Digital redesign of cascaded analogue controllers for sampled-data interval systems

The paper presents a new method for the digital redesign of cascaded analogue controllers for continuous-time parametric interval systems. The bilinear and inverse-bilinear approximation method is developed to carry out discretisation of the predesigned cascaded analogue controller, taking into account intersample behaviour and implementation errors. A dual concept of the proposed digital redesign method is utilised to construct a new pseudodigital observer such that the estimated states of the digitally redesigned digital observer closely match those of the original continuous-time observer at the sampling instants. Using the newly digitally redesigned observer based controllers, the resulting dynamic states of the digitally controlled cascaded sampled-data interval systems are able to closely match those of the original analogously controlled cascaded continuous-time parametric interval systems