Communication disturbance observer approach to control of integral plant with time delay

The presence of time delay can cause stability problems in closed loop systems as it adds large negative phase angle to the system frequency response. The Smith predictor is a well-known method of dealing with fixed and known time delays in control systems. Errors in the knowledge of the time delay will cause degradation of the Smith predictor compensation performance. A solution to this problem is to use a communication disturbance observer. Time delayed integral plants are typical examples of open loop unstable systems with time delay. In this paper, the communication disturbance observer based time delay compensation method is applied to high order time delayed integral plants. A robust stability condition is derived for time delayed feedback control systems with the communication disturbance observer. The effect of the communication disturbance observer Q filter cut-off frequency selection on robust stability is investigated. Simulation results are presented for both constant and time varying delays to illustrate the effectiveness of the proposed communication disturbance observer approach.