Control of systems with sector-bounded nonlinearities: robust stability and command effort minimization by disturbance rejection

The paper shows that a control strategy with disturbance rejection is able to reduce the control effort to a minimum, ensuring at the same time a desired performance level. The disturbance to be rejected is completely unknown except for a sectorial bound. The control unit is endowed with an extended state observer which includes a disturbance dynamics, whose state tracks the unknown disturbance to be rejected. In summary, the novel contributions of the paper are the following. First, we derive a robust stability condition for the proposed control scheme, holding for all the nonlinearities that are bounded by a known (or estimated) maximum slope. Second, we propose a novel approach for designing the observer and state feedback gains, which guarantee robust closed-loop stability. Third, we show that the designed control system yields, with a minimum control effort, the same control performance as a robust state feedback control, which on the contrary may require a larger command activity. Two simulated case studies are presented to show the effectiveness of the proposed approach

The four-tank benchmark: a simple solution by embedded model control

The four-tank benchmark is a multivariate and nonlinear control problem which has been widely studied in the literature. Two pairs of tanks in series are supplied by two pumps. Under certain configurations, the Embedded Model Control approach provides a simple decoupled solution by separately controlling the two output tank levels and treating the input flow as a partly unknown disturbance. Neglected dynamics in a form of unknown delays both in sensors and actuator dynamics is considered. The core of the control unit is a discrete-time embedded model consisting of unknown disturbance dynamics and partly known nonlinear interactions. The embedded model is driven by the plant command and by a feedback vector which is retrieved from the model error. The feedback is capable of keeping updated the unknown disturbance prediction, ready to be cancelled by the control law. The control gains are tuned using two sets of closed-loop eigenvalues in order to trade-off between disturbance rejection and robust stability. Simulated runs under different tank interactions prove design effectiveness

The four-tank control problem: Comparison of two disturbance rejection control solutions

The paper aims to compare and prove a pair of disturbance/uncertainty rejection control laws for the well-known four tank control problems. Control requirements are expressed in terms of a set point sequence as it usual in the literature. Uncertainty class is defined as the union of four sub-classes: unknown disturbance, parametric uncertainty, measurement errors and neglected dynamics. Modelling and design allow insight of the dynamic properties of the problem. They are formulated by a pair of theorems which fix the range of application. Theorem are confirmed by the results simulated runs, and indicate the correct way to further broaden control design applicability. Disturbance rejection (better uncertainty) design is deployed using the Embedded Model Control methodology: only unknown disturbance and parametric uncertainty can be rejected, whereas neglected dynamics effects must be filtered. As a result, simple performance and stability inequality can be formulated in the frequency domain and lead to closed-loop pole placement. Inequalities are such to reveal whether pole placement is feasible and how feasibility can be recovered, an issue which at authors knowledge is rarely encountered in the literature. Simulated runs prove the design procedure

Traditional and Virtual Congress Meetings During the COVID-19 Pandemic and the Post-COVID-19 Era: Is it Time to Change the Paradigm?

The speed and reach of the COVID-19 pandemic have forced rapid changes in how we conduct medical practice and research. The rapid evolution in how scientific meetings are conducted may have long-term benefits. A new reality in which technology and sociality are merged may offer a more engaging and adaptable scientific congress experience with more flexible and dynamic use of content modulated to the needs of each attendee

Modelling soil carbon fate under erosion process in vineyard

Soil erosion processes in vineyards beyond water runoff and sediment transport have a strong effect on soil organic carbon loss (SOC) and redistribution along the slope. The variation of SOC across the landscape determines a difference in soil fertility and vine productivity. The aim of this research was to study erosion of a Mediterranean vineyard, develop an approach to estimate the SOC loss, correlate the vines vigor with sediment and carbon erosion. The study was carried out in a Sicilian (Italy) vineyard, planted in 2011. Along the slope, six pedons were studied by digging 6 pits up to 60cm depth. Soil was sampled in each pedon every 10cm and SOC was analyzed. Soil erosion, detachment and deposition areas were measured by pole height method. The vigor of vegetation was expressed in term of NDVI (Normalized difference Vegetation Index) derived from a satellite image (RapidEye) acquired at berry pre-veraison stage (July) and characterized by 5 spectral bands in the shortwave region, including a band in the red wavelength (R, 630-685 nm) and in the near infrared (NIR, 760-850 nm) . Results showed that soil erosion, sediments redistribution and SOC across the hill was strongly affected by topographic features, slope and curvature. The erosion rate was 46Mg ha-1 y-1 during the first 6 years since planting. The SOC redistribution was strongly correlated with the detachment or deposition area as highlighted by pole height measurements. The approach developed to estimate the SOC loss showed that during the whole study period the off-farm SOC amounts to 1.6Mg C ha-1. As highlighted by NDVI results, the plant vigor is strong correlated with SOC content and therefore, developing an accurate NDVI approach could be useful to detect the vineyard areas characterized by low fertility due to erosion process