Automatic identification method of ventilator air performance test system for unsteady state critical point

Abstract

A ventilator air performance test system unsteady state critical point automatic identification method comprises the following steps: carrying out corresponding test program upgrading on an existing ventilator air performance test system, controlling three variables of resistance adjustment of the test system, and adding automatic steady state determination and peak value detection of a collection program to the program; the critical steady state is automatically judged according to fluctuation of upper and lower limit peak values, and the test efficiency is improved; in the ventilation fan air performance detection process, the air flow unsteady state critical state in the ventilation fan detection process can be effectively recognized, the requirement for product design improvement is met, the after-sales maintenance cost caused by the abnormal phenomenon of an engineering site due to the fact that corresponding working conditions are selected for the engineering site is avoided, and the ventilation fan performance detection method is suitable for popularization and application. And the difficulty of critical unsteady state judgment in the fan detection process in the industry is solved.

Description

Technical Field

[0001] The invention relates to an automatic identification method for a non-steady-state critical point of a ventilator air performance test system. Background Art

[0002] The ventilator air performance test system can be used to test and record the static pressure under different flow rates, draw the corresponding static pressure-flow curve, and provide data reference for the actual application of the fan. In the ventilator air performance test system, it includes a wind chamber, a nozzle wall is arranged in the wind chamber, and a front flow balancing orifice plate and a rear flow balancing orifice plate are respectively arranged on both sides of the nozzle wall. A differential pressure gauge is arranged near the nozzle wall to measure the pressure difference on both sides of the nozzle wall. The measured fan is installed at the inlet end of the wind chamber, and a valve and an auxiliary fan are installed at the outlet end of the wind chamber. There are also multiple static pressure measurement points on the wall of the wind chamber and static pressure measuring instruments are arranged at the static pressure measurement points; the invention patent with authorization announcement number CN100575909C can be used as an example of an existing ventilator air performance test system.

[0003] Centrifugal fans are usually used in medium and large flow areas (high efficiency areas). Due to the product structure itself or design problems, unstable airflow may occur during the test process. For the performance test of the fan, there are currently automated tests and manual tests of the air performance of the fan. By adjusting the test system, constant static pressure or constant flow is used for control. The fluctuation of the airflow of the auxiliary fan at a small flow rate and the valve at a small opening degree are often ignored. These situations are easy to affect the stability of the airflow during the test process, and there is a certain probability of expanding the critical area of ​​the non-steady state. The current non-steady state is usually carried out by human subjective judgment, and the detection equipment and different detection control programs have slightly different manifestations of the actual non-steady-state characteristics of the product. The detection process requires a high level of experience for the tester, and human subjective identification cannot accurately identify and judge. The inability to accurately identify the critical area increases the reference difficulty for technical personnel to improve product design, and creates a risk of misjudgment for after-sales improvement services at the actual engineering application site. Summary of the invention

[0004] In view of the shortcomings existing in the above problems, the present invention provides a method for automatically identifying non-steady-state critical points in a ventilator air performance testing system.

[0005] To achieve the above object, the present invention provides a method for automatically identifying a non-steady-state critical point in a ventilator air performance test system, comprising the following steps: s1. After the fan under test is connected to the test system, the test system runs the fan under test and the auxiliary fan, controls the valve to be 100% open and keeps a set number of nozzles on the nozzle wall in an open state, and adjusts the speed of the auxiliary fan to keep the flow velocity at the opened nozzle within the range of 30-35m / s, so that the static pressure value P measured by the static pressure measuring instrument is 0Pa; s2. Under the static pressure of 0Pa, the test system collects and records the flow pressure difference ΔP fluctuation data measured by the differential pressure meter within three minutes, and calculates the maximum flow under the static pressure of 0Pa according to the value of the flow pressure difference ΔP; s3. Divide the maximum flow rate into intervals of 10% to determine the flow measurement points of 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, and 0%; s4. The flow rate is adjusted in the order of first controlling the auxiliary fan speed and then controlling the valve opening degree, so that the flow rate is adjusted from large to small to the above-mentioned various percentage flow measurement points in sequence, until the test system determines that a certain percentage flow measurement point adjusted has reached a stable state; s5. The flow rate is gradually increased by 1% of the maximum flow rate, first through the valve opening control and then through the auxiliary fan speed control, until the test system returns to the unstable state again. The test system identifies and records the unstable critical point A. If the test system cannot return to the unstable state, the test system determines that the unstable critical point A is 100% of the maximum flow rate; s6. Continue to perform the test of the next percentage flow point in the order of step s3 until the test system determines that the adjusted percentage flow measurement point returns to an unstable state; s7. The flow rate is gradually increased by 1% of the maximum flow rate, first through the valve opening control and then through the auxiliary fan speed control, until the test system returns to a stable state again. The test system identifies and records the non-steady-state critical point B; s8. The value of the non-steady-state critical point A should be greater than 70% of the maximum flow rate, and the value of the non-steady-state critical point B should be less than 50% of the maximum flow rate; s9. Determine the area between the non-steady-state critical point B and the non-steady-state critical point A as the actual use area of ​​the ventilator product.

