Electronic expansion valve control method

Abstract

The present application relates to an electronic expansion valve, and discloses an electronic expansion valve control method, which specifically comprises collecting the target temperature and the actual temperature of the refrigerant at the outlet of the electronic expansion valve, and using a PI control algorithm to calculate the real-time opening degree of the electronic expansion valve in combination with the judgment of the superheat degree. The electronic expansion valve is reasonably controlled by using a mechanical compressor plus an electronic expansion valve thermal management system, so that the battery pack can be quickly cooled, and the compressor will not be damaged due to overshoot caused by compressor speed fluctuation, and the electronic expansion valve is safe and reliable.

Description

Technical Field

[0001] This invention relates to an electronic expansion valve, and more particularly to an electronic expansion valve control method. Background Technology

[0002] New energy vehicles generally include pure electric vehicles and hybrid vehicles. Hybrid vehicles mostly use electric compressors, but the high cost of electric compressors limits their development.

[0003] Although mechanical compressors are much cheaper than electric compressors and have better performance and reliability, they are driven by the engine. Different driving conditions can make it difficult for the compressor speed to be stable, and may even cause large fluctuations. For example, when accelerating rapidly, the refrigerant in the cooling circuit will pass through the electronic expansion valve rapidly. At this time, because the water temperature in the battery pack has not yet reacted, the electronic expansion valve cannot immediately reduce its opening. This can easily cause the electronic expansion valve to overshoot, leading to liquid slugging in the compressor, damaging the compressor, or even causing a safety accident. Summary of the Invention

[0004] This invention addresses the problem of the difficulty in properly controlling the electronic expansion valve in existing mechanical compressors by providing an electronic expansion valve control method.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] An electronic expansion valve control method includes the following steps:

[0007] Step S1: Collect the target temperature and actual temperature of the refrigerant at the outlet of the electronic expansion valve as the given value and the current value;

[0008] Step S2: Upon receiving a battery pack cooling request from the BMS, perform PI regulation on the electronic expansion valve. Specifically, use a PI control algorithm to calculate the real-time opening of the electronic expansion valve.

[0009] Svalve = Kp ×err(k) + Ki×∑err(j) + y0,

[0010] Where Svalve is the real-time opening degree of the electronic expansion valve;

[0011] Kp: Parameter for proportional term calculation;

[0012] Ki: Parameter for integral term operation;

[0013] y0: Initial opening value;

[0014] err(k) is the difference between the actual temperature of the refrigerant at the outlet of the electronic expansion valve and the target temperature;

[0015] ∑err(j)=err(k)+err(k +1)+ err(k +2)+...;

[0016] Step S3: When the superheat of the compressor return gas line is lower than T1, stop adjusting the PI of the electronic expansion valve and keep the electronic expansion valve at its current opening.

[0017] Step S4: If the superheat of the compressor return line increases to T2 under the control of step S3, then PI regulation is performed again, and the current opening is the initial opening value for the next PI regulation.

[0018] If the superheat of the compressor return line continues to decrease to the safe value T3, the opening of the electronic expansion valve is reduced until the superheat increases to T2, and then PI regulation is performed again. The current opening is the initial value for the next PI regulation, where T2>T1>T3.

[0019] Preferably, in step S4, the electronic expansion valve restarts PI regulation, requiring Kp, Ki, and y0 to be re-assigned.

[0020] Preferably, in step S4, when the superheat of the compressor return gas line continues to decrease to a safe value T3, the opening of the electronic expansion valve is reduced at a rate of 2 steps / second.

[0021] This invention, by adopting the above technical solutions, has significant technical effects:

[0022] This invention employs a thermal management system combining a mechanical compressor and an electronic expansion valve. By combining the judgment of overheating, the electronic expansion valve is reasonably controlled, which can quickly cool the battery pack while preventing overshoot damage to the compressor due to compressor speed fluctuations, ensuring safety and reliability. Attached Figure Description

[0023] Figure 1 This is a flowchart of the electronic expansion valve control in Embodiment 1 of the present invention.

[0024] Figure 2 This is a block diagram of the battery pack thermal management system in Embodiment 1 of the present invention. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0026] Example 1

[0027] An electronic expansion valve control method, such as Figure 1 , Figure 2 As shown, it includes the following steps:

[0028] Step S1: Collect the target temperature and actual temperature of the refrigerant at the outlet of the electronic expansion valve as the given value and the current value;

[0029] Step S2: Upon receiving a battery pack cooling request from the BMS, perform PI regulation on the electronic expansion valve. Specifically, use a PI control algorithm to calculate the real-time opening of the electronic expansion valve.

[0030] Svalve = Kp×err(k) + Ki×∑err(j) + y0,

[0031] Where, Swalve is the real-time opening degree of the electronic expansion valve;

[0032] Kp: Parameter for proportional term calculation;

[0033] Ki: Parameter for integral term operation;

[0034] y0: Initial opening value;

[0035] err(k) is the difference between the actual temperature of the refrigerant at the outlet of the electronic expansion valve and the target temperature;

[0036] ∑err(j)=err(k)+err(k +1)+ err(k +2)+...;

[0037] In the PI control, the initial values ​​of parameters Kp, Ki, and y0 are determined by the system software through calibration, which is an existing mature technology.

