The invention discloses a method, a device and a system for controlling power conversion of a frequency converter. The method provided by the invention comprises the following steps: receiving a control command which is used for controlling connection and disconnection of a semiconductor device in a frequency converter by a first chip and a second chip; and resolving a time point executing the command from the control command by the second chip; sending a triggering signal executing the control command to the first chip from the time point by the second chip; and executing the control command in the time point if the condition that the receiving of the triggering signal and the control command is the same operation, and the time point is in the current communication cycle are judged by the first chip. According to the invention, as the connection and disconnection of the semiconductor device are controlled in the accurate time point, the harmonic wave output by the frequency converter is lowered and the stability of the power control is improved.