Susceptibility of controller computers to environmental disruptions and its effects on system stability

Electromagnetic Interference (EMI) causes controller upsets manifested as control-law computation errors in digital computers or transmission disturbances between sensor and/or actuator lines. Though its effects are likely to be transient, frequent occurrences of these upsets may lead to the loss of system stability. In this paper, we compute the stationary probability of those upsets induced due to EMI by using parameters accounting for EMI behavior and the conditional probabilities of upsets in the presence of EMI. The latter represents susceptibility to EMI depending upon the electrical shielding properties of controllers against various intensities and frequencies of EMI. We use a Markov-chain model to describe burst upsets when EMI is present. We then modify a system dynamic equation by including the stochastic features (occurrences/magnitudes) of these upsets, and examine the condition of system stability for the mean behaviors of the modified equation. The derived information about the required level of the stationary probability of upsets is a key to the design and verification of the integrity of reliable controllers. We also present a simple experiment emulating EMI on data transmission to estimate the necessary parameters and a demonstration example about system stability