Preheating device and preheating method for compressor

The invention provides a preheating device for a compressor. The preheating device comprises an inverter circuit and a control unit. The inverter circuit includes first, second and third switching devices. A PWM control module of the control unit outputs first, second and third PWM output module control signals. The PWM output module of the control unit comprises a first counter, a second counter and a third counter, and compares the first PWM output module control signal, the second PWM output module control signal and the third PWM output module control signal with a first count value, a second count value and a third count value with triangular waves of the first counter, the second counter and the third counter respectively to generate a first PWM control signal, a second PWM control signal and a third PWM control signal respectively. And the first, second and third switching devices are respectively controlled to be connected and disconnected so as to respectively control the electric power provided by t