Study of an HVDC Link in Dynamic State Following AC Faults and Commutation Failures Based on Modeling and Real-Time Simulation

Abstract

A 12-pulse high-voltage direct current (HVDC) system based on line-commutated converter (LCC) is modeled and studied in this work. This study is performed and implemented in a real-time simulator using RT-LAB platform HYPERSIM OP-5600. Both internal and external faults create perturbations, interruption in the transit of power, and valve stress in the dynamic state. However, AC fault represents the most common unsymmetrical fault that can occur in the power systems, and also the misfiring control leads to this instability of the whole system and provides an overvoltage across the converter valve. Therefore, understanding the HVDC system fault behavior is very important for modeling, design, and validation of the control system during and after the different kinds of faults. In this study, the HVDC model chosen is based on the first CIGRE HVDC benchmark. Besides, the inverter is connected to a weak AC system. Commutation failure represents also the most common faults that can occur in the inverter valves during the conversion process. This kind of malfunction can be triggered after both the internal and external faults. Therefore, a single phase to ground AC fault of the inverter bus and a misfiring control is applied at one of the inverter valves. Those kinds of faults are applied in the goal to test the control of the system, their influence on the DC recovery, and observing the rising of the commutation failure on the inverter valves in front of two different values of time rising of the mechanism addressed to maintain stability, to ensure a good recovery from the fault and also inhibiting the commutation failures at the converter thyristors. The results are validated by mean of digital real-time simulator HYPERSIM (OP-5600) using the simulation in the loop (SIL) test. The performance of the LCC-HVDC system is investigated where the obtained results show the DC control influence to maintain a good and a safe stability of the system during and after the perturbation.