Abstract: In areas with poor power grid quality, ultra-low voltage input occurs frequently, which makes the communication between indoor unit and outdoor unit of traditional split variable frequency air conditioner appear data loss and frame loss and other problems. As a result, variable frequency air conditioner can not operate normally due to indoor and outdoor communication, which seriously restricts the popularity of variable frequency air conditioner in these areas. Based on the classical current loop communication circuit, proposes a voltage adaptive asynchronous communication. Through voltage adaptive asynchronous communication, according to the current AC input voltage, the communication time ratio (i.e. the ratio of single frame communication duration to single frame communication cycle) is adjusted in real time to maintain sufficient communication power supply voltage to ensure normal communication. It improves the communication reliability of the split variable frequency air conditioner, so as to ensure the reliable operation of the variable frequency air conditioner when the power grid is supplied with ultra-low AC voltage.

Key words: Voltage adaptation, Current loop, Communication time ratio