Anti-surge control method for auxiliary power device of loaded gas compressor

Abstract

The invention discloses an anti-surge control method for an auxiliary power device with a load compressor, which belongs to the technical field of aero-engine power, and comprises the following steps: measuring the total pressure PT of the load compressor and the static pressure PS of an outlet, the PS measuring point being located at the minimum section of the outlet of the load compressor, and the PT measuring point being located at an air entraining pipeline; the outlet conversion flow WAC of the load gas compressor is obtained through calculation of the total pressure PT and the outlet static pressure PS; obtaining a surge point WSET of the load compressor under the determined condition by using the measurement data of the load compressor; when WAClt; and when WAC is larger than WSET, it is judged that the load compressor is about to surge, an anti-surge control valve is opened, and it is guaranteed that WAC is larger than or equal to WSET. The method has the advantage that the influence of measurement errors on anti-surge control is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of aero-engine power, and specifically to an anti-surge control method for an auxiliary power unit with a loaded compressor. Background Art

[0002] The structure of a single-shaft loaded compressor APU mainly consists of three parts: a core engine with a loaded compressor, a fuel and lubricating oil system, and an accessory drive system. The compressor of the APU power section and the load section are coaxial and are both single-stage centrifugal compressors. The air extraction function of the APU is achieved by opening the load control valve and adjusting the inlet guide vane (IGV) angle of the load compressor. A high-power starter / generator is installed on the APU casing to realize the starting and power generation functions of the APU.

[0003] When the auxiliary power unit extracts air to the aircraft air conditioner or starts the main engine, due to different requirements of the aircraft air conditioning package and altitude conditions, the air extraction flow rate requirements are different. When the required air extraction flow rate of the aircraft is small, the resistance at the outlet of the load compressor increases. Since the APU speed and IGV angle remain unchanged, the flow rate will decrease, and the operating point of the load compressor will move along the constant speed line towards the surge boundary. When the operating point exceeds the surge point, the compressor will not be able to operate stably, enter surge, the outlet pressure and flow rate of the compressor will pulsate, and the axial force of the compressor will vibrate at a low frequency, affecting the working safety of the APU.

[0004] Refer to Figure 1 , the existing technical solution is to measure the static pressure PS and total pressure PT at the outlet of the load compressor, and obtain the surge point WSET of the load compressor under certain conditions (constant load compressor speed N, constant inlet temperature T2, constant inlet pressure P2) by using the measured data of the load compressor. When WAC < WSET, it is judged that the load compressor is about to surge, and the anti-surge control valve is opened wide to ensure that WAC ≥ WSET. That is, to ensure that the load compressor operates in the Figure 2 B area in. The defect of the existing technology is that when the air flow velocity is slow in the pipeline at the outlet of the load compressor, PS and PT are relatively close. For example, when the air flow Ma = 0.5, PT / PS = 1.1297, and the measurement error requirements for PT and PS are extremely high. Summary of the Invention

[0005] The present invention provides an anti-surge control method for an auxiliary power unit with a loaded compressor to reduce the influence of measurement error on anti-surge control.

[0006] According to one aspect of the present invention, an anti-surge control method for an auxiliary power unit with a load compressor is provided, including the following steps: measuring the total pressure PT and the outlet static pressure PS of the load compressor, the PS measurement point is located at the minimum cross-section of the load compressor outlet, and the PT measurement point is located in the bleed air pipeline; calculating the outlet converted flow rate WAC of the load compressor through the total pressure PT and the outlet static pressure PS; obtaining the surge point WSET of the load compressor under certain conditions using the measured data of the load compressor; when WAC < WSET, it is determined that the load compressor is about to surge, and the anti-surge control valve is opened wider to ensure that WAC ≥ WSET.

[0007] Optionally, measure the intake pressure P2, and the P2 measurement point is located in the APU intake casing;

[0008] Compare the pressure ratio PT / P2 with πset, where πset is the pressure ratio set value considering the choke margin;

[0009] If PT / P2 < πset, the load compressor is operating near the choke point, and the anti-surge control valve is closed to ensure the bleed air pressure;

[0010] If PT / P2 > πset, then control according to the magnitude relationship between WAC and WSET.

