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In traditional feedback control, a single sampling rate is used for all control loops. Consequently, achieving higher performance by increasing the sampling rate is generally costly. The aim of this paper is to develop a multi-rate control framework to create a breakthrough in the performance/cost trade-off in digital controller implementation. In the proposed approach one of the control loops is implemented at a lower rate of which the feedforward controller is designed through normbased minimalization of the tracking error in this multi-rate framework. By designing and implementing one of the control loops at a lower rate, the cost is reduced and the multi-rate problem is addressed. Through simulation the adequate performance of the proposed multi-rate approach is demonstrated.

A methodology is proposed to design stabilising and robust fixed-order decentralised controllers for heterogeneous vehicular platoons with Cooperative Adaptive Cruise Control (CACC). We consider Linear Time Invariant (LTI) models with constant time-delays at state, input and output. The closed-loop systems of (identical) local controllers and heterogeneous parameter vehicles are modelled by a system of delay differential algebraic equations. The proposed frequency domain approach uses the non-conservative direct optimisation approach towards stabilisation and robustness optimisation of delay systems. In this paper, the design problem of stabilising (identical) controllers achieving L2 string stability for one vehicle look-ahead platoon is reduced to a simultaneous controller design problem for a parameterised (sub)system, where the allowable values of the parameters correspond to heterogeneity (including time-delays) of the vehicles. By treating the heterogeneity in parameters as perturbations contained in specific intervals or regions, we determine the values for pseudo-spectral abscissa and robust induced-L2 norm. Hence, we ensure that the achieved exponential stability and string stability properties along with the overall computational complexity (of designing the controller) are independent of the number of vehicles. The application of CACC is simulated in MATLAB software.

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Beyond performance/cost tradeoffs in motion control: a multirate feedforward design with application to a dualstage wafer system. IEEE Transactions on Control Systems Technology, 28(2), 448-461. [8575151].