Improvement of Variable Cam Timing Multirate Control via Optimal Output Filtering

In traditional digital control design, feedback measurements are assumed to be sampled equidistant in time, in synchronization with the update rate of the digital controller. In practice, limitations due to event-based sampling, communication delays and intermittent data losses in the transmission network may lead to variations in the actual sensor sampling rate, giving rise to multiple sampling rates in the feedback loop. In this paper, we consider sampled-data output-feedback control of the variable cam timing (VCT) system, which is a multirate control problem due to the event-triggered sensing mechanism. The objective is to recover the performance of the ideal single-rate architecture without modifying the existing VCT controller. This is achieved by reconstructing synchronized samples of the feedback signal at control task rate from non-uniform measurement samples provided by the VCT position sensor. The reconstructed synchronized samples are then used in output-feedback with no need to modify the existing controller structure. Fast-rate performance recovery is demonstrated numerically in a simulation model which is constructed and validated with real vehicle data.