電力電子技術(shù)外文翻譯-文庫吧
2024-12-22 17:19 本頁面
【正文】 幾百毫安。 5。保持電流。這是指最低陽極對陰極電流必要可控硅保持在正向?qū)щ姞顟B(tài)進行。該值從 20 到 100 毫安。 AC 操作 一個變化中的可控硅的是以半波運行的直流電壓 RMS 操作。觸發(fā)電壓是由一些電路研制生產(chǎn)在一定的外加 交流信號選擇階段的脈沖。因此，在可控硅打開一個重復(fù)的方式，如圖所示。 SCR 關(guān)閉，當(dāng)然，在每半個周期當(dāng) AC 極性反轉(zhuǎn)。通過改變部分正半周時，觸發(fā)應(yīng)用，有效（ RMS）的直流電壓值應(yīng)用于負載可提高。當(dāng)然，這可能是此直流電壓半波整流電路的最大有效值。如果需要更多的電源，可選用可控硅全波橋式電路。觸發(fā)電壓，現(xiàn)在必須在每半個周期產(chǎn)生并應(yīng)用到可控硅觸發(fā)（門）終端。在過程控制應(yīng)用中，控制器的輸出信號將被用來驅(qū)動電路，改變了在該脈沖被應(yīng)用到門，從而改變了通電的載入時間。加到負載上的電壓脈動直流。此配置不能用于帶負荷操作，需要 交流電壓。 觸發(fā)控制 SCR 在過程控制的應(yīng)用 ， 電路控制信號轉(zhuǎn)換成合適的觸發(fā)信號傳送到 SCR 是必需的。這樣的電路通常是由電子系統(tǒng) 組成， 該系統(tǒng)使用的控制電壓決定交流負載電壓。 控制信號電壓通過一個指示燈來提供相應(yīng)的驅(qū)動器晶體管，從而確保了電源電路控制電路隔離。在低基數(shù)驅(qū)動電容充電慢，直到不會達到周期后期的可控硅的觸發(fā)電壓（因此低負荷功率）。 一個大控制信號提供 在 高調(diào)速系統(tǒng)中 ， 電容器收取的速率 將 要快得多 。然后，可控硅將打開更長的周期，將提供更多的能力來承擔(dān)負載。 電力電子技術(shù) Power Electronic Technology (II) Part A Thyristors In the onstate of the thyristor, t he main current flows from the anode to the cathode. In its offstate, the thyristor can block a forward polarity voltage and not conduct. The thyristor can be triggered into the onstate by applying a pulse of positive gate current for a short duration provided that the device is in its forward blocking state. The forward voltage drop in the onstate is only a few volts (typically 1 to 3 V depending on the device blocking voltage rating). Once the device begins to conduct, it is latched on and the gate current can be removed. T he thyristor cannot be turned off by the gate, and the thyristor conducts as a diode. Only when the anode current tries to go negative under the influence of the circuit in which the thyristor is connected does the thyristor turn off and the current go to zero. This allows the gate to regain control in order to turn the device on at some controllable time after it has again entered the forward blocking state. In reverse bias at voltages below the reverse breakdown voltage, only a negligibly small leakage current flows in the thyristor. Usually the thyristor voltage rating for forward and reverse blocking voltages are the same. Usually the thyristor voltage rating for forward and reverse blocking voltages are the same. Using the same arguments as for diodes, the thyristor can be represented by the idealized characteristics in analyzing converter topologies. In an application of resistant load circuit, control can be exercised over the instant of current conduction during the positive half cycle of source voltage. When the thyristor current tries to reverse itself when the source voltage goes negative, the idealized thyristor would have its current bee zero immediately. However, as specified in the thyristor data sheets, the thyristor current reverses itself before being zero. The important parameter is not the time it takes for the current to bee zero from its negative value, but rather the turnoff time interval t q from the zero crossover of the current to the zero crossover of the voltage across the thyristor. D uring t q a reverse voltage must bemaintained across the thyristor and only after this time is the device capable of blocking a forward voltage without going into its onstate. If a forward voltage is applied to the thyristor before this interval has passed, the device may prematurely turn on and damage to the device and circuit could result. Thyristor data sheets specify with a specified reverse voltage applied during this interval as well as a specified rateofrise of voltage beyond this interval. This interval is sometimes called the circuitmutatedrecovery time of the thyristor. Depending on the application requirements, various types of thyristor are available. In addition to voltage and current ratings, turnoff time , and the forwar
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