A systematized approach to obtain dependable controller specifications for hybrid plants

Abstract

This chapter focuses on the problem that a designer of an automation system controller must solve related with the correct synchronization between different parts of the controller specification when this specification obeys a previously defined structure. If this synchronization is not done according to some rules, and taking some aspects into consideration, some dependability aspects concerning the desired behaviour for the system may not be accomplished. More specifically, this chapter will demonstrate a systematized approach that consists of using the GEMMA (Guide d`Etude des Modes de Marches et d`Arrêts) (Agence Nationale pour le Developpement de la Production Automatisée) [ADEPA], 1992) and the SFC (Sequential Function Chart) (International Electrotechnical Commission [IEC], 2002) formalisms for the structure and specification of all the system behaviour, considering all the stop states and functioning modes of the system. The synchronization of the models, corresponding to the controller functioning modes and the controller stop states, is shown in detail and a systematized approach for this synchronization is presented. For this the advantages and disadvantages of the vertical coordination and horizontal coordination proposed by the GEMMA formalism are discussed and a case study is presented to explain the proposed systematic approach. A complete safe controller specification is developed to control a hybrid plant. Also this chapter presents and discusses a case study that applies a global approach for considering all the automation systems emergency stop requirements. The definition of all the functioning modes and all the stop states of the automation system is also presented according the EN 418 (European Standard [EN], 1992) and EN 60204-1 (EN, 1997) standards. All the aspects related to the emergency stop are focused in a particular way. The proposed approach defines and guarantees the safety aspects of an automation system controller related to the emergency stop. For the controller structure the GEMMA methodology is used; for the controller entire specification the SFC is used and for the controller behaviour simulation the Automation Studio software (FAMIC, 2003) is used.