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Real-Time Calculation Method of DC Voltage and Current to Eliminate the Influence of Signal Delay

In this study, the influences of the signal delay duration between rectifier and inverter in ultra-high voltage direct current (U-HVDC) transmission systems have been analyzed. The simulation results with different signal delay time under the same fault condition show that the signal delay time has a significant influence on the control system response during the fault and recovery periods. In the worst condition, it may lead to a commutation failure in the inverter. To eliminate the influence of the signal delay time on the DC control system, a fast calculation method for computing the voltage and current has been proposed by establishing the equivalent capacitance and inductance of the DC line. A voltage dependent current order limiter is added in the rectifier control system, which can calculate the DC current order value. Based on this concept, this paper proposes an improved control strategy to eliminate the influence of signal delay. The analysis and simulation results show that the calculation method can effectively improve the response speed and shorten the fault recovery time of the HVDC systems.