阅读说明：本技术 一种蒸汽压缩制冷系统的串级节能控制方法 (Cascade energy-saving control method of vapor compression refrigeration system ) 是由 尹晓红 孔德豪 王新立 于 2019-09-06 设计创作，主要内容包括：本发明公开了一种蒸汽压缩制冷系统的串级节能控制方法,包括蒸发器,膨胀阀,冷凝器,压缩机,MPC控制器,PI控制器；制冷需求随环境的改变而改变,外环根据当前制冷量来调节过热度的值,并将该值作为内环中过热度的设定值,同时内环MPC控制器两端分别连接PI控制器输出和蒸汽压缩硬件系统,进而实现对系统设定值的实时跟踪。本发明的有益效果是提高了蒸汽压缩制冷系统的传热效率。(The invention discloses a cascade energy-saving control method of a vapor compression refrigeration system, which comprises an evaporator, an expansion valve, a condenser, a compressor, an MPC controller and a PI controller, wherein the evaporator is connected with the expansion valve; the refrigeration requirement changes along with the change of the environment, the outer loop adjusts the value of the superheat degree according to the current refrigeration quantity, the value is used as the set value of the superheat degree in the inner loop, and meanwhile, the two ends of the inner loop MPC controller are respectively connected with the output of the PI controller and the steam compression hardware system, so that the set value of the system is tracked in real time. The invention has the beneficial effect of improving the heat transfer efficiency of the vapor compression refrigeration system.)

1. A cascade energy-saving control method of a vapor compression refrigeration system is characterized in that: the outlet of the evaporator is connected with the inlet of the compressor, the outlet of the compressor is connected with the inlet of the condenser, the outlet of the condenser is connected with the inlet of the expansion valve, the outlet of the expansion valve is connected with the inlet of the evaporator, and the four are connected in a closed loop manner to form a vapor compression refrigeration system; the PI controller is an outer ring controller, the left side of the PI controller is connected with an MPC controller of the cascade control system, the right side of the PI controller is connected with a vapor compression refrigeration system through a refrigerating capacity-superheat degree model, and the PI controller adjusts and optimizes the superheat degree value of the evaporator in real time when the refrigerating capacity changes and takes the superheat degree value as a set value in an inner ring; the MPC controller is an inner ring controller, the left end and the right end of the MPC controller are respectively connected with a PI controller and a steam compression hardware system of the cascade control system, and the MPC controller adjusts the pressure difference between the actual evaporator and the condenser and the superheat degree of the evaporator in real time and tracks the set value given by the outer ring according to the change of the set value; the inner ring and the outer ring of the cascade control system are connected through the superheat degree of a system variable evaporator, when the system operates normally, the refrigeration requirement changes along with the change of the environment, the outer ring PI controller adjusts the superheat degree value according to the current refrigeration capacity and takes the superheat degree value as the set value of the superheat degree in the inner ring, and meanwhile, the two ends of the inner ring MPC controller are respectively connected with the output of the PI controller and a steam compression hardware system, so that the real-time tracking of the set value of the system is realized.

Technical Field

The invention belongs to the technical field of vapor compression, and relates to a cascade energy-saving control method of a vapor compression refrigeration system.

Background

The vapor compression refrigeration system is a core component of an air conditioning system and is a source for generating cold. To ensure proper operation of the system, the refrigerant in the evaporator must enter the compressor in a vapor state to avoid damaging the compressor components. The conventional control strategy usually adopts a control method to control the refrigerant vapor to enter the compressor in a superheated state, so as to ensure the stable operation of the compressor, but does not consider that the heat transfer efficiency of the system cannot be stabilized at a high level when the refrigerating capacity of the system changes along with the change of the environment. That is, when the cooling capacity is reduced, the superheat degree of the refrigerant (i.e., the difference between the outlet temperature of the refrigerant at the evaporator and the saturation temperature of the refrigerant at the current evaporation pressure) is still maintained at the original set value, which may cause insufficient heat exchange of the system, thereby reducing the system efficiency; however, when the cooling capacity is increased, if the superheat degree is maintained at the superheat value set when the cooling capacity is small, the system may oscillate and be unstable.

Disclosure of Invention

The invention aims to provide a cascade energy-saving control method of a vapor compression refrigeration system.

