Method for controlling electronically controllable expansion valve (EEV) in refrigerant circuit

Abstract

The invention relates to a method for controlling an electronically controllable expansion valve (EEV) in a refrigerant circuit, the refrigerant circuit includes a circulating refrigerant, a compressor, a condenser arranged behind the compressor and in front of the EEV in a flow direction of the refrigerant, and an evaporator arranged behind the EEV and in front of the compressor in the flow direction of the refrigerant, including: determining an evaporation temperature of the refrigerant; determining a target suction pressure of the refrigerant at or behind the output end of the evaporator; determining an actual suction pressure of the refrigerant at or behind the output end of the evaporator, and determining a pressure deviation between the actual and target suction pressures; controlling the compressor based at least in part on the pressure deviation; determining a target temperature of the refrigerant at a predetermined portion of the refrigeration circuit; determining an actual temperature of the refrigerant at or behind the output of the evaporator, and determining a temperature deviation between the actual temperature and a target temperature; the EEV is controlled based at least in part on the temperature deviation.

Description

Technical Field

[0001] The invention relates to a method for controlling an electronically controllable expansion valve (EEV) in a refrigerant circuit. The refrigerant circuit can be a refrigerant circuit in a battery-electrically driven vehicle and is designed to provide thermal energy for the passenger compartment or other components such as, for example, a battery. Background Art

[0002] Refrigerant circuits are used in the prior art for various applications in order to achieve heat transfer in a desired direction. Examples include heating the passenger cabin and / or the battery of a vehicle at cold ambient temperatures and cooling the passenger cabin and / or the battery as required.

[0003] In such refrigerant circuits, physical effects are used so that the evaporation point of the refrigerant can be influenced in a certain temperature range by changing the pressure of the refrigerant. This applies in that the evaporation point increases when the refrigerant pressure increases.

[0004] To increase the pressure, electronically controllable compressors are used in the refrigerant circuit, which increase the pressure in the section of the refrigerant circuit in which the condenser is arranged for discharging thermal energy, for example to the passenger compartment. This section is defined by an electronically controllable expansion valve (EEV), via which the refrigerant is decompressed and brought to a lower pressure level. An evaporator is arranged behind the EEV for absorbing thermal energy, for example from the vehicle environment or from waste heat of other vehicle components.

[0005] Requirements for the refrigeration circuit can be, for example, that the refrigerant in the evaporator should have a certain temperature level in order to have a certain gradient relative to the heat to be dissipated and that the refrigerant temperature downstream of the evaporator should also exceed the evaporation temperature of the refrigerant by a predetermined amount, thereby ensuring that only gaseous refrigerant is sucked in by the compressor.

[0006] In order to meet this requirement, various control methods for expansion valves and compressors have been proposed. However, it has been found that in the methods known to date, disadvantageous interactions between the compressor control and the control of the EEV occur, which lead to a sluggish control and, if necessary, the inability to set a stable operation of the compressor.

[0007] The object of the present invention is to propose an alternative or improved method for controlling an electronically controllable expansion valve in a refrigerant circuit, as well as a control device for an electronically controllable expansion valve, a refrigerant circuit, a computer program for executing the method and a computer-readable data carrier. Summary of the invention

[0008] The objects of the invention are achieved by means of a method according to claim 1, by a control device of an electronically controllable expansion valve (EEV) according to claim 8, by a refrigerant circuit according to claim 9, by a computer program according to claim 10 and by a computer-readable data carrier according to claim 11.

[0009] Advantageous developments, additional features and / or advantages of the invention are revealed in the dependent claims and in the following description.

