Metodologia para auditoria e validação ampla de malhas de controle: estudo de caso para uma caldeira industrial

Abstract

A methodology for control loop management, including performance assessment, diagnosis and fault detection, with a unit wide validation approach is proposed. Using functions named validators, the control loop subsystems and exogenous variables with potential to influence its performance are individually assessed. Among these subsystems are control valves, sensors, controllers and pieces of equipment. For each subsystem a validation function is designed with a defined standard interface that allow the construction of an organized fault tree hierarchical structure, which considers the main cause-effect relationships in the plant unit. It is assumed that the control loops perform as designed and that the impacting causeeffect relationship can be identified. A methodology for control loops audit is proposed as a preliminary stage of a unit wide validation system project. Algorithms already in current engineering practice were used for variables interaction detection, performance assessment, fault diagnosis and optimization of PID controllers. A case study of a boiler unit of a thermoelectric plant, illustrates the methodology of validation. Initially all control loops are analyzed and scanned for main features and dynamical behavior. These preliminary data are used to design and adjust validation functions to supervision main quality variables of the boiler unit, such as superheated steam and energy efficiency. Disturbance events and different operational modes were used to test the validation methodology proposed.