Electronic expansion valve control method based on PID algorithm

Abstract

The invention relates to an electronic expansion valve control method based on a PID (Proportion Integration Differentiation) algorithm, which is characterized by comprising a compressor, an evaporator, an electronic expansion valve and a controller, and comprises the following six steps of: measuring the variable quantity EXV of throttling through a formula; and the controller controls the real-time adjustment of the electronic expansion valve according to the EXV. The method has the advantages that calculation is carried out through multiple variables including the target superheat degree, the current superheat degree, the last-period superheat degree, the specified proportionality coefficient Kp, the integral coefficient Ki and the differential coefficient Kd, the opening degree of the electronic expansion valve is rapidly and accurately adjusted to the target superheat degree of the system, and therefore the suction superheat degree is guaranteed, and the liquid return risk is avoided; and the overall performance of the machine is improved under the optimal superheat degree condition.

Description

Technical Field

[0001] The invention relates to an electronic expansion valve control method based on PID algorithm. Background Art

[0002] Heat pumps are generally used under low temperature conditions, and often work under sub-zero conditions. The evaporator will be frosted for defrosting. After defrosting, the expansion valve fails to maintain the suction superheat above 0°C for a long time, which can easily cause liquid refrigerant to flow back. After defrosting, the expansion valve opening is quickly adjusted to the optimal superheat and reach above 0°C to ensure that the refrigerant returning to the compressor is in a gaseous state, thereby ensuring that the compressor will not be damaged by liquid hammer. Therefore, most heat pump equipment will increase the expansion adjustment speed, but only increasing the adjustment speed will easily cause over-adjustment, resulting in expansion shutdown problems, and because the expansion will quickly readjust in the opposite direction after over-adjustment, the expansion valve will be unable to stabilize after continuous adjustment, resulting in temperature instability. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an electronic expansion valve control method based on PID algorithm, which can realize the control of the expansion valve by the target superheat, the current superheat, the superheat of the previous cycle and the specified proportional coefficient K. p , integral coefficient K i and differential coefficient K d Multiple variables are calculated to quickly and accurately adjust the opening of the electronic expansion valve to the system target superheat, thereby ensuring the suction superheat and avoiding the risk of liquid return. The machine improves the overall performance of the equipment under the optimal superheat condition.

[0004] In order to achieve the above object, the present invention is implemented as follows: it is an energy-saving water boiler, including a compressor, an evaporator, an electronic expansion valve and a controller, wherein the steps are as follows: Step 1: a compressor temperature sensor is set in the compressor to measure the compressor suction temperature T1, an evaporator temperature sensor is set in the evaporator to measure the evaporator middle temperature T2, or a pressure sensor is set in the compressor to measure the pressure in the compressor P1; Step 2, the controller converts the P1 obtained in step 1 through the REFPROP refrigerant property query software to obtain the saturated evaporation temperature T3 of the compressor; Step 3: The controller obtains the real-time suction superheat SH according to the compressor suction temperature T1, the evaporator middle temperature T2 and the compressor saturated evaporation temperature T3 in step 1 and step 2. A ,SH A =T1-T2 or SH A =T3-T2; Step 4: The controller sets the heat pump superheat SH S , the real-time calculated heat absorption superheat SHA and the suction superheat SH of the previous cycle L and SH S For comparison, SH A -SH S =△T1 and SH A -SH L =△T2; Step 5: The controller obtains the three coefficients of heat pump PID control through experiments or simulations. p , integral coefficient K i and differential coefficient K d ; The throttling change △EXV is measured by the formula; △EXV=K i *(K p *△T1+K d *△T2) or △EXV=K p *△T1+K d *△T2; Step 6: The controller controls the real-time adjustment of the electronic expansion valve according to △EXV.

[0005] In the technical solution, the compressor temperature sensor is arranged on the surface of the compressor intake pipe.

[0006] In this technical solution, the pressure sensor is arranged in the suction pipe of the compressor.

[0007] In this technical solution, the evaporator temperature sensor is arranged on the surface of the evaporator.

[0008] Compared with the prior art, the advantages of the present invention are: the target superheat, the current superheat, the superheat of the previous cycle and the specified proportional coefficient K are used to calculate the superheat. p , integral coefficient K i and differential coefficient K d Multiple variables are calculated to quickly and accurately adjust the opening of the electronic expansion valve to the system target superheat, thereby ensuring the suction superheat and avoiding the risk of liquid return. The machine improves the overall performance of the equipment under the optimal superheat condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0010] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0011] In the description of the present invention, the terms "upper", "lower", "top" and "bottom" indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention.

