A flight altitude control method for a rotorcraft with adaptive variable weight load

Abstract

The present invention relates to the field of rotorcraft unmanned aerial vehicle (UAV) control, and more specifically, to a method for adaptively controlling the flight altitude of a UAV with a variable weight load. The mass-adaptive PID control method comprises designing a cascade PID controller for an unloaded UAV, then designing a mass-adaptive controller based on loads of varying masses, considering the placement of the load at the center of gravity of the UAV. The controller's stability is proven using Lyapunov's stability theorem, and finally, the unloaded cascade PID control and the loaded mass-adaptive control are combined into a mass-adaptive PID controller. This control method solves the problem of reducing the impact of load changes on the dynamic response of the control system when the UAV carries different loads or the load mass changes slowly, without changing the originally set PID parameters. This method increases the speed at which the system reaches stability when affected by load changes. Application of this method to UAVs avoids the inconvenience of frequently adjusting PID parameters and improves operational efficiency.

Description

Technical Field

[0001] The present invention relates to the field of rotary-wing UAV control, and in particular to a method for controlling the flight altitude of a rotary-wing UAV with an adaptive variable weight load. Background Art

[0002] Rotorless drones (UAVs), with their vertical takeoff and landing (VTOL), fixed-point hovering, and excellent maneuverability, are widely used in applications such as pesticide spraying, express delivery, and disaster relief. To accomplish these tasks, multi-rotor UAVs must be able to carry payloads and maintain stable flight. Therefore, while ensuring high-performance hardware, a suitable control method can improve mission efficiency.

[0003] Among existing rotary-wing UAV control algorithms, proportional-differential-integral (PID) control is the most widely used in engineering. The PID controller itself offers excellent stability. However, when a rotary-wing UAV is operating with a load, it is placed at the center of gravity of the aircraft. Loads of varying weights or load masses that slowly change over time primarily affect the magnitude of the UAV's z-direction gravity and lift. Failure to set matching PID parameters can affect the system's dynamic performance, specifically its speed. This is especially true for large-scale operations, such as pesticide spraying, where speed requirements are high. Therefore, designing a control method to mitigate the degradation of altitude control caused by varying load weight and improve the speed of rotary-wing UAVs has become a key technology that needs to be addressed. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention proposes a flight altitude control method for a rotorcraft UAV with adaptive variable weight load.

[0005] The technical solution adopted by the present invention is as follows: a method for controlling the flight altitude of a rotorcraft with an adaptive variable weight load, which controls the weight of the unloaded rotorcraft and designs a controller for different loads to achieve control of the rotorcraft carrying a load, including the following steps:

[0006] The unloaded rotor UAV obtains the desired lift control value u according to the desired height through the position loop PID controller and the speed loop PID controller in sequence. PID ;

[0007] The rotor UAV carrying a load obtains the adaptive control quantity u through the mass adaptive cascade PID controller A ;

[0008] The desired lift control quantity u PID and adaptive control quantity u AThe overall control quantity u is obtained by superposition to control the rotor UAV carrying the load.

[0009] Position loop PID control: The position error between the desired height and the actual height is input into the position loop PID controller to obtain the desired speed;

[0010] Speed ​​loop PID control: The speed deviation is obtained by subtracting the desired speed output by the position loop PID controller from the actual speed measured. After obtaining the desired acceleration through the speed loop PID controller, the desired lift control value u is obtained based on the mass of the rotorcraft itself. PID :

[0011] u PID =m0a dz

[0012]

[0013] Among them, a dz is the desired acceleration in the z direction, K Pv ,K Iv ,K Dv They are the proportional differential integral parameters of the speed loop, e v is the speed loop deviation, is the derivative of the velocity deviation, and m0 is the mass of the UAV when it is unloaded.

[0014] The rotor UAV when carrying a load obtains an adaptive control quantity u through a mass adaptive cascade PID controller A , including the following steps:

[0015]

[0016] The estimated load is

[0017]

[0018] Among them, r1 represents a linear filter, k1 is a positive constant, φ is the roll angle, θ is the pitch angle, g is the gravitational acceleration constant, and k m Represents the adaptive controller gain, which is a positive constant;

[0019] Intermediate control quantity is the second-order derivative of the desired height, g is the gravitational acceleration constant, α1 is a positive constant, e p is the height deviation.

