A method for controlling suction superheat of dry water chiller

Abstract

The present invention relates to a method for controlling suction superheat of a dry chiller. The collected suction superheat is substituted into a new independent algorithm, which can simulate the opening of the electronic expansion valve during the whole operation of the unit, analyze and verify the rationality of each coefficient in the algorithm in advance, ensure the precise control of the opening of the electronic expansion valve, and realize the safe, reliable and efficient operation of the unit under various working conditions. The new algorithm introduced in the present invention calculates the increment of the opening. The target opening of the expansion valve in this cycle is the target opening of the previous calculation cycle plus the increment of this calculation plus the protection item. Even after the protective adjustment is performed and the algorithm is jumped back, it is the target opening of the previous calculation cycle plus the increment of this calculation. Therefore, it has the advantages of small fluctuation of the opening of the electronic expansion valve and timely response.

Description

Technical Field

[0001] The present invention relates to the technical field of dry water chillers, and in particular to a method for controlling suction superheat of a dry water chiller, which can be applied to all water chillers with dry evaporators. Background Art

[0002] Many refrigeration host manufacturers currently use Siemens PLC to perform PID control of the suction superheat of the electronic expansion valve. When performing PID control on the electronic expansion valve, due to the invisibility of the PLC internal, it is impossible to fully control its PID algorithm, resulting in frequent problems such as unreasonable opening of the electronic expansion valve, delayed response, and large fluctuations in opening. Therefore, it is difficult to add or change certain controls of the expansion valve, and conflicts will occur, and the expansion valve opening is not ideal in actual use.

[0003] In addition, because the PID formula inside the Siemens PLC is a position type, it directly calculates the target opening of the expansion valve. When protective adjustments are made (such as opening the valve when the exhaust temperature is too high, closing the valve when the exhaust superheat is too low, and closing the valve when the low pressure is too high), and then jumping back to the PID calculation, there is a situation where the target opening is not appropriate. Summary of the invention

[0004] The object of the present invention is to provide a method for controlling suction superheat of a dry chiller to solve the problems encountered in the above-mentioned background technology.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for controlling suction superheat of a dry chiller comprises the following steps:

[0007] Step S01: After the dry chiller is powered on, the system is initialized and the system self-check is completed. At the same time, the electronic expansion valve is initialized to ensure that the opening is 0.

[0008] Step S02, turn on the oil heater. When the main contactor is closed, the oil heater is automatically disconnected. The oil heater and the main contactor are interlocked.

[0009] Step S03: Click the start button of the dry chiller, which is a start command, and the refrigeration pump will start after 5 seconds.

[0010] If the freezing pump has a startup feedback, it will delay for 120 seconds to check whether the freezing water temperature is in the startup area. If it is in the startup area and the shutdown interval is ≥20 minutes, the cooling pump will be turned on. After a delay of 45 seconds, it will check whether the cooling water flow is normal. If the cooling water flow is normal, the startup preparation is complete.

[0011] Step S04, start the compressor with the shortest cumulative running time, and run a certain number of solenoid valves; at the same time, the electronic expansion valve enters the non-regulating stage, and the expansion valve opening is opened from 0 to the starting opening of 15-20%; the compressor completes the starting process and continues to run at 50% load; when the exhaust superheat exceeds the minimum exhaust superheat by 15°C and is maintained for 30 seconds, the electronic expansion valve jumps out of the non-regulating stage and enters the regulating stage.

[0012] Start the 25% adjustable solenoid valve and energize it for 30 seconds, close the other adjustable solenoid valves, start the compressor to complete the star-delta conversion, and determine whether the compressor delta contactor has feedback. If there is no feedback, an alarm will be issued to shut down the machine. If there is feedback, the machine will run at 25% load for 30 seconds. After running at 25% load for 30 seconds, the compressor is loaded to 50% load, and the electronic expansion valve is opened to the specified opening. The specified opening is the larger value of the current opening and the minimum allowable opening U (min).

[0013] During this process, the evaporation pressure is monitored. If the measured evaporation pressure is ≤ d, the expansion valve opening is increased; if the measured evaporation pressure is ≥ e, the expansion valve opening is decreased. d and e are preset values, which are related to the type of refrigerant. The confirmation method is: d = saturated pressure corresponding to the target outlet water temperature - 9 degrees; e = set MOP pressure or actual exhaust pressure - 4 bar, whichever is smaller.

