Staggered sampling to improve stability of multiple-sampler feedback systems

THE PURPOSE of this paper is to present a technique which may be applied to improve the stability of sampled-data feedback control systems having more than one sampler without the use of additional compensating elements, and to illustrate by means of some examples the type of analysis procedure which may be used and the kind of results which may be expected. The technique which is referred to deals with the phasing of samplers in a multiple sampler feedback system to obtain an optimum condition of stability for a given configuration of the system. The technique is principally applicable either to existing systems where it is desired to improve upon a marginally satisfactory degree of stability in the most economical fashion, or to systems where the sampling results from inherent characteristics of the system data measuring or processing elements and is not introduced purposely to utilize the advantages of digital compensation. For the purposes of this paper the discussion will be limited to consideration of multiple sampler feedback systems containing only two samplers operating at the same sampling frequency and it will be assumed that a zero-order hold circuit follows each sampler. The results can be readily extended to systems with more than two samplers. These conditions are not exceedingly restrictive and many practical systems can be conceived which meet them in an engineering sense.