Fault-tolerant control method for fan guide vane of turbofan engine

Abstract

The invention discloses a turbofan engine fan guide vane fault-tolerant control method based on reference model correction. The method comprises the steps that a pressure ratio closed-loop control system for guide vane control is constructed; on the basis of the control system, a reference model is established for error correction; and carrying out optimization design on the reference model, so that the reference model can be switched between an open-loop control plan and the pressure ratio closed-loop control plan. According to the method, the actual value of the guide vane angle does not need to be obtained, fault-tolerant control when the guide vane angle sensor breaks down is achieved, and the fault tolerance of guide vane control is greatly enhanced.

Description

Technical Field

[0001] The present invention belongs to the field of aero-engine fault-tolerant control, and particularly relates to a fault-tolerant control method for a fan guide vane of a turbofan engine based on reference model correction. Background Technique

[0002] An aero-engine can change the flow rate of a fan or a compressor through adjustable guide vanes. At present, the guide vane control of an aero-engine generally adopts open-loop control, that is, by receiving the engine corrected speed signal, changing the angle of the compressor guide vane according to a certain rule, and feeding back the actual value measured by the guide vane angle sensor, so as to change the air flow area and control the air flow rate to improve the engine performance and increase the engine efficiency. When the guide vane sensor fails, since the engine cannot obtain the actual value of the guide vane angle, the control system cannot adjust it reasonably. An abnormal guide vane angle may cause a decrease in engine thrust, an increase in fuel consumption, and a decrease in engine performance and efficiency. In extreme cases, if the failure of the guide vane sensor causes the engine control to fail, it may lead to safety accidents, such as the loss of engine power or uncontrollable engine performance fluctuations. In this regard, foreign countries use a mature airborne model to reconstruct the guide vane, that is, the "soft redundancy" analysis of the sensor. At present, there is no relatively mature research on the airborne model in China. In engineering practice, when the guide vane angle sensor fails, the guide vane is often closed to the minimum position to ensure the safety of the engine. However, the method of closing the guide vane to the minimum will have a certain negative impact on the engine and sacrifice a certain amount of engine performance. Therefore, the research on guide vane fault-tolerant control has gradually become a difficult problem that needs to be urgently overcome in China.

[0003] The above information disclosed in the background technique section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0004] To solve the problems caused by the failure of the above-mentioned guide vane angle sensor, this paper proposes a non-similar guide vane fault-tolerant control plan. This method uses the pressure ratio closed-loop control plan as a backup for the guide vane open-loop control plan, and corrects the control plan based on the reference model for different operating states during the acceleration and deceleration processes. When the sensor fails, the control plan is switched to minimize the following error of the guide vane as much as possible to avoid engine surge. Finally, typical operating point simulations are carried out for a twin-spool turbofan engine. To achieve the above object, the present invention provides the following technical solutions:

[0005] A fault-tolerant control method for a fan guide vane of a turbofan engine based on reference model correction, comprising the following steps:

[0006] Step S100: Construct a pressure ratio closed-loop control system for guide vane control;

[0007] Step S200: Based on the control system, establish a reference model for error correction;

[0008] Step S300: Optimize the reference model so that it can switch between the open-loop control plan and the pressure ratio closed-loop control plan.

[0009] Preferably, in step S100, the pressure ratio closed-loop control system includes: a PI controller, an electro-hydraulic servo valve, an actuator, and a pressure sensor.

[0010] Preferably, the PI controller is used to calculate and output a current signal .

[0011] Preferably, the electro-hydraulic servo valve is used to change the oil pressure in the two chambers of the actuator according to the magnitude and direction of the current signal so that the output displacement of the actuator piston rod changes.

[0012] Preferably, the pressure ratio is sensed by the pressure sensor and further compared with the pressure ratio target value. This process is repeated continuously until the pressure ratio is adjusted to the pressure ratio target value. At this time, the guide vane angle is the target guide vane angle.

[0013] Preferably, in step S200, the reference model includes: an ideal actuator model.

