The Structure of A Commutation Cell
As told above, a commutation cell must be placed between a voltage source and a current source. Depending on the state of the cell, both sources are either connected, or isolated. When isolated, the current source must be shorted, as it is impossible to left it in an open circuit. The basic schematic of a commutation cell is therefore given in figure 3 (top). It uses two switches with opposite states: In the configuration depicted in figure 3, both sources are isolated, and the current source is shorted. When the top switch is on (and the bottom switch is off), both sources are connected.
In reality, it is impossible to have a perfect synchronization between the switches. At one point during the commutation, they would be either both on (thus shorting the voltage source) or off (thus leaving the current source in an open circuit). This is why one of the switches has to be replaced by a diode. A diode is a natural commutation device, i.e. its state is controlled by the circuit itself. It will turn on or off at the exact moment it has to. The consequence of using a diode in a commutation cell is that it makes it unidirectional (see figure 3). A bidirectional cell can be built, but it is basically equivalent to two unidirectional cells connected in parallel.
Read more about this topic: Commutation Cell
Famous quotes containing the words structure and/or cell:
“The structure was designed by an old sea captain who believed that the world would end in a flood. He built a home in the traditional shape of the Ark, inverted, with the roof forming the hull of the proposed vessel. The builder expected that the deluge would cause the house to topple and then reverse itself, floating away on its roof until it should land on some new Ararat.”
—For the State of New Jersey, U.S. public relief program (1935-1943)
“What Mrs. Thatcher did for women was to demonstrate that if a woman had enough desire she could do what she wanted, do anything a man could do.... Mrs. Thatcher did not have one traditional feminine cell in her body.”
—Julie Burchill (b. 1960)