[0038] Step S3: When the superheat of the compressor return gas line is lower than T1 (5°C), stop adjusting the electronic expansion valve PI and keep the electronic expansion valve at its current opening.

[0039] Step S4: If the superheat of the compressor return gas line increases to T2 (7°C) under the control of step S3, then PI adjustment is performed again, and new Kp, Ki, and y0 are assigned. The current opening degree is the initial opening degree value for the next PI adjustment.

[0040] If the superheat of the compressor return line continues to decrease to the safe value T3 (3℃), the opening of the electronic expansion valve is reduced at a rate of 2 steps / second until the superheat increases to T2 (7℃). Then, PI regulation is performed again, and new Kp, Ki, and y0 are assigned. The current opening is the initial value for the next PI regulation. If the superheat is greater than T1 (5℃) but less than T2 (7℃), the current opening of the electronic expansion valve is maintained.

[0041] In this embodiment, in order to ensure control accuracy, the initial working state of the entire system will be different when the PI adjustment is performed again. Therefore, new Kp, Ki, and y0 will be assigned. The reassigned Kp, Ki, and y0 are also obtained according to the calibration, such as assigning Kp = 4 and Ki = 0.01.

[0042] The superheat represented by T2, T1, and T3 refers to the difference between the temperature of saturated steam and the saturated temperature when the steam is heated to a temperature higher than the saturation temperature under saturated pressure conditions. The superheat is T2 > T1 > T3.

[0043] In this embodiment, a pressure and temperature sensor is installed on the return gas pipeline from the electronic expansion valve to the mechanical compressor. The superheat is calculated by collecting the pressure and temperature values. The numbers obtained are different in different application scenarios. For example, in this embodiment, T1=5℃, T2=7℃, and T3=3℃ can be selected.

[0044] In this embodiment, the control of the electronic expansion valve is an innovation that combines the judgment of superheat with the form of a mechanical compressor. The electronic expansion valve judges the difference between the actual temperature of the outlet refrigerant and the target temperature and performs PI regulation, which can quickly respond to the cooling needs of the battery pack.

[0045] When the electronic expansion valve responds normally to the battery pack's cooling needs, a sudden increase in vehicle speed causes a sudden increase in compressor speed, which in turn causes a rapid increase in refrigerant flow. If the refrigerant cannot dissipate heat in time, some of it will flow back to the compressor in liquid form, which can lead to liquid slugging in the compressor.

[0046] To prevent this, the controller monitors the superheat of the gas returning from the electronic expansion valve to the compressor in real time. When the superheat is less than or equal to T1, the opening of the electronic expansion valve is not allowed to increase further. If the superheat continues to decrease to T3, the electronic expansion valve will reduce its opening at a certain rate until the superheat is greater than T3 again. This prevents compressor damage caused by fluctuations in compressor speed.

[0047] It is readily understood that those skilled in the art can combine, split, or reorganize the embodiments provided in this application to obtain other embodiments, none of which exceed the protection scope of this application.

[0048] In summary, the above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the present invention.

Claims

1. A method for controlling an electronic expansion valve, characterized in that... It includes the following steps: Step S1: Collect the target temperature and actual temperature of the refrigerant at the outlet of the electronic expansion valve as the given value and the current value; Step S2: Upon receiving a battery pack cooling request from the BMS, perform PI regulation on the electronic expansion valve. Specifically, use a PI control algorithm to calculate the real-time opening of the electronic expansion valve. Svalve = Kp × err(k) + Ki×∑err(j) + y0, Where, Swalve is the real-time opening degree of the electronic expansion valve; Kp: Parameter for proportional term calculation; Ki: Parameter for integral term operation; y0: Initial opening value; err(k) is the difference between the actual temperature of the refrigerant at the outlet of the electronic expansion valve and the target temperature; ∑err(j)=err(k)+err(k+1)+ err(k+2)+...; Step S3: When the superheat of the compressor return gas line is lower than T1, stop adjusting the PI of the electronic expansion valve and keep the electronic expansion valve at its current opening. Step S4: If the superheat of the compressor return gas line increases to T2 under the control of step S3, then PI adjustment is performed again, and new Kp, Ki, and y0 are assigned. The current opening is the initial opening value for the next PI adjustment. If the superheat of the compressor return line continues to decrease to the safe value T3, the opening of the electronic expansion valve is reduced at a rate of 2 steps / second until the superheat increases to T2. Then, PI regulation is performed again, and new Kp, Ki, and y0 are assigned. The current opening is the initial value for the next PI regulation. If the superheat is greater than T1 but less than T2, the current opening of the electronic expansion valve is maintained, where T2>T1>T3.

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