Modeling and Nonlinear Control Utilizing Unit Complex Numbers

This paper covers the modeling and nonlinear control of the mechanical systems where instead of angle coordinates, unit complex numbers are used as control states. This approach is useful not only to get rid of trigonometric functions, but mainly because it is a specific case of the 3D configuration that utilizes unit hypercomplex numbers (quaternions) as system states, and therefore facilitates its understanding, which represents a contribution to control education. As an example of application, it is considered a particular case of a cube balanced on one of its edges, which is equivalent to a reaction wheel inverted pendulum. The derived nonlinear control law is equivalent to a linear one and is characterized by only three straightforward tuning parameters. Experimental results are presented to validate modeling and control.