[0014] Step S05, after the electronic expansion valve enters the adjustment stage, an algorithm is used to control the suction superheat; at the same time, the compressor adjusts the load according to the water temperature. If the compressor is already at the load position indicating the completion of the startup, that is, 50% load, the load will no longer be reduced, and the current load position will be maintained to continue running.

[0015] The method for adjusting the load of the compressor according to the water temperature is as follows: if the outlet water temperature is in the loading zone and the loading cycle time t1 is reached, the load position of the compressor is loaded to a higher level for operation; if the water temperature is in the holding zone, the load control of the compressor is stopped to maintain the current load position; if the water temperature is in the unloading zone and the unloading cycle time t2 is reached, the load position of the compressor is unloaded for operation to a lower level.

[0016] Step S06, calculate the increment △U(n) ​​of the opening of the electronic expansion valve, △U(n)=m×A×[e(n)-e(n-1)]+m×e(n) / B, where A and B are preset coefficients, and e(n) is the suction superheat deviation; at the same time, set |△U(n)| in this algorithm to ≤3%.

[0017] Suction superheat deviation e(n), e(n) = Ts-Ts′, where Ts is the suction superheat and Ts′ is the set suction superheat; suction superheat Ts = Txq-Tzf, Txq is the suction temperature and Tzf is the evaporation temperature.

[0018] During the first calculation, e(n) is directly assigned to e(n-1); when |e(n)|≤2℃, m=1; when |e(n)|>2℃, m=|e(n) / 2|.

[0019] Step S07, calculate the target opening U(n) of the electronic expansion valve, U(n)=U(n-1)+△U(n)+p(n), wherein p(n) is the system protection item adjustment, and U(n-1) is the current opening of the expansion valve after actuation; that is, the target opening U(n) is the target opening of the previous calculation cycle plus the opening increment of the current calculation cycle plus the protection item adjustment.

[0020] Step S08, calculating the actual opening degree A(n) of the electronic expansion valve, A(n)=U(n), and A(n) is between the minimum allowable opening degree U(min) and the maximum allowable opening degree U(max).

[0021] In the above scheme, p(n) is the system protection item adjustment, p(n)=q(n)+r(n)+x(n), q(n) is the exhaust temperature too high protection, r(n) is the exhaust superheat too low protection, x(n) is the suction pressure too high protection. When p(n)≠0, let △U(n)=0.

[0022] Exhaust temperature over-high protection q(n), the protection priority is 1. When the exhaust temperature exceeds 95℃, the opening is increased by 3% instantly, and then by 1% every 5 seconds. When the exhaust temperature is less than or equal to 95℃, this item is 0;

[0023] Exhaust superheat under-protection r(n), the protection priority is 2. When the exhaust superheat is lower than 15℃, the opening is instantly reduced by 3%, and then the opening is reduced by 1% every 5s; when the exhaust superheat is greater than or equal to 15℃, this item is 0;

[0024] Suction pressure too high protection x(n), this protection priority is 3, when the suction pressure is higher than the calculated value, the valve opening is reduced by 2% in each calculation cycle; when the suction pressure is less than or equal to the calculated value, this item is 0.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention relates to a method for controlling suction superheat of a dry chiller, which substitutes the collected suction superheat into an independent new algorithm, and can simulate the opening of the electronic expansion valve during the entire operation of the unit, analyze and verify the rationality of each coefficient in the algorithm in advance, ensure precise control of the opening of the electronic expansion valve, and realize safe, reliable and efficient operation of the unit under various operating conditions.

[0026] The new algorithm introduced in the present invention calculates the increment of the opening. The target opening of the expansion valve in this cycle is obtained by adding the target opening of the previous calculation cycle to the increment of this calculation and the protection item. Even after protective adjustment, when jumping back to the present algorithm, the target opening of the previous calculation cycle is added to the increment of this calculation. Therefore, it has the advantages of small fluctuation of the opening of the electronic expansion valve and timely response. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The disclosure of the present invention is described with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. In the accompanying drawings, the same reference numerals are used to refer to the same components. Among them:

[0028] Figure 1 It is a schematic diagram of the workflow of the present invention;

[0029] Figure 2 A statistical diagram of the calculation process of the present invention when it is implemented;

[0030] Figure 3 It is a schematic diagram of the trend simulated during the implementation of the present invention. DETAILED DESCRIPTION

[0031] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the present invention is now further described in detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the relevant components of the present invention.

