Fuzzy-PID (Proportion Integration Differentiation) design method for flight control of electric tilting rotorcraft

Abstract

The invention provides a fuzzy-PID (Proportion Integration Differentiation) design method for flight control of an electric tilting rotorcraft. The method comprises the following steps: establishing a flight dynamics model according to the stress and torque of the electric tilting rotorcraft; performing linearization processing on the flight dynamics model; aiming at three flight modes of a helicopter of an electric tilt rotorcraft, a propeller-driven aircraft and tilt transition, an inner and outer double-loop control structure is adopted; for an outer loop of a control system, a fuzzy-PID control method is adopted to carry out control law design, and then a fuzzy-PID controller is constructed according to the control law; aiming at an inner loop of the control system, a PID control method is adopted to carry out control law design, and then a PID controller is constructed according to the control law; and acquiring a difference value between expected input and actual output of the system, and inputting the difference value into the fuzzy-PID controller to adjust parameters of the controller. According to the invention, an ideal flight control effect of the electric tilting rotorcraft is obtained.

Description

Technical Field

[0001] The present invention relates to the field of electric vertical take-off and landing (eVTOL) aircraft, and in particular to a fuzzy-PID design method for flight control of an electric tiltrotor aircraft. Background Art

[0002] Tilt-rotor aircraft have the advantages of helicopter vertical take-off and landing, hovering in the air, and propeller aircraft with high speed and long range. It has three flight modes: helicopter, propeller aircraft and tilt-transition. For tilt-rotor aircraft flight control, under the premise of ensuring flight stability, it is necessary to test the flight control effect from two aspects: dynamic performance and steady-state performance, and also consider the feasibility and ease of implementation of the control method.

[0003] PID control, which has few parameters, simple structure, and does not rely on the precise model of the system, is a widely used flight control method today. However, the PID control parameters are fixed and cannot be adjusted in real time with changes in system errors. It also has poor robustness in the face of external disturbances. As a more general control method, although the self-disturbance rejection control does not rely on the precise model of the system and has good robustness, this control method involves many parameters and the parameter adjustment process is complicated. Although the parameters of adaptive control can be adjusted dynamically, in some cases it may cause poor system stability or even instability. Other advanced control methods with better control effects often require very precise models of the controlled object and are designed specifically according to the various characteristics of the controlled object. This brings challenges to actual flight control with large model errors. Summary of the invention

[0004] In view of the above-mentioned deficiencies of the existing flight control methods, the present invention proposes a fuzzy-PID design method for flight control of an electric tiltrotor aircraft, which can achieve an ideal flight control effect of the electric tiltrotor aircraft.

[0005] The scheme adopted by the present invention is:

[0006] Establish a flight dynamics model based on the forces and moments acting on the electric tilt-rotor aircraft;

[0007] Linearize the flight dynamics model;

[0008] For the three flight modes of electric tiltrotor aircraft, namely helicopter, propeller aircraft and tilt-transition, an internal and external dual-loop control structure is adopted;

[0009] For the control system's outer loop, the fuzzy-PID control method is used to design the control law, and then the fuzzy-PID controller is constructed according to the control law;

[0010] For the inner loop of the control system, the PID control method is used to design the control law, and then the PID controller is constructed according to the control law;

[0011] Obtain the difference between the expected input and the actual output of the system, and input the difference into the fuzzy-PID controller;

[0012] Fuzzy control determines the input scaling factor based on the relationship between the controller input and the domain range, and PID control adjusts the proportional, integral, and differential link coefficients based on the actual output. The above process is repeated to complete the adjustment of the controller parameters.

[0013] The present invention has the following beneficial effects:

[0014] (1) The essence of fuzzy-PID control is to use fuzzy control ideas to correct the parameters of the proportional, integral, and differential links of PID control in real time, which solves the defect that the parameters of traditional PID control are fixed and cannot be adjusted in real time due to changes in the external environment.

[0015] (2) Fuzzy-PID control combines the advantages of fuzzy control and PID control. It does not rely on the system model, has a simple structure, and has a certain degree of robustness. At the same time, the introduction of fuzzy control ideas can make the system response converge quickly to the expected value and improve the dynamic response of the system.

[0016] (3) During the adjustment process of fuzzy-PID control, the parameters that need to be adjusted are only the proportional, integral, and differential coefficients of PID control, and the input scaling coefficient of fuzzy control, a total of only five parameters. In addition, there are clear adjustment methods for adjusting the PID control coefficient and determining the input scaling coefficient, which meets the design requirements of a controller with few parameters and easy adjustment.

