Modeling of Digital Control System for an HVDC Rectifier Terminal

In order to design complex digital control systems such as those for HVDC rectifier terminals which are characterized by a lot of variables to be controlled, strict time limitation and complex relationship between the variables, a modeling method for this type of digital control system is presented. The modeling method is mainly based on Petri nets. In this method, a data flow is used to represent the global variables including inputs, outputs, intermediate variables and events of the control system. This data flow is then divided into functional blocks and each of these blocks is described for its inputs, outputs, functions to be realized and active conditions. Finally, these functional blocks are related by Petri nets to describe their relationship in time. In this paper, the control strategies for an HVDC rectifier terminal, including main control strategy and faults reduction control strategy, are described. Different algorithms used for selection of thyristors to be fired in different operation environments are also discussed. The model was experimented and got satisfactory results.