In this paper, we have developed a nonlinear
backstepping design method for the control of a
360-degree inverted pendulum to achieve our control
objectives. In these two zones, stabilization zone and
swing-up zone, we choose two different controllers to
satisfy each region.
A linear controller is successfully designed by
backstepping method, and it is able to stabilize the
pendulum in the stabilization zone. Although we
choose the situation whose pendulum angle is not
greater than 0.2 radians as the stabilization zone, the
linear controller can indeed stabilize the original
inverted pendulum within 0.8 radians. A nonlinear
controller designed by the same method can swing up
the pendulum from the downward equilibrium point
into stabilization zone, and then raise the pendulum
upright. Although this controller achieves one of the
desired objectives, uprearing the pendulum, it cannot
centre the cart. We need a controller that can not only
remain the pendulum upright, but centre the cart in
any position on the cart.
The combined linear and nonlinear controller has
achieved that the closed-loop system performance is
able to swing the pendulum from down position to
upright and maintain the pendulum at the upright
position within 2.5 seconds. Finally, we can centre the
cart about 2.5 seconds shown in Figure 4.