[0014] Preferably, in step S200, the error correction includes the following steps:

[0015] S201: Obtain the target pressure ratio by sensing the current fan corrected speed and the total inlet temperature, and obtain the current signal , through the designed controller; ;

[0016] S202: Use the current signal of the controller as the input signal of the ideal actuator model, output the analytical guide vane angle and subtract it from the target guide vane angle to convert it into a pressure ratio correction coefficient ;

[0017] S203: Correct the target pressure ratio according to the pressure ratio correction coefficient to obtain the final pressure ratio target value .

[0018] Preferably, the formula for the pressure ratio correction coefficient is as follows:

[0019]

[0020] In the formula, —— A constant related to the adiabatic coefficient of the gas and the ideal gas constant related constant.

[0021] Preferably, the target value of the pressure ratio is as follows:

[0022]

[0023] Preferably, in step S300, the optimization design includes: designing a switch for the control plan;

[0024] The switch is used to switch between the pressure ratio closed-loop control plan and the open-loop control plan.

[0025] Compared with the prior art, the beneficial effects brought by the present invention are as follows: The present invention can convert the change of the air flow rate by directly controlling the actual value of the guide vane angle in the open-loop control plan of the guide vane into indirectly controlling the guide vane angle by controlling the actual value of the pressure ratio in the pressure ratio closed-loop control plan. The present invention does not need to obtain the actual value of the guide vane angle, realizes fault-tolerant control when the guide vane angle sensor fails, and greatly enhances the fault tolerance of the guide vane control. At the same time, the pressure ratio closed-loop control plan is corrected based on the reference model, so that the following error of the guide vane angle is less than a certain threshold, improves the control quality and can smoothly switch after the guide vane sensor fails, enhancing the fault tolerance of the control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flowchart of a fault-tolerant control method for a fan guide vane of a turbofan engine corrected based on a reference model provided by an embodiment of the present invention;

[0027] Figure 2 is a schematic structural diagram of a certain type of dual-rotor afterburning turbofan engine provided by an embodiment of the present invention;

[0028] Figure 3 is a schematic diagram of the principle of a pressure ratio closed-loop control plan provided by another embodiment of the present invention;

[0029] Figure 4 is a schematic diagram of the principle of a fan pressure ratio closed-loop control plan corrected based on a reference model provided by another embodiment of the present invention;

[0030] Figure 5 is a schematic diagram of the principle of a control plan switch provided by another embodiment of the present invention;

[0031] Figure 6 is a simulation comparison diagram of the open-loop and closed-loop plans at the ground point provided by another embodiment of the present invention;

[0032] Reference numerals: 1 - 2: inlet duct, 2 - 22: fan, 25 - 3: high - pressure compressor, 15 - 16: bypass duct, 3 - 4: main combustion chamber, 4 - 45: high - pressure turbine, 45 - 5: low - pressure turbine, 6 - 65: mixing chamber, 65 - 7: afterburner, 7 - 9: nozzle, 8: nozzle throat. Detailed implementation manners

[0033] The following will refer to the attached Figures 1 to 6 The specific embodiments of the present invention will be described in detail. Although the specific embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0034] It should be noted that in the description of the specification and claims, certain terms are used to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. The specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of components as the criterion for distinction. As mentioned throughout the specification and claims, the term "comprising" or "including" is an open - ended term and should be interpreted as "including but not limited to". The subsequent description of the specification is for the purpose of describing the preferred implementation manners of implementing the present invention, but the description is based on the general principles of the specification and is not used to limit the scope of the present invention. The protection scope of the present invention shall be defined by the appended claims.

[0035] For the convenience of understanding the embodiments of the present invention, the following will further explain with specific embodiments as examples in combination with the drawings, and each drawing does not constitute a limitation to the embodiments of the present invention.

