Open-phase detection device and open-phase detection method for three-phase alternating-current power supply

The invention relates to an open-phase detection device and an open-phase detection method of a three-phase alternating-current power supply. The open-phase detection method of the three-phase alternating-current power supply comprises the following steps of: obtaining any two groups of line voltages of the three-phase alternating-current power supply with a first period; obtaining a first digital signal and a second digital signal; performing XOR operation on the first digital signal and the second digital signal to generate a level signal; accumulating a high level time count value when the level signal maintains a high level for a time length, and accumulating a low level time count value when the level signal maintains a low level for a time length; when the high-level time count value is accumulated, the low-level time count value is reset to zero; when the low-level time count value is accumulated, the high-level time count value is reset to zero; and if the high-level time count value is greater than o