Derivation of Logical Information for the Direct Digital Control of HVDC Convertors

Recently proposed methods of direct digital control for HVDC Convertors require the existence of transducers capable of providing fast and accurate logical information. Among the signals required, the beginning and end of conduction of convertor valves and the correct voltage crossovers present the greatest difficulty. The response of transducers based on different principles is investigated for ON-OFF current detection; Hall Effect and differentiating current transformers are found to satisfy the requirements of direct digital control. A set of possible voltage crossover sequences obtained from a comprehensive test involving convertor disturbances and weak a. c. systems, is used to develop a logical scheme to select the correct crossings.