[0036] In one embodiment, as Figure 1 shown, the present invention provides a fault - tolerant control method for the fan guide vane of a turbofan engine based on reference - model correction, including the following steps:

[0037] Step S100: Construct a pressure - ratio closed - loop control plan as a non - similar backup plan for the guide - vane open - loop control plan;

[0038] Step S200: On the basis of the pressure - ratio closed - loop control plan, establish a reference model to correct the guide - vane following error;

[0039] Step S300: Optimize the established reference model so that it can switch between the open-loop control plan and the pressure ratio closed-loop control plan. Currently, the guide vane control of aeroengines generally adopts open-loop control. When the guide vane angle sensor fails, the guide vane is often closed to the minimum position to ensure the safety of the engine. However, closing the guide vane to the minimum will have a certain negative impact on the engine and sacrifice a certain amount of engine performance. The present invention designs a pressure ratio closed-loop control plan and combines it with a switch so that when the guide vane angle sensor fails, it can switch from the original guide vane open-loop control plan to the pressure ratio closed-loop control plan.

[0040] In another embodiment, in step S100, first, a pressure ratio closed-loop control system for guide vane control needs to be constructed, including: a PI controller, an electro-hydraulic servo valve, an actuator, and a pressure sensor. As Figure 3 shown, this system respectively collects the fan speed and total inlet temperature of the engine through a temperature sensor and a speed sensor and uses them as inputs. The pressure ratio control target value interpolated from the corrected speed (i.e., the target pressure ratio) is used as the target value of the PI controller. Then, the actual pressure ratio is obtained through the pressure sensor, and the difference between it and the target pressure ratio is used as the input of the PI controller. The output current signal is calculated through the output signal u(t) of the PI controller. The calculation formula is shown as follows:

[0041]

[0042] In the formula: G - transfer function.

[0043] Then, the electro-hydraulic servo valve changes the oil pressure in the two chambers of the actuator according to the magnitude and direction of the current , causing the output displacement of the actuator piston rod to change. The engine senses the pressure ratio in this state through the pressure sensor , and compares it with the pressure ratio control target value . This process is repeated continuously until the pressure ratio is adjusted to the target value . At this time, the guide vane angle is the target guide vane angle corresponding to this speed.

[0044] In another embodiment, the pressure ratio control target value is linearly interpolated from the actual value of the guide vane under the control of the guide vane open-loop control plan. The interpolation process is as follows:

[0045] First, under the guide vane open-loop control plan, push the throttle lever PLA from the ground idle of 15° to the intermediate state of 65° in 1° steps, and record the corrected speed value at each steady state With the pressure ratio control target value , an interpolation table is formed , ,..., .

[0046] Then, the engine senses the fan speed through the speed sensor and calculates the current converted speed value . According to the value of the position interval of is determined, and then the corresponding pressure ratio control target value is estimated using the linear interpolation formula. The calculation formula is as shown below:

[0047] .

[0048] In another embodiment, in step S200, there is a guide vane following error in the pressure ratio closed-loop control plan during the engine transient state, especially during the afterburning process. That is, at the moment when the afterburner is turned on, the pressure ratio of the fan increases, the flow rate decreases, the fan operating point position moves obliquely upward, and the surge margin of the fan also decreases accordingly. In addition, the total inlet pressure distortion will also cause the surge margin of the fan to decrease. The analysis is as follows:

[0049] As Figure 2 shown, the inlet section 6 of the engine mixing chamber to the throat section 8 of the tailpipe is regarded as a cavity with a volume of V. When the engine turns on the afterburner, the average pressure of the gas inside the cavity becomes larger, that is, the static pressure from the inlet section 6 of the mixing chamber to the throat section 8 of the tailpipe increases. The inlet section 6 of the mixing chamber is the outlet section 16 of the outer duct and the outlet section 5 of the low-pressure turbine, and the static pressures among the three are balanced. So when increases, also increases, and because:

[0050]

[0051] In the formula: ——Total pressure loss of the outer duct, ——Total pressure of this section, ——Average static pressure of the gas at this section.

[0052] It can be seen that with the increase of , the static pressure at the outlet section of the outer duct increases, then the static pressure behind the fan and the total pressure behind the fan both increase, and the pressure ratio of the fan increases. The total pressure behind the low-pressure turbine increases, while the static pressure Remain unchanged, resulting in the turbine pressure ratio to decrease, thereby causing the available power of the low-pressure turbine to decrease, the low-pressure rotor speed to decrease, and the fan flow rate to decrease. The rotor dynamics equation of the low-pressure rotor is as follows:

[0053]

[0054] In the formula: —— The low-pressure rotor speed; —— The moment of inertia of the low-pressure rotor; —— The power consumed by the fan.