[0012] In the present invention, unless otherwise clearly specified and limited, the terms "set", "connected", "located" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or a detachable arrangement or integration; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, which can enable the internal connectivity of two elements or the interaction relationship between the two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0013] like Figure 1 As shown, it is an electronic expansion valve control method based on PID algorithm, which is characterized by including a compressor, an evaporator, an electronic expansion valve and a controller, wherein the steps are as follows: Step 1: a compressor temperature sensor is set in the compressor to measure the compressor suction temperature T1, an evaporator temperature sensor is set in the evaporator to measure the evaporator middle temperature T2, or a pressure sensor is set in the compressor to measure the pressure in the compressor P1; Step 2, the controller converts the P1 obtained in step 1 through the REFPROP refrigerant property query software to obtain the saturated evaporation temperature T3 of the compressor; Step 3: The controller obtains the real-time suction superheat SH according to the compressor suction temperature T1, the evaporator middle temperature T2 and the compressor saturated evaporation temperature T3 in step 1 and step 2. A ,SH A =T1-T2 or SH A =T3-T2; Step 4: The controller sets the heat pump superheat SH S , the real-time calculated heat absorption superheat SH A and the suction superheat SH of the previous cycle L and SH S For comparison, SH A -SH S =△T1 and SH A -SH L =△T2; Step 5: The controller obtains the three coefficients of heat pump PID control through experiments or simulations. p , integral coefficient K i and differential coefficient K d; The throttling change △EXV is measured by the formula; △EXV=K i *(K p *△T1+K d *△T2) or △EXV=K p *△T1+K d *△T2; Step 6: The controller controls the real-time adjustment of the electronic expansion valve according to △EXV.

[0014] Among them, SH S The superheat of a heat pump refers to the degree to which the temperature of the refrigerant vapor exceeds the saturation temperature after it is completely evaporated in the evaporator. In a heat pump system, superheat is an important parameter that affects the efficiency and stability of the system.

[0015] Proportional coefficient K p : Proportional control focuses on the current error value. When an error occurs, proportional control will react immediately and adjust the output to reduce the error. The larger the Kp value, the more sensitive the system is to errors and the faster it adjusts. However, if Kp is too large, it may cause system oscillation or instability.

[0016] Integration coefficient K i : Integral control focuses on the accumulation of past errors. Even if the error is small, integral control will gradually accumulate and react to eliminate long-standing static errors. The larger the Ki value, the stronger the system's ability to eliminate static errors. However, if Ki is too large, it may cause the system to over-adjust and produce oscillations.

[0017] Differential coefficient K d :Derivative control focuses on the changing trend of the error, that is, predicting the future error. When the error change rate is large, the differential control will make adjustments in advance to reduce the future error. The larger the Kd value, the more sensitive the system is to the error change rate, and the earlier the adjustment. However, if Kd is too large, it may cause the system to be too sensitive to noise, resulting in unnecessary adjustments.

[0018] In practical applications, it is necessary to reasonably adjust these three parameters according to the characteristics and requirements of the system. Usually, it is necessary to determine the best parameter combination through experiments or simulations to achieve the best control effect.

[0019] By target superheat, current superheat, superheat of the previous cycle and the specified proportional coefficient K p , integral coefficient K i and differential coefficient K d Multiple variables are calculated to quickly and accurately adjust the opening of the electronic expansion valve to the system target superheat, thereby ensuring the suction superheat and avoiding the risk of liquid return. The machine improves the overall performance of the equipment under the optimal superheat condition.

[0020] In this embodiment, the compressor temperature sensor is arranged on the surface of the compressor suction pipe.

[0021] In this embodiment, the pressure sensor is arranged in the suction pipe of the compressor.

[0022] In this embodiment, the evaporator temperature sensor is arranged on the surface of the evaporator. The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and deformations of these embodiments without departing from the principles and purposes of the present invention still fall within the scope of protection of the present invention.

Claims

1. An electronic expansion valve control method based on PID algorithm, characterized in that It includes a compressor, an evaporator, an electronic expansion valve and a controller, wherein the steps are as follows: Step 1: a compressor temperature sensor is set in the compressor to measure the compressor suction temperature T1, an evaporator temperature sensor is set in the evaporator to measure the evaporator middle temperature T2, or a pressure sensor is set in the compressor to measure the pressure in the compressor P1; Step 2, the controller converts the P1 obtained in step 1 through the REFPROP refrigerant property query software to obtain the saturated evaporation temperature T3 of the compressor; Step 3: The controller obtains the real-time suction superheat SH according to the compressor suction temperature T1, the evaporator middle temperature T2 and the compressor saturated evaporation temperature T3 in step 1 and step 2. A ,SH A =T1-T2 or SH A =T3-T2; Step 4: The controller sets the heat pump superheat SH S , the real-time calculated heat absorption superheat SH A and the suction superheat SH of the previous cycle L and SH S For comparison, SH A -SH S =△T1 and SH A -SH L =△T2; Step 5: The controller obtains the three coefficients of heat pump PID control through experiments or simulations. p , integral coefficient K i and differential coefficient K d ; The throttling change △EXV is measured by the formula; △EXV=K i *(K p *△T1+K d *△T2) or △EXV=K p *△T1+K d *△T2; Step 6: The controller controls the real-time adjustment of the electronic expansion valve according to △EXV.

2. The electronic expansion valve control method based on PID algorithm according to claim 1 is characterized in that The compressor temperature sensor is arranged on the surface of the compressor suction pipe.

3. The electronic expansion valve control method based on PID algorithm according to claim 1 is characterized in that The pressure sensor is arranged in the suction pipe of the compressor.

4. The electronic expansion valve control method based on PID algorithm according to claim 1 is characterized in that The evaporator temperature sensor is arranged on the surface of the evaporator.

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