[0017] (4) The simulation of the flight control of the electric tiltrotor aircraft shows that the parameter response curves of the three flight modes of the electric tiltrotor aircraft, namely, helicopter, tilt transition and propeller aircraft, such as altitude, pitch angle, roll angle, etc., all have good dynamic performance and steady-state performance, indicating that the internal and external dual-loop design method of the electric tiltrotor aircraft flight control law of the present invention can achieve an ideal flight control effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the structure diagram of the flight control system with fuzzy-PID controller

[0019] Figure 2 is the altitude response curve of the helicopter flight mode

[0020] Figure 3 is the yaw rate response curve of the helicopter flight mode

[0021] Figure 4 is the position response curve of the tilt transition flight mode

[0022] Figure 5 This is the roll angle response curve of the propeller aircraft flight mode

[0023] Figure 6 This is the airspeed response curve for propeller aircraft flight mode. DETAILED DESCRIPTION

[0024] This embodiment provides a fuzzy-PID design method for electric tiltrotor flight control, comprising the following steps:

[0025] A flight dynamics model is established based on the forces and moments acting on the electric tiltrotor aircraft: the electric tiltrotor aircraft is divided into multiple components, and the forces and moments of the rotor, nacelle, wing, tail, fuselage and landing gear of the electric tiltrotor aircraft are derived respectively. The dynamic equations and kinematic equations are combined to obtain a six-degree-of-freedom nonlinear flight dynamics model of the electric tiltrotor aircraft.

[0026] Linearize the flight dynamics model: Use the small disturbance linearization method based on Taylor expansion to simplify the nonlinear model of the electric tilt-rotor aircraft into a linearized model by ignoring high-order small terms and retaining only linear terms.

[0027] For the three flight modes of electric tilt-rotor aircraft, namely helicopter, propeller aircraft and tilt-transition, an internal and external double-loop control structure is adopted:

[0028] (1) In helicopter flight mode, the throttle channel is responsible for altitude control, and the other three channels are responsible for attitude control of roll, pitch, and yaw movements. Based on the above characteristics, the outer loop of the throttle channel is the altitude control loop, and the inner loop is the climb rate control loop; the outer loop of the roll channel is the roll angle control loop, and the inner loop is the roll angle rate control loop; the outer loop of the pitch channel is the pitch angle control loop, and the inner loop is the pitch angle rate control loop; the yaw channel can achieve a better heading control effect by using only a single loop, which is the yaw angle rate control loop.

[0029] (2) In the propeller aircraft flight mode, the throttle channel is responsible for flight speed control, while the other three channels are responsible for attitude control of roll, pitch, and yaw movements, and the pitch channel is also responsible for altitude control. Based on the above characteristics, the outer loop of the roll channel is the roll angle control loop, and the inner loop is the roll angle rate control loop; the pitch channel is corrected to a three-loop control structure, with the outer loop being the climb rate control loop, the middle loop being the pitch angle control loop, and the innermost loop being the pitch angle rate control loop; the yaw channel can obtain a better heading control effect by using only a single loop, which is the yaw angle rate control loop; the throttle channel can obtain a better flight speed control effect by using only a single loop, which is the airspeed control loop.

[0030] (3) In the tilt-transition flight mode, flight control includes both the control of the rotor speed and the control of the rudder deflection, so the control system superimposes the helicopter flight mode and the propeller aircraft flight mode, still following the dual-loop control structure.

[0031] For the outer loop of the control system, the fuzzy-PID control method is used to design the control law, and then a fuzzy-PID controller is constructed according to the control law. For the inner loop of the control system, the PID control method is used to design the control law, and then a PID controller is constructed according to the control law.

[0032] For the control system outer loop, use the formula Determine the fuzzy-PID control law. Where, k p ′,k i ′,k d ′ are the proportional, integral and differential coefficients of the fuzzy-PID control law, k p ′=k p +Δk p , k i ′=k i +Δk i , k d ′=k d +Δk d , k p ,k i ,k d They are PID control parameters, Δk p ,Δk i ,Δk d are the fuzzy control parameters respectively.