[0032] According to the technical solution of the present invention, without changing the essential spirit of the present invention, a person skilled in the art can propose a variety of interchangeable structural modes and implementation modes. Therefore, the following specific implementation modes and the accompanying drawings are only exemplary descriptions of the technical solution of the present invention, and should not be regarded as the entirety of the present invention or as a limitation or restriction to the technical solution of the present invention.

[0033] The main unit of the dry chiller mainly includes four major components: compressor, expansion valve, dry evaporator, condenser and related oil return pipeline. The compressor and expansion valve can be operated and controlled by a control system, and the control method involved in the present invention is mainly for the control of the expansion valve.

[0034] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0035] Embodiment 1, as Figure 1 As shown, a method for controlling suction superheat of a dry chiller comprises the following steps:

[0036] Step S01: After the dry chiller is powered on, the system is initialized and the system self-check is completed. At the same time, the electronic expansion valve is initialized to ensure that the opening is 0.

[0037] Step S02, turn on the oil heater. When the main contactor is closed, the oil heater is automatically disconnected. The oil heater and the main contactor are interlocked.

[0038] Step S03: Click the start button of the dry chiller, which is a start command, and the refrigeration pump will start after 5 seconds.

[0039] If the freezing pump has a startup feedback, it will delay for 120 seconds to check whether the freezing water temperature is in the startup area. If it is in the startup area and the shutdown interval is ≥20 minutes, the cooling pump will be turned on. After a delay of 45 seconds, it will check whether the cooling water flow is normal. If the cooling water flow is normal, the startup preparation is complete.

[0040] Step S04, start the compressor with the shortest cumulative running time, and run a certain number of solenoid valves. Specifically, start 25% of the adjustable solenoid valves and energize them for 30 seconds, and close the other adjustable solenoid valves. Start the compressor to complete the star-delta conversion, and determine whether the compressor delta contactor has feedback. If there is no feedback, alarm and shut down. If there is feedback, run at 25% load for 30 seconds. At the same time, the electronic expansion valve enters the non-adjustment stage, and the expansion valve opening is opened from 0 to the starting opening of 15-20%.

[0041] After running at 25% load for 30 seconds, the compressor is loaded to 50% load, and the electronic expansion valve is opened to the specified opening, which is the larger value of the current opening and the minimum allowable opening U (min). The compressor completes the startup process and continues to run at 50% load; when the exhaust superheat exceeds the minimum exhaust superheat by 15°C and maintains for 30 seconds, the electronic expansion valve jumps out of the non-regulation stage and enters the regulation stage.

[0042] The purpose of this step is to keep the evaporation pressure at a low level during the period of waiting for the exhaust superheat to meet the requirements, to prevent the compressor from carrying liquid in the air, and to increase the exhaust temperature and exhaust superheat faster.

[0043] During this process, the evaporation pressure is monitored. If the measured evaporation pressure is ≤ d, the expansion valve opening is increased; if the measured evaporation pressure is ≥ e, the expansion valve opening is decreased. d and e are preset values, which are related to the type of refrigerant. The confirmation method is: d = saturated pressure corresponding to the target outlet water temperature - 9 degrees; e = set MOP pressure or actual exhaust pressure - 4 bar, whichever is smaller.

[0044] Step S05: After the electronic expansion valve enters the adjustment stage, the algorithm is used to control the suction superheat. At the same time, the compressor performs load adjustment according to the water temperature. If the compressor is already at the load position indicating the completion of the startup, that is, 50% load, the load will not be reduced, and the current load position will be maintained to continue operation.

[0045] Among them, the method for load adjustment of the compressor according to the water temperature is: if the outlet water temperature is in the loading zone and the loading cycle time t1 is reached, the load position of the compressor is loaded to a higher level for operation; if the water temperature is in the holding zone, the load control of the compressor is stopped to maintain the current load; if the water temperature is in the unloading zone and the unloading cycle time t2 is reached, the unloading compressor is loaded to a lower level for operation.

[0046] Step S06, calculate the increment △U(n) ​​of the opening of the electronic expansion valve, △U(n)=m×A×[e(n)-e(n-1)]+m×e(n) / B, where A and B are preset coefficients, and e(n) is the suction superheat deviation; at the same time, set |△U(n)| in this algorithm to ≤3%.

