JPH0744915Y2 - heat pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a heat pump for an air conditioner or the like.

(Prior Art) An example of a conventional heat pump is shown in FIGS. 10 and 11.

As shown in FIG. 10, the refrigerant gas discharged from the inverter-driven compressor 1 is condensed and liquefied in the condenser 2, and the electronic expansion valve 3
After being adiabatically expanded by and evaporated and vaporized by the evaporator 4, it returns to the compressor 1 again.

The refrigerant pressure at the outlet of the evaporator 4 detected by the pressure sensor 5 and the refrigerant temperature at the outlet of the evaporator 4 detected by the temperature sensor 6 are input to the controller 7, and the pulse motor 8 is rotated by a command from the controller 7. By doing so, the opening degree of the electronic expansion valve 3 is adjusted to control the refrigerant superheat degree at the outlet of the evaporator 4.

A control block diagram of the controller 7 is shown in FIG.

The refrigerant pressure P ₁ detected by the pressure sensor 5 at each predetermined sampling time is input to the saturation temperature calculating means 15 and converted into the refrigerant saturation temperature θ ₁ corresponding to this pressure P ₁ . This temperature θ ₁ is input to the superheat degree calculating means 16 and the temperature θ ₁ detected by the temperature sensor 6 is detected.
It is compared to _2, the difference therebetween, i.e., the degree of superheat SH of the refrigerant at the outlet of the evaporator 4 (= θ ₂ -θ ₁₎ is calculated. This superheat degree SH is input to the deviation calculation means 17, and is compared with the set superheat degree SP _sh input from the superheat degree setting device 14 here, and the deviation E _sh (= SH-SP _sh ) between them is calculated. This deviation E _sh is
It is input to the PID calculator 18, and the PID constant is used here to perform PID calculation to calculate the valve opening output of the electronic expansion valve 3 corresponding to the degree of superheat, that is, the manipulated variable χ _sh with respect to the control amount.

(Problems to be Solved by the Invention) In the above conventional heat pump, the PID constant used in the PID calculation is constant regardless of the lengths of the refrigerant pipes 9, 10, 11, 12 and the rotation speed of the compressor 1. .

However, since the length of the refrigerant pipe changes depending on the installation condition of the heat pump, and the rotation speed of the compressor 1, that is, the refrigerant circulation amount also changes, the dead time due to the delay in the transportation of the refrigerant is different for each heat pump. Not only does it change significantly, but it also changes with time in individual heat pumps.

The relationship between the rotational speed of the compressor 1, that is, the operating frequency and the dead time of the pipe is shown in FIG. 12, and the relationship between the dead time of the pipe and the stability limit gain constant during proportional control is shown in FIG.

As shown in FIG. 12, as the length of the refrigerant pipe becomes longer, the dead time of the pipe becomes longer as the rotation speed of the compressor 1 becomes smaller, and the system becomes unstable. As shown in, the larger the dead time of the pipe, the smaller the gain constant must be made in order to secure the stability of the system.

However, in order to secure the stability of the system, if the gain constant is made extremely small by setting the PID constant so that it matches the unstable system, the stable system has poor control responsiveness. , If the PID constants are set to match a stable system, there is a problem that hunting occurs in an unstable system, that is, when the pipe length is long and the rotation speed of the compressor is low.

(Means for Solving the Problems) The present invention has been proposed to solve the above problems, and its gist is to provide a compressor, a condenser, an electronic expansion valve, and an evaporator in this order as a refrigerant. In a heat pump connected by a pipe, a superheat degree calculating means for calculating a refrigerant superheat degree at the outlet of the evaporator, and a PID calculating means for performing a PID operation on the electronic expansion valve opening degree corresponding to the calculated superheat degree, From the length of the refrigerant pipe and the rotation speed of the compressor, PI
A heat pump characterized by comprising a feedback control circuit of an electronic expansion valve, which is a fuzzy inference means for selecting a D constant.

(Operation) Since the present invention has the above-described configuration, the PID constant for controlling the PID control of the opening degree of the electronic expansion valve with respect to the refrigerant superheat degree at the evaporator outlet calculated by the superheat degree calculating means is set to the refrigerant pipe. A fuzzy inference means calculates from the length and the number of revolutions of the compressor to select it, and the manipulated variable of the electronic expansion valve is calculated using the selected PID constant.

(Embodiment) One embodiment of the present invention is shown in FIGS. 1 to 9.

The refrigerant circuit of the heat pump is shown in FIG. 2, and an input device 13 such as a switch is connected to the controller 100.

A control block diagram of the controller 100 is shown in FIG. 1, and a flow chart is shown in FIG.

When the control starts, the refrigerant pressure P _{1 at} the outlet of the evaporator 4 detected by the pressure sensor 5 and the refrigerant temperature θ _{2 at} the outlet of the evaporator 4 detected by the temperature sensor 6 are detected every predetermined sampling time. To be done. The pressure P ₁ is input to the saturation temperature calculating means 15 and is converted into the refrigerant saturation temperature θ ₁ corresponding to the pressure P ₁ here. This temperature θ ₁ is input to the superheat degree calculating means 16 and compared there with the temperature θ _2, and the difference between them, that is, the superheat degree SH (= θ ₂ −θ ₁ ) of the refrigerant at the outlet of the evaporator 4 is calculated. To be done. This superheat degree SH is input to the deviation calculation means 17, and is compared with the set superheat degree SP _sh input from the superheat degree setter 14 here, and the deviation E between the two.
_sh (= SH-SP _sh ) is calculated. This deviation E _sh is input to the PID calculator 18, where the PID constant is used for PID calculation to output the valve opening of the electronic expansion valve 3 corresponding to the refrigerant superheat, that is, the manipulated variable χ _{sh with} respect to the control amount. Is calculated.