[0006] Further, in step s1, the fan under test runs at the design speed, the static pressure 0Pa is the arithmetic average of multiple test data of the static pressure measuring instrument within three minutes after the valve opening degree and the auxiliary fan speed are stable.

[0007] Furthermore, in steps s4 to s7, the test system determines whether a certain measuring point has reached a stable state, and processes the flow rate of the measuring point separately according to whether it is less than 90% of the maximum flow rate; when the flow rate of the measuring point is less than 90% of the maximum flow rate, based on the collected upper and lower peak values ​​of the static pressure fluctuation, it is concluded that the fluctuation range of the static pressure value P measured by the static pressure measuring instrument is within ±0.5% of the average static pressure, and the test system is determined to be in a stable state; when the flow rate of the measuring point is not less than 90% of the maximum flow rate, based on the collected upper and lower peak values ​​of the flow pressure difference ΔP fluctuation, it is calculated that the fluctuation range of the flow pressure difference ΔP is within ±0.5% of the average pressure difference, and it is a steady state.

[0008] Furthermore, in step s5, the test system returns to an unstable state again, i.e. Figure 1 The pressure fluctuation point between the pressure fluctuation upper limit 1 and the pressure fluctuation lower limit 1 is reached in step s6, and the test system determines that the adjusted percentage flow measurement point returns to an unstable state, that is, Figure 1 A pressure fluctuation point located between the pressure fluctuation upper limit 2 and the pressure fluctuation lower limit 2 is reached.

[0009] Further, in step s8, if the value of the non-steady-state critical point A or the value of the non-steady-state critical point B does not meet the requirements, the test system determines that the wind turbine under test has defects.

[0010] Furthermore, in step s7, if the auxiliary fan has been adjusted to a zero speed state and the valve is in the process of adjustment, and the flow rate of the opened nozzle is less than 10 m / s, the test system first reduces the number of opened nozzles, then controls the opening degree of the valve, and finally controls the speed of the auxiliary fan to adjust the flow rate of the opened nozzle to within the range of 10-35 m / s.

[0011] The beneficial effects of the present invention compared to the prior art are: It is only necessary to upgrade the corresponding test program on the existing ventilator air performance test system, control the three variables of the test system resistance adjustment, and increase the automatic steady-state judgment and peak detection of the acquisition program. The critical steady state is automatically judged according to the fluctuation of the upper and lower limit peak values, thereby improving the test efficiency. During the ventilator air performance test, the present invention can effectively identify the non-steady-state critical state of the airflow during the ventilator test process, improve the demand for product design improvement, avoid the corresponding working conditions being selected for the engineering site, and cause the after-sales maintenance costs caused by the abnormal phenomena at the engineering site, thereby solving the difficulty of critical non-steady-state judgment in the fan test process in the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the static pressure flow curve of the fan under test; Figure 2The figure is a schematic diagram of the air performance test system of the ventilator involved; Figure 3 This is a schematic diagram for identifying the non-steady-state critical point of the tested fan when operating at ±3% of the design speed. DETAILED DESCRIPTION