[0011] Optionally, in the step of closing the anti-surge control valve to ensure the bleed air pressure, the anti-surge control valve is closed in a fixed rate manner, that is, controlling the collected valve speed Xdot = cont.

[0012] Optionally, if WAC < WSET, the load compressor is operating near the surge boundary, and the anti-surge control valve is opened wider to ensure that the load compressor does not surge;

[0013] If WAC > WSET, close the anti-surge control valve until WAC = WSET to ensure that the bleed air flow is not wasted.

[0014] Optionally, the step of calculating the outlet converted flow rate WAC of the load compressor through the total pressure PT and the outlet static pressure PS uses the formula:

[0015]

[0016] In the formula, k is the air isentropic index k = 1.4, λ is the air flow velocity factor, q(λ) is the gas dynamics flow function, K is the air constant K = 0.0404, P0 is the standard atmospheric pressure of 101.3 kPa, T0 is the standard temperature of 288.15 K, and A is the cross-sectional area of the pressure measurement point.

[0017] Optionally, the certain conditions include that the rotational speed N of the load compressor is constant, the intake temperature T2 is constant, and the intake pressure P2 is constant.

[0018] Optionally, the πset is obtained through a loadable compressor test. During the test, the maximum outlet cross-section of the load compressor is used as the initial value, and the trolley air induction valve is closed in a step-by-step manner until the WAC changes by more than 5%.

[0019] Optionally, the sensor type for measuring the load compressor total pressure PT and the outlet static pressure PS is a Wheatstone bridge pressure sensor.

[0020] Optionally, in the step of comparing the pressure ratio PT / P2 and πset, where πset is the pressure ratio setting value considering the blocking point margin, the blocking point is related to the IGV angle and T2. The blocking point is obtained by continuously opening the downstream cross-section in the compressor test until WAC has no obvious increasing trend, which is defined as the blocking point.

[0021] In summary, the present application includes at least one of the following beneficial technical effects:

[0022] 1. By adjusting the measurement position of static pressure (PS) to the minimum cross-section of the load compressor outlet, the air flow velocity is maximum, the difference between PT and PS increases, and the sensitivity to measurement errors is reduced, thereby improving the measurement accuracy;

[0023] 2. By setting the anti-surge control logic and pressure ratio determination method, it is possible to accurately determine whether the anti-surge control valve needs to be opened when the load compressor approaches the surge point, avoiding unnecessary intervention and preventing misjudgment of entering the surge state;

[0024] 3. In the anti-surge logic control, the opening degree of the anti-surge valve is dynamically adjusted based on the comparison between WAC and WSET, and the comparison between PT / P2 and πset to ensure that the bleed air flow is stable and not wasted, and the compressor maintains efficient operation.

[0025] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0027] Figure 1 This is a schematic diagram of APU bleed air measurement in the prior art;

[0028] Figure 2 This is a schematic diagram of the working principle of the prior art anti-asthma;

[0029] Figure 3 This is a schematic diagram of APU bleed air measurement of the present invention;

[0030] Figure 4 This is the anti-surge working principle diagram of the present invention;

[0031] Figure 5 This is the flowchart of the anti-surge control method for the auxiliary power unit with a loaded compressor of the present invention. Specific embodiments

[0032] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways defined and covered by the following.

[0033] The following combines the attached Figure 3-5 This application is further described in detail.

[0034] The embodiments of this application disclose an anti-surge control method for an auxiliary power unit with a loaded compressor.

