Frequency conversion and power frequency undisturbed switching system and cooling tower fan

The utility model discloses a frequency conversion and power frequency undisturbed switching system which comprises a current transformer, an input reactor, a frequency converter, an output filter, afirst switch, a second switch, a third switch and a controller. The controller is connected with the secondary side of the current transformer, the output end of the power frequency power supply and the output end of the frequency converter, and is used for respectively acquiring the power frequency power supply side sampling current, the power frequency power supply side sampling voltage and thefrequency converter output side sampling voltage and outputting the power frequency power supply side sampling voltage according to the acquired current and voltage; wherein the phase-locked loop is used for controlling the output voltage of the frequency converter to be consistent with the phase, amplitude and frequency of the voltage of the power frequency power supply, and the controller is also used for controlling the