Half cycle selection technique has been used in the earlier envelope cycloconverters to achieve frequency changing of power frequency. However，due to the large number of power semiconductor switches and complexity of control circuits of the envelope cycloconverters, frequency changers where developed based on integral cycle control. These converters are found to be not feasible for frequency changing due to the generations of subharmonics，as well as higher order harmonics in the output voltage waveforms. In the present work an attempt is made to design, build, analyze and investigate a new frequency changer based on a half cycle selection approach. This converter is intended to be used as a drive converter for A.C. single and three-phase systems， as well as D.C. drive applications. Extensive mathematical analyses of the output voltage waveforms for single and three-phase systems are carried out for several selection patterns. These analyses gave full explanation for the harmonic spectrum and behavior of the converter under investigation. A prototype system is designed and built in the laboratory. The system is tested with single and three – phase resistive, induction motor and D.C. motor. The design of the circuit is simple, inexpensive, and can be assembled easily using commercially available components. It is found that there is a well agreement between the theoretical and experimental results.