Bussiness ManagementMBAstrategyHuman ResourceMarketingHospitalityE-commerceInternational Tradingproject managementmedia managementLogisticsFinanceAccountingadvertisingLawBusiness LawEducationEconomicsBusiness Reportbusiness planresearch proposal
英语论文题目英语教学英语论文商务英语英语论文格式商务英语翻译广告英语商务英语商务英语教学英语翻译论文英美文学英语语言学文化交流中西方文化差异英语论文范文英语论文开题报告初中英语教学英语论文文献综述英语论文参考文献
ResumeRecommendation LetterMotivation LetterPSapplication letterMBA essayBusiness Letteradmission letter Offer letter
澳大利亚论文英国论文加拿大论文芬兰论文瑞典论文澳洲论文新西兰论文法国论文香港论文挪威论文美国论文泰国论文马来西亚论文台湾论文新加坡论文荷兰论文南非论文西班牙论文爱尔兰论文
小学英语教学初中英语教学英语语法高中英语教学大学英语教学听力口语英语阅读英语词汇学英语素质教育英语教育毕业英语教学法
英语论文开题报告英语毕业论文写作指导英语论文写作笔记handbook英语论文提纲英语论文参考文献英语论文文献综述Research Proposal代写留学论文代写留学作业代写Essay论文英语摘要英语论文任务书英语论文格式专业名词turnitin抄袭检查
temcet听力雅思考试托福考试GMATGRE职称英语理工卫生职称英语综合职称英语职称英语
经贸英语论文题目旅游英语论文题目大学英语论文题目中学英语论文题目小学英语论文题目英语文学论文题目英语教学论文题目英语语言学论文题目委婉语论文题目商务英语论文题目最新英语论文题目英语翻译论文题目英语跨文化论文题目
日本文学日本语言学商务日语日本历史日本经济怎样写日语论文日语论文写作格式日语教学日本社会文化日语开题报告日语论文选题
职称英语理工完形填空历年试题模拟试题补全短文概括大意词汇指导阅读理解例题习题卫生职称英语词汇指导完形填空概括大意历年试题阅读理解补全短文模拟试题例题习题综合职称英语完形填空历年试题模拟试题例题习题词汇指导阅读理解补全短文概括大意
论文作者:留学生论文论文属性:短文 essay登出时间:2011-04-19编辑:点击率:21012
论文字数:5901论文编号:org201104191725059753语种:中文 Chinese地区:中国价格:免费论文
关键词:Supply HarmonicsElectricity sinusoidal voltagesvoltages
harmonics on the supply and load sides, as shown in Figure 7.6. This could be beneficial
despite the considerable extra cost of the transformers.
i A
Id
Load
Vd
Vd /2
Vd /2
Fig. 7.6 Series 12-pulse system
Instead of connecting the two converter bridges in series, they could also be connected in
parallel to give 12-pulse operation. A parallel 12-pulse arrangement is shown in Figure 7.7.
Parallel connections require special care to ensure adequate balance between the currents
drawn by each bridge. Secondary leakage reactances must be carefully matched and extra
reactors are needed on the DC side to absorb the instantaneous differences between the two
DC voltage waveforms.
When using a 12-pulse system, the 5th and 7th harmonics disappear from line current
waveforms (Figure 7.8) leaving the 11th as the first to appear.
Only harmonics of the order 12k ±1, where k = 1, 2, 3, 4, etc. will be present in the supply
current waveform.
S7: Supply Harmonics
127 EEE8044: Fundamentals
i A Id
Load
Id /2
Id /2
Vd
Vd
Vd
Fig. 7.7 Parallel 12-pulse system
iA
vd
30°
Fig. 7.8 12-pulse current and voltage waveforms
S7: Supply Harmonics
128 EEE8044: Fundamentals
Similarly, a 24-pulse system is produced by connecting two 12-pulse circuits with a 15°
phase shift. Figure 7.9 shows one such system in which the two 12-pulse circuits are
connected in parallel to produce the required 24-pulse system. The 11th and 13th harmonics
now disappear from the supply current waveform leaving the 23rd as the first to appear.
Only harmonics of the order 24k ±1, where k = 1, 2, 3, 4, etc. will be present in a 24-pulse
system.
Id
Id /2 Vd
+ 7.5 deg. Id /2
- 7.5 deg.
Fig. 7.9 24-pulse system
Exercise 7.4
If you were the site engineer at the site described in Exercise 7.3 what would you do to
reduce the levels of harmonic distortion?
Turn to the end of the booklet for the answer to the exercise
S7: Supply Harmonics
129 EEE8044: Fundamentals
7.6.4 Sinusoidal current converters
The use of sinusoidal current converters instead of normal thyristor or diode bridge circuits
will of course reduce the harmonic problem by eliminating these at source. These employ
fast IGBT (Insulated Gate Bipolar Transistors) that allow high switching frequencies to be
used producing a near sinusoidal supply current waveform, as described in Section 8.
7.6.4 Active filters
The same power circuit may also be used as an active filter to prevent harmonic currents
from entering the supply system or to correct the systems’ voltage distortion. Active filters
may be classified as parallel active filters or series active filters according to circuit
configuration.
Parallel active filters
This is the most widely used type of active filter. As the name implies, it is connected in
parallel to the main power circuit as shown in Figure 7.10. The filter is operated to cancel
out the load harmonic currents leaving the supply current free from any harmonic
<本论文由英语论文网提供整理,提供论文代写,英语论文代写,代写论文,代写英语论文,代写留学生论文,代写英文论文,留学生论文代写相关核心关键词搜索。