Effect of network-induced delays in control systems: Application to dc motor control

In a Networked Control System (NCS), sensors, controllers and actuators are connected to the communication network as nodes instead of hardwiring them with point-to-point connections. These networks are also called Fieldbus Networks. The communication network may introduce time delays while exchanging data among devices connected to the shared network medium due to bus arbitration schemes used. These delays can degrade the system performance. The traditional controllers that do not consider the time delays in the design may not perform adequately when applied in NCS. In this paper the impact of these delays on closed loop control system performance measures such as stability, peak overshoot, and settling time are investigated. The paper demonstrates these effects on a control system with a Proportional, Integral, and Derivative (PID) controller using simulation of a DC motor model with MATLAB/Simulink software. A recent paper used the traditional Linear Quadratic Regulator (LQR) design with a delayed state and illustrated the degraded performance for a system with control over wireless networks. This paper suggests the use of a LQR design that takes delays into account for NCS which may not degrade the performance, and illustrates the improved results for a DC motor control system. The paper also studies the robust stability properties of these controllers.