Energy recovery type cascade vehicle heat pump air conditioning system and method

The invention provides an energy recovery type cascade automotive heat pump air conditioning system and method, and belongs to the field of pure electric automobiles, the heat pump air conditioning system comprises a main cycle compressor, a first three-way solenoid valve, a first condenser, a first expansion machine and a first evaporator which are sequentially communicated to form a refrigeration cycle, and a working medium adopted by the refrigeration cycle is R134a or R1234yf; in addition, the system further comprises a heat pump air conditioning system, and a working medium adopted by the heat pump air conditioning system is R134a or R1234yf. Meanwhile, the heat pump air-conditioning system can achieve ultra-low-temperature heating, when the environment temperature is low, the circulation mode of the system is cascade type heating circulation, besides the main circulation loop, the heat pump air-conditioning system further comprises a heating circulation auxiliary loop, and the adopted working medium is