電力系統(tǒng)及其自動(dòng)化外文翻譯--實(shí)時(shí)檢測(cè)諧波和單相電路無(wú)功功率的方法-文庫(kù)吧
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【正文】 Eqs.(I)and (3)，the instantaneous active current and instantaneous reactive current can be calculated. In general， assume the detected voltage and current respectively are ??tus = ? ?nnn nwtU ??? c o s2 (4) ??tis = ? ?nnn nw tI ??? c os2 (5) where nU and nI are the virtual values of the nth harmonic voltage and current, respectively。 w is angle frequency。 n? ， and n? are the phases of the nth harmonic voltage and current, respectively。 and n=1, 2, ??? Then ?)(2 tus? ? ? ? ? ?? ?mnnmn mmnnmn m wtmnUUUnw tnw tUU ???? ???????? ?? c osc osc os2 ,2, + ? ?? ?mnnmn m wtmnUU ?? ????? c os， (6) where， ,22 ?? n nUU (7) and ?mn,denotes the sum of the integers whose subscripts n and m are from 1 to ? In Eq. (6) ， except that 2U isDC ponent, the other items are all AC ponents. So the lowpass filter (LPF) whose cutoff frequency is lower than the lowest frequency of alternating signals must be used to filter )(2tus ， and then 2U is obtained. Similarly， the product of instantaneous current and instantaneous voltage，P， is p= ??tus ??tis = 外文原文 4 ? ? ? ?mnnmn m nw tnw tUI ?? ??? c osc os2 , = ? ?? ?mnnmn m wtmnUIP ?? ???? ? c os, + ? ?? ?mnnmn m wtmnUI ?? ????? c os (8) where P=???1 cosn nnnIU ? (9) and n? = mn ??? is called the power factor angle of the nth ， in Eq.(8 )all the items are AC ponents except for P. Thus the lowpass filter whose cutoff frequency is lower than the lowest frequency of alternating signals must be used to filter p， and then P is obtained. After working out P and 2U ， the functional block diagram is constructed as shown in Fig. 1， where the realtime detection of harmonics and instantaneous reactive currents are performed on the basis of Fryze39。s power definition in singlephase circuit. Although there is a division unit, it is not difficult to realize. Realtime detection of harmonic and reactive current Some Special Applications of the Detecting Method In Fig .l， the outputs ??tip and ??tiq vary with the input ??tus ， so this circuit can provide different reference pensations on the ground of different requirements of electric work. Three cases of application are analyzed as follows. Realtime detection of total reactive currents If the pensation is only for the reactive power, then the reactive currents need 外文原文 5 to be detected. Assume ??tis and ??tus are the current and voltage of the detected objects；then from Eqs. (1)， (2)， (4) and(9)， the outputs ??tip and ??tiq in are obtained (the derivation process is omitted here): ??tip = ? ?nnnn n w tI ?? ?? c osc os2 (10) ??tiq = ? ?nnnn nw tI ?? ?? c oss in2 (11) Obviously， ??tip is the sum of the harmonic active currents, called the total active currents. ??tiq is the sum of the harmonic reactive currents and the fundamental active currents, called the total reactive , ??tiq ,the output in Fig. 1，is used as a reference to pensate the reactive power. When only detecting the total reactive currents， there is no need to detect the unit sinusoidal signal with the same phase as the detected voltage， and hence no need to use the phaselocked loop circuit too. This is one of the merits of this method. Realtime detection of harmonic and fundamental reactive currents If ??tus = ? ?1cos2 ??wt , then, nU = ?????? ??,1,1 ,1,nno (12) Substituting Eq. (12) into Eq.(9)， we obtain P= 11cos?I (13) Then by Eq. (1) ， ??tip is expressed as ??tip = ? ?111 c o sc o s2 ?? ?wtI (14) Obviously, ??tip is the fundamental active part of the detected current, and then??tiq is the sum of harmonic and fundamental reactive currents. Therefore， the output ??tiq is used as a reference value to limit harmonics and pensate reactive 外文原文 6 currents. Since 2U =1， is obtained by simplification of . In , ??tus is an unit sinusoidal signal which has the same phase as the detected voltage and can be obtained from the phaselocked loop circuit. Realtime detection of harmonic and fundamental reactive current Realtime detection of harmonic currents When
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