Abstract
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.
Highlights
Compared with alternating current (AC) transmission systems, ultra-high voltage direct current (U-HVDC) transmission has incomparable advantages in long distance and large capacity electrical transmission processes [1]
An increasing number of U-HVDC transmission projects have been put into operation, leading to the largest AC/DC hybrid grid being formed in China [2], [3]
INFLUENCE OF SIGNAL DELAY TIME ON DC DYNAMIC RESPONSE CAUSED BY AN AC FAULT As it can be seen in Fig. 2, the voltage dependent current order limiter (VDCOL) is located in the inverter, and Idref is transmitted to the rectifier without considering the signal propagation delay time
Summary
Compared with alternating current (AC) transmission systems, ultra-high voltage direct current (U-HVDC) transmission has incomparable advantages in long distance and large capacity electrical transmission processes [1]. The detailed modeling of the CIGRE HVDC benchmark model was built in PSCAD, PSB, and EMTP simulation software [11], [12] Based on this model, many researchers have analyzed the influence of the problems in existing AC/DC systems and have further deployed control strategies through simulation analysis [8], [13], [14]. The above studies have used experiments to verify the effectiveness of the strategies, but neither the signal delay time between the rectifier and the inverter nor its influence on these proposed methods have been considered while performing the experiments and simulation analysis. Li: Real-Time Calculation Method of DC Voltage and Current to Eliminate the Influence of Signal Delay was discussed in [19]. The model, proposed in this paper, is built on the PSCAD simulation software to validate the calculation method and improvement strategy
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