[0047] Suction superheat deviation e(n), e(n) = Ts-Ts', where Ts is suction superheat, Ts' is the set suction superheat, the default is 5 degrees. The so-called suction superheat Ts refers to the difference between the suction temperature Txq measured by the unit's own temperature sensor and the evaporation temperature Tzf. Suction superheat Ts = Txq-Tzf, Txq is the suction temperature, Tzf is the evaporation temperature, and the evaporation temperature Tzf refers to the saturation temperature corresponding to the suction pressure measured by the unit's own pressure sensor.

[0048] The new algorithm of this patent is used to calculate the increment of the opening degree of the electronic expansion valve △U(n), △U(n)=m×A×[e(n)-e(n-1)]+m×e(n) / B, where A and B are preset coefficients. Through simulation tests and actual tests, it is found that A=10 and B=20. If it is not suitable in actual operation, it can be modified according to the actual situation. At the same time, let |△U(n)| in this algorithm ≤3%.

[0049] The reason why |△U(n)|≤3% is that the sampling period is 1 second. The increment △U(n) ​​of the expansion valve is calculated once in each sampling period. The longest time required for the operation of the commonly used Sporlan, Carel and Danfoss electronic expansion valves is 34 seconds. The allowable opening per second is 100 / 34=2.94. In order to prevent the electronic expansion valve from failing to keep up with the calculated increment △U(n) ​​when using the valve, △U(n) ​​is limited to no more than 3.

[0050] During the first calculation, e(n) is directly assigned to e(n-1); when |e(n)|≤2℃, m=1; when |e(n)|>2℃, m=|e(n) / 2|.

[0051] Step S07, calculate the target opening U(n) of the electronic expansion valve, U(n)=U(n-1)+△U(n)+p(n), wherein p(n) is the system protection item adjustment, and U(n-1) is the current opening of the expansion valve after actuation; that is, the target opening U(n) is the target opening of the previous calculation cycle plus the opening increment of the current calculation cycle plus the protection item adjustment.

[0052] During the first calculation, U(n-1) takes the current actual opening, that is, the opening at the last moment of the non-regulation stage. If the evaporation pressure ≤ d or the evaporation pressure ≥ e is not triggered during the entire non-regulation stage, then U(n-1) is the minimum allowable opening U(min), otherwise it is the current opening after the expansion valve is actuated.

[0053] In the above scheme, p(n) is the system protection item adjustment, p(n)=q(n)+r(n)+x(n), q(n) is the exhaust temperature too high protection, r(n) is the exhaust superheat too low protection, x(n) is the suction pressure too high protection. When p(n)≠0, let △U(n)=0.

[0054] Exhaust temperature over-high protection q(n), the protection priority is 1. When the exhaust temperature exceeds 95℃, the opening is increased by 3% instantly, and then by 1% every 5 seconds. When the exhaust temperature is less than or equal to 95℃, this item is 0;

[0055] Exhaust superheat under-protection r(n), the protection priority is 2. When the exhaust superheat is lower than 15℃, the opening is instantly reduced by 3%, and then the opening is reduced by 1% every 5s; when the exhaust superheat is greater than or equal to 15℃, this item is 0;

[0056] Suction pressure too high protection x(n), this protection priority is 3, when the suction pressure is higher than the calculated value, the valve opening is reduced by 2% in each calculation cycle; when the suction pressure is less than or equal to the calculated value, this item is 0.

[0057] When p(n)≠0, let △U(n)=0.

[0058] Step S08, calculate the actual opening degree A(n) of the electronic expansion valve, A(n)=U(n), and A(n) is between the minimum allowable opening degree U(min) and the maximum allowable opening degree U(max). Among them, the minimum allowable opening degree U(min) is 22%, and the maximum allowable opening degree U(max) is 90%, which can be set according to actual needs.

[0059] In simple terms, the calculated target opening U(n) is the target opening of the previous calculation cycle plus the opening increment of the current calculation cycle plus the protection item adjustment. The content of the protection item can be increased as appropriate based on other applications.

[0060] Example 2, taking the dry screw chiller using refrigerant R22 as an example

[0061] (1) At 8:00, the unit is powered on, the system is initialized, and the system self-check is completed. The opening of the electronic expansion valve returns to 0, and the oil heater is turned on.

[0062] (2) Click the start button at 9:00. The refrigeration pump will start after 5 seconds, the cooling pump will start after 120 seconds, and the start-up preparation will be completed after 45 seconds.

