From a mathematical point of view, self-excited oscillation is a kind of free oscillation that appears in some nonlinear systems. A typical example is the system described by Vanderbilt equation, and the equation form is MX-f (1-x2) x-kx = 0 (m >; 0,f & gt0,k & gt0)。 Where x and x are the first and second derivatives of the variable x, the analysis shows that when the value of x is small, the damping f is negative, so the motion diverges; When the value of x is large, the damping f is positive, so the motion is attenuated. Therefore, regardless of the initial conditions, the motion of the system tends to be a continuous oscillation, that is, self-excited oscillation.