The finite time convergence of the second order sliding Super-twisting algorithm is analyzed by using a nonsmooth
quadratic-like Lyapunov function. For the constant disturbance, the finite time convergence is proved through
Lyapunov equation, and the optimal estimation of the convergence time is presented. For the time varying disturbance,
the finite time convergence of Super-twisting is guaranteed when the parameters satisfy the algebraic Riccati equation, and
the estimation of the convergence time is provided. Finally, simulation results show the correction of the theoretical analysis.