Adaptive sampling frequency for sampled-data control systems

摘要

Sampled-data control systems generally have fixed samplingfrequencies which must be set high enough to give satisfactoryperformance for all anticipated conditions, A study is madehere of an adaptive system which varies the sampling frequencyby measuring a system parameter. It is shown, that a samplerfollowed by a zero-order hold whose sampling period is controlledby the absolute value of the first derivative of theerror signal will be a more "efficient" sampler than a fixed frequency sampler. That is, over a given time interval, fewersamples are needed with the variable frequency system than witha fixed frequency system while maintaining essentially the sameresponse characteristics. Analog computer studies of simple type 1 and type 2sampled-data servo systems with error sampling and unity feedbackverified the method . Standard analog computer components wereused to set up a simulated servo system, a rate detector, absolutevalue detector, a voltage controlled oscillator, and asampler and zero-order hold. The system described reduced the number of samples requiredfor response to a step input to about three-quarters that requiredin a fixed sampling frequency system. Over a long period of time,savings in the number of samples required can be expected to bebetween twenty-five and fifty per cent. In many applications,the saving produced by reducing the overall number of samplesrequired may outweigh the added complexity of the adaptivesampling frequency system.