[0010] According to a first aspect, the present disclosure discloses a method for controlling an electronically controllable expansion valve (EEV) in a refrigerant circuit, the refrigerant circuit comprising at least a circulating refrigerant, a compressor, a condenser arranged behind the compressor in a flow direction of the refrigerant and in front of the EEV, and an evaporator arranged behind the EEV in a flow direction of the refrigerant and in front of the compressor, the method comprising the following steps:

[0011] S1. Determine the desired evaporation temperature T of the refrigerant V ;

[0012] S2. Determine the evaporation temperature T of the refrigerant at or behind the output end of the evaporator V The corresponding target suction pressure P Ist ;

[0013] S3. Determine the actual suction pressure P of the refrigerant at or behind the output end of the evaporator Ist , and determine the actual suction pressure P Ist and target suction pressure P Soll Pressure deviation Δ P ;

[0014] S4. Based at least in part on the pressure deviation Δ P To control the compressor;

[0015] S5. Determine the target temperature T of the refrigerant at a predetermined location of the refrigeration circuit. Soll ;

[0016] S6. Determine the actual temperature T of the refrigerant at the predetermined location Ist , and determine the actual temperature T Ist With the target temperature T Soll The temperature deviation between T ;

[0017] S7. Based at least in part on the temperature deviation Δ T To control the EEV.

[0018] According to another aspect, the present disclosure discloses a control device for an electronically controllable expansion valve (EEV) in a refrigerant circuit, the refrigerant circuit comprising at least: a circulating refrigerant; a compressor having a compressor control device; a condenser arranged behind the compressor and in front of the EEV in the flow direction of the refrigerant; an evaporator arranged behind the EEV and in front of the compressor in the flow direction of the refrigerant; and a device for determining a temperature signal and transmitting it to the control device, wherein the temperature signal reflects the actual temperature T of the refrigerant at or behind the output end of the evaporator. Ist and a device for determining a pressure signal and transmitting it to the compressor control device and the control device, wherein the pressure signal reflects the actual suction pressure P of the refrigerant at or after the output end of the evaporator Ist ; wherein the control device is set up to execute the method described above.

[0019] According to another aspect, the present disclosure discloses a refrigerant circuit, which includes: an electronically controllable expansion valve (EEV); a control device for the EEV; a circulating refrigerant; a compressor having a compressor control device; a condenser arranged behind the compressor and in front of the EEV in the flow direction of the refrigerant; an evaporator arranged behind the EEV and in front of the compressor in the flow direction of the refrigerant; and a device for determining a temperature signal and transmitting it to the control device, wherein the temperature signal reflects the actual temperature T of the refrigerant at or behind the output end of the evaporator. Ist and a device for determining a pressure signal and transmitting it to the compressor control device and the control device, wherein the pressure signal reflects the actual suction pressure P of the refrigerant at or after the output end of the evaporator Ist ; wherein the control device of the EEV is set up to execute the method described above.

[0020] According to a further aspect, the disclosure discloses a computer program for executing the method described above when the computer program is executed by a control device of an electronic expansion valve (EEV) or is stored on a computer-readable data carrier.

[0021] According to a further aspect, the present disclosure discloses a computer-readable data carrier having stored thereon a computer program.

[0022] In the method, in step S7 the EEV can be controlled both on the basis of the temperature deviation ΔT and also on the basis of the pressure deviation ΔP.

[0023] In step S7 , the EEV can be controlled selectively using a PID control scheme (proportional-integral-derivative), using a PD control scheme (proportional-derivative), or using a quasi-PD control scheme.

[0024] Step S7 can include the following steps:

[0025] S7a-Comparing the pressure deviation ΔP with a predetermined tolerance value ε and determining, based on the comparison, the actual suction pressure P Ist is around the target suction pressure P Soll is within or outside the tolerance range determined by the tolerance value ε;

[0026] S7b-Based on the determination made in step S7a, at the actual suction pressure P Ist Around the target suction pressure P Soll If the actual suction pressure P is outside the predetermined tolerance range, the EEV is controlled by the PD control scheme or the quasi-PD control scheme in step S7, and the actual suction pressure P Ist Around the target suction pressure P Soll If the predetermined tolerance range is within the range, the EEV is controlled using a PID control scheme in step S7.

[0027] Steps S7a and S7b can be repeatedly performed in a loop.

[0028] In step S7, the input variable for the control of the EEV can be the temperature deviation Δ T , and the output variable of the control is the opening cross section of the EEV.

[0029] The predetermined point of the refrigeration circuit can be located at or after the output of the evaporator.

[0030] In step S5, the target temperature T can be determined as follows S , so that the target temperature is higher than the evaporation temperature T V To a predetermined degree.

