CAN-based networked path-tracking control of a 4WS4WD electric vehicle: Minimum sampling period

Abstract

An earlier work of the authors presented a multi-input multi-output (MIMO) path-tracking control system (PTCS) for an autonomous version of the four-wheel steering four-wheel drive (4WS4WD) electric vehicle. This PTCS has a supervisor module controlling eight motor control system modules. Since a serial communication link has several advantages over point-to-point wiring, the practical implementation planned by the authors of the PTCS has these nine modules forming feedback loops over a Controller Area Network (CAN) protocol-based serial link, thereby forming a networked control system (NCS). However, the MIMO nonlinear loops in the PTCS turn the selection of the minimum and maximum sampling periods TS min and TS max for a digital implementation, while factoring the time delays introduced by the communication, into a non-trivial task. Almost all the available literature on CAN-based NCS treats the protocol as a black box involving uncertain communication delays, resulting in high order controllers that are conservative. This paper solves the controller order and conservativeness problem by determining Ts min through a systematic audit of the time delays caused by the communication and by controller code execution, and validates the theoretical results through a hardware-in-the-loop simulation. The techniques shown are promising for applications involving coordination of multiple actuators and for CAN-based NCS.