Linear flight control method of UAV

Flight control of UAV is one of the main problems in UAV research field. During the flight, it will be disturbed by various kinds, such as noise and drift of sensors, strong wind and turbulence, changes in payload and model changes caused by excessive inclination, etc. All these will seriously affect the flying quality of aircraft, so the control technology of UAV is particularly important. Traditional control methods mainly focus on attitude and altitude control, in addition, some control methods are used to control speed, position, heading and 3D trajectory tracking. The control methods of multi-rotor UAV can be summarized as the following three main aspects.

1 linear flight control method

Conventional aircraft control methods and early attempts to control aircraft are based on linear flight control theory, among which there are PID, H∞, LQR and gain scheduling methods.

1.PID PID control is a traditional control method, which is one of the most successful and widely used control methods at present. Its control method is simple, no modeling work is needed, and the physical meaning of parameters is clear, so it is suitable for control with low flight accuracy requirements.

2.H∞ H∞ is a robust control method. Classical control theory does not require the precise mathematical model of the controlled object to solve the problem of multi-input multi-output nonlinear system. Modern control theory can quantitatively solve the problem of multi-input multi-output nonlinear system, but it completely depends on the mathematical model describing the dynamic characteristics of the controlled object. Robust control can solve the problem of modeling error caused by interference and other factors, but its calculation is very large and depends on high-performance processors. At the same time, because it is a frequency domain design method, it is relatively difficult to adjust parameters.

3.LQR LQR is one of the successful methods used to control UAV. Its object is a linear system that can be expressed by state space expression, and its objective function is the integral of quadratic function of state variable or control variable. Moreover, the use of Matlab software provides a good simulation condition for the control method of LQR, which is more convenient for engineering implementation.

4. Gain scheduling method Gain scheduling means that when the system is running, the parameters of the controller will change with the change of scheduling variables, and the system will run in different regions with different control laws according to the scheduling variables to solve the problem of system nonlinearity. The algorithm consists of two parts. The first part mainly completes event-driven and realizes parameter adjustment. If the operation of the system changes, the mode can be identified and switched through this part; The second part is error drive, and its control function is realized by the selected mode. This control method has excellent performance in the control of vertical takeoff and landing, fixed-point hovering and path tracking of rotary-wing UAV.