Mario Garcia-Sanz

Nondiagonal MIMO QFT Controller Design for Darwin-Type Spacecraft With Large Flimsy Appendages

This paper deals with the design of robust control strategies to govern the position and attitude of a Darwin-type spacecraft with large flexible appendages. The satellite is one of the flyers of a multiple spacecraft constellation for a future ESA mission. It presents a 6 × 6 high order multiple-input multiple―output (MIMO) model with large uncertainty and loop interactions introduced by the flexible modes of the low-stiffness appendages. The scientific objectives of the satellite require very demanding control specifications for position and attitude accuracy high disturbance rejection, loop-coupling attenuation, and low controller order. The paper demonstrates the feasibility of a sequential nondiagonal MIMO quantitative feedback theory (QFT) strategy controlling the Darwin spacecraft and compares the results with H-infinity and sequential diagonal MIMO QFT designs.

Automatic Loop-Shaping of QFT Robust Controllers Via Genetic Algorithms

Abstract One of the main problems when designing robust controllers using Quantitative Feedback Theory (QFT) is the great effort needed to make the loopshaping stage. In this paper, a new automatic loop-shaping procedure to design QFT controllers is developed. It is based on Genetic Algorithms (GAs). In contrast with typical approaches that require some restrictive assumptions, GAs use only the information provided by a cost function, without further assumptions about the search space. An appropriate cost function, taken into account both minimisation of high frequency gain and satisfaction of performance control specifications, is developed. Three illustrative examples are given to show the proposed methodology.

Benchmarking of control strategies for ATAD technology: a first approach to the automatic control of sludge treatment systems.

Autothermal Thermophilic Aerobic Digestion (ATAD technology) is a promising alternative to conventional digestion systems. Aeration is a key factor in the performance of these kinds of reactors, in relation to effluent quality and operating costs. At present, the realisation of automatic control in ATADs is in its infancy. Additionally, the lack of robust sensors also makes the control of these processes difficult: only redox potential and temperature sensors are reliable for operation in full-scale plants. Based as it is on the existing simulation protocols for benchmarking of control strategies for wastewater treatment plants (WWTP), this paper presents the definition and implementation of a similar protocol but specifically adapted to the needs of ATAD technology. The implemented simulation protocol has been used to validate two different control strategies for aeration (ST1 and ST2). In comparison to an open-loop operation for the ATAD, simulation results showed that the ST1 strategy was able to save aeration costs of around 2-4%. Unlike ST1, ST2 achieved maximum sludge stabilisation but at the expense of higher aeration costs.

Automatic loop-shaping of QFT robust controllers

This paper introduces a methodology to design automatically QFT (Quantitative Feedback Theory) robust controllers for SISO (single input-single output) plants with model uncertainty. The method generalizes previous automatic loop-shaping techniques, avoiding restrictive assumptions about the search space. This methodology applies two strategies: a) Evolutionary Algorithms, and b) Genetic Algorithms (GA). In both cases the objective is to search the QFT robust controller that fulfils the control specifications for the whole set of plant models within the uncertainty. Each strategy has been applied to a benchmark in order to validate the techniques.

Robust QFT tracking controller design for a car equipped with 4-wheel steer-by-wire

In the present paper, a non-diagonal multi-input multi-output (MIMO) Quantitative Feedback Theory (QFT) controller design methodology is applied to control the lateral and yaw motions of a car equipped with four-wheel steering. The overall objective is to track the sideslip angle and yaw-rate with the aim of achieving satisfactory performance specifications for the vehicle lateral dynamics, regarding the rejection of external disturbances on yaw rate and sideslip angle, minimizing the interaction as much as possible and taking into account the model uncertainty.

MIMO quantitative robust control of a wastewater treatment plant for biological removal of nitrogen and phosphorus

This paper applies a recent full-matrix multi- input-multi-output QFT controller design methodology to simultaneously regulate nitrogen and phosphorus concentrations in the effluent of a wastewater treatment plant (WWTP) according to environmental standard policies. The robust controller is based on two terms: a non-diagonal pre- compensator for decoupling and a diagonal controller for robust performance and stability. Simulation results show the benefits of the control strategy for WWTP-type complex processes with large channel-interaction and uncertainty.

NON-DIAGONAL MULTIVARIABLE ROBUST QFT CONTROL OF A WASTEWATER TREATMENT PLANT FOR SIMULTANEOUS NITROGEN AND PHOSPHORUS REMOVAL

Abstract This paper presents the application of a robust non-diagonal multivariable control design method, based on the Quantitative Feedback Theory (QFT), to the control of a complex wastewater treatment plant (WWTP) with biological removal of nitrogen and phosphorus. The control objective is to simultaneously regulate the concentration of ammonia, nitrates and phosphorus in the plant effluent. The manipulated variables are the dissolved oxygen (DO) level in the aerobic reactor, the sludge recycling flow from the settler and the amount of ferric hydroxide added to chemically precipitate the phosphorus. Thus, the system becomes a three-input-three-output control structure with model parameter uncertainty. A robust non-diagonal multivariable QFT method is used to design a fully populated matrix controller. This sequential method reduces the interactions between control loops, increases the robust stability and fulfils the robust performance specifications defined by the user. It also considers non-minimum phase aspects by avoiding the introduction of right-half plane transmission zeros due to the controller elements. Simulations carried out by using the IWA ASM2d model under WEST® software validate the proposed control methodology.

A novel approach to Airborne Wind Energy: Overview of the EAGLE System project

This paper describes the design, modeling and development of a novel Airborne Wind Energy system (the EAGLE System), designed to handle a 2.5 kW, 25 kW or 100 kW aloft generator at varying altitudes. The system combines a hybrid tethered lighter-than-air and aerodynamic lift based flyer supporting a counter-rotating wind power generator payload, and a nonlinear-robust MIMO control system, with longitudinal and lateral control capabilities. Within this design, the power generation and lift systems are separate and do not rely on each other for operation. Overviews of the modeling, controller design, payload variations, and future prototyping are included topics.

Full-matrix inverse-based MIMO QFT control design for spacecraft flying in formation

Abstract This paper introduces a reformulation to design full-matrix Quantitative Feedback Theory (QFT) controllers for multi-input-multi-output (MIMO) plants with model uncertainty. It considers a double-step procedure: an inverse-based decoupling and a consecutive loop-by-loop quantitative robust control design. The method generalizes several previous non-diagonal MIMO QFT techniques, avoiding some required prior hypotheses of such former methods, and simplifies the design procedure. It deals with two classical control problems: reference tracking and disturbance rejection at plant output. The paper ends applying the new technique to the design of a MIMO controller for a spacecraft flying in a formation that is moving with respect to a central body in a circular orbit.

QFT robust control of a Vega-type space launcher

This paper deals with the position and attitude control of a Vega-type space launcher. The first part of the paper develops a general model of the launcher that takes into account the gravity, air density and mass variation. It also derives a linear model with uncertainty for the dominant dynamics, taking the nonlinear characteristics of the system as parametric uncertainty. The second part introduces the design of a set of robust QFT controllers to govern the pitch and yaw angles and the z coordinate. Finally, the system is validated by means of an intense campaign of simulations.