JPS6160342B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to the control of a refrigeration system having a capacity control compressor, an electric expansion valve, etc., and its purpose is to stabilize the refrigeration system when the capacity of the capacity control compressor changes. It is intended to force the driver to drive.

Recently, electric expansion valves with good controllability have been used as expansion valves for throttling refrigerant in refrigeration equipment. For example, the conventional refrigeration system shown in Fig. 3 has a compressor 1, a condenser 2,
It is composed of a refrigerant circuit 5 consisting of an electric expansion valve 3 and an evaporator 4, and the electric expansion valve 3 is equipped with a heater 6,
It is composed of a bimetal 7, a needle 8, and a valve 9. The bimetal 7 heated by the heater 6 moves the needle 8 in the axial direction and changes the opening area of the valve 9. The heater 6 controls the temperature of the refrigerant in the evaporator and the temperature of the refrigerant sucked into the compressor 1 using a negative temperature sensitive resistance element (hereinafter referred to as a thermistor) 1.
0 and 11, and is controlled by a controller 12 that changes the output voltage so that the temperature difference becomes a predetermined value. That is, the thermistors 10 and 11 control the pseudo degree of superheat of the refrigerant sucked into the compressor 1 to a predetermined value. In this conventional refrigeration system, when the capacity of the compressor 1 does not change, stable operation is possible using the electric expansion valve 3, but when the compressor 1 is capacity controllable and its capacity control range is wide, the compressor The response of the electric expansion valve to a capacity change rate of 1 is slow, making the refrigeration system unstable, and in extreme cases, the electric expansion valve 3 may fall into an uncontrollable state. That is, the control signal for the electric expansion valve 3 is the resistance value of the thermistors 10 and 11, and there is a delay in detecting the refrigerant temperature value due to the heat capacity of the thermistors 10 and 11. Bimetal 7 with heater 6
There is a displacement delay of the needle 8 caused by the heating structure, and when the capacity of the compressor 1 increases, there is a significant delay in the corresponding increase in the opening area of the valve 9 of the electric expansion valve 3, which increases the throttling resistance of the refrigerant. increases,
As the refrigerant circulation is interrupted and the refrigerant pressure in the evaporator 4 decreases, the state of the refrigerant at the point where the temperature is measured by the thermistor 10 of the evaporator 4 becomes superheated steam. As a result, it becomes impossible to detect a pseudo degree of superheating of the refrigerant sucked into the compressor, and the difference in temperature detected by the thermistors 10 and 11 becomes small. As a result, the refrigerant circulation would be further restricted and the refrigeration system would be unable to continue operating.

The present invention aims to solve the above problems and provide a refrigeration system that can operate stably.

FIG. 1 shows an embodiment of the refrigeration system of the present invention, which is a separate type refrigeration system in which one outdoor unit 13 and one indoor unit 14 are connected. Outdoor unit 13
is the compressor 15 and the motor 1 that drives the compressor 15
6. A condenser 17, an outdoor fan 18 that ventilates the condenser 17, a motor 19 that drives the fan 18, an expansion valve 20 that can electrically change the refrigerant throttling resistance, and detects the temperature of the refrigerant sucked into the compressor 15. Negative temperature sensitive resistance element (hereinafter referred to as thermistor) 21
The indoor unit 14 includes an evaporator 22, an indoor fan 23 for ventilating indoor air to the evaporator 22, a motor 24 for driving the fan 23, a room temperature detector 25, a room temperature setting device 26, and a room temperature setting device 26 for the evaporator 22. A thermistor 27 is provided to detect the temperature of the evaporative refrigerant. These compressor 15, condenser 17, electric expansion valve 20, and evaporator 22 are sequentially connected by refrigerant piping 28 to form a refrigerant circuit 29. The evaporator 22 acts as a refrigerant for indoor air to perform a cooling operation.