[0020] The problem solved by the technology of the present invention is: when a rotary-wing UAV carries loads of different masses, the controller parameter control effect is poor when no-load and it is inconvenient to change the parameters when the cascade PID control method is applied. A mass-adaptive PID application is proposed, which makes it possible for the PID controller parameters to be changed within a certain range without changing with the load mass, while not affecting the rapidity.

[0021] The technical solution of the present invention is: a control method based on the combination of mass adaptive control and cascade PID, which realizes the control of the rotor UAV by cascading PID for the control of the airborne multi-rotor UAV and mass adaptive control for the load, including the following steps:

[0022] When no-load, a cascade PID height control is designed for the rotorcraft: the desired height is used as the controller input, and the height deviation is used to design the position loop PID, thereby obtaining the desired speed and speed deviation. The speed loop PID is designed to obtain the desired lift, thereby obtaining the control input when no-load.

[0023] When a load is placed at the center of gravity of a rotary-wing UAV, and the load weight changes over time, a mass adaptive controller is designed for the rotary-wing UAV. Without changing the PID parameters, the mass adaptive controller is applied to compensate for the influence of the change in load weight on the control effect.

[0024] This paper proposes a method for controlling the altitude of a rotary-wing UAV based on mass adaptive PID under different load conditions. The main advantages of this method are summarized as follows:

[0025] 1) Cascade PID has good control effect and robustness, which can ensure the stability of the rotorcraft when it is empty;

[0026] 2) Construct a linear filter to simplify controller design;

[0027] 3) When loaded, the introduction of the mass adaptive controller ensures system stability and speed without changing the PID parameters. This improves the situation in engineering applications where the PID parameters need to be adjusted due to changes in load weight, which reduces the working efficiency of the drone. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a diagram showing the design structure of the adaptive cascade PID control of the present invention;

[0029] Figure 2 This is a load mass estimation result diagram of the present invention;

[0030] Figure 3 This is the z-axis trajectory tracking diagram of the cascade PID controller of the present invention;

[0031] Figure 4 This is the trajectory tracking diagram of the adaptive cascade PID controller in the z-axis direction of the present invention. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] A method for controlling the flight altitude of a rotorcraft with an adaptive variable weight load is provided, wherein the method is characterized in that the rotorcraft carrying a load is controlled by controlling the weight of the unloaded drone itself and designing a controller for different loads, and comprises the following steps:

[0034] When the rotorcraft is unloaded, the position loop PID and speed loop PID are used in sequence to obtain the desired lift according to the desired height. When the rotorcraft is carrying a load, a mass adaptive cascade PID controller is designed in combination with the mass adaptive method.

[0035] Position loop PID control: The desired height is input to the position control of the cascade PID controller, and the desired speed is obtained according to the position error;

[0036] Speed ​​loop PID control: The speed deviation is obtained by subtracting the expected speed output by the position loop from the actual speed measured, and the speed loop PID controller is designed. After the expected acceleration is obtained, the expected lift is obtained based on the mass of the rotorcraft itself.

[0037] When a payload is placed at the center of gravity of the drone and the payload or payload mass changes, the total mass of the drone changes. If the PID controller parameters are not changed, the PID controller alone will degrade the system's dynamic performance, especially its speed. Introducing a mass-adaptive controller can effectively address this issue. By adding mass-adaptive control, the system's speed can be guaranteed to be unaffected by the payload mass without changing the PID parameters.

[0038] The method for controlling the altitude of a rotary-wing UAV based on mass adaptive PID includes the following steps:

[0039] Select the north-east direction to establish the earth coordinate system, the front-right-rear direction to establish the body coordinate system, and establish the rotor UAV altitude dynamics model;

[0040] Design a cascade PID controller for the unloaded rotor UAV to control its altitude;

[0041] Consider the case of a rotorcraft carrying a load. Assuming that the load is placed at the center of gravity of the aircraft, that is, the load does not affect the center of gravity of the aircraft, the total mass of the aircraft changes after carrying the load, which mainly affects the lift control in the vertical direction. The dynamic equation of the aircraft in the z direction is taken as the research object;

[0042] A linear filter is constructed to reduce the order of the system so that the height error and its derivative have the same convergence characteristics as the filter, simplifying the controller design.

[0043] Combining the filter expression and its derivative expression with the dynamic equation in the z-axis direction, a mass adaptive controller is designed for the load mass change.

[0044] Backstepping control is used to estimate the mass of the load and an adaptive control law is designed to make the mass estimation error approach 0. Lyapunov stability theory is used to prove that the height error and speed error eventually converge to 0.

