Correct Answer : Option (D) : Cycloconverter
Explanation : A cycloconverter is a kind of AC to AC converter based on thyristors that converts AC at one frequency to ac of another frequency without the involvement of a dc source. It is used primarily to increase or decrease the frequency of the output voltage(s) with respect to the frequency of the input voltage(s), without using any AC-DC nor DC-AC converters during the process. The supply side of the cycloconverter is considered as the input, while the load side is considered the output of it.