An interpolation method for discretisation of a two degree-of-freedom analogue controller and system with state, input and output delays is presented. A Newton centre interpolation formula is used for discretisation of a continuous-time system with state, input and output delays. Also, a Newton backward extrapolation formula and Chebyshev quadrature formula are employed to carry out output-feedback digital redesign of a two degree-of-freedom controller for the delayed analogue system. The developed digital redesign method is then extended to perform discretisation of a Smith predictor for an input-delayed analogue system. The newly developed output-feedback state-matching digital redesign method provides an alternative methodology for indirect digital design of a continuous-time system with state, input and output delays.
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