Heat pump system and control method thereof

A heat pump system, comprising an indoor unit and an outdoor unit communicated through a refrigerant pipeline, wherein the outdoor unit comprises a compressor, a first heat exchanger, a first throttling device, and a change-over valve, and the indoor unit comprises a second heat exchanger, and wherein the refrigerant pipeline has a refrigerant gas-phase pipeline and a refrigerant liquid-phase pipeline, which is characterized in that a heat storage unit is arranged on the refrigerant gas-phase pipeline between the indoor unit and the outdoor unit, the heat storage unit comprising a first branch and a second branch arranged in parallel, wherein the first branch is provided with a heat storage heat exchanger and a second throttling device, and the second branch is provided with a control valve device capable of cutting off refrigerant flowing through the second branch in a controlled manner,

• wherein, the heat pump system is capable of operating in a cooling mode, a heating mode, a heat storage and heating mode, and a defrosting mode, where,
• in the cooling mode, the second throttling device is turned off, so that no refrigerant passes through the heat storage heat exchanger, and the control valve device is turned on so that the refrigerant flows from the second heat exchanger of the indoor unit to the change-over valve of the outdoor unit through the second branch, and then enters a suction port of the compressor;
• in the heating mode, the second throttling device is turned on with a tiny opening, and the control valve device is turned on to allow the refrigerant to flow from the change-over valve of the outdoor unit to the second heat exchanger of the indoor unit through the second branch;
• in the heat storage and heating mode, the second throttling device is fully turned on with the first throttling device playing a throttling role to store heat in the heat storage heat exchanger, and the control valve device is turned off, so that no refrigerant passes through the second branch;
• or the second throttling device is partially turned on to allow at least a portion of the refrigerant to flow through the heat storage heat exchanger, and the control valve device is turned on to allow most of the refrigerant to pass through the second branch;
• and
• in the defrosting mode, the first throttling device is fully turned on with the second throttling device playing a throttling role to allow the refrigerant to flow through the heat storage heat exchanger to absorb heat for evaporation, and the control valve device is turned off so that no refrigerant passes through the second branch.