Abstract: This paper deals in detail with the design of feedback control system for variable speed constant frequency electrical power. The aim of designing a feedback control system is, besides assuring the power system of good dynamic and static characteristics, to suppress strongly the d.c, subharmonic and low harmonic components in the output voltage of cycloconverter, to reduce the weight of outpus filter and increase composed the system effi -ciency. For these purpose the control strategy composed of negative differential feedback parallel compensation, integral propotional series compensation and output voltage regulator is presented based on establishing the power circuit transfer function model. The design principle and methds of control circuit are describled and a series of experimental studies are carried out. The experiment results show that the proposed control strategy has a significant effect on the suppression of harmonics in the output with frequencies lower than 7 times of the fundermental frequency.The control strategy can also be used in d.c-a.c inverter.