Over-temperature protection method of variable frequency driving device and variable frequency driving device

The invention provides an over-temperature protection method for a variable-frequency driving device and the variable-frequency driving device, and the method comprises the steps: obtaining the input voltage of a power circuit and the output voltage and output current of a driving circuit in real time in the operation process of an AC motor, and calculating a preliminary over-temperature threshold value of a power module of the driving circuit; comparing the initial over-temperature threshold value with a maximum temperature value allowed by the power module to determine a final over-temperature threshold value; obtaining the temperature of the power module, and judging whether the temperature of the power module exceeds a final over-temperature threshold value or not, so as to adjust the speed instruction when the temperature exceeds the final over-temperature threshold value, and enable the drive circuit to drive the AC motor to work according to the adjusted speed instruction; therefore, the over-temperatu