A Comprehensive Coupled Methodology for Calculation and Suppression of DC Bias in UHVDC Transmission Systems

In the field of Ultra High Voltage Direct Current (UHVDC) transmission, direct current (DC) bias currents can adversely affect the normal operation of transformers. This paper analyzes the computation of DC bias currents in a UHVDC system operating in monopolar mode with the earth serving as the return path. The indirect field-circuit coupling method proposed for calculating DC bias currents reduces the computation time to less than 1/20000 of that required by the direct coupling method used in commercial software, while ensuring accuracy. Based on this method, a multi-valued genetic algorithm is developed to optimize the configuration of DC bias resistive-capacitive suppression devices. This optimization reduces the demand for these devices by 23.9%, thus enhancing economic benefits and the potential for engineering applications.