## Improvement of stability of zeros in discrete-time multivariable systems using fractional-order hold.(English)Zbl 1047.93033

The zeros of multivariable sampled-data systems depend on the hold device used in discrete-time systems. Some techniques for control system design cannot be applied if a plant has unstable zeros. Here, the stability properties of the limiting zeros of the discrete-time multivariable systems with fractional-order hold devices is investigated.
A fractional-order hold is a generalization of a first-order hold. For signal reconstruction an adjustable design parameter $$\beta$$ is available. With $$\beta=1$$ a first-order hold is obtained. An approximation of this device for a simple implementation is described.
It is shown that the zeros of discrete-time multivariable systems can be located inside the stability region by choosing a suitable $$\beta$$ with the described hold devices when the zero-order hold fails to do so.
With experimental results presented in the paper it is shown that the control performance is superior to systems with zero-order holds.

### MSC:

 93C57 Sampled-data control/observation systems 93C35 Multivariable systems, multidimensional control systems 93C55 Discrete-time control/observation systems 93D20 Asymptotic stability in control theory
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