Bandwidth Reduction and Convergence Analysis of Extremum Seeking Control with Feedback Encoding

• Main Authors: Vikum Sri Wijesinghe, Upeka Kanchana Premaratne
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2016-11-01
• Series: Frontiers in Mechanical Engineering
• Subjects: networked control systems; Encoding schemes; Extremum seeking control; Network Traffic Reduction; Memory Based Event Triggering; Event Triggered Adaptive Differential Modulation
• Online Access: http://journal.frontiersin.org/Journal/10.3389/fmech.2016.00011/full

Frequently a physical plant of a control system has an optimum operating point such as the spark (or injection) time of an internal combustion engine that results in maximum torque. Extremum Seeking Control (ESC) is a method of adaptive control capable of locating and maintaining a plant at such an optimum operating point in real time. It is capable of doing so with minimal a priori knowledge of the plant and can also track slowly varying changes. Input perturbed ESC schemes that use periodic dither signals have the disadvantage of requiring a high bandwidth for sampling and correlating the plant output with the dither signal. If the feedback path were to be implemented over a packet switched communication network, the high bandwidth requirement could result in increased congestion and consequently packet delays and dropouts. As a solution encoding using sporadic (aperiodic) sampling techniques can be used in the feedback path of the ESC scheme to reduce the required bandwidth. However, in order to ensure convergence of the ESC scheme with encoding, the effect of the signal reconstruction error due to encoding on the critical correlation stage has to be investigated. The contribution of this paper is an investigation of the convergence requirements and bandwidth performance of two encoding schemes; Memory Based Event Triggering (MBET) and Event Triggered Adaptive Differential Modulation (ETADM). The results show that MBET can fail for objective functions with plateaus. ETADM fails when the number of ETADM steps used for reconstructing the plant output per perturbation cycle are too low to allow correlation. In terms of bandwidth reduction MBET performs better than ETADM (97% and 70% respectively). However, the use of MBET results in a longer convergence time.