[0013] like Figure 1 , Figure 2 As shown, a method for automatically identifying a non-steady-state critical point in a ventilator air performance test system according to an embodiment of the present invention comprises the following steps: s1. After the fan under test is connected to the test system, the test system runs the fan under test and the auxiliary fan, controls the valve to be 100% open and keeps a set number of nozzles on the nozzle wall in an open state, and adjusts the speed of the auxiliary fan to keep the flow velocity at the opened nozzle within the range of 30-35m / s, so that the static pressure value P measured by the static pressure measuring instrument is 0Pa; s2. Under the static pressure of 0Pa, the test system collects and records the flow pressure difference ΔP fluctuation data measured by the differential pressure meter within three minutes, and calculates the maximum flow under the static pressure of 0Pa according to the value of the flow pressure difference ΔP; s3. Divide the maximum flow rate into intervals of 10% to determine the flow measurement points of 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, and 0%; s4. The flow rate is adjusted in the order of first controlling the auxiliary fan speed and then controlling the valve opening degree, so that the flow rate is adjusted from large to small to the above-mentioned various percentage flow measurement points in sequence, until the test system determines that a certain percentage flow measurement point adjusted has reached a stable state; s5. The flow rate is gradually increased by 1% of the maximum flow rate, first through the valve opening control and then through the auxiliary fan speed control, until the test system returns to the unstable state again. The test system identifies and records the unstable critical point A. If the test system cannot return to the unstable state, the test system determines that the unstable critical point A is 100% of the maximum flow rate; s6. Continue to perform the test of the next percentage flow point in the order of step s3 until the test system determines that the adjusted percentage flow measurement point returns to an unstable state; s7. The flow rate is gradually increased by 1% of the maximum flow rate, first through the valve opening control and then through the auxiliary fan speed control, until the test system returns to a stable state again. The test system identifies and records the non-steady-state critical point B; s8. The value of the non-steady-state critical point A should be greater than 70% of the maximum flow rate, and the value of the non-steady-state critical point B should be less than 50% of the maximum flow rate; s9. Determine the area between the non-steady-state critical point B and the non-steady-state critical point A as the actual use area of ​​the ventilator product.

[0014] In step s1, the fan under test runs at the design speed, and the static pressure 0Pa is the arithmetic average of multiple test data of the static pressure measuring instrument within three minutes after the valve opening degree and the auxiliary fan speed are stable.

[0015] In step s4 to step s7, the test system determines whether a certain measuring point has reached a stable state, and processes the flow of the measuring point separately according to whether it is less than 90% of the maximum flow; when the flow of the measuring point is less than 90% of the maximum flow, according to the collected upper and lower peak values ​​of the static pressure fluctuation, it is concluded that the fluctuation range of the static pressure value P measured by the static pressure measuring instrument is within ±0.5% of the average static pressure, and the test system is determined to be in a stable state; when the flow of the measuring point is not less than 90% of the maximum flow, according to the collected upper and lower peak values ​​of the flow pressure difference ΔP fluctuation, it is calculated that the fluctuation range of the flow pressure difference ΔP is within ±0.5% of the average pressure difference, and it is a steady state.

[0016] In step s5, the test system returns to an unstable state again, i.e. Figure 1 The pressure fluctuation point between the pressure fluctuation upper limit 1 and the pressure fluctuation lower limit 1 is reached in step s6, and the test system determines that the adjusted percentage flow measurement point returns to an unstable state, that is, Figure 1 A pressure fluctuation point located between the pressure fluctuation upper limit 2 and the pressure fluctuation lower limit 2 is reached.

[0017] In step s8, if the value of the non-steady-state critical point A or the value of the non-steady-state critical point B does not meet the requirements, the test system determines that the wind turbine under test has defects.

[0018] In step s7, if the auxiliary fan has been adjusted to zero speed and the valve is in the process of adjustment, and the flow rate of the opened nozzle is less than 10m / s, the test system first reduces the number of opened nozzles, then controls the opening degree of the valve, and finally controls the speed of the auxiliary fan to adjust the flow rate of the opened nozzle to within the range of 10-35m / s.

[0019] It is only necessary to upgrade the corresponding test program on the existing ventilator air performance test system, control the three variables of the test system resistance adjustment, and increase the automatic steady-state judgment and peak detection of the acquisition program. The critical steady state is automatically judged according to the fluctuation of the upper and lower limit peak values, thereby improving the test efficiency. During the ventilator air performance test, the present invention can effectively identify the non-steady-state critical state of the airflow during the ventilator test process, improve the demand for product design improvement, avoid the corresponding working conditions being selected for the engineering site, and cause the after-sales maintenance costs caused by the abnormal phenomena at the engineering site, thereby solving the difficulty of critical non-steady-state judgment in the fan test process in the industry.

