Frequency Domain Analysis of a RTOS in Control Applications

FRANCISCO E. PAEZ; RICARDO CAYSSIALS; JOSÉ M. URRIZA; EDGARDO FERRO; JAVIER OROZCO

CABA

Congreso;  Seventh Argentine Symposium and Conference on Embedded Systems; 2016

Control applications are implemented using realtimeoperating systems. Digital control theory is based onsampling intervals that have to be strictly met in order to getpredictable behaviors. However, a real-time system may introduceexecution jitters that may cause unpredictable effects on thecontrol application. Stability, overshoot and settling time maybe affected when an inadequate real-time system is used. Severalpapers have proposed different mechanisms to measure the jitterthat a real time system produces. However, jitter can not betranslated as a performance criterion in control theory. On theother hand, frequency domain techniques are widely appliedin control theory for designing control strategies, as well asanalyzing and measuring the performance of control mechanisms.In this paper, frequency domain analysis is used to measurethe perturbations that a real-time operating system may produceon a control application. Harmonic distortion is defined asa criterion to evaluate the control performance of the theapplication. Experiments show that higher priority tasks arelikely to be used for control tasks since the perturbation producedup to an utilization factor of 70% is adequate for most controlapplications.