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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Commutation cell ： ウィキペディア英語版 Commutation cell The commutation cell is the basic structure in power electronics. It is composed of an electronic switch (today a high-power semiconductor, not a mechanical switch) and a diode. It was traditionally referred to as a chopper, but since switching power supplies became a major form of power conversion, this new term has become more popular. The purpose of the commutation cell is to "chop" DC power into square wave alternating current. This is done so that an inductor and a capacitor can be used in an LC circuit to change the voltage. This is in theory a lossless process, and in practice efficiencies above 80-90% are routinely achieved. The output is then usually run through a filter to produce clean DC power. By controlling the on and off times (the duty cycle) of the switch in the commutation cell, the output voltage can be regulated. This basic principle is the core of most modern power supplies, from tiny DC-DC converters in portable devices to huge switching stations for high voltage DC power transmission. ==Connection of two power elements== A Commutation cell connects two power elements, often referred to as sources, although they can either produce or absorb power. Some requirements to connect power sources exist. The impossible configurations are listed in figure 1. They are basically: * a voltage source cannot be shorted, as the short circuit would impose a zero voltage which would contradict the voltage generated by the source; * in an identical way, a current source cannot be placed in an open circuit; * two (or more) voltage sources cannot be connected in parallel, as each of them would try to impose the voltage on the circuit; * two (or more) current sources cannot be connected in series, as each of them would try to impose the current in the loop. This applies to classical sources (battery, generator), but also to capacitors and inductors: At a small time scale, a capacitor is identical to a voltage source, and an inductor to a current source. Connecting two capacitors with different voltage level in parallel therefore corresponds to connecting two voltage sources, one of the forbidden connections of figure 1. The figure 2 illustrates the poor efficiency of such connection. One capacitor is charged to a voltage V, and is connected to a capacitor with the same capacity, but discharged. Before the connection, the energy in the circuit is $E=\backslash fracC\backslash cdot\; V^2$, and the quantity of charges Q is equal to $C\backslash cdot\; U$. After the connection has been made, the quantity of charges is constant, and the total capacitance is $2C$. Therefore the voltage across the capacitances is $\backslash frac=\backslash frac$. The energy in the circuit is then $\backslash frac(2C)\backslash left(\backslash frac\backslash right)^2=\backslash frac$. Therefore half of the energy has been dissipated during the connection. The same applies with the connections in series of two inductances. The magnetic flux ($\backslash Phi=L\backslash cdot\; I$) remains constant before and after the commutation. As the total inductance after the commutation is 2L, the current becomes $\backslash frac$ (see figure 2). The energy before the commutation is $\backslash fracL\backslash cdot\; I^2$. After, it is $\backslash fracL\backslash cdot\; \backslash left(\backslash frac\backslash right)^2$. Here again, half of the energy is dissipated during the commutation. As a result, it can be seen that a commutation cell can only connect a voltage source to a current source (and vice versa). However, using inductors and capacitors, it is possible to transform the behaviour of a source: for example two voltage sources can be connected through a converter if it uses an inductor to transfer energy. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Commutation cell」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.