Cascaded energy storage system and energy storage method thereof

A cascaded energy storage system, comprising:

• a gas storage which is divided into at least one air chamber and at least one working medium gas chamber by a flexible diaphragm, pressure of the air chamber being equal to pressure of the working medium gas chamber, and volume of the air chamber and volume of the working medium gas chamber being capable of being adjusted by contraction and expansion of the flexible diaphragm;
• an air compression and energy release assembly which communicates with the air chamber, and is configured to introduce compressed air into the air chamber and release the compressed air;
• a working medium gas-liquid conversion assembly comprising a working medium compression assembly, a working medium expansion assembly and a liquid storage assembly, wherein the liquid storage assembly comprises a liquid storage tank and a liquid heater;
• an outlet of the working medium gas chamber, the working medium compression assembly and an inlet of the liquid storage tank are sequentially connected through a working medium hydraulic pipeline;
• an outlet of the liquid storage tank, the working medium expansion assembly, a hot side of the liquid heater and an inlet of the working medium gas chamber are sequentially connected through a working medium vaporization pipeline;
• and the outlet of the liquid storage tank, and a cold side of the liquid heater and the inlet of the liquid storage tank are sequentially connected through a pressure maintaining pipeline;
• and
• a heat storage assembly, configured to release heat or store heat to the air compression and energy release assembly and the working medium gas-liquid conversion assembly under different working conditions of the air compression and energy release assembly and the working medium gas-liquid conversion assembly.