INVESTIGATION OF WIRELESS NETWORKED CONTROL SYSTEM FOR A MULTI-LOOP PLANT

Wireless network has the potential in control systems because it reduces the
amount of space and cost of laying wires and cables. However, wireless network has
some limitations such as time delay and loss of data. This is because as the number of
nodes increase, the time delay also increases. Similarly, when there are multiple loops
trying to send signals at the same time within the same bandwidth, the signals only can
be sent based on queue. Hence when the bandwidth is busy the signals have to be sent
many times and this can cause loss of data. In order to investigate the effects of wireless
network on the performance of two heat exchanger plants, several open-loop control
systems have been modelled in from these plants. Transfer functions from each loop
involved have been obtained through lab experiments and statistical modelling. PID
tuning parameters are calculated and tuned for each loop using Ziegler-Nichols,
Cohen-Coon or Skogestad tuning method. PI controllers are used for all loops in this
project. Using the controller and plant parameters, the control system is recreated in
Matlab TrueTime where data is transmitted over a wireless network. From Matlab
TrueTime, the effects of using a wireless network in controlling a heat exchanger plant
simulation are different in performance and stability of the plant. From the simulation,
it can be observed that the time delay is the main factor considered. The performance
of all controllers of all loops are affected by time delay in Wireless Networked Control
Systems (WNCS). The rise time and the settling time are slower when simulated in
Matlab TrueTime.