[0045] The overall controller of the UAV system carrying a payload consists of a cascade PID controller when unloaded and a mass adaptive controller when loaded;

[0046] The design of the cascade PID controller under no-load conditions includes the following steps:

[0047] 1) Design of cascade PID controller for no-load operation

[0048] When no-load, the position loop PID and speed loop PID are designed according to the desired height, and the control law of the cascade PID controller is obtained as follows:

[0049] u PID =m0a dz

[0050] Among them, m0 is the mass of the rotorcraft when it is empty, a dz The expected acceleration in the height direction of the position loop PID output;

[0051] 2) Design of mass adaptive controller when carrying load

[0052] Design a linear filter to reduce the system order:

[0053]

[0054] Among them, r1 represents a linear filter, e p and are the height deviation and its derivative with respect to time, respectively.

[0055] In order to simplify the expression, the intermediate control quantity Y1 is introduced:

[0056]

[0057] in, is the second derivative of the desired height, g is the gravitational acceleration constant, and α1 is a positive constant.

[0058] Estimated value of load mass for:

[0059]

[0060] Among them, k m Represents the adaptive controller gain, which is a positive constant.

[0061] The adaptive control law is:

[0062]

[0063] Where φ is the roll angle, θ is the pitch angle, and k1 is a positive constant.

[0064] 3) Proof of stability of quality adaptive controller

[0065] The adaptive control law can ensure that the mass estimation error tends to 0. At the same time, according to the Lyapunov theorem and the LaSalle invariance principle, it is proved that when t→∞, the proposed method can make the position error and velocity error in the z direction converge to 0, so the system is stable.

[0066] 4) Quality adaptive PID controller design

[0067] The overall control law of the mass adaptive PID controller is:

[0068] u=u PID +u A

[0069] Among them, the cascade PID controller is designed for the case of no-load rotorcraft, and the adaptive controller is used to compensate for the impact of load on PID parameters.

[0070] See also Figure 1 Adaptive cascade PID control design structure diagram. The present invention provides a method for controlling the height of a rotorcraft based on mass adaptive PID under different load conditions. The specific steps are as follows: (1) Design of PID controller when no load

[0071] Assuming that the height direction is the negative direction of the z-axis of the constructed coordinate system, the height error is defined as

[0072] e p =p dz -p z

[0073] Among them, p dz is the desired height in the z direction, p z is the actual height measured in the z direction.

[0074] The position loop PID design is as follows

[0075]

[0076] From the above formula, we can get the expected velocity v in the z direction dz , e p and They represent the height error and its derivative with respect to time, K Pp ,K Ip ,K Dp is the position loop PID parameter.

[0077] The velocity error is defined as

[0078] e v =v dz -v z

[0079] Among them, v z is the actual height measured in the z direction.

[0080] The speed loop PID design is as follows

[0081]

[0082] The expected acceleration in the z direction is obtained from the above formula, K Pv ,K Iv ,K Dv Represents the speed loop PID parameters. The PID controller designed for airborne UAV is designed as follows

[0083] u PID =m0a dz

[0084] Where m0 is the mass of the drone when it is empty.

[0085] (2) Quality adaptive controller design

[0086] When the UAV is carrying a load, consider placing the load at the center of gravity of the UAV and considering the change in the total mass of the UAV. This will mainly affect the controller parameters in the z direction, so consider the height dynamic model in the z direction:

[0087]

[0088] Where m represents the mass of the payload carried by the rotorcraft, represents the second-order derivative of the desired altitude with respect to time, φ is the roll angle, θ is the pitch angle, and u A is the adaptive control law, and g is the gravitational acceleration constant.

[0089] Introducing a linear filter to reduce the order of the system

[0090]

[0091] Taking the derivative of both sides of the equation with respect to time, we can get

[0092]

[0093] but

[0094]

[0095] In order to make the expression more concise and clear, the intermediate control quantity is introduced

[0096]

[0097] but

[0098]

[0099] The estimated load mass is

[0100]

[0101] The quality adaptive control law is

[0102]

[0103] (3) Proof of stability of adaptive controller

[0104] Defining mass estimation error

[0105]

[0106] The load mass is constant or changes slowly, so there is

[0107] but

[0108]

[0109] Select the Lyapunov function as follows

[0110]

[0111] V1 is positive definite, then its derivative is

[0112]

[0113] From the above, we can see that when the mass estimation error approaches 0, It is negative semidefinite. Based on the LaSalle invariance principle, when time approaches infinity, the height error and its derivative will converge asymptotically to 0. According to the Lyapunov stability theory, it can be proved that the system is stable.