[0033] The input of the PID control part in the fuzzy-PID controller is the system error e, the input of the fuzzy control is the system error e and the error change rate ec, and the output is Δk p ,Δk i ,Δk d ; The domain of the fuzzy control input e and ec is (-3,3), and the output Δk p ,Δk i ,Δk d The domain of the fuzzy control is (-4,4). The linguistic variables of the input and output of the fuzzy control in the corresponding domain are negative large, negative medium, negative small, zero, positive small, positive medium, and positive large; among them, the membership functions corresponding to the linguistic variables negative large and positive large are Gaussian functions, and the membership functions corresponding to the other linguistic variables are trigonometric functions; the Madani fuzzy reasoning method is used to complete the construction of the fuzzy-PID controller, and the implementation principle is as follows Figure 1 shown.

[0034] For the control system inner loop, use the formula Determine the PID control law and construct the controller.

[0035] Obtain the difference between the expected input and actual output of the system, input the difference into the fuzzy-PID controller, and adjust the controller parameters: for the control system inner loop, the requirements for rapidity are high, and the system adjustment time is required to be short; for the control system outer loop, the requirements for stability are high, and the system steady-state error and overshoot are required to be small.

[0036] from Figures 2 to 6 The simulation results show that the parameter response curves of altitude, yaw rate, position, roll angle, airspeed and other parameters of the three flight modes including helicopter, tilt-rotor transition and propeller aircraft all have good dynamic and steady-state performances. The internal and external dual-loop design method of the electric tilt-rotor aircraft flight control law of the present invention can obtain an ideal flight control effect.

[0037] The above embodiment only expresses one implementation mode of the present invention, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several improvements and modifications without departing from the principle of the present invention are all within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the attached claims.

Claims

1. A fuzzy-PID design method for electric tiltrotor flight control, characterized in that: include: Establish a flight dynamics model based on the forces and moments acting on the electric tilt-rotor aircraft; Linearize the flight dynamics model; For the three flight modes of electric tiltrotor aircraft, namely helicopter, propeller aircraft and tilt-transition, an internal and external dual-loop control structure is adopted; For the control system's outer loop, the fuzzy-PID control method is used to design the control law, and then the fuzzy-PID controller is constructed according to the control law; For the inner loop of the control system, the PID control method is used to design the control law, and then the PID controller is constructed according to the control law; The difference between the expected input and the actual output of the system is obtained, and the difference is input into the fuzzy-PID controller to adjust the controller parameters.

2. The method according to claim 1, characterized in that: For the outer loop of the control system, the fuzzy-PID control method is used to design the control law, and then a fuzzy-PID controller is built according to the control law; for the inner loop of the control system, the PID control method is used to design the control law, and then a PID controller is built according to the control law, including: Using formula Determining the fuzzy-PID control law; Among them, k p ′, k i ′, k d ′ are the proportional, integral and differential coefficients of the fuzzy-PID control law, k p ′=k p +Δk p , k i ′=k i +Δk i , k d ′=k d +Δk d , k p ,k i ,k d They are PID control parameters, Δk p ,Δk i ,Δk d are the fuzzy control parameters respectively; Determine that the input of PID control in the fuzzy-PID controller is the system error e, the input of fuzzy control is the system error e and the error change rate ec, and the output is Δk p ,Δk i ,Δk d ; Determine that the domain of the fuzzy control input e and ec is (-a, a), and the output Δk p ,Δk i ,Δk d The domain of is (-b,b), where a>0, b>0; Determine that the linguistic variables of the input and output of the fuzzy control in the corresponding domain are all negative large, negative medium, negative small, zero, positive small, positive medium, and positive large; among them, the membership functions corresponding to the linguistic variables negative large and positive large are Gaussian functions, and the membership functions corresponding to the other linguistic variables are trigonometric functions; The fuzzy algorithm of the fuzzy-PID controller is determined using the Madani fuzzy inference method.

3. The method according to claim 1, characterized in that: Obtain the difference between the expected input and the actual output of the system, and input the difference into the fuzzy-PID controller to adjust the controller parameters, including: The system error is determined by the formula e(t)=r(t)-y(t), and the system error e(t) is input into the fuzzy-PID controller to adjust the controller parameters, where r(t) is the expected input of the system, y(t) is the actual output of the system, and e=e(t). According to the fuzzy control input e and ec, the corresponding input scaling factor k is determined respectively e and k ec It is used to make the input quickly enter the domain range. The PID control part adjusts the proportional, integral, and differential link coefficients according to the actual output, and repeats the above process to complete the adjustment of the controller parameters.

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