In view of the disadvantages of the traditional AC/AC converter circuit

such as too many power devices

complex control and low power factor

on the basis of plugged pulse AC-AC frequency conversion control principle

according to average value of output voltage followed by the change of expected voltage

a AC-AC variable frequency circuit structure of three-phase input three-phase output circuit and a six-phase input to threephase output circuit with continuous output frequency are designed. It is found that there is no limit on the output voltage frequency of this type of AC/AC converter

the continuous variation of output frequency can be realized.Finally

three-phase to three-phase and six-phase to three-phase with continuous output frequency AC-AC variable frequency speed regulating system are designed respectively

and the simulation models for these two speed control systems are established in MATLAB/SIMULINK simulation environment. The theoretical analysis is consistent with the simulation results

which verifies the correctness and feasibility of this kind of variable frequency speed control system.