The PID constant used in this PID calculation is selected by the fuzzy reasoner 19.

A block diagram of the fuzzy reasoner 19 is shown in FIG. 4 and a flow chart is shown in FIG.

The length L of the refrigerant pipe of each heat pump is input from the input device 13 to the fuzzy variable grade calculating means 20 of L, where the fuzzy variable grade for the membership function input from the L membership function storing means 21. Is calculated. Incidentally, as shown in FIG. 6, the storage means 21 stores a membership function of a fuzzy variable corresponding to the refrigerant pipe length L.

The operating frequency f is input from the compressor 1 to the fuzzy variable grade calculating means 22 of f, and the fuzzy variable grade for the membership function input from the membership function storing means 23 of f is calculated here. Note that, as shown in FIG. 7, the storage means 23 stores a membership function of a fuzzy variable corresponding to the operating frequency of the compressor 1.

The fuzzy variable grades calculated by these calculating means 20 and 22 are input to the fuzzy variable grade calculating means 24 of K, T _I and T _d , based on the control rules input from the control rule storing means 25. The minimum values of the fuzzy variable grades of K, T _I and T _d are calculated.

The control rule storage means 25 stores the control rules shown in FIG.

The minimum value of K calculated by the calculation means 24 is input to the weighted average calculation means 26, and the weighted average value is calculated based on the membership function input from the storage means 27 of the membership function of K. .

Similarly, the minimum value of T ₁ calculated by the calculation means 24 is input to the weighted average calculation means 28, and the weighted average value is calculated based on the membership function input from the storage means 29 of the membership function of T ₁ here. Is calculated.

Similarly, the minimum value of T _d calculated by the calculation means 24 is input to the weighted average calculation means 30, and the weighted average value is calculated based on the membership function input from the storage means 31 of the membership function of T _d. Is calculated.

In addition, as shown in FIG.
Membership functions corresponding to K, T _I and T _d are stored.

6 to 9, VS is very small, S is small,
MS is slightly small, M is medium, MB is slightly large, B is large, and VB is very large.

The PID constants K, T _I , and T _d thus obtained are input to the PID calculator 18, where the manipulated variable χ _sh of the electronic expansion valve 3 is expressed by Calculated by

Note that K is a gain, T _s is a sampling time, T _d is a differentiation time, T _I is an integration time, and χ _hso is an initial value.

This manipulated variable χ _sh is input to the pulse motor 8, and the opening of the electronic expansion valve 3 is adjusted by the rotation of the pulse motor 8.

(Effects of the Invention) In the present invention, a superheat degree calculating means for calculating a refrigerant superheat degree at an outlet of an evaporator, a PID calculating means for performing a PID operation on an electronic expansion valve opening corresponding to the calculated superheat degree, and a refrigerant Equipped with a feedback control circuit for the electronic expansion valve, which is a fuzzy inference means that selects the PID constant from the length of the pipe and the rotation speed of the compressor, so the PID constant corresponds to the refrigerant pipe length and the rotation speed of the compressor. Can be selected.

As a result, the opening degree of the electronic expansion valve can be set to an opening degree suitable for the dead time of the pipe, therefore, the response characteristic of the state quantity of the refrigerant during the unsteady operation of the heat pump is improved, and as a result, the efficiency of the heat pump is improved. Also improves.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 9 show one embodiment of the present invention. FIG. 1 is a control block diagram of a controller, FIG. 2 is a refrigerant circuit diagram of a heat pump, and FIG. The control flowchart of the controller, Fig. 4 is the block diagram of the fuzzy reasoner,
Fig. 5 is a flowchart of the fuzzy reasoner, Fig. 6 is a diagram showing the membership function of the refrigerant pipe length, Fig. 7 is a diagram showing the membership function of the operating frequency of the compressor, and Fig. 8 is a PID. FIG. 9 is a diagram showing a constant membership function, and FIG. 9 is a table showing control rules. 10 to 13 show an example of a conventional heat pump.
Fig. 11 is a refrigerant circuit diagram, Fig. 11 is a control block diagram of the controller, Fig. 12 is a diagram showing the relationship between the operating frequency of the compressor and the dead time of the pipe, and Fig. 13 is the dead time of the pipe and the stability limit gain constant. It is a diagram showing the relationship of. Compressor …… 1, condenser …… 2, electronic expansion valve …… 3, evaporator …… 4, controller …… 100, refrigerant pipe …… 9,1
0, 11, 12, superheat calculation means …… 16, PID calculator …… 18,
Fuzzy reasoner …… 19

Claims (1)

[Scope of utility model registration request] 1. A heat pump in which a compressor, a condenser, an electronic expansion valve and an evaporator are connected in this order by a refrigerant pipe, and superheat degree calculating means for calculating the refrigerant superheat degree at the outlet of the evaporator, Of the electronic expansion valve consisting of a PID calculation means for calculating the PID of the electronic expansion valve opening corresponding to the degree of superheat, and a fuzzy inference means for selecting a PID constant from the length of the refrigerant pipe and the rotation speed of the compressor. A heat pump comprising a feedback control circuit.