Model-Free Sliding Mode Control Algorithms including Application to a Real-World Quadrotor

Abstract

Sliding mode control is a robust nonlinear control algorithm that has been used to implement tracking controllers for unmanned aircraft systems that are robust to modeling uncertainty and exogenous disturbances, thereby providing excellent performance for autonomous operation. A significant advance in the application of sliding mode control for unmanned aircraft systems would be adaptation of a model-free sliding mode control algorithm, since the most complex and time-consuming aspect of implementation of sliding mode control is the derivation of the control law with incorporation of the system model, a process required to be performed for each individual application of sliding mode control. The performance of various model-free sliding mode control algorithms was compared in simulation using a variety of aerial system models and real-world disturbances (e.g. the effects of discretization and state estimation). The two best performing algorithms were shown to exhibit very similar behavior. These two algorithms were implemented on a quadrotor (both in simulation and using real-world hardware) and the performance was compared to a traditional PID based controller using the same state estimation algorithm and control setup. Simulation results show the model-free sliding mode control algorithms exhibit similar performance to PID controllers without the tedious tuning process. Comparison between the two model-free sliding mode control algorithms showed very similar performance as measured by the quadratic means of tracking errors. Flight testing showed that while a model-free sliding mode control algorithm can control real-world hardware, further characterization and significant improvements are required before it is a viable alternative to conventional control algorithms. Large tracking errors were observed for both the model-free sliding mode control and PID based flight controllers and the performance was characterized as unacceptable for most applications. The poor performance of both controllers suggests tracking errors can be attributed to errors in state estimation. Further testing with improved state estimation would allow for more conclusions to be drawn.

Complete Model-Free Siding Mode Control (CMFSMC)

“…This CMFSMC takes all types of systems/models as a bounded uncertainty. Therefore, it includes all the other partial MFSMC approaches as its special cases which require additional assumptions such as system model structures, unitary input gain (Precup, Radac, Roman, and Petriu 2017), state measurable (Schulken and Crassidis 2018), extra effort to deal with chattering effect, based on discrete time approaches (Crassidis and Reis 2016). Further the novelty lays in the introduction of two equalities to assign the derivative of the sliding functions, which generally bridges the designs of those model-based SMC and model-free SMC.…”

Improved model-free fractional-order intelligent proportional–integral fractional-order sliding mode control with anti-windup compensator

“…A data-driven model-free adaptive sliding mode control (MFASMC) approach is proposed by Wang et al (2016c), where extensive simulation experiments are conducted using a SimMechanics model of the robotic exoskeleton to show the performance of the system. MFSMCS have been considered in several applications such as: wind turbine (Aboulem et al, 2019), Double Fed Induction Generator (Li et al, 2016), real-world quadrotor (Schulken and Crassidis, 2018), and glycemia regulation systems (Tian et al, 2019).…”