[0055] Generally, the distance between the common operating point and the stall point is used to describe the surge margin of the fan . On the same speed line, the farther the operating point deviates from the common operating line and approaches the stall boundary, the smaller the surge margin. The closer it is to the lower boundary, the more sharply the pressure ratio decreases and the flow rate increases slowly. The surge margin formula is as follows:

[0056]

[0057] In the formula: —— The fan corrected flow rate; " "—— The position of the stall point; " "—— The position of the current operating point, —— The pressure ratio of the fan.

[0058] Through the above analysis, it can be seen that at the moment when afterburner is turned on, the pressure ratio of the fan increases, the flow rate is small, the fan flow rate decreases, the position of the fan operating point moves obliquely upward, and the surge margin of the fan also decreases accordingly. In addition, the total inlet pressure distortion will also cause the surge margin of the fan to decrease.

[0059] In another embodiment, in step S200, the reference model is mainly based on the physical structure and working principle of the actuator. As Figure 4 shown, the present invention also designs an ideal actuator model, which mainly includes an electro-hydraulic servo valve, a metering valve, and an actuator.

[0060] In another embodiment, the reference model includes:

[0061] The displacement of the actuator and the current signal of the controller

[0062]

[0063] Where: A——Integral gain; ——Analysis time of the reference model.

[0064] The metering valve analyzes the guide vane angle The calculation process is as follows:

[0065]

[0066] Where: ——Initial guide vane angle.

[0067] The reference model uses The current signal of the controller As the input, the output model analyzes the guide vane angle , and then makes a difference with the target guide vane angle to convert it into a pressure ratio correction coefficient to correct the pressure ratio target value. The corrected value is subtracted from the actual pressure ratio again and used as The input of the controller.

[0068] In another embodiment, in step S200, the guide vane following error correction based on the reference model includes the following steps:

[0069] S201: Obtain the target pressure ratio by sensing the current fan conversion speed and total inlet temperature , and obtain the current signal through the designed controller; specifically, collect the fan speed of the engine and the total inlet temperature through a temperature sensor and a speed sensor respectively and use them as inputs. The pressure ratio control target value interpolated with the conversion speed (i.e., the target pressure ratio) is used as the target value of the PI controller. Then, obtain the actual pressure ratio through a pressure sensor. The difference between it and the target pressure ratio is used as the input of the PI controller. Exemplarily, this difference in pressure ratio is converted into a time quantity u(t) that changes with t, so as to calculate and output the current signal through the following formula. Those skilled in the art are well aware that according to the principle of automatic control, the idea of closed-loop control is exactly based on continuously controlling the output based on the difference, and in the process of control, continuously approaching the difference to an acceptable level in engineering or approaching 0. As mentioned above, the calculation formula of the current signal i is as follows:

[0070]

[0071] Where: G——Transfer function.

[0072] Then, the electro-hydraulic servo valve is based on the current The oil pressure in the two chambers of the actuator for changing the size and direction changes the output displacement of the actuator piston rod, causing the engine to sense the pressure ratio in this state through the pressure sensor , and compare it with the target value of the pressure ratio control . This process is continuously repeated until the pressure ratio is adjusted to the target value . At this time, the guide vane angle is the target guide vane angle corresponding to this rotational speed .