[0031] The predetermined point of the refrigeration circuit can be at or after the output of the condenser.

[0032] In step S5, the target temperature T can be determined as follows S , so that the target temperature is higher than the evaporation temperature T V To a predetermined degree. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is explained in more detail below with reference to the attached schematic and not true-to-scale drawings according to the embodiments. In the present invention, features can be designed in a positive manner, that is, in existence, or in a negative manner, that is, in non-existence. In the description, negative features are not explicitly explained as features if it is not emphasized that the feature does not exist according to the present invention. That is, the invention that is actually implemented and not designed by the prior art is to omit these features. The absence of features (negative features) in the embodiments indicates that the features are optional. In the merely exemplary figures (figures) of the accompanying drawings, it is shown:

[0034] Figure 1 A refrigerant circuit according to one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0035] Figure 1 A refrigerant circuit 10 is shown, in which a refrigerant circulates, for example driven by a refrigerant pump (not shown). The refrigerant comprises in particular propane (R290) and / or CO2 (R744). The flow direction of the refrigerant is Figure 1 Indicated by arrow 15. In this case, the refrigerant absorbs heat at the evaporator 400, for example from the surroundings of the vehicle or from the waste heat of specific vehicle components, and releases this heat to the condenser 300, for example to the passenger compartment or to the battery. Optionally, further heat sources and heat sinks can also be arranged in the refrigeration circuit 10.

[0036] To increase the temperature level of the refrigerant, the refrigerant is brought to a higher pressure by an electronically controllable compressor 200 arranged between the evaporator 400 and the condenser 300. To expand the refrigerant, an electronically controllable expansion valve (EEV) 100 is arranged after the condenser 300.

[0037] The desired temperature T of the refrigerant in the evaporator 400 Soll It is usually variable according to the situation and depends on different factors. For example, in the case where the secondary side of the evaporator 400 is air, the refrigerant temperature T Soll It should not be too cold in order to avoid ice formation in the evaporator 400 due to moisture from the surrounding environment. On the contrary, an excessively high temperature T of the refrigerant in the evaporator 400 Soll The heat absorption would be reduced, which in turn would lead to a too low heat release at the condenser 300 and thus could lead to moisture and odor problems in the passenger cabin.

[0038] In addition, the refrigerant temperature T at a predetermined location of the refrigerant circuit 10 is adjusted according to the structure of the corresponding refrigeration circuit 10. Soll Additional requirements were made.

[0039] For example, in a particular system, such as a receiver / dryer system, the refrigerant temperature after the evaporator 400 is T Soll Should exceed the evaporation temperature T of the refrigerant V The predetermined amount ensures that only gaseous refrigerant is sucked into the compressor 200. The refrigerant temperature T Soll Exceeds the evaporation temperature T of the refrigerant at the evaporator output V The temperature range is also called "superheat" or "superheat degree".

[0040] Another requirement for the refrigeration circuit 10 may be that “subcooling” of the refrigerant must be achieved downstream of the condenser 300 , for example in a battery system. “Subcooling” means that T Soll is lower than the evaporation temperature T of the refrigerant V A temperature of a predetermined measure.

[0041] In the context of the further description, an embodiment is described by way of example in which the predetermined point is located at or downstream of the outlet of the evaporator 400 and at which superheating must be ensured.

[0042] The refrigerant circuit 10 can be controlled in such a way that in step S1 the desired evaporation temperature T of the refrigerant is determined as a function of the above-mentioned boundary conditions. V In step S2, the evaporation temperature T of the refrigerant at a specific pressure level is V The known relationship between the refrigerant temperature T at or after the output end of the evaporator 400 is determined by V The corresponding target suction pressure P Ist .

[0043] In step S3, the actual suction pressure P of the refrigerant at or after the output of the evaporator 400 is determined by a suitable device 205 and at a suitable frequency. Ist , for example, by a pressure sensor arranged at this location, and a corresponding pressure signal is sent to the compressor control device 210, which Figure 1 In the figure, the connection 201 is used to indicate the existence of the target value and the actual value of the suction pressure. P =P Ist -P Soll To determine the actual suction pressure P Ist and target suction pressure P Soll Pressure deviation Δ P .