The technical scheme adopted by the invention comprises an evaporator, an expansion valve, a condenser, a compressor, an MPC controller and a PI controller; the outlet of the evaporator is connected with the inlet of the compressor, the outlet of the compressor is connected with the inlet of the condenser, the outlet of the condenser is connected with the inlet of the expansion valve, the outlet of the expansion valve is connected with the inlet of the evaporator, and the four are connected in a closed loop manner to form a vapor compression refrigeration system; the PI controller is an outer ring system controller, the left side of the PI controller is connected with an MPC controller of an inner ring system, the right side of the PI controller is connected with a steam compression refrigerating system through a refrigerating capacity-superheat degree model, the PI controller adjusts and optimizes the superheat degree value of the evaporator in real time when the refrigerating capacity changes, the value is used as a set value in the inner ring system, the MPC controller is an inner ring system controller, and the left end and the right end of the MPC controller are respectively connected with the PI controller and a steam compression hardware system of the outer ring system; according to the change of the set value, the MPC controller adjusts the superheat degree of the actual evaporator and the pressure difference of the refrigerant between the evaporator and the condenser in real time and tracks the set value given by the outer ring; the inner loop system and the outer loop system are connected through the superheat degree of a system variable evaporator to form a cascade control system, wherein the outer loop PI controller provides a set value of the superheat degree of the evaporator for the inner loop MPC controller; when the system normally operates, the refrigeration requirement changes along with the change of the environment, the outer loop adjusts the value of the superheat degree according to the current refrigeration quantity, the value is used as the set value of the superheat degree in the inner loop system, and two ends of the inner loop MPC controller are respectively connected with the output of the PI controller and the steam compression hardware system, so that the real-time tracking of the set value of the superheat degree and the pressure difference of the system is realized.

Drawings

Fig. 1 is a cascade control system configuration for a vapor compression refrigeration system.

In the figure, 1 is an evaporator, 2 is an expansion valve, 3 is a condenser, 4 is a compressor, 5 is an MPC controller, and 6 is a PI controller.

Detailed Description

The present invention will be described in detail with reference to the following embodiments.

As shown in figure 1, the vapor compression refrigeration system of the invention is characterized in that an outlet of an evaporator 1 is connected with an inlet of a compressor 4, an outlet of the compressor 4 is connected with an inlet of a condenser 3, an outlet of the condenser 3 is connected with an inlet of an expansion valve 2, an outlet of the expansion valve 2 is connected with an inlet of the evaporator 1, and the four are connected in a closed loop manner to form a vapor compression hardware system. The PI controller 6 is an outer ring controller, the left side of the PI controller is connected with the MPC controller 5 of the cascade control system, the right side of the PI controller is connected with the vapor compression refrigeration system through a refrigerating capacity-superheat degree model, when the refrigerating capacity changes, the PI controller 6 adjusts and optimizes the superheat degree value of the evaporator in real time, and the superheat degree value is used as a set value of the MPC controller. The PI controller adopts a PI control method, namely, an actual output value and a set value are subtracted to obtain a control deviation, the control deviation is linearly combined through a Proportional link (Proport) and an Integral link (Integral) to form a deviation control quantity, and the control deviation is reduced through continuous iteration, so that the actual output value approaches the set value step by step. In the model, the required refrigerating capacity and the actual refrigerating capacity are gradually approximated by comparing the required refrigerating capacity with the actual refrigerating capacity and iterating according to the combination of the difference values. When the actual refrigerating capacity of the system is equal to the required refrigerating capacity, the deviation is 0, the input quantity of the system is not changed any more, the optimal superheat value of the refrigerant in the evaporator is calculated by utilizing the established refrigerating capacity-superheat model, and the superheat value at the moment is the superheat set value (described by a PI control algorithm) of the inner loop system. The MPC controller 5 is an inner loop system controller, and the left end and the right end are respectively connected with the PI controller 6 and the steam compression hardware system of the cascade control system. According to the change of a superheat degree set value (namely the difference between the temperature of the refrigerant at the outlet of the evaporator and the saturation temperature) of the refrigerant provided by the output of the outer ring PI controller in the evaporator, the MPC controller 5 adjusts the rotating speed of the compressor and the opening of the expansion valve in real time, realizes that the actual value of the superheat degree of the evaporator 1 tracks the superheat degree set value given by the outer ring PI controller, and adjusts the actual pressure difference (the pressure difference of the refrigerant between the evaporator 1 and the condenser 3) to ensure the stability of the system. The inner ring and the outer ring of the cascade control system are connected through the superheat degree of the system variable evaporator 1.

The working process is as follows: as shown in fig. 1, when the system is in normal operation, the refrigeration demand changes with the change of the environment, the outer loop adjusts the value of the superheat degree according to the current refrigeration quantity, and the value is used as the set value of the superheat degree in the inner loop, and meanwhile, two ends of the inner loop MPC controller 5 are respectively connected with the output of the PI controller 6 and the vapor compression hardware system, so that the set value of the system is tracked in real time, and finally, the heat transfer efficiency is always kept at a higher level under the condition that the system is in stable operation.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not intended to limit the present invention in any way, and all simple modifications, equivalent variations and modifications made to the above embodiments according to the technical spirit of the present invention are within the scope of the present invention.