[0073] S202: Use the current signal of the controller as the input signal of the ideal actuator, and the output model analyzes the guide vane angle , then subtract it from the target guide vane angle to convert it into a pressure ratio correction coefficient to correct the target value of the pressure ratio. The formula is as follows:

[0074]

[0075] In the formula, —— a constant related to the adiabatic coefficient of the gas and the ideal gas constant ;

[0076] S203: According to the correction coefficient, correct the target value of the pressure ratio control to obtain the final target value of the pressure ratio . The formula is as follows:

[0077]

[0078] In another embodiment, in step S300, the optimization design includes:

[0079] A switch for the control plan is designed to switch between the control plan designed for the present invention (i.e., the pressure ratio closed-loop control plan) and the original open-loop control plan, as Figure 5 shown

[0080] In the case of no failure, the controlled quantity of the control system is the guide vane angle, and precise feedback is provided by the guide vane angle sensor to achieve open-loop control of the fan pressure ratio. However, when the relevant sensor fails, the control plan switch switches the system from the open-loop plan to the pressure ratio closed-loop control plan based on the reference model correction, relying on the sensor data without failure to provide feedback to ensure that the system can still operate stably under fault conditions. After the fault is eliminated, the pressure ratio closed-loop control plan based on the reference model correction is switched back to the original open-loop plan

[0081] Next, simulation experiments are used to verify the effectiveness of the method described in the present invention

[0082] The simulation verification is carried out at the ground operating point with a height H = 0 m and a Mach number Mahe = 0. The simulation data of the pressure ratio closed-loop control plan based on reference model correction designed by the present invention is compared with the guide vane open-loop control plan. The simulation results are as Figure 6 shown. Among them, the red solid line is the simulation curve using the guide vane open-loop control plan; the blue solid line is the simulation curve using the pressure ratio closed-loop control plan based on reference model correction designed by the present invention. The simulation results show that the control method proposed by the present invention can effectively guarantee the fault tolerance ability of the guide vane control system, significantly reduce the guide vane following error, and maintain the surge margin and thrust output performance of the engine under problems such as sensor failures. Especially in the afterburner state, this method can avoid the negative impact of traditional control strategies on engine performance, providing higher reliability and fault tolerance for the design of the full-authority digital electronic control system (FADEC). Therefore, it shows that the fault-tolerant control method for the fan guide vane of the turbofan engine based on reference model correction of the present invention is effective.

[0083] The present invention has been introduced in detail above. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A fault-tolerant control method for the fan guide vane of a turbofan engine based on reference model correction, characterized in that Including the following steps: Step S100: Construct a closed-loop pressure ratio control system for guide vane control; Step S200: Based on the control system, establish a reference model for error correction; Step S300: Optimize the reference model so that it can switch between the open-loop control plan and the closed-loop pressure ratio control plan.

2. The method according to claim 1, wherein Preferably, in step S100, the closed-loop pressure ratio control system includes: a PI controller, an electro-hydraulic servo valve, an actuator, and a pressure sensor.

3. The method according to claim 2, wherein The PI controller is used to calculate the output current signal .

4. The method according to claim 3, wherein The electro-hydraulic servo valve is used to change the oil pressures in two chambers of the actuator cylinder according to the magnitude and direction of the current signal so as to change the output displacement of the piston rod of the actuator cylinder.

5. The method according to claim 4, wherein The pressure ratio is sensed by the pressure sensor and further compared with the pressure ratio target value. This process is repeated continuously until the pressure ratio is adjusted to the pressure ratio target value, and the guide vane angle at this time is the target guide vane angle.

6. The method according to claim 1, characterized in that, In step S200, the reference model includes: an ideal actuator model.

7. The method according to claim 6, wherein In step S200, the error correction includes the following steps: S201: Obtain the target pressure ratio by sensing the converted rotational speed of the current fan and the total inlet temperature , and obtain the current signal through the controller; S202: Using the current signal of the controller as the input signal of the ideal actuator model, and outputting the analytical guide vane angle to subtract from the target guide vane angle and converting it into a pressure ratio correction coefficient ; S203: Correct the target pressure ratio according to the pressure ratio correction coefficient to obtain the final target value of the pressure ratio .

8. The method according to claim 7, wherein The pressure ratio correction coefficient The formula is as follows: ； In the formula, —— A constant related to the adiabatic coefficient of the gas and the ideal gas constant related constant.

9. A switch for performing the method according to any one of claims 1 to 8, characterized in that, The switch is used to switch between the closed-loop pressure ratio control plan and the open-loop control plan.

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