[0114] (4) Quality adaptive cascade PID controller design

[0115] A cascade PID control method is designed for the unloaded rotorcraft, and the parameters of the PID controller are adjusted according to the system performance.

[0116] When carrying a load, a mass adaptive controller is designed to adapt to changes in the load mass;

[0117] The overall control law of the rotor UAV carrying a payload is:

[0118] u=u PID +u A

[0119] (5) Simulation of quality adaptive cascade PID controller

[0120] The algorithm is verified using a quadrotor drone as an example;

[0121] First, assuming the unladen mass of the rotorcraft is 4 kg and the payload is 0.5 kg, and the input signal is a step signal with an amplitude ranging from 3 to 10, representing the aircraft taking off and first flying to the desired altitude of 3 meters and then rising to the desired altitude of 10 meters, verify the impact of adding a mass adaptive controller on the system's dynamic performance.

[0122] Next, see Figure 2 The mass estimation results are shown in the figure. Taking a 0.5kg payload as an example, the present invention provides a mass estimation method. The figure shows that while there is a large mass estimation deviation during takeoff and ascent, the deviation quickly converges to zero, and good estimation results are achieved during stable flight operations.

[0123] The final simulation results show the drone's altitude tracking performance when it takes off, first flying to a height of three meters and then to a height of ten meters. The simulation results show the drone's altitude tracking performance when it is empty, and the loads it carries are 0.5kg, 1kg, 1.5kg, and 2kg. The simulation time is set to 10 seconds.

[0124] See also Figure 3 Cascade PID controller z-axis trajectory tracking and Figure 4 Adaptive cascade PID controller z-axis trajectory tracking. Comparing the two figures, we can see that after setting the PID controller parameters without changing them, it can be found that the tracking effect will be affected by the load quality when only PID control is used, especially the rapidity is affected, and there is a small amount of overshoot. After adding mass adaptive control, the change of load quality has almost no effect on the control effect of the system. At the same time, the rapidity of the system is improved by about 12%, which greatly saves operation time and improves operation efficiency.

[0125] The above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, but these descriptions should not be understood as limiting the scope of the present invention. The scope of protection of the present invention is defined by the appended claims, and any changes based on the claims of the present invention are within the scope of protection of the present invention.

Claims

1. A method for controlling the flight altitude of a rotorcraft with an adaptive variable weight load, characterized in that: By controlling the weight of the unloaded UAV and designing controllers for different loads, the control of the rotor UAV carrying a load is achieved, including the following steps: The unloaded rotor UAV obtains the desired lift control value u according to the desired height through the position loop PID controller and the speed loop PID controller in sequence. PID ; The rotor UAV carrying a load obtains the adaptive control quantity u through the mass adaptive controller A ; The desired lift control quantity u PID and adaptive control quantity u A The overall control quantity u is obtained by superposition to control the rotor UAV carrying the load.

2. The method for controlling the flight altitude of a rotorcraft with an adaptive variable weight load according to claim 1, characterized in that: Position loop PID control: The position error between the desired height and the actual height is input into the position loop PID controller to obtain the desired speed; Speed ​​loop PID control: The speed deviation is obtained by subtracting the desired speed output by the position loop PID controller from the actual speed measured. After obtaining the desired acceleration through the speed loop PID controller, the desired lift control value u is obtained based on the mass of the rotorcraft itself. PID : u PID =m0a dz Among them, a dz is the desired acceleration in the z direction, K Pv ,K Iv ,K Dv They are the proportional differential integral parameters of the speed loop, e v is the speed loop deviation, is the derivative of the velocity deviation, and m0 is the mass of the UAV when it is unloaded.

3. The method for controlling the flight altitude of a rotorcraft with an adaptive variable weight load according to claim 1, wherein: The rotor UAV when carrying a load obtains an adaptive control quantity u through a mass adaptive controller A , including the following steps: The estimated load is Among them, r1 represents a linear filter, k1 is a positive constant, φ is the roll angle, θ is the pitch angle, g is the gravitational acceleration constant, and k m Represents the quality adaptive controller gain, which is a positive constant; Intermediate control quantity is the second-order derivative of the desired height, g is the gravitational acceleration constant, α1 is a positive constant, e p is the height deviation.

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