The invention provides a frequency converter. The frequency converter comprises a main circuit, a driving circuit, a control circuit and a user function circuit. The driving circuit comprises driving optocouplers for driving upper bridge IGBTs (insulated gate bipolar transistor) of the main circuit, and a driving chip driving lower bridge IGBTs (insulated gate bipolar transistor); the user function circuit comprises a digital isolator connected with the control circuit; the original secondary distance of the digital isolator is larger than a first preset distance; the safety distance between the user function circuit and the control circuit is larger than a second preset distance. The number of the driving optocouplers in the driving circuit is half of that in the prior art; meanwhile, the low-cost digital isolator in the user function circuit achieves insulation of the user function circuit from the control circuit and enables the user function circuit to maintain a distance from the control circuit, so that the user function circuit can be weak in voltage to avoid electric shock of a user; the isolator is lower in total cost than the prior art, so that the problem of avoiding electric shock with high cost in the prior art can be avoided.