Control quality improvement of dc motor on basis of its linearization and compensation of unmodeled dynamics

The aim of this research is to develop an approach to DC motor control as an alternative to the conventional cascade control. Disadvantages of the mentioned classical method are shown, including inability to compensate effectively the influence of unknown dynamics and disturbances (load torque). The solution to these problems lies in the joint use of: 1) the feedback linearization method to separate the unknown dynamics from the control object description and 2) the second Lyapunov method to compensate it. A DC motor linearization based on the solution of the inverse dynamics problem is proposed in this research. It allows to consider limitations on physical signals of current and voltage of anchor circuit. A linear adapter with real-time adjusted parameters on the basis of formulas obtained with the help of the Lyapunov second method is proposed to compensate the unmodeled drive dynamics. The formulas distinctive feature is that when they are used, it is necessary to know the control object gain sign only. The stability of the system with an adapter is proved using Uniform Ultimate Boundedness. Experimental verification of the proposed approach is conducted using the DC drive model with non-stationary parameters. As an example, it is shown that the adaptive system is able to compensate the plant non-stationarity, when the armature circuit parameters are changed by 1.5 times from their nominal values, the inertia moment is changed by two times from its nominal value, and the load torque is equaled to half of the value of the torque, which corresponds to the motor cutoff current. A discussion of the results and further research aims are shown at the end of the paper.