The capacity of the compressor 15 can be controlled by controlling the rotation speed of the motor 16, and the rotation speed of the motor 16 is controlled by a control device 30 that controls the voltage and frequency of its power source. A is a commercial power supply (three-phase here), which is used as the primary power supply, and the control device 30 has six diodes D ₁ ,
It is rectified by a rectifier circuit B consisting of D ₂ , D ₃ , D ₄ , D ₅ , D ₆ , a chopper coil CH ₁ , and a capacitor C ₁ and converted into a DC power supply, and the chopper control circuit F is supplied by the speed signal generated in the speed signal circuit E. is activated to turn on the transistor Tr ₂ of the chopper circuit C.
OFF, control the voltage of the DC power supply, and connect the controlled power supply to the CH ₂ coil and the capacitor.
The adjusted _and smoothed DC power is input to the bridge inverter control circuit G, and the bridge inverter control circuit G generates a frequency corresponding to this DC voltage, which is connected to the chopper circuit C. The transistors Tr ₂ , Tr ₃ , Tr ₄ , Tr ₅ , Tr ₆ , and Tr ₇ of the bridge inverter circuit D are turned on and off.
Then, three-phase rectangular wave power is generated and supplied to the motor 16. Note that the transistors Tr ₂ , Tr ₃ , Tr ₄ , Tr ₅ ,
Diodes D ₇ , D ₈ , D ₉ , D ₁₀ , D ₁₁ , and D ₁₂ connected in parallel with Tr _{6 and} Tr 7 pass the reverse starting force from the motor 16 when each transistor is turned off. It protects each transistor. H is a load signal generator, which generates a difference signal between the room temperature detector 25 and the room temperature setter 26, which is a variable resistor that commands the set temperature of the room temperature, and inputs it to the speed signal circuit E to generate a speed signal. to occur.

31 is a control circuit for the expansion valve 20, and the thermistor 27 controls the refrigerant evaporation temperature T _E of the evaporator 22.
, the thermistor 21 detects the suction refrigerant temperature T _S of the compressor 15, and the temperature difference ΔT (= T _S
-T _E ) and a reference signal of the temperature difference ΔT provided therein, a difference signal generator I controls the PID operation PI operation, etc., and generates an output, and the speed signal A capacitance change signal circuit J that detects the output change rate of the circuit E and outputs an output corresponding to this output change rate, that is, the capacity change rate of the compressor, and the output from the capacitance change signal circuit J and the difference signal generator I. and a valve control circuit K that controls the throttle resistance of the expansion valve 20 based on the value of the output from the expansion valve 20. In this embodiment, this valve control circuit K
The configuration is such that the expansion valve 20 is controlled by the sum of the outputs of the difference signal generator I and the capacitance change signal circuit J.

Next, the operation of the refrigeration system shown in FIG. 1 will be explained with reference to the operation diagram shown in FIG. This operation explanatory diagram shows the output R of the speed signal circuit E corresponding to the rotational speed of the compressor 15, the speed change rate ΔR/Δt indicating the rate of change in time Δt of this output R, and the valve opening area of the expansion valve 20. 3 shows changes in the output V _EX of the valve control circuit K, the valve opening area B of the expansion valve 20, and the temperature difference ΔT in the refrigerant temperature over time t.

Until time _t0 , the load on the refrigeration system is constant, the output R of the speed signal circuit E is a constant value of _R0 , and the compressor 15 is rotating at a constant speed. At this time, ΔR/Δt corresponding to the speed change rate is zero, and the output V _EX of the valve control circuit K
is controlled by the output of the difference signal generator I and its value becomes V ₀ , the valve opening area B of the expansion valve 20 becomes a constant value B ₀ , and the temperature difference ΔT of the refrigerant detected by thermistors 21 and 27 is It remains constant and stable operation continues. If the load on the refrigeration equipment increases at time t ₀ at this time, for example, if the room temperature rises rapidly and is detected by the room temperature detector 25, or if the set temperature of the room temperature is lowered by the room temperature setting device 26, The load signal generator H increases the output R of the speed signal circuit E with a certain appropriate time constant T, and as a result, the chopper control circuit F causes the power supply voltage and frequency of the motor 16 to correspond to the output R. As the load increases, the compressor 15 speeds up and is controlled to operate at a capacity commensurate with the load. The rate of change ΔR/Δt of the output R increases rapidly at time T ₀ , then gradually decreases and becomes zero again. This rate of change ΔR/Δ
An output corresponding to t is output from the capacitance change signal circuit J to the valve control circuit K. Valve control circuit K of this output
The value corresponding to the output of V _EX is shown by the dashed-dotted line a, while the dashed line b is the output V _EX of the valve control circuit K corresponding to the output of the difference signal generator I,
The total output V _EX is the output shown by the solid line c, which is the sum of these values, and even with this value, the valve opening area B of the expansion valve 20 is controlled in a direction to be larger than B ₀ .
During a predetermined period of time after this time _t0 , the output V _EX of the valve control circuit K increases rapidly due to the input of a large input signal from the capacity change signal circuit J, and the compressor capacity increases due to the valve opening area of the expansion valve 20. The corresponding delay can be reduced. As a result, even if the output R of the speed signal circuit E changes to R _H as shown in FIG.
5, a large amount of unevaporated refrigerant liquid does not return, and the refrigerant in the evaporator 22 does not become extremely overheated, allowing stable operation of the refrigeration system.