[0020] In order to facilitate the understanding of the present invention, the following description is given in conjunction with the accompanying drawings during specific use; Case 1: Assume that the value of the non-steady critical point A of a certain type of fan is 75% of the maximum flow rate, and the value of the non-steady critical point B is 25% of the maximum flow rate. The air performance test system identifies the non-stable critical point as follows: s1. After the fan under test is connected to the test system, the test system runs the fan under test and the auxiliary fan, controls the valve to be 100% open and keeps a set number of nozzles on the nozzle wall in an open state, and adjusts the speed of the auxiliary fan to keep the flow velocity at the opened nozzle within the range of 30-35m / s, so that the static pressure value P measured by the static pressure measuring instrument is 0Pa; s2. Under the static pressure of 0Pa, the test system collects and records the flow pressure difference ΔP fluctuation data measured by the differential pressure meter within three minutes, and calculates the maximum flow under the static pressure of 0Pa according to the value of the flow pressure difference ΔP; s3. The flow rate is adjusted in the order of first controlling the auxiliary fan speed and then controlling the valve opening degree. At the measurement points of 90% and 80% of the maximum flow rate, the test system determines that the above measurement points are all in an unstable state; s4. The flow rate is adjusted in the order of first controlling the auxiliary fan speed and then controlling the valve opening. At the measurement point of 70% of the maximum flow rate, the test system determines that the measurement point is in a stable state; s5. The flow rate is gradually increased by 1% of the maximum flow rate, first through the valve opening control and then through the auxiliary fan speed control. The test system determines that the maximum flow state measurement points of 71%, 72%, 73%, 74%, and 75% are all stable states, and recognizes that the maximum flow state measurement point of 76% is an unstable state, thereby determining that the value of the unstable critical point A is 75% of the maximum flow rate; s6. The flow rate is adjusted in the order of first controlling the auxiliary fan speed and then controlling the valve opening. At the measurement points of 60%, 50%, and 40% of the maximum flow rate, the test system determines that the above measurement points are all in a stable state. At the measurement point of 30% of the maximum flow rate, the test system determines that the measurement point is in an unstable state. s7. The flow rate is gradually increased by 1% of the maximum flow rate, first through the valve opening control and then through the auxiliary fan speed control. The test system determines that the 31%, 32%, 33%, and 34% maximum flow state measurement points are all unstable states, and recognizes that the 35% maximum flow state measurement point is a stable state, thereby determining that the value of the unstable critical point B is 35% of the maximum flow rate; s8. The value of the non-steady-state critical point A should be greater than 70% of the maximum flow rate, and the value of the non-steady-state critical point B should be less than 50% of the maximum flow rate; s9. Determine that the actual use area of ​​the ventilator product should be between 35% and 75% of the maximum flow rate.

[0021] In addition, when the fan under test is actually used, it may operate under the condition of ±3% of the design speed. The fan air performance test system can also identify the critical point of the ±3% design speed condition, as follows: +3% design speed According to the non-steady critical point A measured by s5, the non-steady critical point A is reproduced through program constant flow control, the resistance K of the whole system is kept unchanged, the speed of the measured fan is increased by 3%, and it is re-determined whether this point is the critical pressure steady-state point: if the pressure fluctuation is kept within ±0.5%, the valve opening is increased by fine-tuning the valve, and the change of the maximum flow is controlled by 1%, and the critical pressure stable point A+ with a speed increase of 3% is obtained; if the pressure fluctuation exceeds ±0.5%, the valve opening is reduced by fine-tuning the valve, and the change of the maximum flow is controlled by 1%, and the critical pressure stable point A+ with a speed increase of 3% is obtained, see Figure 3 .

[0022] According to the non-steady critical point B measured by s7, the non-steady critical point B is reproduced through program constant flow control, the resistance K of the whole system is kept unchanged, the speed of the measured fan is increased by 3%, and it is re-determined whether this point is the critical steady-state point of pressure: if the pressure fluctuation remains at ±0.5%, the valve opening is reduced by fine-tuning the valve, and the change of the maximum flow is controlled by 1%, and the critical stable point of pressure with a speed increase of 3% is obtained. If the pressure fluctuation exceeds ±0.5%, the valve opening is increased by fine-tuning the valve, and the change of the maximum flow is controlled by 1%, and the critical stable point of pressure with a speed increase of 3% is obtained. B+, see Figure 3 .