[0044] In step S4, the electronic compressor control 210 controls the compressor at least partially as a function of the pressure deviation Δ as an input variable for the control. PTo control the compressor 200, the pressure deviation is determined by the compressor control device 210 at a suitable frequency, that is, as a time Δ P (t) is a function of t. Further input variables can also be taken into account by the compressor control 210.

[0045] In step S5, the control device 110 for controlling the EEV 100 determines a target temperature T of the refrigerant at a predetermined location of the refrigerant circuit 10, that is, at or after the output end of the evaporator 400. Soll As already explained above, if superheating is to be ensured, the target temperature T is determined in this way: Soll , so that the target temperature exceeds the evaporation temperature T of the refrigerant V A specific measure, which can optionally be obtained by summing the Soll =T V +Δ T (where the constant term Δ T is superheat) or by quadrature solution T Soll =cT V (wherein the constant factorial distance c from the evaporation temperature is the superheat) to take this into account.

[0046] In step S6, the actual temperature T of the refrigerant at a predetermined location, in the described embodiment, at or after the output of the evaporator 400, is determined. Ist Here, the actual temperature T of the refrigerant is determined by a device arranged at this location. Ist A suitable device 105, for example a temperature sensor, can determine the actual temperature T of the refrigerant at or after the output of the evaporator 400. Ist . The actual temperature T Ist is transmitted to the control device 110, which Figure 1 This is indicated by line 101 .

[0047] Likewise, in step S6, the control device 110 performs the T =T Ist -T Soll To determine the actual temperature T Ist With the target temperature T Soll The temperature deviation between T .

[0048] In step S7, the control device 110 controls the temperature deviation Δ as an input variable of the control at least in part. T (t) to control the EEV 100, where t represents the temperature deviation Δ T Dependence on time. Temperature deviation Δ T(t) is determined virtually quasi-continuously with a suitable frequency by the control device 110. The output variable of the control is the opening cross section u(t) of the EEV 100, again as a time-dependent function.

[0049] The PID control scheme (proportional-integral-derivative) is used as the control scheme in the control device 110. The PID control scheme is known in principle and is based on the control variable u(t) and the process variable Δ T (t) the following relationship between:

[0050]

[0051] In this K P , K i and K d All are process variables Δ T The proportional component (Kp), integral component (Ki) and differential component (K d ) has a non-negative coefficient.

[0052] Since a change in the opening cross section u(t) of the EEV 100 also affects the suction pressure of the refrigerant upstream of the compressor 200, mutual influences of the compressor control 210 and the control 110 may occur, which is also referred to as “crosstalk” and may result in an inability to stably set the desired pressure P of the refrigerant downstream of the evaporator. Soll .

[0053] Therefore, in the embodiment of the present invention, the pressure deviation Δ P The actual suction pressure P is determined based on the comparison. Ist is around the target suction pressure P Soll The tolerance range P determined by the tolerance value ε T =P Soll Within or outside ±ε.

[0054] Based on the determination made in step S7a, the actual suction pressure P Ist Around the target suction pressure P Soll The predetermined tolerance range P T In the case other than the above, the EEV 100 is controlled in step 7b using a PD control scheme (proportional-derivative) or a quasi-PD control scheme. To this end, in the case of the PD scheme, the coefficient K mentioned in equation 1 can be iis set to zero. In the case of a quasi-PD control scheme, the integral component is selected to be very small, which means that a very small, but not vanishing coefficient for Ki appears in equation 1. The control scheme then behaves similarly to a PD control scheme, so the term quasi-PD control scheme is used within the scope of this application.

[0055] At the actual suction pressure P Ist Around the target suction pressure P Soll The predetermined tolerance range P T In the case of the above, the PID control scheme is used to control the EEV 100. Steps S7a and S7b are repeated in a cyclic manner at a suitable frequency.

[0056] Advantages of this embodiment include that the compressor 200 does not reach the target suction pressure P Soll Tolerance range P T During the time period, the EEV 100 is controlled only with the proportional component and the derivative component of the control scheme of Equation 1. Thus, the compressor 200 can reach the target value P more quickly than when the EEV 100 is set to a fixed opening value. Soll , and despite this there is almost superheat. Regulation close to superheat improves the efficiency of operation.

