A novel structure of time delayed control systems with communication disturbance observer

This paper proposes a novel structure of time delayed control systems with communication disturbance observer (CDOB). Time delay problem is one of difficult issues in control engineering and the effects seriously induces performance deterioration and destabilization. Therefore, many kinds of time delay compensation methods or stabilization methods have been proposed so far. As one of those methods, a time delay compensation method based on the concept of network disturbance (ND) and CDOB has been proposed. The method sufficiently compensates time delay without using delay time model. The stability of the method also has been studied in detail and it has been verified that the stability depends on the value of a cutoff frequency of a low-pass filter (LPF) in CDOB. Since the value always has constraint caused by some limitations of devices, the dependency is not desirable. In this paper, a novel structure of the time delayed control systems with CDOB, the stability of which does not depend on the value of cutoff frequency, is proposed. The method eliminates the time delay element from the characteristic polynomial. Therefore the system is not destabilized by time delay anymore. Furthermore, the system can be designed easily by stability criteria for rational characteristic polynomials. The validity is verified by stability analysis (Nyquist diagram) and simulation results. Finally, we make some remarks on the design of time delayed control systems with CDOB.