates that the 87Sr/86Sr ratios of speleothems in the 1# and 4# mainly reflect the variation in the relative proportions from the soil system (soil water) and bedrock dissolution overlying the cave. It is, therefore, feasible to use the strontium isotopic signals of speleothems as an indicator for soil chemical weathering intensity, and consequently as a monsoon proxy in the study area.