[0057] Furthermore, the inventors have determined that in many applications the parameters for the PD control mode and the PID control mode do not have to be changed, so that only one parameter set is required. Ist Around the target suction pressure P Soll The predetermined tolerance range P T In other cases, simply replace the coefficient K in the equation mentioned in equation 1 i Set to zero.

[0058] Furthermore, it is ensured that the compressor 200 can be stabilized, which, as already described above, is not necessarily the case in the prior art, in which the integral part K of the control scheme shown in equation 1 is activated prematurely. i It may result that the compressor 200 cannot reach the operating point or reaches it only later through P Soll The specified absorption power.

[0059] If the integral component K iIf the control of the EEV 100 is always active, this can lead to an interaction with the compressor control 210. On the one hand, this leads to a longer settling time of the compressor control, but on the other hand, it also leads to a fluctuating control of the EEV 100. The reason for this is that the compressor control 210 and the control device 110 partially interfere with each other. The control described above therefore leads to less overshoot and a faster settling time of the control of the EEV 100.

[0060] By controlling the opening cross section instead of a specific valve position, it is achieved that the control of the EEV 100 does not have to take these nonlinear effects into account. This leads to improved and simplified controller parameter recognition and avoids parameter switching in the control device 110. In addition, since the valve characteristic curve of the EEV 100 is not dependent on the control, the conversion to a new drive is significantly easier.

[0061] In an embodiment of the present invention, the compressor control device 210 and the control device 100 are as shown in Figure 1 As shown in FIG. 1 , it is integrated into a higher-level control device 50 .

[0062] It should be pointed out that the numbering of steps S1 to S7 does not necessarily imply a chronological order. Thus, for example, in one embodiment of the invention, steps S1 to S4 are executed largely in parallel with steps S5 to S7.

[0063] The invention is not limited to the exemplary embodiments described and shown. Rather, the invention also includes all special developments within the scope of the invention defined by the claims.

[0064] In addition to the described and illustrated embodiments, further embodiments are conceivable which may include further variants and combinations of features.

Claims

1. A method for controlling an electronically controllable expansion valve (EEV) (100) in a refrigerant circuit (10), the refrigerant circuit (10) comprising at least a circulating refrigerant, a compressor (200), a condenser (300) arranged behind the compressor (200) and in front of the EEV (100) along the flow direction of the refrigerant, and an evaporator (400) arranged behind the EEV (100) and in front of the compressor (200) along the flow direction of the refrigerant, the method comprising the following steps: S1. Determine the desired evaporation temperature T of the refrigerant V ; S2. Determine the refrigerant at or behind the output end of the evaporator (400) and the evaporation temperature T V The corresponding target suction pressure P Ist ; S3. Determine the actual suction pressure P of the refrigerant at or behind the output end of the evaporator (400) Ist , and determine the actual suction pressure P Ist and target suction pressure P Soll Pressure deviation Δ P ; S4. Based at least in part on the pressure deviation Δ P to control the compressor (200); S5. Determine the target temperature T of the refrigerant at a predetermined location of the refrigeration circuit (10) Soll ; S6. Determine the actual temperature T of the refrigerant at the predetermined location Ist , and determine the actual temperature T Ist With the target temperature T Soll The temperature deviation between T ; S7. Based at least in part on the temperature deviation Δ T to control the EEV (100).

2. The method according to claim 1, characterized in that: In step S7, not only the temperature deviation Δ T And also based on the pressure deviation Δ P to control the EEV (100).

3. The method according to claim 2, characterized in that In step S7, the EEV (100) is optionally controlled using a PID control scheme (proportional-integral-derivative), using a PD control scheme (proportional-derivative), or using a quasi-PD control scheme.