Next, at time t ₁ , the load on the refrigeration system decreases, and the output R of the speed signal circuit E changes from R _H to R _L with a time constant T.
If the output R changes due to the change rate ΔR/
Δt has a negative value. As a result, the output V _EX of the valve control circuit K is the output of the expansion valve 2 due to the output of the difference signal generator I.
0 _minus the output of the capacitance change signal circuit J, the expansion valve 20 rapidly closes its opening area, and as a result, the expansion valve 2
The responsiveness to changes in the compressor capacity becomes good, and unevaporated refrigerant liquid does not return to the compressor 15, making stable operation possible. When the capacity reduction rate of the compressor 15 becomes constant, the output from the capacity change signal circuit J disappears, and the expansion valve 20 is controlled in accordance with the output from the difference signal generator I.
As a result, during constant capacity operation of the compressor, the expansion valve 20 is controlled according to the refrigerant temperature, making it possible to control the degree of pseudo superheat to be constant, thereby enabling efficient operation. In Fig. 2, the output R of the speed signal circuit E
We have shown a case in which there is a large change in the output R, that is, the compressor capacity, while the refrigeration system is in operation, but the rate of change ΔR/Δt is small at this time, and the valve control There is little influence on the output V _EX of the circuit K, and the expansion valve 20 is mostly controlled by refrigerant temperature detection.

In the above embodiment, the case where the capacity of the compressor is continuously changed has been explained, but it can also be applied to the case where the capacity is controlled in multiple stages. It is also clear that compressor capacity control can be applied to methods other than changing the rotational speed. In addition to controlling the refrigerant throttling resistance with a heater and bimetal, the expansion valve can also be controlled magnetically with an electromagnetic coil (although in this case, the delay in response is small due to the heater and bimetal system) or electrically with other methods. It is clear that the method is fine. However, in this case, it is necessary to reduce the ratio of the compressor capacity change rate to the expansion valve control, and in this case, there is an effect of reducing the delay in refrigerant temperature detection that occurs when detecting with a thermistor or the like.

As is clear from the above embodiments, the refrigeration system of the present invention includes a capacity control compressor, a condenser, an expansion valve that electrically changes the refrigerant throttling resistance, an evaporator, and a refrigerant circuit that detects the refrigerant temperature. temperature detection means, capacity change detection means for detecting a temporal change rate of capacity increase of said capacity control compressor, and said expansion valve based on a composite value of a signal from said temperature detection means and a signal from said capacity change detection means. Equipped with a control device that has valve control means to control the expansion valve, it can speed up the response speed of the expansion valve when the compressor capacity changes, enabling stable continuous operation of the refrigeration system, and preventing large changes in the compressor capacity. When the compressor capacity changes, the expansion valve can be controlled by mainly detecting the refrigerant temperature. It becomes possible to operate the refrigeration equipment efficiently.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the refrigeration system of the present invention, FIG. 2 is an explanatory diagram of the operation of the refrigeration system, and FIG. 3 is a refrigerant circuit diagram of a conventional refrigeration system. 15...capacity control compressor, 17...condenser, 2
0... Expansion valve, 22... Evaporator, 29... Refrigerant circuit, 31... Control circuit, I... Difference signal generator (temperature detection means), J... Capacity change signal circuit (capacity change detection means) , K...Valve control circuit (valve control means).

Claims (1)

[Claims] 1. A refrigerant circuit composed of a capacity control compressor, a condenser, an expansion valve that electrically changes the refrigerant throttling resistance, and an evaporator, a temperature detection means that detects the refrigerant temperature, and a temporal change in the capacity increase of the capacity control compressor. A refrigeration system comprising a control device having a capacity change detection means for detecting a ratio, and a valve control means for controlling the expansion valve by a composite value of a signal from the temperature detection means and a signal from the capacity change detection means.