[0035] Referring to Figure 5 , the anti-surge control method for the auxiliary power unit with a loaded compressor includes the following steps:

[0036] Measure the total pressure PT and the outlet static pressure PS of the loaded compressor. The PS measurement point is located at the minimum cross-section of the outlet of the loaded compressor, and the PT measurement point is located in the air intake pipeline;

[0037] Calculate the outlet converted flow rate WAC of the loaded compressor through the total pressure PT and the outlet static pressure PS;

[0038] Obtain the surge point WSET of the loaded compressor under certain conditions with the measurement data of the loaded compressor;

[0039] When WAC < WSET, it is judged that the loaded compressor is about to surge, and the anti-surge control valve is opened wide to ensure that WAC ≥ WSET.

[0040] First, by measuring the total pressure PT and outlet static pressure PS of the load compressor, the pressure state of the compressor outlet can be accurately obtained, as shown in Figure 3. Setting the static pressure measurement point at the minimum cross-section of the outlet helps to obtain a more accurate pressure difference at the point with the largest flow rate, thereby improving the measurement accuracy. Next, the outlet conversion flow (WAC) of the load compressor is calculated using the aerodynamic formula using these pressure data, so as to understand the actual flow of the compressor under the current working conditions. Then, based on the test data of the load compressor under certain conditions (such as constant compressor speed, inlet temperature, and inlet pressure), its surge point (WSET) is obtained, that is, the critical flow value at which the compressor may enter the surge state. By comparing the converted flow WAC calculated in real time with the surge point WSET, when it is found that WAC is less than WSET, it means that the load compressor is about to enter the surge state. At this time, the system will automatically open the anti-surge control valve to increase the bleed air flow to ensure that WAC is always greater than or equal to WSET, thereby preventing the compressor from entering the surge state and ensuring that it can operate stably within a safe range.

[0041] Specifically, the steps for calculating the outlet conversion flow WAC of the load compressor by the total pressure PT and the outlet static pressure PS use the formula:

[0042]

[0043] Wherein, k is the air isentropic index k = 1.4, λ is the air flow velocity factor, q(λ) is the gas dynamics flow function, K is the air constant K = 0.0404, P0 is the standard day atmospheric pressure 101.3 kPa, T0 is the standard day temperature 288.15 K, and A is the cross-sectional area of ​​the pressure measuring point.

[0044] When the downstream of the load compressor outlet is smooth enough, the gas critical state will appear at the PS measuring point, that is, MA=1 at the PS measuring point, and the gas will be blocked. At this time, if the anti-surge control valve is still opened, refer to Figure 4 The actual WAC is basically no longer increased in the C area. Figure 4 The PT measuring point in the figure will be affected by the downstream, resulting in a decrease in PT while the PS remains unchanged, causing the WAC calculated based on equations 1 to 3 to be less than the actual situation. Under the condition that the airflow downstream of the aircraft bleed air is smooth, the calculated WAC may enter area A of Figure 4, causing the control logic to incorrectly judge APU surge, and then control the anti-surge control valve to open. After the anti-surge control valve is opened, the situation is further aggravated.

[0045] To solve this problem, the control logic is set as follows:

[0046] Measure the intake pressure P2, the P2 measurement point is located at the APU intake casing;

[0047] Compare the pressure ratio PT / P2 with πset, where πset is the pressure ratio setting value considering the blockage margin;

[0048] If PT / P2<πset, the load compressor is working near the blockage point, close the anti-surge control valve to ensure the bleed air pressure;

[0049] If PT / P2>πset, control is performed based on the size relationship between WAC and WSET. If WAC<WSET, the load compressor operates near the surge boundary, and the anti-surge control valve is opened to ensure that the load compressor does not surge. If WAC>WSET, the anti-surge control valve is closed until WAC=WSET to ensure that the bleed air flow is not wasted.

