CYCLOCONVERTERS
The cycloconverter operates in all four quadrants during a period. A pause (dead time) at least as small as the time required by the switch-over logic occurs after the current reaches zero, i.e. between the transfer to operation in the quadrant corresponding to the other direction of current flow.
If control signal value alters sinusoidally with the desired frequency, then the waveform depicted in figure a) consists of a single-phase voltage with a large harmonic current. If the load is inductive, the current will present less distortion than voltage as shown in figure b).
Three single-phase cycloconverters may be combined to build a three-phase cycloconverter. The three-phase cycloconverters find an application in low frequency, high power requirements.
Control speed of large synchronous motors in the low speed range is one of the most common applications of three-phase cycloconverters. The figure shows a diagram for this application. They are also used to control slip frequency in wound rotor induction machines, for supersynchronous cascade (Scherbius system).
Control speed of large synchronous motors in the low speed range is one of the most common applications of three-phase cycloconverters. The figure shows a diagram for this application. They are also used to control slip frequency in wound rotor induction machines, for supersynchronous cascade (Scherbius system).
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