The control law in UAV

In the three articles provided in the first chapter, the feedback control method similar to PID control is adopted to control the UAV. This control method has a special name: DFBC (Differential Flatness Based Control). Of course, due to the good property of differential flatness of quadrotor UAV, another control method applied to UAV: NMPC (nonlinear model predictive control) also got a bonus. When using NMPC control method, it is necessary to calculate the error of each state quantity in order to calculate the cost function, so in the process of error calculation, the expectation of state quantity can be obtained through the differential flatness property of UAV. If we design the state quantity as follows:

Then their expectations can be obtained by trajectory and its derivatives and differential flatness, which makes the attitude expectation and angular velocity expectation of UAV more accurate. The following is a detailed introduction to DFBC control, and the specific content of NMPC control will be written in detail when you have time.

Generally, DFBC control adopts cascade controllers, that is, position expectation, speed expectation, acceleration expectation, position feedback and speed feedback are input into the high-level position controller, and the acceleration output is obtained through this controller, and the expected thrust and attitude are obtained by using the acceleration output, and the expected angular velocity and angular acceleration are obtained by using the differential flatness property, and finally they are input into the low-level attitude controller together with attitude feedback and angular velocity feedback. Finally, the angular acceleration output is obtained, which is brought into the attitude dynamics formula, and the final three-axis torque output is obtained. The thrust and three-axis torque are converted into single motor thrust or speed of four motors through the transformation matrix, and they are sent to the motors to complete the control. Here is a control block diagram in the paper, which can be used for simple reference.