[0023] -3% of the design speed According to the non-steady critical point A measured by s5, the non-steady critical point A is reproduced through program constant flow control, the resistance K of the whole system is kept unchanged, the speed of the tested fan is reduced by 3%, and it is re-determined whether this point is the critical steady-state point of pressure: if the pressure fluctuation is kept within ±0.5%, the valve opening is increased by fine-tuning, and the change of the maximum flow is controlled by 1%, and the critical stable point A- of the pressure with a speed reduction of 3% is obtained; if the pressure fluctuation exceeds ±0.5%, the valve opening is reduced by fine-tuning, and the change of the maximum flow is controlled by 1%, and the critical stable point A- of the pressure with a speed reduction of 3% is obtained, see Figure 3 .

[0024] According to the non-steady critical point B measured by s7, the non-steady critical point B is reproduced through program constant flow control, the resistance K of the whole system is kept unchanged, the speed of the tested fan is reduced by 3%, and it is re-determined whether this point is the critical steady-state point of pressure: if the pressure fluctuation remains at ±0.5%, the valve opening is further reduced by fine-tuning the valve, and the change of the maximum flow is controlled by 1%, and the critical stable point of pressure with a speed reduction of 3% B- is obtained; if the pressure fluctuation exceeds ±0.5%, the valve opening is further increased by fine-tuning the valve, and the change of the maximum flow is controlled by 1%, and the critical stable point of pressure with a speed reduction of 3% B- is obtained, see Figure 3 .

[0025] Case 2: Assume that the value of the non-steady critical point A of a certain type of fan is 100% of the maximum flow rate (that is, there is no non-steady critical point A), and the value of the non-steady critical point B is 25% of the maximum flow rate. The air performance test system identifies the non-stable critical point as follows: s1. After the fan under test is connected to the test system, the test system runs the fan under test and the auxiliary fan, controls the valve to be 100% open and keeps a set number of nozzles on the nozzle wall in an open state, and adjusts the speed of the auxiliary fan to keep the flow velocity at the opened nozzle within the range of 30-35m / s, so that the static pressure value P measured by the static pressure measuring instrument is 0Pa; s2. Under the static pressure of 0Pa, the test system collects and records the flow pressure difference ΔP fluctuation data measured by the differential pressure meter within three minutes, and calculates the maximum flow under the static pressure of 0Pa according to the value of the flow pressure difference ΔP; s3. Divide the maximum flow rate into intervals of 10% to determine the flow measurement points of 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, and 0%; s4. The flow rate is adjusted in the order of first controlling the auxiliary fan speed and then controlling the valve opening degree. At the measurement point of 90% of the maximum flow rate, the test system determines that the above measurement point is in a stable state; s5. The flow rate is gradually increased by 1% of the maximum flow rate in the order of first controlling the valve opening degree and then controlling the auxiliary fan speed. The test system determines that the maximum flow state measurement points of 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, and 100% are all stable states. Because the test system can never return to the unstable state, the test system determines that the unstable critical point A is 100% of the maximum flow rate; s6. The flow rate is adjusted in the order of first controlling the auxiliary fan speed and then controlling the valve opening. At the measurement points of 80%, 70%, 60%, 50%, and 40% of the maximum flow rate, the test system determines that the above measurement points are all in a stable state. At the measurement point of 30% of the maximum flow rate, the test system determines that the measurement point is in an unstable state. s7. The flow rate is gradually increased by 1% of the maximum flow rate, first through the valve opening control and then through the auxiliary fan speed control. The test system determines that the 31%, 32%, 33%, and 34% maximum flow state measurement points are all unstable states, and recognizes that the 35% maximum flow state measurement point is a stable state, thereby determining that the value of the unstable critical point B is 35% of the maximum flow rate; s8. The value of the non-steady-state critical point A should be greater than 70% of the maximum flow rate, and the value of the non-steady-state critical point B should be less than 50% of the maximum flow rate; s9. Determine that the actual use area of ​​the ventilator product should be between 35% and 100% of the maximum flow rate.

