Time-Varying Formation Tracking for Multiple UAVs with Nonholonomic Constraints and Input Quantization via Adaptive Backstepping Control

An adaptive control approach is presented for time-varying formation control of multiple UAVs with nonholonomic constraints and input quantization. The UAVs are described by nonholonomic kinematic model and autopilot model with uncertainties. A transverse function is designed to release the nonholonomic constraints. To avoid chattering, an enhanced hysteretic quantizer is utilized to process the input signals. The quantized signals are analyzed by a new decomposition method to release some restrictions. Based on Lyapunov stability theory, the adaptive backstepping controller is proposed for the formation tracking of multiple UAVs. Tuning functions are devised to make estimations of the unknown parameters and disturbances. A transformation function is applied to the control inputs to eliminate quantization effect. Stability analysis proves that the tracking errors can converge to the origin asymptotically, and all the signals in the closed-loop system are globally bounded. A simulation example is provided to illustrate the effectiveness of the proposed approach. Based on the control approach, the multi-UAV system can track the reference trajectory while forming and maintaining the predefined formation shape.