State-dependent differential Riccati equation to track control of time-varying systems with state and control nonlinearities

•Tracking problem in SDDRE domain was investigated.•Backward integration was found the most precise solution for SDDRE tracking.•Application of SDDRE tracking was shown for rigid and flexible joint manipulators.•A general program was released for controlling any kind of robot obeys D–H rules.

This work studies an optimal control problem using the state-dependent Riccati equation (SDRE) in differential form to track for time-varying systems with state and control nonlinearities. The trajectory tracking structure provides two nonlinear differential equations: the state-dependent differential Riccati equation (SDDRE) and the feed-forward differential equation. The independence of the governing equations and stability of the controller are proven along the trajectory using the Lyapunov approach. Backward integration (BI) is capable of solving the equations as a numerical solution; however, the forward solution methods require the closed-form solution to fulfill the task. A closed-form solution is introduced for SDDRE, but the feed-forward differential equation has not yet been obtained. Different ways of solving the problem are expressed and analyzed. These include BI, closed-form solution with corrective assumption, approximate solution, and forward integration. Application of the tracking problem is investigated to control robotic manipulators possessing rigid or flexible joints. The intention is to release a general program for automatic implementation of an SDDRE controller for any manipulator that obeys the Denavit–Hartenberg (D–H) principle when only D–H parameters are received as input data.

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