Optimization of Zero-Flux Control in DCCTs by a New Feedforward Control Scheme

Current transformers (CT) based on fluxgate principle are applied in HVDC energy transmission systems for dc current measurement. The state of the art zero flux control is maintained by a combination of dc and ac controller circuits. In this paper a new feedforward scheme is presented, which replaces the ac controller, leading to a simpler and even more accurate zero flux control. Moreover, the robustness of the sensor against external magnetic fields is increased. The performance of the new control scheme is proven by control theory, simulation and measurements.