[0050] By introducing the comparison between the pressure ratio PT / P2 and the set value πset, it is possible to accurately identify whether the load compressor is at or close to the blocking point. When the downstream of the load compressor outlet is smooth enough, the airflow velocity at the PS measuring point reaches the speed of sound (i.e., MA=1), which causes the airflow to be blocked at this position, and continuing to open the anti-surge control valve cannot increase the actual converted flow WAC. At this time, although PT decreases and PS remains unchanged, the WAC calculated based on the measured total pressure PT and static pressure PS will appear to be lower than the actual situation, which is easy to cause misjudgment, thinking that the load compressor is close to the surge state, and then mistakenly opening the anti-surge control valve, leading to further misoperation. By measuring the intake pressure P2 and comparing the pressure ratio PT / P2 with the set πset, the control system can determine whether the load compressor is operating near the blocking point. If the pressure ratio PT / P2 is less than πset, it means that the load compressor is indeed close to the blocking point. At this time, the anti-surge control valve is closed or reduced to ensure the normal maintenance of the bleed air pressure and avoid further misjudgment and intervention. If the pressure ratio PT / P2 is greater than πset, it means that the compressor is not at the blocking point, and normal anti-surge control can be performed based on the comparison between the converted flow WAC and the surge point WSET. This control logic that determines the blocking point by the pressure ratio can effectively avoid the WAC calculation error caused by the blocking state, thereby preventing the system from mistakenly judging that it has entered the surge state, ensuring the accuracy of anti-surge control and the stable operation of the compressor.

[0051] In the step of closing the anti-surge control valve to ensure the bleed air pressure, the anti-surge control valve is closed at a fixed rate, that is, the collected valve speed Xdot=cont is controlled. The method of closing the anti-surge control valve at a fixed rate can ensure that the change in the valve opening is linear and controllable, thereby avoiding large pressure fluctuations or unnecessary surge risks in the system due to too fast valve adjustment. If the anti-surge control valve is closed too quickly, the bleed air pressure may suddenly increase, causing unstable airflow changes, and further affecting the normal operation of the entire auxiliary power unit (APU). If it is closed too slowly, the bleed air pressure may not be restored in time, affecting the efficiency of the compressor and causing a slow response of the system.

[0052] The determination conditions include constant load compressor speed N, constant intake temperature T2, and constant intake pressure P2. Such settings are to simplify control logic and calculations, ensure that the determination of surge point WSET is more accurate and controllable, and make the load compressor consistent and stable during monitoring and adjustment. Stable compressor operating environment can reduce interference from external conditions, making the comparison between converted flow WAC and surge point WSET more accurate and reliable.

[0053] πset is obtained through a loadable compressor test. During the test, the maximum outlet cross-section of the load compressor is used as the initial value, and the trolley bleed valve is closed in a step-by-step manner until the WAC changes by more than 5%. This method of gradually reducing the bleed valve allows for detailed observation of the flow changes of the load compressor under different operating conditions, ensuring that when the WAC changes by more than 5%, the critical state of the compressor approaching surge can be accurately captured; by gradually closing the bleed valve, the compressor outlet flow can be dynamically adjusted to avoid instability or measurement errors caused by sudden valve adjustments or rapid changes in operating conditions. This can effectively reduce unnecessary misjudgments and ensure that the set πset value is more in line with the actual operating conditions of the compressor.

[0054] Specifically, during the measurement process, the type of sensor for measuring the load compressor total pressure PT and the outlet static pressure PS is a Wheatstone bridge pressure sensor.

[0055] Compare the pressure ratio PT / P2 with πset, where πset is the pressure ratio setting value considering the blocking point margin. The blocking point is related to the IGV angle and T2. The blocking point is obtained by continuously opening the downstream cross-section in the compressor test until there is no obvious increase trend in WAC, which is defined as the blocking point.

[0056] Specifically, the definition of the blocking point is closely related to the fluid dynamics characteristics of the compressor. When the compressor reaches the blocking point, the airflow reaches the speed of sound at a certain section of the compressor, forming a local "airflow blockage" phenomenon, that is, the airflow speed can no longer be increased, and the flow rate no longer increases with the expansion of the outlet section or other changes in operation. At this time, the loaded compressor has reached its maximum working capacity, and further increasing the outlet section will not produce a larger flow rate, indicating that the airflow has reached the maximum throughput of the compressor under this condition. By gradually opening the downstream section in this test method and observing the change trend of WAC, the critical point where the airflow reaches the maximum flow rate, that is, the blocking point, can be clearly and accurately captured. The advantage of this definition is that it is based on the dynamic flow change under actual operating conditions to ensure that the determination of the blocking point is based on actual operating conditions rather than theoretical assumptions. Therefore, it can avoid the offset of the blocking point position due to changes in operating conditions (such as differences in IGV angle and inlet temperature T2), thereby improving the accuracy of anti-surge control.