[0026] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for automatically identifying non-steady critical points in a ventilator air performance test system, characterized in that: The following steps are involved: s1. After the fan under test is connected to the test system, the test system runs the fan under test and the auxiliary fan, controls the valve to be 100% open and keeps a set number of nozzles on the nozzle wall in an open state, and adjusts the speed of the auxiliary fan to keep the flow velocity at the opened nozzle within the range of 30-35m / s, so that the static pressure value P measured by the static pressure measuring instrument is 0Pa; s2. Under the static pressure of 0Pa, the test system collects and records the flow pressure difference ΔP fluctuation data measured by the differential pressure meter within three minutes, and calculates the maximum flow under the static pressure of 0Pa according to the value of the flow pressure difference ΔP; s3. Divide the maximum flow rate into intervals of 10% to determine the flow measurement points of 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, and 0%; s4. The flow rate is adjusted in the order of first controlling the auxiliary fan speed and then controlling the valve opening degree, so that the flow rate is adjusted from large to small to the above-mentioned various percentage flow measurement points in sequence, until the test system determines that a certain percentage flow measurement point adjusted has reached a stable state; s5. The flow rate is gradually increased by 1% of the maximum flow rate, first through the valve opening control and then through the auxiliary fan speed control, until the test system returns to the unstable state again. The test system identifies and records the unstable critical point A. If the test system cannot return to the unstable state, the test system determines that the unstable critical point A is 100% of the maximum flow rate; s6. Continue to perform the test of the next percentage flow point in the order of step s3 until the test system determines that the adjusted percentage flow measurement point returns to an unstable state; s7. The flow rate is gradually increased by 1% of the maximum flow rate, first through the valve opening control and then through the auxiliary fan speed control, until the test system returns to a stable state again. The test system identifies and records the non-steady-state critical point B; s8. The value of the non-steady-state critical point A should be greater than 70% of the maximum flow rate, and the value of the non-steady-state critical point B should be less than 50% of the maximum flow rate; s9. Determine the area between the non-steady-state critical point B and the non-steady-state critical point A as the actual use area of ​​the ventilator product.

2. The method for automatically identifying the non-steady critical point of a ventilator air performance test system according to claim 1, characterized in that: In step s1, the fan under test runs at the design speed, and the static pressure 0Pa is the arithmetic average of multiple test data of the static pressure measuring instrument within three minutes after the valve opening degree and the auxiliary fan speed are stable.

3. The method for automatically identifying the non-steady critical point of a ventilator air performance test system according to claim 2, characterized in that: In step s4 to step s7, the test system determines whether a certain measuring point has reached a stable state, and processes the flow of the measuring point separately according to whether it is less than 90% of the maximum flow; when the flow of the measuring point is less than 90% of the maximum flow, according to the collected upper and lower peak values ​​of the static pressure fluctuation, it is concluded that the fluctuation range of the static pressure value P measured by the static pressure measuring instrument is within ±0.5% of the average static pressure, and the test system is determined to be in a stable state; when the flow of the measuring point is not less than 90% of the maximum flow, according to the collected upper and lower peak values ​​of the flow pressure difference ΔP fluctuation, it is calculated that the fluctuation range of the flow pressure difference ΔP is within ±0.5% of the average pressure difference, and it is a steady state.

4. The method for automatically identifying the non-steady critical point of a ventilator air performance test system according to claim 3 is characterized in that: In step s5, the test system returns to the unstable state again, that is, it reaches the pressure fluctuation point between the pressure fluctuation upper limit 1 and the pressure fluctuation lower limit 1 in Figure 1. In step s6, the test system determines that the adjusted percentage flow measurement point returns to the unstable state, that is, it reaches the pressure fluctuation point between the pressure fluctuation upper limit 2 and the pressure fluctuation lower limit 2 in Figure 1.

5. The method for automatically identifying the non-steady critical point of a ventilator air performance test system according to claim 4, characterized in that: In step s8, if the value of the non-steady-state critical point A or the value of the non-steady-state critical point B does not meet the requirements, the test system determines that the wind turbine under test has defects.

6. The method for automatically identifying the non-steady critical point of a ventilator air performance test system according to claim 5, characterized in that: In step s7, if the auxiliary fan has been adjusted to zero speed and the valve is in the process of adjustment, and the flow rate of the opened nozzle is less than 10m / s, the test system first reduces the number of opened nozzles, then controls the opening degree of the valve, and finally controls the speed of the auxiliary fan to adjust the flow rate of the opened nozzle to within the range of 10-35m / s.

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