4. The method according to claim 3, characterized in that Step S7 includes the following steps: S7a-The pressure deviation Δ P is compared with a predetermined tolerance value ε and the actual suction pressure P is determined based on the comparison Ist is around the target suction pressure P Soll The tolerance range P determined by the tolerance value ε T Inside or outside; S7b-Based on the determination made in step S7a, at the actual suction pressure P Ist At around the target suction pressure P Soll If the actual suction pressure P is outside the predetermined tolerance range, the EEV (100) is controlled by a PD control scheme or a quasi-PD control scheme in step S7, and the actual suction pressure P Ist At around the target suction pressure P Soll The predetermined tolerance range P T If the condition is within the range, the EEV (100) is controlled using a PID control scheme in step S7.

5. The method according to claim 4, characterized in that The steps S7a and S7b are repeatedly performed in a loop.

6. The method according to any one of claims 1 to 5, characterized in that In step S7 , the input variable of the control of the EEV ( 100 ) is the temperature deviation DT, and the output variable of the control is the opening cross section of the EEV ( 100 ).

7. The method according to any one of claims 1 to 6, characterized in that The predetermined location of the refrigeration circuit (10) is located at or after the output end of the evaporator (400).

8. The method according to any one of claims 1 to 7, characterized in that In step S5 , the target temperature TS is determined in such a way that it is higher than the evaporation temperature TV by a predetermined amount.

9. The method according to any one of claims 1 to 6, characterized in that The predetermined location of the refrigeration circuit (10) is located at or behind the output end of the condenser (300).

10. The method according to claim 9, characterized in that In step S5 , the target temperature TS is determined in such a way that it is lower than the evaporation temperature TV by a predetermined amount.

11. A control device (110) for an electronically controllable expansion valve (EEV) (100) in a refrigerant circuit (10), the refrigerant circuit (10) comprising at least: - circulating refrigerant; - A compressor (200) having a compressor control device (210); - a condenser (300) arranged behind the compressor (200) and in front of the EEV (100) in the flow direction of the refrigerant; - an evaporator (400) arranged behind the EEV (100) and in front of the compressor (200) in the flow direction of the refrigerant; - means (105) for determining a temperature signal and transmitting it to the control device (110), wherein the temperature signal reflects the actual temperature TIst of the refrigerant at a predetermined location of the refrigeration circuit (10); and - means (205) for determining a pressure signal and transmitting it to the compressor control device (210) and to the control device (110), wherein the pressure signal reflects the actual suction pressure PIst of the refrigerant at or after the output end of the evaporator (400); Therein, the control device (110) is configured to carry out the method according to any one of claims 1 to 11.

12. The control device (110) according to claim 11, characterized in that: The predetermined location of the refrigeration circuit (10) is located at or after the output end of the evaporator (400).

13. The control device (110) according to claim 10, characterized in that: The predetermined location of the refrigeration circuit (10) is located at or behind the output end of the condenser (300).

14. A refrigerant circuit (10), comprising: - an electronically controllable expansion valve (EEV) (100); - a control device (110) for said EEV (100); - circulating refrigerant; - A compressor (200) having a compressor control device (210); - a condenser (300) arranged behind the compressor (200) and in front of the EEV (100) in the flow direction of the refrigerant; - an evaporator (400) arranged behind the EEV (100) and in front of the compressor (200) in the flow direction of the refrigerant; - means (105) for determining a temperature signal and transmitting it to the control device (110), wherein the temperature signal reflects the actual temperature TIst of the refrigerant at a predetermined location of the refrigeration circuit (10); and - means (205) for determining a pressure signal and transmitting it to the compressor control device (210) and to the control device (110), wherein the pressure signal reflects the actual suction pressure PIst of the refrigerant at or after the output end of the evaporator (400); Therein, a control device (110) of the EEV (100) is configured to carry out a method according to any one of claims 1 to 11.

15. The refrigerant circuit (10) according to claim 14, characterized in that: The predetermined location of the refrigeration circuit (10) is located at or after the output end of the evaporator (400).

16. The refrigerant circuit (10) according to claim 14, characterized in that: The predetermined location of the refrigeration circuit (10) is located at or behind the output end of the condenser (300).

17. Computer program for carrying out the method according to any one of claims 1 to 11, when the computer program is executed by a control device (110) of the electronic expansion valve (EEV) (100) or is stored on a computer-readable data carrier.

18. A computer-readable data carrier having stored thereon a computer program according to claim 17.

Images