[0063] (3) At 9:02:50, the compressor starts at 25% load, the oil heater is turned off, and the electronic expansion valve enters the non-regulatory stage. The expansion valve opening is opened from 0 to the starting opening of 18% (settable). At 9:03:20, the compressor is loaded to 50% load, and the electronic expansion valve is opened to the specified opening of 22%. The compressor completes the startup process and continues to run at 50% load. Assuming that the evaporation pressure ≤ d or the evaporation pressure ≥ e is not triggered during the entire non-regulatory stage, the electronic expansion valve maintains the specified opening of 22%. Assuming that the exhaust superheat exceeds the minimum exhaust superheat by 15°C after 120 seconds and is maintained for 30 seconds, the electronic expansion valve jumps out of the non-regulatory stage at 9:05:50 and enters the regulating stage.

[0064] (4) After the electronic expansion valve enters the adjustment stage, a new algorithm is used to control the suction superheat. At the same time, the compressor performs load adjustment according to the water temperature.

[0065] (5) The suction superheat Ts′ is set to 5 degrees. The current suction superheat Ts is assumed to be 10 degrees, and no system protection item is triggered, that is, p(n)=0. In the first calculation, the suction superheat deviation e(n)=e(n-1)=Ts-Ts′=5, m=|e(n) / 2|=2.5, and U(n-1) is the opening of 22% at the last moment of the non-regulation stage. Then the opening increment △U(n) ​​calculated at 9:05:50 is △U(n)=m×A×[e(n)-e(n-1)]+m×e(n) / B=2.5×10×[5-5]+2.5×5 / 20=0.625, and the calculated target opening is U(n)=U(n-1)+△U(n)+p(n)=22+0.625+0=22.625. Since the calculated target opening is between the minimum allowable opening U(min) and the maximum allowable opening U(max), the actual opening is A(n)=U(n)=22.625.

[0066] (6) At 9:05:51, assuming that the current suction superheat Ts drops to 9.99 degrees and no system protection item is triggered, that is, p(n) = 0. Suction superheat deviation e(n) = e(n-1) = Ts-Ts′ = 4.99, m = |e(n) / 2| = 2.495, U(n-1) = 22.625, then the opening increment △U(n) ​​calculated at 9:05:51 = m×A×[e(n)-e(n-1)]+m×e(n) / B=2.495×10×[4.99-5]+2 .495×4.99 / 20=0.373, the calculated target opening U(n)=U(n-1)+△U(n)+p(n)=22.625+0.373+0=22.998. Since the calculated target opening is between the minimum allowable opening U(min) and the maximum allowable opening U(max), the actual opening A(n)=U(n)=22.998.

[0067] (7) Repeat the calculation according to the above algorithm to simulate the change trend of suction superheat and the change trend of electronic expansion valve opening. It has been verified that the coefficient A = 10 and B = 20 are appropriate. Some calculation results are shown in Figure 1 As shown in Figure 2 shown.

[0068] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for controlling suction superheat of a dry chiller, characterized in that: The following steps are involved: Step S01: After the dry chiller is powered on, the system is initialized and the system self-check is completed. At the same time, the electronic expansion valve is initialized to ensure that the opening is 0; Step S02, turn on the oil heater. When the main contactor is closed, the oil heater is automatically disconnected, and the oil heater and the main contactor are interlocked; Step S03, click the start button of the dry chiller, which is the start command, and turn on the refrigeration pump after 5 seconds; Step S04, starting the compressor with the shortest cumulative running time, and running a certain number of solenoid valves; at the same time, the electronic expansion valve enters the non-adjustment stage, and the expansion valve opening is opened from 0 to the starting opening of 15-20%; The compressor completes the startup process and continues to run at 50% load; when the exhaust superheat exceeds the minimum exhaust superheat by 15°C and maintains for 30 seconds, the electronic expansion valve jumps out of the non-regulation stage and enters the regulation stage; Step S05: After the electronic expansion valve enters the adjustment stage, the algorithm is used to control the suction superheat; at the same time, the compressor performs load adjustment according to the water temperature. If the compressor is already at the load position indicating the completion of the startup, that is, 50% load, the load will not be reduced, and the current load position will be maintained to continue running; Step S06, calculating the increment △U(n) ​​of the opening of the electronic expansion valve, △U(n)=m×A×[e(n)-e(n-1)]+m×e(n) / B, where A and B are preset coefficients, and e(n) is the suction superheat deviation; at the same time, let |△U(n)| in this algorithm be ≤3%; Step S07, calculating the target opening U(n) of the electronic expansion valve, U(n)=U(n-1)+△U(n)+p(n), wherein p(n) is the system protection item adjustment, and U(n-1) is the current opening after the expansion valve is actuated; that is, the target opening U(n) is the target opening of the previous calculation cycle plus the opening increment of the current calculation cycle plus the protection item adjustment; Step S08, calculating the actual opening degree A(n) of the electronic expansion valve, A(n)=U(n), and A(n) is between the minimum allowable opening degree U(min) and the maximum allowable opening degree U(max).