[0057] 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 controlling surge prevention of an auxiliary power unit with a loaded compressor, characterized in that: It includes the following steps: Measure the total pressure PT of the load compressor and the static pressure PS at the outlet. The PS measurement point is located at the minimum cross-section of the load compressor outlet, and the PT measurement point is located on the bleed air pipeline; Obtain the converted flow rate WAC at the outlet of the load compressor by calculating based on the total pressure PT and the static pressure PS at the outlet; Obtain the surge point WSET of the load compressor under determined conditions using the measurement data of the load compressor; When WAC < WSET, it is judged that the load compressor is about to surge, and open the anti-surge control valve to ensure WAC ≥ WSET.

2. The anti-surge control method for an auxiliary power unit with a loaded compressor according to claim 1, characterized in that: It also includes the following steps: Measure the intake pressure P2, and the P2 measurement point is located on the APU intake casing; Compare the pressure ratio PT / P2 with πset, where πset is the set value of the pressure ratio considering the choke margin; If PT / P2 < πset, the load compressor operates near the choke point, close the anti-surge control valve to ensure the bleed air pressure; If PT / P2 > πset, then control according to the magnitude relationship between WAC and WSET.

3. The anti-surge control method for an auxiliary power unit with a load compressor according to claim 2, characterized in that: In the step of closing the anti-surge control valve to ensure the bleed air pressure, the anti-surge control valve is closed in a fixed rate manner, that is, control the valve speed Xdot collected = cont.

4. The anti-surge control method for an auxiliary power unit with a load compressor according to claim 2, characterized in that: If WAC < WSET, the load compressor operates near the surge boundary, open the anti-surge control valve to ensure that the load compressor does not surge; If WAC > WSET, close the anti-surge control valve until WAC = WSET to ensure that the bleed air flow is not wasted.

5. The anti-surge control method for an auxiliary power unit with a load compressor according to claim 1, characterized in that: The step of obtaining the converted flow rate WAC at the outlet of the load compressor by calculating based on the total pressure PT and the static pressure PS at the outlet uses the formula: In the formula, k is the air isentropic exponent k = 1.4, λ is the air flow velocity factor, q(λ) is the gas dynamics flow function, K is the air constant K = 0.0404, P0 is the standard atmospheric pressure of 101.3 kPa, T0 is the standard temperature of 288.15 K, and A is the cross-sectional area of the pressure measurement point.

6. The anti-surge control method for an auxiliary power unit with a load compressor according to claim 1, characterized in that: The determined conditions include that the rotational speed N of the load compressor is constant, the intake temperature T2 is constant, and the intake pressure P2 is constant.

7. The anti-surge control method for an auxiliary power unit with a load compressor according to claim 6, characterized in that: The πset is obtained through tests on the load compressor. During the test, take the maximum of the load compressor outlet cross-section as the initial value, and close the test bench bleed air valve in steps until the change in WAC exceeds 5%.

8. The anti-surge control method for an auxiliary power unit with a load compressor according to claim 1, characterized in that: The sensor type for measuring the total pressure PT and the static pressure PS of the load compressor is a Wheatstone bridge type pressure sensor.

9. The anti-surge control method for an auxiliary power unit with a loaded compressor according to claim 8, characterized in that: In the step of comparing the pressure ratio PT / P2 and πset, where πset is the pressure ratio setting value considering the blocking point margin, the blocking point is related to the IGV angle and T2. The blocking point is obtained by continuously opening the downstream cross-section in the compressor test until WAC has no obvious increasing trend, which is defined as the blocking point.

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