2. A method for controlling suction superheat of a dry chiller according to claim 1, characterized in that: In step S03, if the freezing pump has a startup feedback, it will delay for 120 seconds to detect whether the freezing water temperature is in the startup area. If it is in the startup area and the shutdown interval is ≥20 minutes, the cooling pump will be turned on. After a delay of 45 seconds, it will be detected whether the cooling water flow is normal. If the cooling water flow is normal, the startup preparation is complete.

3. The method for controlling suction superheat of a dry chiller according to claim 1, characterized in that: In step S04, 25% of the adjustable solenoid valves are started and energized for 30 seconds, and other adjustable solenoid valves are closed. The compressor is started to complete the star-delta conversion, and it is determined whether there is feedback from the compressor delta contactor. If there is no feedback, an alarm is triggered and the machine is shut down. If there is feedback, the machine runs at 25% load for 30 seconds. After running at 25% load for 30 seconds, the compressor is loaded to 50% load, and the electronic expansion valve is opened to the specified opening, which is the larger value of the current opening and the minimum allowable opening U (min).

4. A method for controlling suction superheat of a dry chiller according to claim 3, characterized in that: During this process, the evaporation pressure is monitored. If the measured evaporation pressure is ≤ d, the expansion valve opening is increased; if the measured evaporation pressure is ≥ e, the expansion valve opening is decreased. d and e are preset values, which are related to the type of refrigerant. The confirmation method is: d = saturated pressure corresponding to the target outlet water temperature - 9 degrees; e = set MOP pressure or actual exhaust pressure - 4 bar, whichever is smaller.

5. The method for controlling suction superheat of a dry chiller according to claim 1, characterized in that: In step S05, the method for adjusting the load of the compressor according to the water temperature is as follows: if the outlet water temperature is in the loading zone and the loading cycle time t1 is reached, the load position of the compressor is loaded to a higher level for operation; if the water temperature is in the holding zone, the load control of the compressor is stopped to maintain the current load position; If the water temperature is in the load reduction zone and the load reduction cycle time t2 is reached, the load reduction compressor will be loaded to a lower level for operation.

6. A method for controlling suction superheat of a dry chiller according to claim 1, characterized in that: In step S06, the suction superheat deviation e(n), e(n) = Ts-Ts', where Ts is the suction superheat, Ts' is the set suction superheat; the suction superheat Ts = Txq-Tzf, Txq is the suction temperature, and Tzf is the evaporation temperature.

7. A method for controlling suction superheat of a dry chiller according to claim 1, characterized in that: In step S06, during the first operation, e(n) is directly assigned to e(n-1); when |e(n)|≤2°C, m=1; when |e(n)|>2°C, m=|e(n) / 2|.

8. The method for controlling suction superheat of a dry chiller according to claim 1, characterized in that: In step S07, p(n) is the system protection item adjustment, p(n)=q(n)+r(n)+x(n), q(n) is the exhaust temperature too high protection, r(n) is the exhaust superheat too low protection, and x(n) is the suction pressure too high protection.

9. A method for controlling suction superheat of a dry chiller according to claim 8, characterized in that: Exhaust temperature over-high protection q(n), the protection priority is 1. When the exhaust temperature exceeds 95℃, the opening is increased by 3% instantly, and then by 1% every 5 seconds. When the exhaust temperature is less than or equal to 95℃, this item is 0; Exhaust superheat under-protection r(n), the protection priority is 2. When the exhaust superheat is lower than 15℃, the opening is instantly reduced by 3%, and then the opening is reduced by 1% every 5s; when the exhaust superheat is greater than or equal to 15℃, this item is 0; Suction pressure too high protection x(n), this protection priority is 3, when the suction pressure is higher than the calculated value, the valve opening is reduced by 2% in each calculation cycle; when the suction pressure is less than or equal to the calculated value, this item is 0.

10. A method for controlling suction superheat of a dry chiller according to claim 8, characterized in that: When p(n)≠0, let △U(n)=0.

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